An unindetified line_in_xray_spectra_of_the_adromeda_galaxy_and_perseus_galax...Sérgio Sacani
This document summarizes an analysis of X-ray spectra from the Andromeda galaxy and Perseus galaxy cluster observed with the XMM-Newton X-ray observatory. The analysis identified a weak unidentified line at an energy of approximately 3.5 keV in the spectra of both objects. The line strength increases towards the centers of the objects and is stronger in Perseus than in Andromeda. The line properties are consistent with originating from the decay of dark matter particles, though an instrumental or astrophysical source cannot be ruled out based on individual objects. Future detections or non-detections in additional targets could help reveal the nature of this line.
A close pair_binary_in_a_distant_triple_supermassive_black_hole_systemSérgio Sacani
This document reports the discovery of a triple supermassive black hole system through radio observations. Very Long Baseline Interferometry observations revealed two flat-spectrum radio cores, labelled J1502SE and J1502SW, within the galaxy J1502S, separated by about 140 parsecs. Analysis of archival data provides further evidence of this close black hole pair through the detection of 'S-shaped' radio emission between the two cores, indicative of jet precession caused by the binary black holes. This is the closest black hole pair yet discovered and demonstrates a new method for finding binary black holes that cannot be spatially resolved with current instruments.
1) The document reports on phase-resolved emission spectroscopy observations of the exoplanet WASP-43b using the Hubble Space Telescope.
2) The observations tracked the planet over three full orbits and measured its thermal emission as a function of orbital phase, allowing the researchers to construct a map of the planet's atmospheric thermal structure.
3) The results found large day-night temperature variations at all measured altitudes, with temperature monotonically decreasing with increasing pressure. A low Bond albedo of 0.07-0.18 and offset of the hottest point from the substellar point were also derived.
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest f...Sérgio Sacani
This document describes a public release of photometric redshifts and galaxy properties from multi-wavelength data in the Abell-2744 and MACS-J0416 galaxy cluster fields observed as part of the Frontier Fields program. Photometric redshifts were estimated using six different methods and have an accuracy of 3-5%. Accounting for gravitational lensing magnification, the H-band number counts agree with CANDELS at bright magnitudes but extend to intrinsically fainter galaxies of H=32-33. The Frontier Fields data allow probing galaxy stellar masses 0.5-1.5 dex lower than in wide fields, including sources with masses of 107-108 solar masses at z>5. Star formation rates can be detected 1
A highly magnetized twin-jet base pinpoints a supermassive black holeSérgio Sacani
Supermassive black holes (SMBH) are essential for the production of jets in radio-loud active galactic nuclei (AGN). Theoretical
models based on (Blandford & Znajek 1977, MNRAS, 179, 433) extract the rotational energy from a Kerr black hole, which could
be the case for NGC1052, to launch these jets. This requires magnetic fields on the order of 103 G to 104 G. We imaged the vicinity
of the SMBH of the AGN NGC1052 with the Global Millimetre VLBI Array and found a bright and compact central feature that is
smaller than 1.9 light days (100 Schwarzschild radii) in radius. Interpreting this as a blend of the unresolved jet bases, we derive the
magnetic field at 1 Schwarzschild radius to lie between 200 G and 8:3 104 G consistent with Blandford & Znajek models.
Evidence for a_complex_enrichment_history_of_the_stream_from_fairall_9_sightlineSérgio Sacani
This study analyzes absorption spectra of the Magellanic Stream (MS) toward the quasar Fairall 9, obtained using the Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS) and the Very Large Telescope Ultraviolet and Visible Echelle Spectrograph (VLT/UVES). The spectra reveal absorption from multiple velocity components of the MS, indicating multiphase gas. Surprisingly, the sulfur abundance is found to be high ([S/H] = -0.30), five times higher than other MS sightlines, while the nitrogen abundance is lower ([N/H] = -1.15). This points to a complex enrichment history, where the gas toward Fair
A kiloparsec scale_internal_shock_collision_in_the_jet_of_a_nearby_radio_galaxySérgio Sacani
This document summarizes observations of a collision between two knots (B and C) in the jet of the nearby radio galaxy 3C 264 using Hubble Space Telescope imaging from 1994 to 2014. Knot B was found to have an apparent speed of 7.0c, much faster than other knots. Knots B and C showed simultaneous brightening in 2014, indicating the beginning of their collision. Analysis suggests the collision will dissipate kinetic energy with a conversion efficiency to radiation of at least 0.1%, providing a way to study particle acceleration in astrophysical jets.
Galaxy dynamics and the mass density of the universeSérgio Sacani
Dynamical evidence accumulated over the
past 20 years has convinced astronomers that luminous matter
in a spiral galaxy constitutes no more than 10% of the mass of
a galaxy. An additional 90% is inferred by its gravitational
effect on luminous material. Here I review recent observations
concerning the distribution of luminous and nonluminous
matter in the Milky Way, in galaxies, and in galaxy clusters.
Observations of neutral hydrogen disks, some extending in
radius several times the optical disk, confirm that a massive
dark halo is a major component of virtually every spiral. A
recent surprise has been the discovery that stellar and gas
motions in ellipticals are enormously complex. To date, only for
a few spheroidal galaxies do the velocities extend far enough to
probe the outer mass distribution. But the diverse kinematics
of inner cores, peripheral to deducing the overall mass distribution,
offer additional evidence that ellipticals have acquired
gas-rich systems after initial formation. Dynamical results are
consistent with a low-density universe, in which the required
dark matter could be baryonic. On smallest scales of galaxies
[10 kiloparsec (kpc); H. = 50 kmsec'lmegaparsec'11 the
luminous matter constitutes only 1% of the closure density. On
scales greater than binary galaxies (i.e., .100 kpc) all systems
indicate a density -10% of the closure density, a density
consistent with the low baryon density in the universe. If
large-scale motions in the universe require a higher mass
density, these motions would constitute the first dynamical
evidence for nonbaryonic matter in a universe of higher
density.
An unindetified line_in_xray_spectra_of_the_adromeda_galaxy_and_perseus_galax...Sérgio Sacani
This document summarizes an analysis of X-ray spectra from the Andromeda galaxy and Perseus galaxy cluster observed with the XMM-Newton X-ray observatory. The analysis identified a weak unidentified line at an energy of approximately 3.5 keV in the spectra of both objects. The line strength increases towards the centers of the objects and is stronger in Perseus than in Andromeda. The line properties are consistent with originating from the decay of dark matter particles, though an instrumental or astrophysical source cannot be ruled out based on individual objects. Future detections or non-detections in additional targets could help reveal the nature of this line.
A close pair_binary_in_a_distant_triple_supermassive_black_hole_systemSérgio Sacani
This document reports the discovery of a triple supermassive black hole system through radio observations. Very Long Baseline Interferometry observations revealed two flat-spectrum radio cores, labelled J1502SE and J1502SW, within the galaxy J1502S, separated by about 140 parsecs. Analysis of archival data provides further evidence of this close black hole pair through the detection of 'S-shaped' radio emission between the two cores, indicative of jet precession caused by the binary black holes. This is the closest black hole pair yet discovered and demonstrates a new method for finding binary black holes that cannot be spatially resolved with current instruments.
1) The document reports on phase-resolved emission spectroscopy observations of the exoplanet WASP-43b using the Hubble Space Telescope.
2) The observations tracked the planet over three full orbits and measured its thermal emission as a function of orbital phase, allowing the researchers to construct a map of the planet's atmospheric thermal structure.
3) The results found large day-night temperature variations at all measured altitudes, with temperature monotonically decreasing with increasing pressure. A low Bond albedo of 0.07-0.18 and offset of the hottest point from the substellar point were also derived.
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest f...Sérgio Sacani
This document describes a public release of photometric redshifts and galaxy properties from multi-wavelength data in the Abell-2744 and MACS-J0416 galaxy cluster fields observed as part of the Frontier Fields program. Photometric redshifts were estimated using six different methods and have an accuracy of 3-5%. Accounting for gravitational lensing magnification, the H-band number counts agree with CANDELS at bright magnitudes but extend to intrinsically fainter galaxies of H=32-33. The Frontier Fields data allow probing galaxy stellar masses 0.5-1.5 dex lower than in wide fields, including sources with masses of 107-108 solar masses at z>5. Star formation rates can be detected 1
A highly magnetized twin-jet base pinpoints a supermassive black holeSérgio Sacani
Supermassive black holes (SMBH) are essential for the production of jets in radio-loud active galactic nuclei (AGN). Theoretical
models based on (Blandford & Znajek 1977, MNRAS, 179, 433) extract the rotational energy from a Kerr black hole, which could
be the case for NGC1052, to launch these jets. This requires magnetic fields on the order of 103 G to 104 G. We imaged the vicinity
of the SMBH of the AGN NGC1052 with the Global Millimetre VLBI Array and found a bright and compact central feature that is
smaller than 1.9 light days (100 Schwarzschild radii) in radius. Interpreting this as a blend of the unresolved jet bases, we derive the
magnetic field at 1 Schwarzschild radius to lie between 200 G and 8:3 104 G consistent with Blandford & Znajek models.
Evidence for a_complex_enrichment_history_of_the_stream_from_fairall_9_sightlineSérgio Sacani
This study analyzes absorption spectra of the Magellanic Stream (MS) toward the quasar Fairall 9, obtained using the Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS) and the Very Large Telescope Ultraviolet and Visible Echelle Spectrograph (VLT/UVES). The spectra reveal absorption from multiple velocity components of the MS, indicating multiphase gas. Surprisingly, the sulfur abundance is found to be high ([S/H] = -0.30), five times higher than other MS sightlines, while the nitrogen abundance is lower ([N/H] = -1.15). This points to a complex enrichment history, where the gas toward Fair
A kiloparsec scale_internal_shock_collision_in_the_jet_of_a_nearby_radio_galaxySérgio Sacani
This document summarizes observations of a collision between two knots (B and C) in the jet of the nearby radio galaxy 3C 264 using Hubble Space Telescope imaging from 1994 to 2014. Knot B was found to have an apparent speed of 7.0c, much faster than other knots. Knots B and C showed simultaneous brightening in 2014, indicating the beginning of their collision. Analysis suggests the collision will dissipate kinetic energy with a conversion efficiency to radiation of at least 0.1%, providing a way to study particle acceleration in astrophysical jets.
Galaxy dynamics and the mass density of the universeSérgio Sacani
Dynamical evidence accumulated over the
past 20 years has convinced astronomers that luminous matter
in a spiral galaxy constitutes no more than 10% of the mass of
a galaxy. An additional 90% is inferred by its gravitational
effect on luminous material. Here I review recent observations
concerning the distribution of luminous and nonluminous
matter in the Milky Way, in galaxies, and in galaxy clusters.
Observations of neutral hydrogen disks, some extending in
radius several times the optical disk, confirm that a massive
dark halo is a major component of virtually every spiral. A
recent surprise has been the discovery that stellar and gas
motions in ellipticals are enormously complex. To date, only for
a few spheroidal galaxies do the velocities extend far enough to
probe the outer mass distribution. But the diverse kinematics
of inner cores, peripheral to deducing the overall mass distribution,
offer additional evidence that ellipticals have acquired
gas-rich systems after initial formation. Dynamical results are
consistent with a low-density universe, in which the required
dark matter could be baryonic. On smallest scales of galaxies
[10 kiloparsec (kpc); H. = 50 kmsec'lmegaparsec'11 the
luminous matter constitutes only 1% of the closure density. On
scales greater than binary galaxies (i.e., .100 kpc) all systems
indicate a density -10% of the closure density, a density
consistent with the low baryon density in the universe. If
large-scale motions in the universe require a higher mass
density, these motions would constitute the first dynamical
evidence for nonbaryonic matter in a universe of higher
density.
Water vapour absorption in the clear atmosphere of a Neptune-sized exoplanetGOASA
1) The transmission spectrum of the exoplanet HAT-P-11b was observed using Hubble and Spitzer space telescopes.
2) Water vapor absorption was detected at 1.4 micrometers in the atmosphere, indicating a clear atmosphere down to 1 mbar pressure.
3) The detection of water vapor and relatively large atmospheric scale height places an upper limit on the abundance of heavy elements in the atmosphere of around 700 times the solar value, consistent with core accretion planet formation theories.
Detection of the_central_star_of_the_planetary_nebula_ngc6302Sérgio Sacani
This document reports on the first direct detection of the central star of the planetary nebula NGC 6302 using the Wide Field Camera 3 on the Hubble Space Telescope. Photometry of the central star was obtained in two narrowband filters, F469N and F673N, from which the reddening was estimated to be c=3.1, corresponding to AV=6.6 magnitudes of extinction. Comparison to evolutionary tracks suggests the central star has a temperature of around 200,000 K, luminosity of 2000 L☉, and the nebula is around 2,200 years old. The high extinction from dust in the nebula had previously prevented direct detection of the central star.
1) Researchers observed 15 transits of the exoplanet GJ 1214b using the Hubble Space Telescope to measure its transmission spectrum from 1.1 to 1.7 microns.
2) The transmission spectrum was featureless, inconsistent with cloud-free atmospheres dominated by water, methane, carbon monoxide, nitrogen, or carbon dioxide.
3) The most likely explanation for the featureless spectrum is the presence of high-altitude clouds in the planet's atmosphere, which block the transmission of stellar light through the lower atmosphere.
Supermassive black holes in galaxy centres can grow by the accretion
of gas, liberating enormous amounts of energy that might
regulate star formation on galaxy-wide scales1–3
. The nature of
gaseous fuel reservoirs that power black hole growth is nevertheless
largely unconstrained by observations, and is instead routinely
simplified as a smooth, spherical inflow of very hot gas
in accordance with the Bondi solution4
. Recent theory5–7 and
simulations8–10 instead predict that accretion can be dominated by
a stochastic, clumpy distribution of very cold molecular clouds,
though unambiguous observational support for this prediction remains
elusive. Here we show observational evidence for a cold,
clumpy accretion flow toward a supermassive black hole fuel reservoir
in the nucleus of the Abell 2597 Brightest Cluster Galaxy
(BCG), a nearby (z = 0.0821) giant elliptical galaxy surrounded
by a dense halo of hot plasma11–13. Under the right conditions,
thermal instabilities can precipitate from this hot gas, producing a
rain of cold clouds that fall toward the galaxy’s centre14, sustaining
star formation amid a kiloparsec-scale molecular nebula that inhabits
its core15. New interferometric sub-millimetre observations
show that these cold clouds also fuel black hole accretion, revealing
“shadows” cast by molecular clouds as they move inward at ∼ 300
km s−1
toward the active supermassive black hole in the galaxy
centre, which serves as a bright backlight. Corroborating evidence
from prior observations16 of warmer atomic gas at extremely high
spatial resolution17, along with simple arguments based on geometry
and probability, indicates that these clouds are within the innermost
hundred parsecs of the black hole, and falling closer toward
it
The wonderful complexity_of_the_mira_ab_systemSérgio Sacani
The ALMA observations of the Mira AB binary system reveal an amazingly complex circumstellar environment shaped by multiple dynamical processes. In the blue wing of the CO emission line, opposing large arcs form a bubble structure around Mira A, possibly created by the wind from Mira B blowing into Mira A's expanding envelope. In the main line component, spiral arcs are seen around Mira A that appear relatively flat and oriented in the orbital plane. An accretion wake is also visible trailing Mira B. The companion is marginally resolved with a separation of 0.487 arcseconds from Mira A.
The document summarizes research from images taken by the New Horizons spacecraft of Charon, Pluto's largest moon. The images reveal Charon has a reddish polar cap at its north pole. Thermal models show the pole experiences long periods of extreme cold temperatures due to Charon's high obliquity and long seasons. The researchers hypothesize that methane and other volatiles escaping from Pluto's atmosphere become cold-trapped at Charon's winter pole, where they are processed by radiation into non-volatile organic compounds that remain on the surface to form the red cap. Spectral and compositional evidence supports this mechanism of seasonal accumulation of photolyzed volatiles to explain Charon's unique polar color
PROBING FOR EVIDENCE OF PLUMES ON EUROPA WITH HST/STISSérgio Sacani
Roth et al. (2014a) reported evidence for plumes of water venting from a southern high latitude
region on Europa – spectroscopic detection of off-limb line emission from the dissociation
products of water. Here, we present Hubble Space Telescope (HST) direct images of Europa in
the far ultraviolet (FUV) as it transited the smooth face of Jupiter, in order to measure absorption
from gas or aerosols beyond the Europa limb. Out of ten observations we found three in which
plume activity could be implicated. Two show statistically significant features at latitudes similar
to Roth et al., and the third, at a more equatorial location. We consider potential systematic
effects that might influence the statistical analysis and create artifacts, and are unable to find any
that can definitively explain the features, although there are reasons to be cautious. If the
apparent absorption features are real, the magnitude of implied outgassing is similar to that of the
Roth et al. feature, however the apparent activity appears more frequently in our data.
This study analyzed transit observations of the Neptune-mass exoplanet GJ 436b taken with the Hubble Space Telescope. The transmission spectrum was found to be featureless, ruling out cloud-free hydrogen-dominated atmosphere models with high significance. The flat transmission spectrum is consistent with either an atmosphere containing high-altitude clouds located at a pressure of around 1 millibar, or a relatively hydrogen-poor atmosphere with 3% hydrogen and helium by mass. Bayesian atmospheric modeling showed that cloudy hydrogen-dominated or high-metallicity hydrogen-poor atmospheres provide the best fits to the data. Further observations are needed to distinguish between these scenarios.
The document summarizes observations of periodic increases in luminosity from a young protostar, L54361, arising from variable accretion rates. Key points:
- L54361's luminosity varies periodically every 25.34 days, increasing by a factor of 10 in about a week as material is accreted from a circumbinary disk onto the central protostar.
- This periodic pulsed accretion is attributed to the gravitational influence of an unseen binary companion perturbing the circumbinary disk.
- Follow-up observations found spatially resolved scattered light structures that vary with the same period, supporting the interpretation of variable illumination from pulsed accretion.
The document summarizes observations of two giant radio lobes emanating from the center of the Milky Way galaxy. The lobes extend about 60 degrees from the galactic center and correspond closely with previously observed gamma-ray "Fermi bubbles". The lobes contain three ridge-like substructures that curve towards the galactic west as they extend away from the center. Strong magnetic fields of up to 15 microgauss permeate the lobes. The observations indicate that the radio lobes originate from a biconical outflow driven by intense star formation in the galactic center, rather than activity from the supermassive black hole, and have transported a huge amount of magnetic energy into the galactic halo over at least the past 10 million years.
On some structural_features_of_the_metagalaxySérgio Sacani
Progress in a group of investigations designed
to discover some of the structural details in individual galaxies and in the
Metagalaxy is reported in the following pages.
(a) The first section is concerned with the distribution of cluster-type
Cepheids in high galactic latitude. To the 169 already known in latitudes,
greater than or equal to ± 20o
, the systematic variable star programme carried
on at Harvard has added 312, mostly fainter than magnitude 13-0. With
allowance for absorption and for uncertainties yet remaining in the mean
absolute magnitude of these stars, the thickness of the Milky Way, so far
as this type of star is concerned, is not less than twenty-five kiloparsecs ;
he extent of the Milky Way in its own plane, by the same criterion, is more
than thirty kiloparsecs, perhaps much more.
(b) The extent of the Milky Way in the anti-centre quadrant is considered
on the basis of classical and cluster-type Cepheids ; provisionally
it is found that the galactic system reaches to a distance of at least ten
kiloparsecs in longitude 150o
.
(r) More than six hundred new variables have been found in the Large
Magellanic Cloud and measured for position, ranges and median magnitudes ;
the frequency of periods is not unlike that for the classical Cepheids in the
galactic system ; the light curves also are comparable in all details. The
Magellanic Cepheids, like the galactic classical Cepheids, are concentrated
in regions of high star-density.
(d) Further study of the period-luminosity relation in the Large Magellanic
Cloud permits its revision and strengthening for the Cepheids of
highest absolute magnitude. An observed deviation from the relation
that had previously been found for the Small Cloud is probably to be
attributed to scale error in the magnitude system. No seriously disturbing
This document summarizes research on determining temperatures, luminosities, and masses of the coldest known brown dwarfs. The key findings are:
1) Precise distances were measured for a sample of late-T and Y dwarfs using Spitzer Space Telescope astrometry, allowing accurate calculation of absolute fluxes, luminosities, and temperatures.
2) Y0 dwarfs were found to have temperatures of 400-450 K, significantly warmer than previous estimates, and masses of 5-20 times Jupiter's mass.
3) While having similar temperatures, Y dwarfs showed diverse spectral energy distributions, suggesting temperature alone does not determine spectra. Physical properties like gravity, clouds and chemistry also influence spectra.
A thirty-four billion solar mass black hole in SMSS J2157–3602, the most lumi...Sérgio Sacani
From near-infrared spectroscopic measurements of the Mg II emission line doublet, we estimate the black hole (BH) mass of the quasar, SMSS J215728.21–360215.1, as being (3.4 ± 0.6) × 1010 M⊙ and refine the redshift of the quasar to be z = 4.692. SMSS J2157 is the most luminous known quasar, with a 3000 Å luminosity of (4.7 ± 0.5) × 1047 erg s−1 and an estimated bolometric luminosity of 1.6 × 1048 erg s−1 , yet its Eddington ratio is only ∼0.4. Thus, the high luminosity of this quasar is a consequence of its extremely large BH – one of the most massive BHs at z > 4.
The Internal Structure of Asteroid (25143) Itokawa as Revealed by Detection o...WellingtonRodrigues2014
- The authors detected an acceleration in the rotation rate of asteroid (25143) Itokawa through photometric observations spanning 2001 to 2013.
- By measuring rotational phase offsets between observed and modeled lightcurves, they found a YORP acceleration of 3.54 ± 0.38 × 10−8 rad day−2, equivalent to a decrease in the asteroid's rotation period of about 45 ms per year.
- Thermophysical modeling of the detailed shape model from the Hayabusa spacecraft could not reconcile the observed YORP strength unless the asteroid's center of mass is shifted by about 21 m along its long axis. This suggests Itokawa has two components with different densities that merged, either from a
A vast thin_plane_of_corotating_dwarf_galaxies_orbiting_the_andromeda_galaxySérgio Sacani
1. A study using data from the Pan-Andromeda Archaeological Survey finds that approximately half of the dwarf galaxy satellites orbiting the Andromeda galaxy are confined to a highly planar structure that is at least 400 kiloparsecs in diameter but only 14.1 kiloparsecs thick.
2. Radial velocity measurements reveal that 13 of the 15 dwarf galaxies within this structure share the same sense of rotation around Andromeda.
3. The existence of this thin, co-rotating planar structure of dwarf galaxies provides strong evidence that a significant fraction of satellite galaxies can have coherent orbital and angular momentum properties within their host galaxy.
The shadow _of_the_flying_saucer_a_very_low_temperature_for_large_dust_grainsSérgio Sacani
Os astrónomos usaram o ALMA e os telescópios do IRAM para fazer a primeira medição direta da temperatura dos grãos de poeira grandes situados nas regiões periféricas de um disco de formação planetária que se encontra em torno de uma estrela jovem. Ao observar de forma inovadora um objeto cujo nome informal é Disco Voador, os astrónomos descobriram que os grãos de poeira são muito mais frios do que o esperado: -266º Celsius. Este resultado surpreendente sugere que os modelos teóricos destes discos precisam de ser revistos.
Uma equipa internacional liderada por Stephane Guilloteau do Laboratoire d´Astrophysique de Bordeaux, França, mediu a temperatura de enormes grãos de poeira que se encontram em torno da jovem estrela 2MASS J16281370-2431391 na região de formação estelar Rho Ophiuchi, a cerca de 400 anos-luz de distância da Terra.
Esta estrela encontra-se rodeada por um disco de gás e poeira — chamado disco protoplanetário, uma vez que se encontra na fase inicial da formação de um sistema planetário. Este disco é visto de perfil quando observado a partir da Terra e a sua aparência em imagens no visível levou a que se lhe desse o nome informal de Disco Voador.
Os astrónomos utilizaram o ALMA para observar o brilho emitido pelas moléculas de monóxido de carbono no disco da 2MASS J16281370-2431391. As imagens revelaram-se extremamente nítidas e descobriu-se algo estranho — em alguns casos o sinal recebido era negativo. Normalmente um sinal negativo é fisicamente impossível, mas neste caso existe uma explicação, que leva a uma conclusão surpreendente.
Lenz et al. discovered that soft particles at the nano- and microscale can form "clumpy crystals" where particles partially overlap and form regular lattices of clumps. This challenges ideas that soft materials will behave similarly to atomic and molecular systems. The discovery provides another example of how soft materials display unconventional behavior. An analysis of the satellites orbiting Andromeda found that about half are rotating coherently in a thin planar structure, providing a new constraint on galaxy formation theories. Further evidence suggests organized planar distributions of satellites may be common for nearby galaxy groups. The findings compound issues with the number of predicted versus observed satellites and suggest the structures themselves are not ancient.
We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using
a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts
of the stellar disk of the LMC (r < 10 degrees from the center). These data have higher resolution
than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in
the northern periphery, with no comparable counterparts in the South. We compare these data to
detailed simulations of the LMC disk outskirts, following interactions with its low mass companion,
the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field.
The simulations are used to assess the origin of the northern structures, including also the low density
stellar arc recently identified in the DES data by Mackey et al. (2015) at ∼ 15 degrees. We conclude
that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar
structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to
constrain the LMC’s interaction history with and impact parameter of the SMC. More generally, we
find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for
1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion
around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are
driven by dwarf-dwarf interactions.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
This document reports the discovery of a newly discovered optical Einstein ring (ER) called the "Canarias Einstein Ring". It was discovered serendipitously in imaging data from the Dark Energy Camera. Follow-up spectroscopy with the Gran Telescopio CANARIAS confirmed the nature of the system, with the lens being an early-type galaxy at a redshift of z=0.581 and the source being a starburst galaxy at z=1.165. Analysis of the system determined the Einstein radius to be 2.16 arcseconds and the total enclosed mass producing the lensing effect to be 1.86 ± 0.23 × 1012 solar masses.
An extremely high_altitude_plume_seen_at_mars_morning_terminatorSérgio Sacani
Artigo da revista Nature que descreve as plumas de alta altitude identificadas pairando sobre a superfície do planeta Marte e propõem duas hipóteses para o fenômeno.
This document summarizes the discovery and characterization of Kepler-432 b, a massive exoplanet in a highly eccentric orbit around a red giant star. Key findings include:
1) Radial velocity measurements from the CAFE spectrograph revealed Kepler-432 b has a mass of 4.87 ± 0.48 MJup and moves in a highly eccentric orbit (e = 0.535 ± 0.030) around its host star.
2) Simultaneous modeling of Kepler photometry and radial velocity data determined Kepler-432 b has a radius of 1.120 ± 0.036 RJup and orbits every 52.5 days.
3) Analysis of high-resolution images found a nearby star
Water vapour absorption in the clear atmosphere of a Neptune-sized exoplanetGOASA
1) The transmission spectrum of the exoplanet HAT-P-11b was observed using Hubble and Spitzer space telescopes.
2) Water vapor absorption was detected at 1.4 micrometers in the atmosphere, indicating a clear atmosphere down to 1 mbar pressure.
3) The detection of water vapor and relatively large atmospheric scale height places an upper limit on the abundance of heavy elements in the atmosphere of around 700 times the solar value, consistent with core accretion planet formation theories.
Detection of the_central_star_of_the_planetary_nebula_ngc6302Sérgio Sacani
This document reports on the first direct detection of the central star of the planetary nebula NGC 6302 using the Wide Field Camera 3 on the Hubble Space Telescope. Photometry of the central star was obtained in two narrowband filters, F469N and F673N, from which the reddening was estimated to be c=3.1, corresponding to AV=6.6 magnitudes of extinction. Comparison to evolutionary tracks suggests the central star has a temperature of around 200,000 K, luminosity of 2000 L☉, and the nebula is around 2,200 years old. The high extinction from dust in the nebula had previously prevented direct detection of the central star.
1) Researchers observed 15 transits of the exoplanet GJ 1214b using the Hubble Space Telescope to measure its transmission spectrum from 1.1 to 1.7 microns.
2) The transmission spectrum was featureless, inconsistent with cloud-free atmospheres dominated by water, methane, carbon monoxide, nitrogen, or carbon dioxide.
3) The most likely explanation for the featureless spectrum is the presence of high-altitude clouds in the planet's atmosphere, which block the transmission of stellar light through the lower atmosphere.
Supermassive black holes in galaxy centres can grow by the accretion
of gas, liberating enormous amounts of energy that might
regulate star formation on galaxy-wide scales1–3
. The nature of
gaseous fuel reservoirs that power black hole growth is nevertheless
largely unconstrained by observations, and is instead routinely
simplified as a smooth, spherical inflow of very hot gas
in accordance with the Bondi solution4
. Recent theory5–7 and
simulations8–10 instead predict that accretion can be dominated by
a stochastic, clumpy distribution of very cold molecular clouds,
though unambiguous observational support for this prediction remains
elusive. Here we show observational evidence for a cold,
clumpy accretion flow toward a supermassive black hole fuel reservoir
in the nucleus of the Abell 2597 Brightest Cluster Galaxy
(BCG), a nearby (z = 0.0821) giant elliptical galaxy surrounded
by a dense halo of hot plasma11–13. Under the right conditions,
thermal instabilities can precipitate from this hot gas, producing a
rain of cold clouds that fall toward the galaxy’s centre14, sustaining
star formation amid a kiloparsec-scale molecular nebula that inhabits
its core15. New interferometric sub-millimetre observations
show that these cold clouds also fuel black hole accretion, revealing
“shadows” cast by molecular clouds as they move inward at ∼ 300
km s−1
toward the active supermassive black hole in the galaxy
centre, which serves as a bright backlight. Corroborating evidence
from prior observations16 of warmer atomic gas at extremely high
spatial resolution17, along with simple arguments based on geometry
and probability, indicates that these clouds are within the innermost
hundred parsecs of the black hole, and falling closer toward
it
The wonderful complexity_of_the_mira_ab_systemSérgio Sacani
The ALMA observations of the Mira AB binary system reveal an amazingly complex circumstellar environment shaped by multiple dynamical processes. In the blue wing of the CO emission line, opposing large arcs form a bubble structure around Mira A, possibly created by the wind from Mira B blowing into Mira A's expanding envelope. In the main line component, spiral arcs are seen around Mira A that appear relatively flat and oriented in the orbital plane. An accretion wake is also visible trailing Mira B. The companion is marginally resolved with a separation of 0.487 arcseconds from Mira A.
The document summarizes research from images taken by the New Horizons spacecraft of Charon, Pluto's largest moon. The images reveal Charon has a reddish polar cap at its north pole. Thermal models show the pole experiences long periods of extreme cold temperatures due to Charon's high obliquity and long seasons. The researchers hypothesize that methane and other volatiles escaping from Pluto's atmosphere become cold-trapped at Charon's winter pole, where they are processed by radiation into non-volatile organic compounds that remain on the surface to form the red cap. Spectral and compositional evidence supports this mechanism of seasonal accumulation of photolyzed volatiles to explain Charon's unique polar color
PROBING FOR EVIDENCE OF PLUMES ON EUROPA WITH HST/STISSérgio Sacani
Roth et al. (2014a) reported evidence for plumes of water venting from a southern high latitude
region on Europa – spectroscopic detection of off-limb line emission from the dissociation
products of water. Here, we present Hubble Space Telescope (HST) direct images of Europa in
the far ultraviolet (FUV) as it transited the smooth face of Jupiter, in order to measure absorption
from gas or aerosols beyond the Europa limb. Out of ten observations we found three in which
plume activity could be implicated. Two show statistically significant features at latitudes similar
to Roth et al., and the third, at a more equatorial location. We consider potential systematic
effects that might influence the statistical analysis and create artifacts, and are unable to find any
that can definitively explain the features, although there are reasons to be cautious. If the
apparent absorption features are real, the magnitude of implied outgassing is similar to that of the
Roth et al. feature, however the apparent activity appears more frequently in our data.
This study analyzed transit observations of the Neptune-mass exoplanet GJ 436b taken with the Hubble Space Telescope. The transmission spectrum was found to be featureless, ruling out cloud-free hydrogen-dominated atmosphere models with high significance. The flat transmission spectrum is consistent with either an atmosphere containing high-altitude clouds located at a pressure of around 1 millibar, or a relatively hydrogen-poor atmosphere with 3% hydrogen and helium by mass. Bayesian atmospheric modeling showed that cloudy hydrogen-dominated or high-metallicity hydrogen-poor atmospheres provide the best fits to the data. Further observations are needed to distinguish between these scenarios.
The document summarizes observations of periodic increases in luminosity from a young protostar, L54361, arising from variable accretion rates. Key points:
- L54361's luminosity varies periodically every 25.34 days, increasing by a factor of 10 in about a week as material is accreted from a circumbinary disk onto the central protostar.
- This periodic pulsed accretion is attributed to the gravitational influence of an unseen binary companion perturbing the circumbinary disk.
- Follow-up observations found spatially resolved scattered light structures that vary with the same period, supporting the interpretation of variable illumination from pulsed accretion.
The document summarizes observations of two giant radio lobes emanating from the center of the Milky Way galaxy. The lobes extend about 60 degrees from the galactic center and correspond closely with previously observed gamma-ray "Fermi bubbles". The lobes contain three ridge-like substructures that curve towards the galactic west as they extend away from the center. Strong magnetic fields of up to 15 microgauss permeate the lobes. The observations indicate that the radio lobes originate from a biconical outflow driven by intense star formation in the galactic center, rather than activity from the supermassive black hole, and have transported a huge amount of magnetic energy into the galactic halo over at least the past 10 million years.
On some structural_features_of_the_metagalaxySérgio Sacani
Progress in a group of investigations designed
to discover some of the structural details in individual galaxies and in the
Metagalaxy is reported in the following pages.
(a) The first section is concerned with the distribution of cluster-type
Cepheids in high galactic latitude. To the 169 already known in latitudes,
greater than or equal to ± 20o
, the systematic variable star programme carried
on at Harvard has added 312, mostly fainter than magnitude 13-0. With
allowance for absorption and for uncertainties yet remaining in the mean
absolute magnitude of these stars, the thickness of the Milky Way, so far
as this type of star is concerned, is not less than twenty-five kiloparsecs ;
he extent of the Milky Way in its own plane, by the same criterion, is more
than thirty kiloparsecs, perhaps much more.
(b) The extent of the Milky Way in the anti-centre quadrant is considered
on the basis of classical and cluster-type Cepheids ; provisionally
it is found that the galactic system reaches to a distance of at least ten
kiloparsecs in longitude 150o
.
(r) More than six hundred new variables have been found in the Large
Magellanic Cloud and measured for position, ranges and median magnitudes ;
the frequency of periods is not unlike that for the classical Cepheids in the
galactic system ; the light curves also are comparable in all details. The
Magellanic Cepheids, like the galactic classical Cepheids, are concentrated
in regions of high star-density.
(d) Further study of the period-luminosity relation in the Large Magellanic
Cloud permits its revision and strengthening for the Cepheids of
highest absolute magnitude. An observed deviation from the relation
that had previously been found for the Small Cloud is probably to be
attributed to scale error in the magnitude system. No seriously disturbing
This document summarizes research on determining temperatures, luminosities, and masses of the coldest known brown dwarfs. The key findings are:
1) Precise distances were measured for a sample of late-T and Y dwarfs using Spitzer Space Telescope astrometry, allowing accurate calculation of absolute fluxes, luminosities, and temperatures.
2) Y0 dwarfs were found to have temperatures of 400-450 K, significantly warmer than previous estimates, and masses of 5-20 times Jupiter's mass.
3) While having similar temperatures, Y dwarfs showed diverse spectral energy distributions, suggesting temperature alone does not determine spectra. Physical properties like gravity, clouds and chemistry also influence spectra.
A thirty-four billion solar mass black hole in SMSS J2157–3602, the most lumi...Sérgio Sacani
From near-infrared spectroscopic measurements of the Mg II emission line doublet, we estimate the black hole (BH) mass of the quasar, SMSS J215728.21–360215.1, as being (3.4 ± 0.6) × 1010 M⊙ and refine the redshift of the quasar to be z = 4.692. SMSS J2157 is the most luminous known quasar, with a 3000 Å luminosity of (4.7 ± 0.5) × 1047 erg s−1 and an estimated bolometric luminosity of 1.6 × 1048 erg s−1 , yet its Eddington ratio is only ∼0.4. Thus, the high luminosity of this quasar is a consequence of its extremely large BH – one of the most massive BHs at z > 4.
The Internal Structure of Asteroid (25143) Itokawa as Revealed by Detection o...WellingtonRodrigues2014
- The authors detected an acceleration in the rotation rate of asteroid (25143) Itokawa through photometric observations spanning 2001 to 2013.
- By measuring rotational phase offsets between observed and modeled lightcurves, they found a YORP acceleration of 3.54 ± 0.38 × 10−8 rad day−2, equivalent to a decrease in the asteroid's rotation period of about 45 ms per year.
- Thermophysical modeling of the detailed shape model from the Hayabusa spacecraft could not reconcile the observed YORP strength unless the asteroid's center of mass is shifted by about 21 m along its long axis. This suggests Itokawa has two components with different densities that merged, either from a
A vast thin_plane_of_corotating_dwarf_galaxies_orbiting_the_andromeda_galaxySérgio Sacani
1. A study using data from the Pan-Andromeda Archaeological Survey finds that approximately half of the dwarf galaxy satellites orbiting the Andromeda galaxy are confined to a highly planar structure that is at least 400 kiloparsecs in diameter but only 14.1 kiloparsecs thick.
2. Radial velocity measurements reveal that 13 of the 15 dwarf galaxies within this structure share the same sense of rotation around Andromeda.
3. The existence of this thin, co-rotating planar structure of dwarf galaxies provides strong evidence that a significant fraction of satellite galaxies can have coherent orbital and angular momentum properties within their host galaxy.
The shadow _of_the_flying_saucer_a_very_low_temperature_for_large_dust_grainsSérgio Sacani
Os astrónomos usaram o ALMA e os telescópios do IRAM para fazer a primeira medição direta da temperatura dos grãos de poeira grandes situados nas regiões periféricas de um disco de formação planetária que se encontra em torno de uma estrela jovem. Ao observar de forma inovadora um objeto cujo nome informal é Disco Voador, os astrónomos descobriram que os grãos de poeira são muito mais frios do que o esperado: -266º Celsius. Este resultado surpreendente sugere que os modelos teóricos destes discos precisam de ser revistos.
Uma equipa internacional liderada por Stephane Guilloteau do Laboratoire d´Astrophysique de Bordeaux, França, mediu a temperatura de enormes grãos de poeira que se encontram em torno da jovem estrela 2MASS J16281370-2431391 na região de formação estelar Rho Ophiuchi, a cerca de 400 anos-luz de distância da Terra.
Esta estrela encontra-se rodeada por um disco de gás e poeira — chamado disco protoplanetário, uma vez que se encontra na fase inicial da formação de um sistema planetário. Este disco é visto de perfil quando observado a partir da Terra e a sua aparência em imagens no visível levou a que se lhe desse o nome informal de Disco Voador.
Os astrónomos utilizaram o ALMA para observar o brilho emitido pelas moléculas de monóxido de carbono no disco da 2MASS J16281370-2431391. As imagens revelaram-se extremamente nítidas e descobriu-se algo estranho — em alguns casos o sinal recebido era negativo. Normalmente um sinal negativo é fisicamente impossível, mas neste caso existe uma explicação, que leva a uma conclusão surpreendente.
Lenz et al. discovered that soft particles at the nano- and microscale can form "clumpy crystals" where particles partially overlap and form regular lattices of clumps. This challenges ideas that soft materials will behave similarly to atomic and molecular systems. The discovery provides another example of how soft materials display unconventional behavior. An analysis of the satellites orbiting Andromeda found that about half are rotating coherently in a thin planar structure, providing a new constraint on galaxy formation theories. Further evidence suggests organized planar distributions of satellites may be common for nearby galaxy groups. The findings compound issues with the number of predicted versus observed satellites and suggest the structures themselves are not ancient.
We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using
a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts
of the stellar disk of the LMC (r < 10 degrees from the center). These data have higher resolution
than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in
the northern periphery, with no comparable counterparts in the South. We compare these data to
detailed simulations of the LMC disk outskirts, following interactions with its low mass companion,
the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field.
The simulations are used to assess the origin of the northern structures, including also the low density
stellar arc recently identified in the DES data by Mackey et al. (2015) at ∼ 15 degrees. We conclude
that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar
structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to
constrain the LMC’s interaction history with and impact parameter of the SMC. More generally, we
find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for
1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion
around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are
driven by dwarf-dwarf interactions.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
This document reports the discovery of a newly discovered optical Einstein ring (ER) called the "Canarias Einstein Ring". It was discovered serendipitously in imaging data from the Dark Energy Camera. Follow-up spectroscopy with the Gran Telescopio CANARIAS confirmed the nature of the system, with the lens being an early-type galaxy at a redshift of z=0.581 and the source being a starburst galaxy at z=1.165. Analysis of the system determined the Einstein radius to be 2.16 arcseconds and the total enclosed mass producing the lensing effect to be 1.86 ± 0.23 × 1012 solar masses.
An extremely high_altitude_plume_seen_at_mars_morning_terminatorSérgio Sacani
Artigo da revista Nature que descreve as plumas de alta altitude identificadas pairando sobre a superfície do planeta Marte e propõem duas hipóteses para o fenômeno.
This document summarizes the discovery and characterization of Kepler-432 b, a massive exoplanet in a highly eccentric orbit around a red giant star. Key findings include:
1) Radial velocity measurements from the CAFE spectrograph revealed Kepler-432 b has a mass of 4.87 ± 0.48 MJup and moves in a highly eccentric orbit (e = 0.535 ± 0.030) around its host star.
2) Simultaneous modeling of Kepler photometry and radial velocity data determined Kepler-432 b has a radius of 1.120 ± 0.036 RJup and orbits every 52.5 days.
3) Analysis of high-resolution images found a nearby star
Discovery two embedded_clusters_with_wise_in_the_galactic_latitude_cloud_hrk8...Sérgio Sacani
Artigo descreve descoberta feita por astrônomos brasileiros de dois aglomerados estelares localizados bem distante da região tradicional onde eles normalmente são encontrados. Esses aglomerado formam estrelas e com isso pôde-se mostrar que o processo de formação de estrelas da Via Láctea pode ocorrer em locais inesperados.
Remnants of the_sagittarius_dwarf_spheroidal_galaxy_around_the_young_globular...Sérgio Sacani
This document summarizes the discovery of a low surface brightness stellar system around the young globular cluster Palomar 12. Photometry revealed a main sequence feature indicative of a more metal-poor stellar population than Pal 12, located at a similar distance of 17-24 kpc. The system was also detected 2 degrees north of Pal 12, indicating a minimum diameter of 0.9 kpc. Its color-magnitude diagram and position on the sky suggest it is debris from the tidal disruption of the Sagittarius dwarf spheroidal galaxy. The distances and orbit of Pal 12 also support this origin.
1. O ESO é uma organização intergovernamental de pesquisa em astronomia com 14 países membros na Europa. Ele opera vários observatórios no Chile, incluindo o Very Large Telescope.
2. O documento discute os termos do potencial acordo para o Brasil se tornar membro do ESO, contribuindo com cerca de 250 milhões de euros nos próximos 10 anos.
3. Embora a maioria da comunidade astronômica brasileira apoie a adesão, alguns apontam preocupações sobre o impacto no financiamento da pesquisa no
Artigo que descreve a descoberta do exoplaneta Kepler-432b, um exoplaneta mais massivo que Júpiter que orbita uma estrela gigante vermelha bem próximo e numa órbita extremamente alongada.
The closest known_flyby_of_a_star_to_the_solar_systemSérgio Sacani
The closest known flyby of a star to the solar system was a low-mass binary star system called WISE J072003.20-084651.2, also known as "Scholz's star". By integrating the orbits of this 0.15 solar mass binary system and the Sun, astronomers found that it passed within 0.25 parsecs (52,000 AU) of the Sun about 70,000 years ago, within the outer bounds of the Oort Cloud. This is the closest encounter with a star to the solar system that has been well-constrained in distance and velocity. While the flyby likely had a negligible impact on long-period comets from the Oort Cloud, it highlights the possibility
Disc dark matter_in_the_galaxy_and_potential_cycles_of_extraterrestrial_impac...Sérgio Sacani
This document discusses potential periodic cycles of extraterrestrial impacts, mass extinctions, and geological events on Earth. It proposes that:
1) Mass extinctions and impact cratering may exhibit cycles of around 26-30 million years that could be linked to the Sun's vertical oscillations through the Galactic plane around every 30-42 million years.
2) Near the Galactic plane, comets in the Oort Cloud could be perturbed by Galactic tidal forces and a possible thin dark matter disc, producing periodic comet showers and impacts on Earth linked to extinction events.
3) Records of geological events like tectonism and volcanism also show a potential cycle of around 30 million years that could be linked to the
Storm in teacup_a_radio_quiet_quasar_with_radio_emitting_bubblesSérgio Sacani
Artigo descreve descoberta feita com o VLA de uma tempestade nas ondas de rádio em uma galáxia até então calma, o que traz conclusões sobre a evolução das galáxias.
Using the inclinations_of_kepler_systems_to_prioritize_new_titius_bode_based_...Sérgio Sacani
Artigo descreve como cientistas aplicaram a relação de Titius-Bode nos dados do Kepler para prever a existência de bilhões de exoplanetas parecidos com a Terra na Via Láctea.
This document provides a summary of NASA's fiscal year 2016 budget request. Key points include:
- The total budget request for NASA in FY2016 is $18.529 billion, an increase from FY2015 enacted levels.
- The largest programs are Space Operations ($4 billion), Exploration ($4.5 billion), and Science ($5.288 billion). Science funding supports Earth Science, Planetary Science, Astrophysics, and Heliophysics programs.
- Development of the James Webb Space Telescope is the largest line item within Science, though funding is decreasing as the project nears completion.
- Exploration funding focuses on development of the Space Launch System, Orion spacecraft, and Commercial Crew Program.
The muse 3_d_view_of_the_hubble_deep_field_southSérgio Sacani
Artigo mostra como foram as observações feitas com o MUSE, o novo instrumento do VLT do campo profundo do Hubble. Além de descobrir 20 novos objetos, o MUSE conseguiu medir as propriedades das galáxias e até representar as mais próximas em 3 dimensões.
This document provides an overview of electron spin resonance (ESR) spectroscopy. It discusses how ESR works by applying a magnetic field to induce transitions between electron spin energy levels, which are split due to interactions between unpaired electrons and their environment. Specifically, it describes how orbital interactions and nuclear hyperfine interactions affect the ESR spectrum. It also discusses experimental considerations like microwave frequencies, magnetic field strengths, sensitivity, saturation effects, and nuclear hyperfine interactions. The goal is to provide fundamentals of ESR spectroscopy and introduce its capabilities for studying organic and organometallic radicals and complexes.
Artigo descreve o código computacional utilizado no filme interstellar para gerar o buraco negro Gargantua e como isso trouxe conclusões e ideias sobre os buracos negros em rotação.
An ultraluminous quasar_with_a_twelve_billion_solar_mass_black_hole_at_redshi...Sérgio Sacani
1) Researchers discovered an ultraluminous quasar, SDSS J010013.021280225.8, at a redshift of 6.30, making it the most distant and luminous quasar known.
2) Spectral analysis estimates the black hole at its center has a mass of 1.2 billion solar masses, consistent with an Eddington-limited accretion rate.
3) The quasar has an ionized proximity zone estimated to be 26 million light years across, significantly larger than found for other high-redshift quasars, suggesting its high luminosity.
- The document derives the second order Friedmann equations from the quantum corrected Raychaudhuri equation (QRE), which includes quantum corrections terms.
- One correction term can be interpreted as dark energy/cosmological constant with the observed density value, providing an explanation for the coincidence problem.
- The other correction term can be interpreted as a radiation term in the early universe that prevents the formation of a big bang singularity and predicts an infinite age for the universe by avoiding a divergence in the Hubble parameter or its derivative at any finite time in the past.
Artigo descreve a descoberta de um sistema de anéis 200 vezes maior do que o sistema de anéis de Saturno num exoplaneta orbitando a jovem estrela J1407
Probing the jet_base_of_blazar_pks1830211_from_the_chromatic_variability_of_i...Sérgio Sacani
This document summarizes ALMA observations of the blazar PKS 1830-211 taken over multiple epochs in 2012. The blazar is lensed by a foreground galaxy, producing two resolved images (NE and SW) separated by 1". The observations were taken at frequencies corresponding to 350-1050 GHz in the blazar rest frame. Analysis of the flux ratio between the two images over time and frequency revealed a remarkable frequency-dependent behavior, implying a "chromatic structure" in the blazar jet. This is interpreted as evidence for a "core-shift effect" caused by plasmon ejection very near the base of the jet. The observations provide a unique probe of activity in the region where plasma acceleration occurs in blazar
This document summarizes an infrared survey of the massive star forming region RCW 57 (NGC 3576) using L-band (3.5 μm) data from SPIREX and JHKs data from 2MASS. Over 50% of the 209 sources detected showed infrared excess, indicating circumstellar disks. Comparison to other surveys supports a very high initial disk fraction (>80%) around massive stars, though disks may dissipate faster around high-mass stars. 33 sources only detected at L-band indicate heavily embedded, massive Class I protostars. Diffuse PAH emission was also detected throughout RCW 57.
Alma observations of_feed_and_feedback_in_nearby_seyfert_galaxiesSérgio Sacani
The ALMA observations of NGC 1433 reveal a nuclear gaseous spiral structure within the central kpc. This spiral winds up into a pseudo-ring at ~200 pc from the center. Near the nucleus, there is intense high-velocity CO emission up to 200 km/s that is interpreted as an outflow, involving 3.6 million solar masses of molecular gas and a flow rate of ~7 solar masses per year. The outflow could be driven by both the central star formation and AGN through its radio jets. Continuum emission at 0.87 mm is detected only at the very center and likely comes from thermal dust emission from the molecular torus expected in this Seyfert 2 galaxy.
Forming intracluster gas in a galaxy protocluster at a redshift of 2.16Sérgio Sacani
Galaxy clusters are the most massive gravitationally bound structures in the Universe, comprising thousands of galaxies and
pervaded by a diffuse, hot “intracluster medium” (ICM) that dominates the baryonic content of these systems. The formation
and evolution of the ICM across cosmic time1
is thought to be driven by the continuous accretion of matter from the large-scale
filamentary surroundings and dramatic merger events with other clusters or groups. Until now, however, direct observations of
the intracluster gas have been limited only to mature clusters in the latter three-quarters of the history of the Universe, and we
have been lacking a direct view of the hot, thermalized cluster atmosphere at the epoch when the first massive clusters formed.
Here we report the detection (about 6σ) of the thermal Sunyaev-Zeldovich (SZ) effect2
in the direction of a protocluster. In fact,
the SZ signal reveals the ICM thermal energy in a way that is insensitive to cosmological dimming, making it ideal for tracing
the thermal history of cosmic structures3
. This result indicates the presence of a nascent ICM within the Spiderweb protocluster
at redshift z = 2.156, around 10 billion years ago. The amplitude and morphology of the detected signal show that the SZ
effect from the protocluster is lower than expected from dynamical considerations and comparable with that of lower-redshift
group-scale systems, consistent with expectations for a dynamically active progenitor of a local galaxy cluster.
Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of
1011.5 K. Relativistic boosting can increase its observed value, but apparent brightness temperatures
much in excess of 1013 K are inaccessible using ground-based very long baseline interferometry (VLBI)
at any wavelength. We present observations of the quasar 3C 273, made with the space VLBI mission
RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as
small as 26 µas (2.7 light months) and brightness temperature in excess of 1013 K. These measurements
challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive
black holes and require a much higher Doppler factor than what is determined from jet apparent
kinematics.
Keywords: galaxies: active — galaxies: jets — radio continuum: galaxies — techniques: interferometric
— quasars: individual (3C 273)
X-Ray Properties of NGC 253ʼs Starburst-driven OutflowSérgio Sacani
We analyze image and spectral data from ≈365 ks of observations from the Chandra X-ray Observatory of the
nearby, edge-on starburst galaxy NGC 253 to constrain properties of the hot phase of the outflow. We focus our
analysis on the −1.1 to +0.63 kpc region of the outflow and define several regions for spectral extraction where we
determine best-fit temperatures and metal abundances. We find that the temperatures and electron densities peak in
the central ∼250 pc region of the outflow and decrease with distance. These temperature and density profiles are in
disagreement with an adiabatic spherically expanding starburst wind model and suggest the presence of additional
physics such as mass loading and nonspherical outflow geometry. Our derived temperatures and densities yield
cooling times in the nuclear region of a few million years, which may imply that the hot gas can undergo bulk
radiative cooling as it escapes along the minor axis. Our metal abundances of O, Ne, Mg, Si, S, and Fe all peak in
the central region and decrease with distance along the outflow, with the exception of Ne, which maintains a flat
distribution. The metal abundances indicate significant dilution outside of the starburst region. We also find
estimates of the mass outflow rates, which are 2.8 Me yr−1 in the northern outflow and 3.2 Me yr−1 in the southern
outflow. Additionally, we detect emission from charge exchange and find it makes a significant contribution (20%–
42%) to the total broadband (0.5–7 keV) X-ray emission in the central and southern regions of the outflow.
Alma observations of_feeding_and_feedback_in_nearby_seyfert_galaxies_outflow_...Sérgio Sacani
ALMA observations of the Seyfert 2 galaxy NGC 1433 reveal a nuclear gaseous spiral structure within a nuclear ring encircling a nuclear stellar bar. Near the nucleus, there is intense high-velocity CO emission interpreted as an AGN-driven molecular outflow. The outflow involves a molecular mass of 3.6 million solar masses and a flow rate of about 7 solar masses per year. Continuum emission at the center is likely thermal dust emission from a molecular torus expected in this Seyfert 2 galaxy. The observations probe gas dynamics within 24 parsecs of the active galactic nucleus.
MUSE sneaks a peek at extreme ram-pressure stripping events. I. A kinematic s...Sérgio Sacani
- MUSE observations of the galaxy ESO137-001 reveal an extended gaseous tail over 30 kpc long traced by H-alpha emission, providing evidence of an extreme ram pressure stripping event as the galaxy falls into the massive Norma galaxy cluster.
- Analysis of the H-alpha kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center, with gravitational interactions not appearing to be the main mechanism of gas removal.
- The stripped gas retains evidence of the disk's rotational velocity out to around 20 kpc downstream, indicating the galaxy is moving radially along the plane of the sky, while
This document describes observations of the galaxy ESO137-001 using the MUSE instrument on the VLT. The key points are:
1) MUSE observations reveal an extended gas tail stretching over 30 kpc from the galaxy, tracing ongoing ram pressure stripping as it falls into the Norma galaxy cluster.
2) Analysis of the gas kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center.
3) The stripped gas retains evidence of the disk's rotational velocity out to 20 kpc downstream, indicating the galaxy is moving radially through the cluster. Beyond this the gas shows greater turbulence,
Cold Molecular Gas in Merger Remnants. I. Formation of Molecular Gas DiscsGOASA
- 80% (24/30) of the merger remnants with robust CO detections showed kinematical signatures of rotating molecular gas disks (including nuclear rings) based on their velocity fields. The sizes of these disks varied significantly from 1.1 kpc to 9.3 kpc.
- In 54% of the sources, the size of the molecular gas disks was more compact than the K-band effective radius, possibly formed from past gas inflows triggered by dynamical instabilities during mergers.
- The remaining 46% had more extended gas disks relative to the stellar component, possibly forming late-type galaxies with central stellar bulges.
- The study suggests that nuclear and extended molecular gas disks are common in
This document summarizes new results from a study of proper motions in the optical jet of the galaxy M87 using over 13 years of Hubble Space Telescope imaging data. Key findings include:
1) Superluminal velocities (above the speed of light) were measured for knots as far out as knot C in the jet, suggesting these speeds persist over large distances.
2) Significant apparent accelerations both parallel and transverse to the jet axis were found, as well as evidence for stationary features in some knots.
3) Complex motions including differing velocities between nearby features and changes in velocity over time were observed throughout the jet, placing constraints on theoretical jet models.
The document analyzes Spitzer Infrared Spectrograph (IRS) observations of warm molecular hydrogen (H2) gas in M51. It finds that the six H2 lines observed have distinct emission distributions across the galaxy. Lower J lines like H2 S(0) peak in the spiral arms, while higher J lines like H2 S(3) peak at the nucleus. The observations are used to model the H2 excitation temperature and mass in a warm (100-300 K) and hot (400-1000 K) phase. The warm gas peaks at 11 M_sun/pc^2 in the spiral arms, while the hot gas peaks at 0.24 M_sun/pc^2 at the
Detection of an_unindentified_emission_line_in_the_stacked_x_ray_spectrum_of_...Sérgio Sacani
1. Researchers detected a previously unknown emission line in the stacked X-ray spectrum of 73 galaxy clusters observed by XMM-Newton. 2. The line was detected at an energy of 3.55-3.57 keV and was seen independently in subsamples of clusters. 3. The line was also detected in Chandra observations of the Perseus cluster but not in observations of the Virgo cluster. 4. The nature of this line is unclear - it could be a thermal line from an undetected element, or potentially the decay line of a hypothesized dark matter particle called a sterile neutrino. Further observations are needed to determine the origin of the line.
Water vapour absorption_in_the_clear_atmosphere_of_a_neptune_sized_exoplanetSérgio Sacani
This document summarizes research on the transmission spectrum of the exoplanet HAT-P-11b, a Neptune-sized planet. Observations from the Hubble Space Telescope and Spitzer Space Telescope detected water vapor absorption in the planet's atmosphere at a wavelength of 1.4 micrometers. Analysis of the spectrum indicates the atmosphere is predominantly clear down to 1 mbar and has a hydrogen abundance similar to solar values. Atmospheric modeling suggests a metallicity around 190 times that of the Sun's, in agreement with core accretion planet formation theories. This makes HAT-P-11b the smallest exoplanet to date with a detected molecular signature in its atmosphere, providing new insights into the composition and formation of Neptune-sized
X-rays from a Central “Exhaust Vent” of the Galactic Center ChimneySérgio Sacani
Using deep archival observations from the Chandra X-ray Observatory, we present an analysis of
linear X-ray-emitting features located within the southern portion of the Galactic center chimney,
and oriented orthogonal to the Galactic plane, centered at coordinates l = 0.08◦
, b = −1.42◦
. The
surface brightness and hardness ratio patterns are suggestive of a cylindrical morphology which may
have been produced by a plasma outflow channel extending from the Galactic center. Our fits of the
feature’s spectra favor a complex two-component model consisting of thermal and recombining plasma
components, possibly a sign of shock compression or heating of the interstellar medium by outflowing
material. Assuming a recombining plasma scenario, we further estimate the cooling timescale of this
plasma to be on the order of a few hundred to thousands of years, leading us to speculate that a
sequence of accretion events onto the Galactic Black Hole may be a plausible quasi-continuous energy
source to sustain the observed morphology
Radio continum emission_of_35_edge_on_galaxies_observed_with_the_vlaSérgio Sacani
Usando um dos maiores rádio observatórios do mundo, o Very Large Array do National Radio Astronomy, um grupo de astrônomos descobriram que os halos ao redor dos discos das galáxias espirais são muito mais comuns do que se pensava anteriormente.
A equipe, dirigida pela Dra. Judith Irwin, da Universidade de Queens, em Kingston, ON, Canadá, observou 35 galáxias espirais próximas de lado, de 11 a 137 milhões de anos-luz de distância da Terra.
As galáxias espirais, como a nossa própria Via Láctea ou a famosa Galáxia de Andrômeda, possuem uma vasta maioria de suas estrelas, gás, e poeira num disco plano em rotação com braços espirais. A maior parte da luz e das ondas de rádio observadas com telescópios veem de objetos localizados nesse disco.
“Nós sabíamos antes que alguns halos existiam, mas, usando o poder total do VLA atualizado e o poder total de algumas técnicas de processamento de imagens, nós descobrimos que esses halos são muito mais comuns entre as galáxias espirais do que nós pensávamos antes”, explicou a Dra. Irwin.
Magnetic fields and relativistic electrons fill entire galaxy clusterSérgio Sacani
- The authors analyzed deep LOFAR radio observations of the galaxy cluster Abell 2255, detecting radio synchrotron emission distributed over an unprecedented scale of at least 5 megaparsecs, well beyond the cluster outskirts.
- This pervasive radio emission indicates that shocks and turbulence efficiently transfer kinetic energy into relativistic particles and magnetic fields throughout the cluster, including the periphery.
- The strength of the emission requires magnetic field energy densities at least 100 times higher than expected from simple compression of primordial fields, suggesting efficient dynamo action even in the cluster outskirts.
Detection of an_unidentified_emission_line_in_the_stacked_xray_spectrum_of_ga...Sérgio Sacani
This document describes the detection of an unidentified emission line in the stacked X-ray spectrum of 73 galaxy clusters observed by XMM-Newton. The line was detected at an energy of 3.55-3.57 keV in independent analyses of the MOS and PN instruments. The line was also seen in Chandra observations of the Perseus cluster. Possible explanations discussed include an atomic transition in thermal plasma, or the decay of sterile neutrino dark matter particles. However, the origin is unclear and requires further observation.
Similar to Alma multi line_imaging_of_the_nearby_starburst_ngc_253 (20)
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
Phenomics assisted breeding in crop improvementIshaGoswami9
As the population is increasing and will reach about 9 billion upto 2050. Also due to climate change, it is difficult to meet the food requirement of such a large population. Facing the challenges presented by resource shortages, climate
change, and increasing global population, crop yield and quality need to be improved in a sustainable way over the coming decades. Genetic improvement by breeding is the best way to increase crop productivity. With the rapid progression of functional
genomics, an increasing number of crop genomes have been sequenced and dozens of genes influencing key agronomic traits have been identified. However, current genome sequence information has not been adequately exploited for understanding
the complex characteristics of multiple gene, owing to a lack of crop phenotypic data. Efficient, automatic, and accurate technologies and platforms that can capture phenotypic data that can
be linked to genomics information for crop improvement at all growth stages have become as important as genotyping. Thus,
high-throughput phenotyping has become the major bottleneck restricting crop breeding. Plant phenomics has been defined as the high-throughput, accurate acquisition and analysis of multi-dimensional phenotypes
during crop growing stages at the organism level, including the cell, tissue, organ, individual plant, plot, and field levels. With the rapid development of novel sensors, imaging technology,
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PPT on Direct Seeded Rice presented at the three-day 'Training and Validation Workshop on Modules of Climate Smart Agriculture (CSA) Technologies in South Asia' workshop on April 22, 2024.
Immersive Learning That Works: Research Grounding and Paths ForwardLeonel Morgado
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The use of Nauplii and metanauplii artemia in aquaculture (brine shrimp).pptxMAGOTI ERNEST
Although Artemia has been known to man for centuries, its use as a food for the culture of larval organisms apparently began only in the 1930s, when several investigators found that it made an excellent food for newly hatched fish larvae (Litvinenko et al., 2023). As aquaculture developed in the 1960s and ‘70s, the use of Artemia also became more widespread, due both to its convenience and to its nutritional value for larval organisms (Arenas-Pardo et al., 2024). The fact that Artemia dormant cysts can be stored for long periods in cans, and then used as an off-the-shelf food requiring only 24 h of incubation makes them the most convenient, least labor-intensive, live food available for aquaculture (Sorgeloos & Roubach, 2021). The nutritional value of Artemia, especially for marine organisms, is not constant, but varies both geographically and temporally. During the last decade, however, both the causes of Artemia nutritional variability and methods to improve poorquality Artemia have been identified (Loufi et al., 2024).
Brine shrimp (Artemia spp.) are used in marine aquaculture worldwide. Annually, more than 2,000 metric tons of dry cysts are used for cultivation of fish, crustacean, and shellfish larva. Brine shrimp are important to aquaculture because newly hatched brine shrimp nauplii (larvae) provide a food source for many fish fry (Mozanzadeh et al., 2021). Culture and harvesting of brine shrimp eggs represents another aspect of the aquaculture industry. Nauplii and metanauplii of Artemia, commonly known as brine shrimp, play a crucial role in aquaculture due to their nutritional value and suitability as live feed for many aquatic species, particularly in larval stages (Sorgeloos & Roubach, 2021).
Unlocking the mysteries of reproduction: Exploring fecundity and gonadosomati...AbdullaAlAsif1
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When I was asked to give a companion lecture in support of ‘The Philosophy of Science’ (https://shorturl.at/4pUXz) I decided not to walk through the detail of the many methodologies in order of use. Instead, I chose to employ a long standing, and ongoing, scientific development as an exemplar. And so, I chose the ever evolving story of Thermodynamics as a scientific investigation at its best.
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Slides from talk:
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https://www.etran.rs/2024/en/home-english/
Alma multi line_imaging_of_the_nearby_starburst_ngc_253
1. Accepted to the Astrophysical Journal
Preprint typeset using LATEX style emulateapj v. 5/2/11
ALMA MULTI–LINE IMAGING OF THE NEARBY STARBURST NGC 253
Meier, David S.1,2,3
, Walter, Fabian4,2
, Bolatto, Alberto D.5
, Leroy, Adam K.4
, Ott, J¨urgen2
, Rosolowsky,
Erik7
, Veilleux, Sylvain8,5
, Warren, Steven R.5
, Weiß, Axel9
, Zwaan, Martin A.10
, Zschaechner, Laura K.4
Draft version January 26, 2015
ABSTRACT
We present spatially resolved (⇠50 pc) imaging of molecular gas species in the central kilopar-
sec of the nearby starburst galaxy NGC 253, based on observations taken with the Atacama Large
Millimeter/submillimeter Array (ALMA). A total of 50 molecular lines are detected over a 13 GHz
bandwidth imaged in the 3 mm band. Unambiguous identifications are assigned for 27 lines. Based
on the measured high CO/C17
O isotopic line ratio (&350), we show that 12
CO(1 0) has moder-
ate optical depths. A comparison of the HCN and HCO+
with their 13
C–substituted isotopologues
shows that the HCN(1–0) and HCO+
(1–0) lines have optical depths at least comparable to CO(1–0).
H13
CN/H13
CO+
(and H13
CN/HN13
C) line ratios provide tighter constraints on dense gas properties
in this starburst. SiO has elevated abundances across the nucleus. HNCO has the most distinctive
morphology of all the bright lines, with its global luminosity dominated by the outer parts of the
central region. The dramatic variation seen in the HNCO/SiO line ratio suggests that some of the
chemical signatures of shocked gas are being erased in the presence of dominating central radiation
fields (traced by C2H and CN). High density molecular gas tracers (including HCN, HCO+
, and CN)
are detected at the base of the molecular outflow. We also detect hydrogen recombination lines that,
like their ↵ counterparts, show compact, centrally peaked morphologies, distinct from the molecular
gas tracers. A number of sulfur based species are mapped (CS, SO, NS, C2S, H2CS and CH3SH) and
have morphologies similar to SiO.
Subject headings: galaxies: formation — galaxies: evolution — individual galaxy (NGC 253) —
astrochemistry; ISM — radio lines
1. INTRODUCTION
Characterizing the physical properties of the molecular
gas phase in galaxies, the key phase for star formation
(review by Kennicutt & Evans 2012), is among the main
drivers in the studies of nearby galaxies. The 12
CO line
is by far the brightest millimeter–wave molecular line in
the interstellar medium (ISM) and has therefore been the
main tracer of the molecular medium in both low– and
high–redshift studies (e.g., reviews by Bolatto, Leroy &
Wolfire 2013 and Carilli & Walter 2013). Even though
CO emission is a reasonable tracer of the morphology
and mass associated with the molecular ISM, observa-
tions of other tracer molecules, that have di↵erent crit-
ical densities and excitation temperatures, provide key
information to constrain the physical processes in the
1 New Mexico Institute of Mining and Technology, 801 Leroy
Place, Socorro, NM, USA; E-mail: dmeier@nmt.edu
2 National Radio Astronomy Observatory, Pete V. Domenici
Array Science Center, P.O. Box O, Socorro, NM, 87801, USA
3 Adjunct Astronomer, National Radio Astronomy Observa-
tory
4 Max-Planck Institut f¨ur Astronomie, K¨onigstuhl 17, D-
69117, Heidelberg, Germany
5 University of Maryland, College Park, Department of As-
tronomy and Joint Space–Science Institute
6 National Radio Astronomy Observatory, 520 Edgemont
Road, Charlottesville, VA 22903, USA
7 Department of Physics, University of Alberta, Edmonton AB
T6G 2E1, Canada
8 Department of Astronomy, University of Maryland, College
Park, MD 20742, USA
9 Max Planck Institut f¨ur Radioastronomie, Auf dem Hgel 69,
53121 Bonn
10 European Southern Observatory, Karl-Schwarzschild-Str.
2, D-85748 Garching bei M¨unchen, Germany
ISM. Studying a whole suite of molecular line tracers
sheds light on the chemical state of the ISM, including
the gas cooling and ionization balance in the molecular
ISM. Ultimately, surveying provides the means by which
to characterize molecular cloud conditions that are af-
fected by the galactic environment, including feedback
and shocks caused by star formation, and dynamical pro-
cesses within a galaxy (e.g., Meier & Turner 2005).
Millimeter line surveys of nearby galaxies using single–
dish telescopes have shown that their spectra are rich in
molecular lines (e.g., Usero et al. 2004, Martin et al. 2006,
Costagliola et al. 2011, Snell et al. 2011, Aladro et al.
2011, 2013). However, given the resolution of single–dish
telescopes, most of these studies could only provide in-
tegrated measurements, making it di cult to investigate
spatial changes in chemical properties. Spatially resolved
surveys using millimeter interferometers have been lim-
ited to only a handful of transitions due to small band-
widths and low sensitivity (e.g., Meier & Turner 2005,
2012, Meier et al. 2014, Martin et al. 2014). These
studies demonstrate the presence of strong chemical dif-
ferentiation can exist within the molecular gas in nearby
galaxies and their usefulness for constraining the evolu-
tionary properties of the nucleus.
The newly commissioned ALMA facility is revolution-
izing chemical studies of galaxies. Its sensitivity, even
in ‘Early Science’ mode is unprecedented, and molecules
that are typically significantly fainter than the brightest
ones (i.e., CO, HCN, HCO+
, CN) can be detected in rea-
sonable integration times. In addition ALMA’s large in-
stantaneous bandwidth of ⌫ =8 GHz implies that mul-
tiple lines (in particular in the 3 mm band where ⌫/⌫ is
arXiv:1501.05694v1[astro-ph.GA]23Jan2015
2. 2 Meier, Walter, Bolatto et al.
highest) are covered in each observation. The study pre-
sented here does not intend to discuss the details of every
detected line but instead present the data and highlight the
rich chemistry provided by ALMA’s new capabilities, in
the nearby starburst galaxy NGC 253. This paper com-
plements two other studies of NGC 253 using the same
dataset, one describing the molecular outflow revealed in
12
CO emission (Bolatto et al. 2013, hereafter B13) and
the other constraining the molecular clump properties in
the central starburst region using the brightest dense gas
tracers available (Leroy et al. 2014, hereafter L14).
The paper is structured as follows: Sec. 2 briefly sum-
marizes the observations, data reduction and data prod-
ucts. In Sec. 3 we present our identification of the rich
suite of molecular line emission in the galaxy. We then
proceed to sketch a simple picture of the conditions in the
central region of NGC 253, by focusing on several groups
of key molecular gas tracers (Sec. 4). We conclude by
providing a short summary in Sec. 5. Throughout the pa-
per we adopt a distance to NGC 253 of 3.5 Mpc (Rekola
et al. 2005), i.e., 1” corresponds to 17 pc at that distance.
The systemic velocity of NGC 253 is ⇠250 km s 1
(e.g.,
Houghton et al. 1997).
2. OBSERVATIONS AND DATA REDUCTION
Observations: We have mapped NGC 253 with ALMA
in cycle 0 (16 antenna array) in two di↵erent frequency
setups and configurations. Details regarding the obser-
vations and data reduction can be found in B13 and
L14 and we here summarize the observational parameters
that are most relevant for the current study. Both se-
tups covered an instantaneous bandwidth of 8 GHz each:
The first frequency setup, covering 85.6–89.6 GHz (lower
side–band, LSB) and 97.4–101.4 GHz (upper side–band,
USB), is a central 3–point mosaic along the major axis
in the extended configuration (average beam size: ⇠2”,
⇠35 pc). This mosaic covers the central 10
(1 kpc) of
NGC 253’s starburst. The second setup covers 99.8–
103.7 GHz (LSB) and 111.8–115.7 GHz (USB) and is a 7–
point mosaic of NGC 253’s center in the compact configu-
ration. This yields an average beam size of ⇠4” (⇠70 pc)
and a field of view of roughly 1.50
(⇠1.5 kpc).
Data reduction: All of the calibration and imaging of
the data cubes was completed within CASA, including
self–calibration to remove residual phase and flux calibra-
tion errors. After imaging, much of the remaining analy-
sis was performed with IDL scripts with some use of the
Miriad and Matlab software packages. Most of the data
presented here is based on the continuum–subtracted
cube, where the continuum was defined in those spec-
tral regions where no line emission was evident. Our
final cube has 20 km s 1
velocity resolution and a typical
RMS of ⇠2.0 mJy beam 1
(extended, LSB: 1.9 mJy, ex-
tended, USB: 2.1 mJy, compact, LSB: 2.0 mJy, compact,
USB: 3.3 mJy).
Final data cubes: We display the information in the
data cubes in two complementary fashions: through a
position–velocity (pV) diagram along the major axis of
NGC 253 in Fig. 1; a representation similar to long–slit
spectroscopy in optical/NIR astronomy (Fig. 1). The
second (Fig. 2) is a single spectrum taken toward a cen-
tral molecular peak (position 5). As outlined above, the
data consist of four final data cubes, the LSB and USB
cubes for the extended configuration, and those for the
compact configuration. Figs. 1 and 2 also show our line
identification (see also Tab. 1), as further discussed in
Sec. 3.
Integrated line maps: We created line cubes for each
line, and then blanked those with a mask derived from
the CO(1-0) line (by far the brightest line in the band-
pass). The integrated intensity map for a given line was
then derived by simply adding all data in the respective
data cube (without any further flux cuto↵). Integrated
line maps are corrected for primary beam attenuation
and are shown in Fig. 3.
Uncertainties: We calculated error maps by taking the
number of channels per pixel into account. An inspec-
tion of the data cubes revealed that these error maps
provide too optimistic uncertainties, as they do not ac-
count for artifacts (in particular the negative ‘bowl’ due
to the missing short spacings) in the current data. We
thus adopt a conservative 10% error for pixels that have
been detected at high S/N (> 10), where the noise N
is from taken from our error maps. For pixels that are
detected at lower S/N (5<S/N<10) we adopt an even
more conservative 30% uncertainty, to also account for
possible issues in baseline determination. We ignore all
pixels that have a S/N <5 in the analysis that follows.
We present our line intensity measurements towards 10
positions in NGC 253 (Fig. 4, coordinates in Tab. 1) in
Tab. 1. Toward the center of the galaxy (in particu-
lar region 6, Fig. 4) line emission is observed against
strong continuum (L14). Some resulting absorption will
decrease the integrated line signal at these locations. Be-
cause of this the fluxes toward this location should be
considered highly uncertain.
Spatial filtering: As ALMA is an interferometer it acts
as a spatial filter, sampling only a range of spatial scales.
So the observations will potentially resolve out some flux.
In the compact (extended) configuration spatial scales of
12 – 47 k (23 – 100 k ) [90th percentile] were sampled,
corresponding to 4.400
– 1800
(200
– 900
). Hence the observa-
tions should adequately sample fluxes uniform over ⇠1000
(in one channel). The one exception to this is 12
CO(1–0),
which has been zero-spacing corrected and therefore de-
tects all flux (see discussion in B13). It is not possible to
estimate the percentage of detected flux for every line in
the survey because suitable single-dish observations are
often not available. We do, however, determine this frac-
tion for a number of transitions where possible. For the
following transitions we calculate detected flux percent-
ages over single-dish beam of ⇠22 00
– ⇠2800
of: HCN(1–
0) — 100 % (Paglione et al 1995), HCO+
(1–0) — 55 %
(Martin et al. 2009), C17
O(1–0) — 60 % (Henkel et al.
2014), SiO(2–1) — 110 % (Martin et al. 2009), CN(1–0;3
2
– 1
2 ) — 60 % (Henkel et al. 2014), C2H(1–0;3
2 – 1
2 ) — 60
% (Nakajima et al. 2011) and HNCO(404–303) — 50 %
(Nguyen-Q-Rieu et al. 1991) [though this value is highly
uncertain because HNCO does not peak where Nguyen-
Q-Rieu et al. pointed]. Therefore, it appears that the
data consistently detect at least 50 % of their respective
single dish fluxes. Furthermore our discussion focuses on
the compact clumps of emission, where much higher frac-
tions of the flux are detected (&90 %). (In fact, spatial
filtering of the interferometer actually a↵ords advantages
because it allows the separation of these compact struc-
tures from any extended di↵use medium that can domi-
3. ALMA Multi–line Imaging of the Nearby Starburst Galaxy NGC 253 3
TABLE 1
Observed Emission Lines
Transition Rest Frequency Setup Comments
(GHz)
HC15N(J = 1 0) 86.054 ext, LSB tent. ID
SO(JN =22-11) 86.09395 ext, LSB
H13CN(1–0) 86.34016 ext, LSB
HCO(JKaKc =11,0–00,0) 86.67076 ext, LSB
H13CO+(1–0) 86.75429 ext, LSB
SiO(2–1; v=0) 86.84696 ext, LSB
HN13C(1–0) 87.09085 ext, LSB
C2H(N=1-0;J=3/2-1/2) 87.31690 ext, LSB main C2H FS component
C2H(1-0;1/2-1/2) 87.40199 ext, LSB secondary C2H FS component
U 87.567 ext, LSB poss. ID: SiN(2 1; 5/2 3/2)
CH3NH2(31 30) 87.785 ext, LSB tent. ID
NH2CHO(41,3 31,2) 87.853 ext, LSB tent. ID
HNCO(40,4 30,3) 87.92524 ext, LSB
H(52) 88.40569 ext, LSB
HCN(1–0) 88.63160 ext, LSB
HCO+(1–0) 89.18852 ext, LSB
34SO(32 21) 97.720 ext, USB tent. ID
CS(2–1) 97.98095 ext, USB
CH3CH2CN 98.525 ext, USB tent. ID; blend: (116 107) & (117 107)
U 98.667 ext, USB no obvious ID
H(40)↵ 99.02295 ext, USB
H(50) 99.22521 ext, USB
SO(32 21) 99.29987 ext, USB
U 99.669 ext, USB no obvious ID
C2S(78 67) 99.86651 ext, USB
HC3N(11–10) 100.07640 ext, USB, comp, LSB
U 100.542 ext, USB, comp, LSB poss. ID: CH2CN(52,3 42,2; 9/2 7/2)
U 100.612 ext, USB, comp, LSB poss. IDs: CH2CN(50,5 40,4; 9/2 7/2)
CH3CH2CN(111,10 101,9)
U 100.632 ext, USB, comp, LSB poss. IDs: NH2CN(51,4 41,3);
CH2CN(52,4 42,3; 11/2 9/2)
U 100.992 ext, USB, comp, LSB poss. ID: CH3CH2OH(82,7 818)
CH3SH(40 30)A+E 101.13916 ext, USB; comp, LSB
CH3SH(42 32)A 101.180 ext, USB; comp, LSB tent. ID
H2CS(31,3 21,2) 101.47788 comp, LSB ortho-H2CS
CH2CO(51,4 441,3 ) 101.892 comp, LSB tent. ID
U 101.988 comp, LSB no obvious ID
NH2CHO(51,5 41,4) 102.070 comp, LSB tent. ID
CH3C2H(6k 5k) 102.54798 comp, LSB
H2CS 103.04054 comp, LSB para: (32,2 22,1), (30,3 20,2), (32,1 22,0)
C2S(88 77) 103.64075 comp, LSB
CH3CHO(61,5 51,5)A+ 112.247 comp, USB tent. ID
C17O(1–0) 112.35928 comp, USB
HCOOH 112.459 comp, USB tent. ID, blend: (53,3 43,2) & (53,2 43,1)
CN(1-0;1/2-1/2) 113.19128 comp, USB secondary CN FS group
CN(1-0;3/2-1/2) 113.49097 comp, USB main CN FS group
U 114.218 comp, USB poss. IDs: CO(1-0; v=1);
C4H(12-11; 25/2-23/2& 23/2-21/2)
U 114.605 comp, USB no obvious ID
CH3CHO(60,6 50,5)A++E 114.952 comp, USB
NS(5/2-3/2;7/2-5/2) 115.15394 comp, USB blended with CO
CO(1–0) 115.27120 comp, USB Bolatto et al. 2013
NS(5/2-3/2;7/2-5/2) 115.55625 comp, USB
Note. — Note: species in italics represent tentative identifications. In these cases, the frequency listed is the observed one corrected to rest
frequency based on the known velocity field and does not reflect the rest frequency of the tentatively identified line. Lines labeled U are the ones
that we could not securely identify, and in some cases we give possible ID’s in the last column.
nate single-dish observations.) Finally, we avoid compar-
ing line intensities derived from di↵erent array configura-
tions wherever possible in this study, to further mitigate
against di↵erences in resolved flux. Hence we conclude
that uncertainties in line ratios due to di↵erent degrees
of missing flux are .10 %.
3. RESULTS
3.1. The Nucleus of NGC 253
The nucleus of NGC 253 is characterized by the inner
portion of NGC 253’s large–scale bar: The highly inclined
(i ' 78 deg) nuclear disk extends from the very center out
to a radius, r & 370 pc. In some transitions emission is
seen out to the edge of the mosaic. The outer part of
the nuclear disk (the ‘outer nuclear disk’) is suggested to
represent the location where gas flowing radially inward
along the large-scale bar collects between the outer and
inner Lindblad resonance (Garcia-Burillo et al. 2000).
Embedded within the outer disk is a compact (r ' 170
4. 4 Meier, Walter, Bolatto et al.
Fig. 1.— Position–velocity cut along the major axis of the central bar of NGC 253 (equivalent to an optical/near–infrared long–slit
spectrum). Angular o↵sets are given with respect to the galaxy center. The left two panels show the lower and upper sidebands of the
extended ALMA configuration, the right two panels the corresponding sidebands of the compact configuration. Identified molecular spectral
lines are labeled (secure: bold, tentative: italics, see Tab. 1 for a full description of transitions). The CO line is completely saturated in this
presentation and the HCN, HCO+ and CN lines are partially saturated. Table 1 lists the coordinate about which the o↵sets are referenced.
TABLE 2
NGC 253 Positions
Region RA(2000.0) DEC(2000.0)
1 00 47 33.041 -25 17 26.61
2 00 47 32.290 -25 17 19.10
3 00 47 31.936 -25 17 29.10
4 00 47 32.792 -25 17 21.10
5 00 47 32.969 -25 17 19.50
6 00 47 33.159 -25 17 17.41
7 00 47 33.323 -25 17 15.50
8 00 47 33.647 -25 17 13.10
9 00 47 33.942 -25 17 11.10
10 00 47 34.148 -25 17 12.30
Map 00 47 33.100 -25 17 17.50
Note. — Coordinates of the 10 regions in NGC 253 (indicated in
Fig. 4) for which intensities have been measured (see Tab. 1). The
coordinates of (0, 0) reference position of the maps is also given.
pc) region exhibiting a large quantity of high density gas
and intense star formation, which is discussed in detail
in Section 4.2. A molecular gas outflow/wind is being
driven from this inner nuclear disk, as discussed in B13.
We have selected 10 individual locations that span the
nuclear disk and the base of the molecular outflow in
NGC 253 (Tab. 1). Regions 3–9 trace the inner starburst
disk from west to east and regions 5 and 6 are coincident
with the detected millimeter continuum emission in the
galaxy (L14). Regions 1 and 10 are located at the west-
ern and eastern base of the southern molecular outflow
(B13). Region 2 indicates the shocked region towards the
north. The GMC physical properties in these regions are
discussed in detail in L14. We further caution that some
of our line measurements towards region 6 (the center)
may be a↵ected by absorption and continuum subtrac-
tion uncertainties (as discussed in Sec. 2).
In Tab. 1 we provide a summary of all detected lines
(column 1), their rest frequencies (column 2) and obser-
vational setup (column 3). For each of our 10 regions,
we measure the peak integrated intensity (in K km s 1
)
at that position and report the values in Tab. 1. We
5. ALMA Multi–line Imaging of the Nearby Starburst Galaxy NGC 253 5
86 86.5 87 87.5 88 88.5 89
10
2
S
!
(mJybeam
−1
)
HC
15
N
SO
H13
CN
H13
CO+
SiO
HN
13
C
C
2
H
complex
HNCO
H52"
HCN HCO
+
98 98.5 99 99.5 100 100.5 101 101.5 102 102.5 103 103.5
Frequency (GHz)
CS
H40#
SO
HC3
N
CH
3
SH
H2
CS
NH2
CHO
CH3
C2
H
H2
CS C2
S
Extended
Compact
112.5 113 113.5 114 114.5 115 115.5
C17
O
HCOOH
CN
CN
CO (v=1)/C4
H NS
CO
NS
Fig. 2.— Extracted spectrum near the center of NGC 253 (position 5 in Fig. 4), on a logarithmic scale. To deal with subtle issues
regarding the bandpass calibration, the data have been independently continuum subtracted for each spectral window. After that, the
average continuum flux density in a given spectral window was added to the spectrum. The flux density o↵set between the observations
obtained in the compact and extended configurations is real; the observations in the compact configuration recover more of the extended
flux. As in Fig. 1, identified molecular spectral lines are labeled (secure: bold, tentative: italics, see Tab. 1 for full description of transitions).
measure all values from beam–matched maps, i.e., all the
compact and extended configuration data have been con-
volved to a common resolution, respectively (this com-
mon resolution is given in column 4 of Tab. 1, whereas
column 3 gives the original resolution). We have dis-
cussed our uncertainty estimates in Sec. 2. Tab. 1 also
includes the intensity measurement in each transition for
the entire galaxy (columns 5 and 6).
3.2. Molecular Emission Across NGC 253’s Nucleus
Fig. 1 shows the position–velocity (pV) diagram ori-
ented along the molecular bar (i.e., along the major axis
of the galaxy) of all four data cubes. This figure shows
the richness of the ALMA data cubes, and the challenges
in finding the correct line identification. Already from
this presentation it is clear that the emission of the dif-
ferent line species emerge from di↵erent regions in the
galaxy.
We detect at least 50 emission lines in total of which
27 have unambiguous identifications. This corresponds
to a detection ratio of one line every ⇠0.25 GHz. Species
printed in italics are tentative IDs (13 lines). These lines
have clear candidate transitions from a species not yet
well established in extragalactic systems (see Sec. 3.3).
The candidate IDs are given in column 4 of Tab. 1. In
some cases we were not able to find a plausible line identi-
fication or the broadness of the spectral line prohibited a
unique identification. Those lines are labeled U (uniden-
tified; 10 cases). In those cases we give our best estimate
for each feature’s rest frequency in column 2.
We show line maps for 27 of the bright, unblended lines
in Fig. 3. In Fig. 4 we select out six species that summa-
rize the basic morphological patterns seen in the sample.
Each represent key tracers of the di↵erent phases of the
molecular gas, as discussed below. These are: 12
CO, a
tracer for the overall molecular gas distribution, 12
C17
O,
an optically thin tracer of molecular gas emission, C2H, a
photon-dominated region (PDR) tracer, H40↵, a hydro-
gen recombination line and H II region tracer, HCN, a
high–density gas tracer and HNCO, a weak shock tracer.
From Figs. 3 and 4 it is apparent that the morpholo-
gies change significantly between species (as is already
evident from Fig. 1). Molecular gas column densities re-
main quite large across the entire nuclear disk, maintain-
ing N(H2) & 1023
cm 2
over much of the disk (Sec. 3.4).
The wide range of dense gas tracers observed demon-
strates that dense gas is present across much of this re-
gion, but the dense gas fraction increases toward the in-
ner disk (L14). The millimeter hydrogen recombination
lines, including for the first time H lines, show that
dense H II regions associated with the young starburst
(or possibly AGN; Mohan et al. 2002) are confined to
the innermost part of this inner disk. Species like C2H,
CN and CH3C2H also dominate from this inner nuclear
disk. HNCO, on the other hand, is dominated by the
outer nuclear disk.
The brightest and most widespread transitions (HCN,
HCO+
and CN) show weak emission extended vertically
between 1 and 2, following the base of the molecular
outflow, suggesting there is dense molecular gas here.
However, we do not discuss the dense gas tracers in the
outflow in detail here due to the di culties dealing with
the morphology of the maps above and below the disk in
the presence of the negative ’bowl’.
3.3. Tentative and Unidentified Lines
There are a number of detected lines for which no clear
identification was possible. We have listed tentative iden-
tifications in Tab. 1 – in some cases no plausible species
were found, and these lines constitute unidentified (U)
lines. The majority of these tentative identifications (but
not tentative detections) match prominent transitions
6. 6 Meier, Walter, Bolatto et al.
Dec.Offset(")
H
13
CN
86.34 GHz
−40
−30
−20
−10
0
10
20
30
40
0
0.5
1
1.5
2
H
13
CO
+
86.75 GHz
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
SiO
86.85 GHz
0
0.5
1
1.5
2
Dec.Offset(")
HN
13
C
87.09 GHz
−40
−30
−20
−10
0
10
20
30
40
0
0.2
0.4
0.6
0.8
C
2
H
87.32 GHz
0
1
2
3
4
5
6
7
8
C
2
H
87.40 GHz
0
0.5
1
1.5
2
2.5
3
3.5
R.A. Offset (")
Dec.Offset(")
HNCO
87.93 GHz
−40−30−20−10010203040
−40
−30
−20
−10
0
10
20
30
40
0
0.5
1
1.5
2
2.5
R.A. Offset (")
H52!
88.41 GHz
−40−30−20−10010203040
0
0.1
0.2
0.3
0.4
0.5
0.6
R.A. Offset (")
HCN
88.63 GHz
−40−30−20−10010203040
0
5
10
15
20
Fig. 3.— Integrated intensity maps of selected molecules in our observations (Tab. 1). The respective intensity scale (in units of K km s 1)
is shown in each panel. The name of the line and its rest frequency are given in the top right corner of each panel. The beam size is shown
in the bottom right corner. Tentatively identified lines are labeled in italics.
from larger molecules, including the aldehydes CH3CHO
and NH2CHO, cyanides CH2CN and CH3CH2CN and
a number of organics of similar complexity, CH2CO,
HCOOH and CH3CH2OH. These molecules are abun-
dant in the Galactic center (e.g., Cummins et al. 1986)
and are expected to be detectable at our sensitivity in
NGC 253. If follow–up, multi-line studies confirm these
IDs then they would represent their first extragalactic
detections.
3.4. Excitation and Abundances
When appropriate, an estimate of abundances is made
for the detected species. Molecular column densities
Nmol are determined assuming optically thin LTE emis-
sion:
Nmol =
✓
3kQeEu/kTex
8⇡3⌫Sulµ2
0gu
◆
Imol, (1)
where Sul the line strength, and gu’s and Eu are the
upper state degeneracy and energy, respectively, Q is
the partition function, µo is the dipole moment in debye
and Tex is the excitation temperature associated with
the transition (e.g., Turner 1991). For the symmetric
(CH3SH) and asymmetric (HNCO, H2CS) tops Q is pro-
portional to T
3/2
ex , whereas Q for the linear rotors (the
rest) is proportional to Tex.
To calculate abundances it is necessary to adopt an
Tex. Since this survey covers only one band, gas exci-
tation is not the focus of this project. The only lines
7. ALMA Multi–line Imaging of the Nearby Starburst Galaxy NGC 253 7
Dec.Offset(")
HCO
+
89.19 GHz
−40
−30
−20
−10
0
10
20
30
40
0
5
10
15
20 CS
97.98 GHz
0
2
4
6
8
10
12
H40!
99.02 GHz
0
0.5
1
1.5
2
Dec.Offset(")
H50"
99.23 GHz
−40
−30
−20
−10
0
10
20
30
40
−0.1
0
0.1
0.2
0.3
0.4
0.5
SO
99.30 GHz
0
0.5
1
1.5
2
HC
3
N
100.08 GHz
0
2
4
6
8
10
12
R.A. Offset (")
Dec.Offset(")
CH
3
SH
101.14 GHz
−40−30−20−10010203040
−40
−30
−20
−10
0
10
20
30
40
−0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
R.A. Offset (")
H
2
CS
101.48 GHz
−40−30−20−10010203040
0
0.2
0.4
0.6
0.8
R.A. Offset (")
NH
2
CHO?
102.06 GHz
−40−30−20−10010203040
−0.1
0
0.1
0.2
0.3
0.4
0.5
Fig. 3.— Cont.
that are detected and directly constrain gas excitation is
a pair of SO transitions, SO(32 21) and SO(22 11).
From this pair, an excitation temperature is estimated,
via:
Tex =
10.09 K
ln( R
2.18 )
, (2)
where R is the intensity ratio, SO(32 21)/SO(22 11).
Towards the inner nuclear disk this ratio has a value of
R'2.5. There is some evidence for the ratio to increase
towards the outer nuclear disk (R.4), but the faintness
of SO(22 11) limits what can be said. For these ratios,
we estimate the inner disk to have an excitation temper-
ature of 74 K in SO, dropping to Tex .17 K. Indirect
methods of estimating Tex can also be achieved by ra-
diative transfer modeling (see section 4.2). There Tex is
found to range between ⇠6 – 45 K. Therefore, Tex likely
falls between at least 10 – 75 K, across much of the nu-
clear region. Ott et al. (2005) use NH3 to estimate gas
kinetic temperatures, Tkin, across the inner nuclear disk
of approximately twice the 74 K measured here, however
Knudsen et al. (2007) (and this paper) favor Tkin nearer
this value for HCN and HCO+
(see section 4.2). The
drop in Tex toward the outer nuclear disk region reflects
SO becoming more strongly sub-thermal in lower density
gas.
The relevant excitation temperature for a given species
/ transition depends on a number of factors, including
gas density, opacity, molecular structure and location
within the nucleus. For transitions with e↵ective critical
densities significantly above the gas density, Tex will be
lower than the Tkin (subthermal excitation). Changes in
nH2
and Tkin with position in the nucleus imply changes
in excitation. The e↵ective critical density of a species
8. 8 Meier, Walter, Bolatto et al.
Dec.Offset(")
CH
3
C
2
H
102.55 GHz
−40
−30
−20
−10
0
10
20
30
40
0
1
2
3
4
H
2
CS
103.04 GHz
−0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7 C
17
O
112.36 GHz
0
0.5
1
1.5
2
Dec.Offset(")
CN
113.19 GHz
−40
−30
−20
−10
0
10
20
30
40
0
10
20
30
40
CN
113.49 GHz
0
20
40
60
80
CO(v=1)/CH
4
?
114.22 GHz
−0.2
0
0.2
0.4
0.6
0.8
1
1.2
R.A. Offset (")
Dec.Offset(")
CH
3
CHO?
114.94 GHz
−40−30−20−10010203040
−40
−30
−20
−10
0
10
20
30
40
−0.2
0
0.2
0.4
0.6
R.A. Offset (")
CO
115.27 GHz
−40−30−20−10010203040
100
200
300
400
500
600
700
800
R.A. Offset (")
NS
115.56 GHz
−40−30−20−10010203040
0
0.5
1
1.5
2
Fig. 3.— Cont.
depends on line opacity, ⌧, (photons become an e↵ec-
tive ’collision’ partner) and hence abundances, with high
opacity lowering critical densities, ncr, roughly in pro-
portion to ⌧. Finally, even in the case that a transition
is thermalized, the LTE calculated columns are strict up-
per limits because it assumes that all transitions of the
molecule are thermalized up to arbitrarily high energies.
With these caveats stated, abundances are the impor-
tant astrochemical variable and so we report ’reference’
ranges. In Table 1, abundances are reported for Tex
ranging from 10 K (first number in each entry) to 75 K
(second number). Also included in the the table are ncr
(not including opacity e↵ects) for the transitions. It is
expected that for the inner nuclear disk positions tran-
sitions with moderate ncr (e.g., C17
O, HNCO, H2CS,
C2H, HCO+
, and SO) will have Tex at the high end of
the range. High ncr transitions and outer nuclear disk
locations likely will have Tex (and hence abundances) at
the low end of the range. Future, follow up, multi-line
studies of di↵erent species are necessary to narrow these
quoted ’reference’ value ranges.
To convert Nmol to fractional abundances we also re-
quire H2 column density, N(H2). N(H2) is most easily
obtained from the CO(1-0) brightness and an empirical
conversion factor, XCO. We adopt a CO-to-H2 conver-
sion factor of XCO = 0.5 ⇥ 1020
cm 2
(K km s 1
) 1
.
This is a factor of four lower than typical for the Galac-
tic disk (Strong et al. 1988; Hunter et al. 1997; Bolatto
et al. 2013a), but consistent with what has been previ-
ously estimated for NGC 253 (e.g. Paglione et al. 2001,
B13, L14). Uncertainties in XCO are significant, likely
at the ±2⇥ level, and in section 4.1 some discussion of
its validity in the context of optical thin C17
O(1–0) is
discussed.
9. ALMA Multi–line Imaging of the Nearby Starburst Galaxy NGC 253 9
Dec.Offset(")
CO
115.27 GHz
total molecular gas
−30
−20
−10
0
10
20
30
100
200
300
400
500
C17
O
112.36 GHz
!<1 molecular gas
0
0.5
1
1.5
C
2
H
87.32 GHz
PDR
0
1
2
3
4
5
6
7
1
2
3
4
5
6
7
8
910
R.A. Offset (")
Dec.Offset(")
H40"
99.02 GHz
RRL
−30−20−100102030
−30
−20
−10
0
10
20
30
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
R.A. Offset (")
HCN
88.63 GHz
dense gas
−30−20−100102030
0
2
4
6
8
10
12
14
R.A. Offset (")
HNCO
87.93 GHz
weak shocks
−30−20−100102030
0
0.5
1
1.5
2
Fig. 4.— Collection of key molecular gas tracers in NGC 253. From top left to bottom right: CO(1–0) (main molecular gas tracer),
C17O(1–0) (optically thin tracer of the molecular gas), C2H (PDR tracer), H40↵ (radio recombination line), HCN (high density gas tracer),
HNCO (shock tracer). The crosses and labels (bottom left panel) mark the di↵erent regions defined in the galaxy. Logarithmic contours
start at 1 K km s 1 and increase/decrease (white/grey) by a factor of 3 from one contour to the next. The beam size is indicated in the
bottom left corner of each panel.
4. DISCUSSION
In the following we present a broad discussion of the
chemistry in the nuclear region of NGC 253. The primary
goal is to obtain spatially resolved views of the di↵erent
molecular environments in and around the starburst cen-
ter.
We begin our discussion by studying the main tracer of
the molecular gas, 12
CO, its isotopologues, and implied
molecular gas opacity in Sec. 4.1. In Sec. 4.2 we con-
tinue with a similar discussion of the isotopologues of the
main tracers of the dense molecular gas phase (H13
CN,
H13
CO+
, HN13
C). This is followed by a discussion of
tracers of PDRs, (Sec. 4.3), shock tracers (HNCO and
SiO; Sec. 4.4), Sulfur species (Sec. 4.5), hydrogen recom-
bination lines (Sec. 4.6), and other tentatively identified
species (Sec. 4.7) detected in our study. A schematic
picture summarizes the overall chemistry of the central
region of NGC 253 in the conclusions/summary section
(Sec. 5).
4.1. CO Isotopologues and Gas Opacity
Our data cover a number of isotopologues (i.e.
molecules where one atom is replaced with an isotope).
Given the fact that atomic isotopes are much less abun-
dant than the main atom, many of these isotopologue
lines have low optical depth compared to the main
species. Isotopologue ratios thus provide insights into the
optical depth of the main lines and can also be used to
constrain isotopic abundance ratios. The isotopic abun-
dance ratio ultimately can provide insights into stellar
nucleosynthesis and possible variations of the stellar ini-
tial mass function (IMF). In the discussion that follows
we do not interpret the sometimes anomalous line ratios
found for region 6 (i.e. the region that is coincident with
the central continuum emission) as it is likely that in
some cases our measurements are a↵ected by absorption
(Sec. 2).
A comparison of the brightness of the C17
O(1–0) tran-
sition to the 12
CO(1–0) transition [hereafter CO(1–0)]
can provide important constraints on the total H2 col-
umn. Being an optically thin version of CO, even in
this extreme star formation environment, it permits CO
abundances to be determined by ‘counting molecules’ if
the [CO/C17
O] abundance ratio is known.
The [CO/C17
O] abundance ratio is constrained based
on existing measurements and nucleosynthetic expecta-
tions. In the Galaxy, [CO/C17
O] is .1900 at the solar
radius and drops to ⇠900 in the Galactic center (e.g.,
Wilson & Rood 1994, Ladd 2004, Wouterloot et al. 2008).
This decrease in the [CO/C17
O] abundance is consistent
with 17
O being a secondary chemical evolution product
formed from reactions between primary 16
O and a pro-
10. 10 Meier, Walter, Bolatto et al.
ton in intermediate mass stars. Therefore, in a strongly
processed location like the center of a starburst, a low
value of the CO/C17
O abundance ratio is expected, so
we adopt [CO/C17
O] = 1000, which is approximately the
Galactic center value referenced above, as our nominal
value.
As shown in Fig. 5, this isotopologue line ratio is fairly
constant with position in NGC 253 and large (&350). For
a ratio 16
O/17
O of 1000 in NGC 253, the measured ratio
nominally implies a 12
CO opacity of ⇠2.5, a moderate
value for the main CO line. Raising the intrinsic 16
O/17
O
abundance to 2000 gives a 12
CO opacity of order ⇠5.5.
Various non-LTE e↵ects can occur in a starburst en-
vironment that could alter the observed CO/C17
O line
ratio. Examples that artificially inflate the CO/C17
O
line ratio include: 1) CO has a higher excitation tem-
perature than C17
O because CO has high opacity and
its emission is dominated by warmer, externally heated
edges of the GMCs while C17
O is dominated by the
cooler interiors. 2) Isotope–selective photo-dissociation
makes the cloud sizes smaller in C17
O than CO. Or,
3) due to the absence of radiative trapping in C17
O,
C17
O is subthermal relative to CO and therefore fainter
(e.g., Meier & Turner 2001). The first two would be
expected to be pronounced close to the nuclear star for-
mation. However, interestingly, no evidence is seen for
an increase in the CO/C17
O ratio towards the inner disk,
where PDRs are enhanced (Sec. 4.3) and warm gas dom-
inates. But if there is a decrease in density away from
the inner disk then the third option can operate in the
outer disk, partially compensating for the first two. For
CO/13
CO abundances [CO/13
CO] & 60 (Martin et al.
2010), CO opacities estimated from the CO/C13
O line
ratios are ⇠5 (e.g., Paglione et al. 2004, Sakamoto et al.
2011). This scenario is consistent with CO/C17
O data
(and CO/C18
O) if non-LTE e↵ects are at most a factor of
⇠2. We conclude that, despite the large column density
towards NGC 253’s nucleus, CO(1–0) is only modestly
opaque. It is likely that this low optical depth is due to
increased line widths due to turbulence, the molecular
outflow, non-circular motions and/or elevated gas tem-
peratures that reduce the CO opacity per unit velocity.
The moderate CO optical depth is also reflected in the
implied sub-Galactic CO-to-H2 conversion factor in star-
bursts like NGC 253 (Harrison et al. 1999, Downes &
Solomon 1998, Meier & Turner 2001; Bolatto, Leroy &
Wolfire 2013). A comparison of the LTE C17
O column to
the H2 column estimated by an XCO of 0.5 ⇥ 1020
cm 2
(K km s 1
) 1
, gives a value for [C17
O/H2] constant (to
within 20 %) of 1.9 ⇥ 10 7
across positions 3-10 (using
Eq. 1 and Tex=75 K, Sec. 3.4). If [CO/C17
O] = 1000
and [CO/H2] = 10 4
, then we would expect a value of
[C17
O/H2] ' 10 7
. The level of agreement between the
two methods of constraining N(H2) is reasonable, being
less than the uncertainties in each method. The small
di↵erences are an indicator of the uncertainty in N(H2).
Agreement could be made exact by raising [C17
O/H2]
and/or by lowering the adopted Tex.
4.2. Dense Gas Tracers and their Isotopologues
The commonly observed dense gas line ratios,
HCO+
/HCN, HNC/HCN and HCO+
/HNC ratios are
predicted to be sensitive to gas density, cosmic ray ion-
ization and possibly the X-ray versus UV ionization rate
or the present of mechanical heating (e.g., Kohno et
al. 2001, Meijerink & Spaans 2005, Gracia-Carpio et al.
2006, Knudsen et al. 2007, Papadopolous 2007, Krips et
al. 2008, Baan et al. 2008, Loenen et al. 2008, Meijerink
et al. 2011, Kazandjian et al. 2012). HCO+
(1–0) ef-
fective critical densities are nearly a factor of five lower
than HCN, so to first order, elevated HCO+
/HCN and
HCO+
/HNC ratios are expected in moderate density gas
(nH2 ⇠ 104.5
cm 3
). As densities increase, both transi-
tions thermalize and the ratio tends to unity. Moreover,
HNC/HCN ratios are expected to drop in energetic en-
vironments because HNC is preferential destroyed in hot
gas (e.g., Schilke et al. 1992, Meier & Turner 2005). If
these transitions have high optical depths, which is prob-
able given the large columns of dense gas, all ratios are
driven toward unity. As a result of the large inferred
optical depths, changes in these main isotopic line ra-
tios due to interesting physical/chemical changes will be
partially hidden.
Here we focus on the dense gas properties in the cen-
tral starburst region of NGC 253. The HCO+
/HCN
intensity ratio (Fig. 5) is observed to be slightly less
than unity and exhibits very little change over the in-
ner disk (except for position 2 and 3). This sug-
gests that both HCN(1–0) and HCO+
(1–0) are optically
thick and slightly subthermal across much of the nucleus
(Knudsen et al. 2007). Here we add new HCN/H13
CN,
HCO+
/H13
CO+
, H13
CO+
/H13
CN, and HN13
C/H13
CN
intensity ratios to further constrain dense gas properties.
The isotopologues of HCN, HCO+
, and HNC have lower
optical depths and allow estimates of the line opacity and
changes in the abundance ratio of these species.
The observed HCN/H13
CN and HCO+
/H13
CO+
both
have values of 10 - 15 over much of the inner nuclear disk
(Fig. 5). The fact that these ratios are much lower than
the expected [12
C/13
C] ratio of &60 (Mart´ın et al. 2010)
clearly demonstrates that both HCN(1–0) and HCO+
(1–
0) have opacities greater than one. This confirms the
conclusions of earlier work (Knudsen et al. 2007). For
A =12
C/13
C abundance ratios of 80 above and LTE as-
sumptions, both HCN and HCO+
have ⌧ ' 5 8. Inter-
estingly this is an optical depth similar or slightly larger
than inferred for CO(1–0) from C17
O. This is expected
because the HCN/H13
CN and HCO+
/H13
CO+
ratios are
quite similar to the observed CO/13
CO line ratios (e.g.,
Paglione et al. 2004; Sakamoto et al. 2011). Such optical
depths for HCN and HCO+
are large. For a Tex=75 K,
inferred optically thin HCN abundances are ⇠ 2.5⇥10 8
(Table 4). However, if the isotopologues of HCN, HCO+
and HNC have a lower excitation temperature than the
main species (likely true, see below), then LTE inferred
opacities are lower limits.
The H13
CO+
/H13
CN ratio in particular shows larger
variation (Fig. 5) than seen in the main isotopic ratios.
Moreover the average values of the ratios are di↵erent.
Toward the two main inner disk GMCs (positions 5 and
7) HCO+
/HCN and H13
CO+
/H13
CN have very similar
ratios, but toward the outer nuclear disk the isotopic
dense gas ratios decrease relative to their main versions.
Likewise the average HN13
C/H13
CN ratio of ⇠0.35 is
significantly lower than the single-dish value for the main
11. ALMA Multi–line Imaging of the Nearby Starburst Galaxy NGC 253 11
Fig. 5.— CO and dense gas line ratios (Secs. 4.1 and 4.2). The respective line ratio is given in each panel. The x–axis number corresponds
to the region number as defined in Sec. 3.2 and Fig. 4. The horizontal line in each panel shows the value for the entire galaxy (i.e., the
global ratio). Uncertainties are determined from Table 1.
species ratio (⇠0.74; Baan et al. 2008). The fact that the
isotopologue substituted species have ratios farther from
unity is consistent with the expectation that high optical
depth in the main lines artificially drives the ratio closer
to unity. These isotopologue ratios tend to move NGC
253 further into the PDR-like ratio parameter space of
Baan et al. (2008), consistent with dense gas abundance
ratios influenced by warm, PDR across the inner nuclear
disk.
Given the lower opacities of the isotopologues of HCN,
HCO+
, and HNC, it is expected that subthermal exci-
tation will be the most relevant non-LTE consideration,
therefore it is worth modeling the physical conditions
implied by these lines. Knudsen et al. (2007) have mod-
eled the main isotopologues, including selected J tran-
sitions. Here we carry out an independent large velocity
gradient (LVG) radiative transfer modeling focusing on
the isotopic line ratios. Line ratios are modeled as they
are to first order independent of the unknown areal fill-
ing factor, and therefore constrain the parameter space
more precisely. The model used is patterned after the
models of Meier et al. (2008), with Jmax extended to
20 and collisional coe cients adapted from the Leiden
LAMDA database (van der Tak et al. 2007; see Table
4 for references to the individual molecular rate coe -
cients). To model the radiative transfer, assumptions
must be made about the abundance per velocity gradi-
ent. Models with a wide range of abundance per velocity
gradient (10 11.33
10 7.67
km 1
s pc) were calculated.
In general it is not easy to obtain agreement for the line
ratios of HCN/HCO+
, HCN/H13
CN, HCO+
/H13
CO+
,
H13
CO+
/H13
CN, HN13
C/H13
CO+
and HN13
C/H13
CN.
HCO+
’s e↵ective critical density is significantly lower
than HCN and so HCO+
abundances have to be low com-
pared to HCN to obtain ratios of HCO+
/HCN lower than
unity. But pushing HCO+
abundances too low causes
disagreement with the isotopic ratios. If we focus only
on the five isotopic line ratios, then reasonable solutions
that match all are found over a fairly narrow range of pa-
rameter space. We adopt XHCN /dv/dr = 10 8.1
km 1
s
pc and XHCO+/dv/dr = XHNC/dv/dr = 10 8.85
km 1
s pc, consistent with XHCN ' 2.3 ⇥ 10 8
, XHCO+ '
XHNC ' 4.2 ⇥ 10 9
and a velocity gradient of ⇠3 km
s 1
pc 1
. For the isotopologues, a 12
C/13
C ratio of 80 is
adopted. These values are in reasonable agreement with
the values listed in Table 4 and the observed gas kinemat-
ics. There is room to adjust the abundances per veloc-
ity gradient of the five species individually, but keeping
HCO+
and HNC abundances equal does an acceptable
job. The low abundance of HCO+
demanded relative to
12. 12 Meier, Walter, Bolatto et al.
HCO /HCN+
n(H_2)
T_KIN
20 40 60 80 100 120 140 160 180 200
6.5
6.0
5.5
5.0
4.5
4.0
3.5
HCN/H CN13
n(H_2)
T_KIN
20 40 60 80 100 120 140 160 180 200
6.5
6.0
5.5
5.0
4.5
4.0
3.5
HCO / H CO+ 13 +
n(H_2)
T_KIN
20 40 60 80 100 120 140 160 180 200
6.5
6.0
5.5
5.0
4.5
4.0
3.5
H CO /H CN13 + 13
n(H_2)
T_KIN
20 40 60 80 100 120 140 160 180 200
6.5
6.0
5.5
5.0
4.5
4.0
3.5
HN C/H CO13 13 +
n(H_2)
T_KIN
20 40 60 80 100 120 140 160 180 200
6.5
6.0
5.5
5.0
4.5
4.0
3.5
HN C/H CN13 13
n(H_2)
T_KIN
20 40 60 80 100 120 140 160 180 200
6.5
6.0
5.5
5.0
4.5
4.0
3.5
Fig. 6.— LVG modeling of the inner nuclear disk. The acceptable model predicted parameter space for (clockwise) HCN/HCO+
HCN/H13CN, HCO+/H13CO+, H13CO+/H13CN, HN13C/H13CO+, and HN13C/H13CN1–0 transitions. Contours are the ±1 observed
line ratio for the average of position 5 and 7. Tick marks indicate the direction of the favored parameter space if it is not obvious. Adopted
abundance per velocity gradient values from the six di↵erent species are discussed in section 4.2. The cross marks an example set of
parameters (Tkin = 80 K, nH2
= 104.75 cm 3) that is within 1 of with all five isotopic ratios. The HCN/HCO+ line ratio is not matched,
but is within 30 % of the predicted ratio.
HCN is a direct consequence of its lower e↵ective critical
density.
Figure 6 displays the acceptable parameter space for
the ratios observed toward the inner nuclear disk (av-
erage of the ratios toward positions 5 and 7) displayed
in Figure 5. When admitting uncertainties, good agree-
ment to all five ratios is obtained for nH2 = 104.5 5.0
cm 3
and Tkin = 60 120 K. The cross in Figure 6
marks the location of a representative good fit to all
lines. Its values are nH2
= 104.75
cm 3
and Tkin = 80
K. Tkin below 60 K challenges the observed ratios for
H13
CO+
/H13
CN and HN13
C/H13
CN , and Tkin > 120 K
begins to disagree with HCO+
/H13
CO+
. Strictly speak-
ing the HCO+
/HCN ratio is not matched, however the
disagreement is small (⇠30 %), and at the level that we
expect other complications such as line width variation
and transition depend filling factors to become impor-
tant. The degree of internal consistency obtained in these
simple uniform physical condition models is encouraging.
The favored densities and kinetic temperatures of the
dense gas isotopologues match well those previously
found in Knudsen et al. (2007), with a range overlap-
ping but favoring about 0.25 dex lower densities. These
results confirm Knudsen et al. (2007)’s conclusions that
HCN, HNC and (to a somewhat lesser degree) HCO+
are moderately subthermally excited. The dense gas iso-
topologues are even more strongly subthermal. For the
above favored model, we obtain Tex = 34 K and 44 K
for HCN and HCO+
, respectively. Corresponding opac-
ities ⌧ are 13 and 2.4 for HCN and HCO+
. For the
isotopologues, Tex [⌧] are 7.2 K [2.4], 16 K [0.27] and 5.3
K [0.71] for H13
CN, H13
CO+
and HN13
C, respectively.
LVG modeling demonstrates that while the main tran-
sition line opacities crudely match those predicted from
LTE, the isotopologue opacities are significantly larger
than 12
⌧/A. This stems from the fact that the e↵ective
critical density of a transition is dependent on its opac-
ity (radiative trapping), so the isotopologues are more
strongly subthermal. As a result, the level populations
of the isotopologues settle into the lowest J transitions
more e ciently, raising their opacity. This explains the
well known e↵ect that isotopic line ratios are gas den-
sity probes (e.g., Meier et al. 2001). Furthermore this
is strong evidence that the main species, particularly of
13. ALMA Multi–line Imaging of the Nearby Starburst Galaxy NGC 253 13
Fig. 7.— Same as Fig. 5, but for PDR tracer line ratios (Sec. 4.3).
HCN, must have opacities well in excess of unity.
The slightly larger HCN/H13
CN and HCO+
/H13
CO+
ratios together with somewhat lower HN13
C/H13
CN ra-
tios toward the outer nuclear disk are consistent with
warm gas that is ⇠0.5 dex lower in density. However,
the decrease in the H13
CO+
/H13
CN ratio toward the
outer disk is somewhat unexpected as gas density is de-
creasing in this region. Raising Tkin significantly will
lower the H13
CO+
/H13
CN ratio slightly even at lower
density but only by ⇠10 % for Tkin up 300 K. This
e↵ect does not appear to be strong enough to explain
the observed ratio, and so this ratio is evidence for a
small, but genuine abundance enhancement of HCN and
its isotopologue relative to HCO+
and HNC across the
nuclear disk — or conversely a decrease of both the iso-
topologues of HCO+
and HNC relative to H13
CN. In-
voking mechanical heating may be a viable candidate for
elevating HCN at the expense of HCO+
and HNC (Loe-
nen et al. 2008, Mejierink et al. 2011, Rosenberg et al.
2014), because hotter gas converts HNC to HCN (e.g.,
Schilke et al 1992). If mechanical heating is more pro-
nounced at the base of the outflow in the outer disk then
this may explain the further drop in H13
CO+
/H13
CN
here. However this possibility is speculative so we con-
sider the explanation for the lower H13
CO+
/H13
CN ratio
unsettled.
4.3. PDR Tracers
Given the strong radiation field in NGC 253’s center,
the presence of PDR tracers are expected and observed.
PDRs warm gas and maintain significant amounts of car-
bon in ionized form (e.g., Tielens & Hollenbach 1985), so
tracers include species that form rapidly from C+
and
H or H2. These include simple hydrocarbons, such as
CH, C2H, c-C3H2 and molecules that form directly from
these species, like CN (e.g. Fuente et al. 1993, Sternberg
& Dalgarno 1995, R¨ollig et al. 2007). In molecular gas
strongly irradiated by UV photons we expect such species
to exhibit elevated abundances. The two main PDR trac-
ers in our dataset are CN and C2H. C2H has a critical
density that is significantly lower than CN (see Table 4),
and therefore traces somewhat more di↵use PDRs.
Both CN and C2H exhibit fine/hyperfine structure
splitting and so their opacity can be determined directly.
For C2H the theoretical LTE C2H(3/2-1/2)/C2H(1/2-
1/2) ratio should be 2.3 in the optically thin limit (for
the subset of blended lines included), dropping to 1
when optically thick. We observe a global ratio of ⇠2.4
(Fig. 7). Likewise for CN, the CN(3/2-1/2)/CN(1/2-1/2)
fine structure ratio is 2 (Fig. 7), which is what we observe
for the inner nuclear disk of NGC 253. Both CN and C2H
are likely optically thin and therefore their intensities are
proportional to their column densities.
The maps of these two species are strongly dominated
by the innermost disk locations, 4–7, where star forma-
tion is most intense and where the ionized/molecular
outflow originates. Fig. 7 displays both the CN(1–0;
3/2–1/2)/CO(1–0) (hereafter CN/CO) and the C2H(1–
0;3/2–1/2)/HCN(1–0) (hereafter C2H/HCN) line ra-
tios11
. Both ratios decrease significantly from the in-
ner (CN/CO ' 0.11; C2H/HCN ' 0.45) to the outer
(CN/CO ' 0.035; C2H/HCN ' 0.18) nuclear disk. This
behavior is explained by a combination of an increased
PDR fraction and di↵erential optical depth. To sep-
arate these e↵ects, ratios were calculated between op-
tically thin proxies for CO and HCN, CN/C17
O and
C2H/H13
CN (Fig. 7). In both cases the trend for en-
hanced PDR tracers in the inner disk is seen, though
11 These two ratios are chosen instead of the more common ratio,
CN/HCN (e.g., Boger & Sternberg 2005), because only they can
be obtained from matched array configurations in our dataset.
14. 14 Meier, Walter, Bolatto et al.
less pronounced. The average CN/C17
O ratio is .20 in
the outer disk and a factor of ⇠2 higher towards the in-
ner disk region). Likewise, for C2H/H13
CN, the outer
disk average is ⇠2 and the inner disk average is 3.5-
4.5. The fact that C2H/H13
CN and CN/C17
O both show
the same magnitude of an e↵ect suggests that density
changes across the nucleus are not controlling the line
ratio. Hence it appears that PDRs constitute a larger
fraction of the dense gas towards the inner nuclear disk.
Simple hydrocarbons exhibit elevated abundances in this
environment. We note that the more complex hydrocar-
bon symmetric top, CH3C2H, has a rather similar mor-
phology to CN and C2H, suggesting that its abundance
can also be elevated in PDRs.
We also note that the PDR tracers are observed in the
base of the molecular outflow. This is consistent with
the recent detection of C2H in the molecular outflow in
the nucleus of Ma↵ei 2 (Meier & Turner 2012).
4.4. Shock Tracers
Given the intense star forming environment in
NGC 253’s center and its associated outflow of molec-
ular gas (B13), we expect the presence of shocked gas
tracers. Our dataset includes two common extragalac-
tic shock tracers, SiO (e.g., Garcia-Burillo et al. 2000)
and HNCO (Meier & Turner 2005). HNCO is thought
to come from dust ice mantle sublimation (where due
to filling factor reasons ice mantle evaporation in hot
cores is invisible on larger scales), while SiO is enhanced
by ejection of significant Si from sputtered silicate grain
cores in high velocity shocks (e.g., Meier & Turner 2005,
Rodriguez-Ferndandez et al. 2010, Tideswell et al. 2010,
Martin-Pintado et al. 1992).
SiO emission is distributed across the nucleus in a se-
ries of compact sources with some relative enhancement
seen toward the eastern outer nuclear disk. Calculated
SiO abundances (X(SiO) ⇠ 10 9
) confirm that SiO is
elevated across the entire nuclear disk. This SiO value is
comparable to that seen locally on GMC scales in ‘shock
regions’ in other nearby spiral galaxies (e.g., Usero et
al. 2006, Meier & Turner 2012) and slightly larger than
found in previous NGC 253 SiO measurements (di↵er-
ences are due to di↵erent adopted Tex and N(H2) values;
Garcia-Burillo et al. 2000). These abundances are much
larger than observed toward quiescent Galactic molecular
clouds (. 10 11
; e.g., Zuirys et al. 1989, Martin-Pintado
et al. 1992).
Interestingly, HNCO has the most distinctive morphol-
ogy of all the bright lines, being completely dominated
by the outer locations of the disk. Such an enhance-
ment at the outer edges of the nuclear disk is also seen
in several other nearby barred nuclei, IC 342, Ma↵ei 2
and NGC 6946 (Meier & Turner 2005; 2012). Estimated
HNCO abundances reach ⇠ 10 8
across the outer nuclear
disk and decrease to ⇠ 10 9
towards the inner nuclear
disk. HNCO abundance in quiescent Galactic clouds ap-
proach this inner disk value (e.g. Marcelino et al. 2009,
Tideswell et al. 2010).
Assuming SiO traces shocks, then the SiO/HCN line
ratio can be considered to first order an indicator of
the fraction of the dense gas that is experiencing strong
shocks. HNCO/SiO ratio is often considered a tracer of
shock strength, because the shocks need to be stronger
to elevate the SiO abundance (e.g., Usero et al. 2006).
In Fig. 8 we present these two ratios across the nuclear
disk of NGC 253. The SiO/HCN intensity ratio is fairly
flat across the disk with slight elevations seen towards re-
gions 2 and 3. This indicates that shocks are uniformly
present over much of the nuclear disk in NGC 253. The
HNCO/SiO ratio in the outer nuclear disk matches the
ratio observed in bar shock regions of nearby spirals like
IC 342 (Meier & Turner 2005, Usero et al. 2006) and Maf-
fei 2 (Meier & Turner 2012) well. Towards the inner disk
the ratio drops dramatically to a value of ⇠0.17. Only
M 82 has a ratio anywhere near this low (Garcia-Burillo
et al. 2000, Martin et al. 2009).
At face value this extremely low HNCO/SiO ratio in
the inner disk could be taken to indicate that shock
strengths decrease away from the core. However, the SiO
morphology and abundance suggests that, even in the
outer disk, shock strengths are strong enough to keep
SiO high relative to HCN. Therefore other e↵ects that
further alter the HNCO morphology besides simple shock
strength must be considered. Two important second or-
der e↵ects that can alter the HNCO/SiO ratio (see Meier
& Turner 2012 for a thorough discussion): 1) HNCO has
a significantly higher photodissociation rate than SiO, so
its shock signatures are erased more easily in the pres-
ence of PDRs/UV radiation fields. 2) SiO is a linear top
molecule so its partition function is / Tex, while HNCO
is an asymmetric top molecule, with a partition func-
tion / T1.5
ex . So in hot gas, HNCO’s lower energy states
depopulate more rapidly than SiO. For HNCO this ef-
fect is mitigated at Tex ⇠ 5 20 K by the fact that
Eu(HNCO) is ⇠ 11 K compared to SiO’s value of 6.3 K,
but if Tex ⇠ 75 K in the inner disk then this could be a
pronounced e↵ect.
In the inner nuclear disk, the gas is hot and PDR dom-
inated (see Sec. 4.3), so we expect that both act to drive
down the HNCO/SiO ratio in the center. Therefore it
appears we are observing the starburst (and outflow) ac-
tively in the process of erasing the signatures grain man-
tles species in the inner disk (Mart´ın et al. 2009a,b). In
this context it is not surprising that its HNCO/SiO ratio
is similar to M 82’s, a nucleus where PDRs have com-
pleted the task of erasing the weak shock tracers (Takano
et al. 1995, Garcia-Burillo et al. 2001)
4.5. Sulfur Species
We detect a significant number of sulfureted species,
including CS, SO, NS, H2CS, CH3SH and C2S. When
accounting for the di↵erent array configurations used to
observe them, CS, SO, H2CS and NS all have quite sim-
ilar morphologies. They tend to be dominated by the
dense GMCs, with a preference toward the clouds on the
northeast side of the continuum peak (7 and 8), whereas
the PDR/hydrocarbons tend to favor the southwestern
side of the inner disk (position 5). Interestingly, the mor-
phology of the sulfuretted species, particularly CS and
SO are very similar to SiO. Assuming SiO traces shocked
gas (Sec. 4.4), this hints at a possible connection between
the S species and shocked gas. This is somewhat unex-
pected, at least for CS, given that in other nearby nuclei
it has been argued that CS is primarily a PDR tracer
(e.g., Meier & Turner 2005; Mart´ın et al. 2009). Ev-
idently a mix of shocks and strong radiation fields are
capable of maintaining high abundances of SiO and CS,
though not HNCO.
15. ALMA Multi–line Imaging of the Nearby Starburst Galaxy NGC 253 15
Fig. 8.— Same as Fig. 5, but for shock tracer ratios (Sec. 4.4)
Fig. 9.— Same as Fig. 5, but for sulfur species line ratios (Sec. 4.5).
The CS/SO abundance ratio is sensitive to the C+
/O
abundance ratio and it has been argued to be either a
tracer of the C/O abundance ratio (⇠ 0.4 in the Galaxy),
or early vs. late time chemistry (e.g., Heithausen et al.
1998, Nilsson et al. 2000). So when C or C+
is nearly
as abundant as atomic O, CS is strongly favored over
SO. Our observed SO/CS intensity ratio is ⇠0.1–0.18
over much of the nuclear disk (Fig. 9). This corresponds
to a CS/SO abundance ratio of >1.5–3 (higher if CS is
optically thick), in good agreement with Galactic star
forming regions. Nilsson et al. (2000) find values ranging
between 0.4–5, with most at ⇠2.
Likewise, the NS/SO (and NS/CS) abundance ratios
are particularly sensitive to atomic C and O abundances.
NS is formed from the neutral-neutral reactions, S + NH
! NS + H and N + SH ! NS + H. Atomic O destroys
both NS and its parent SH, converting them to NO and
SO, respectively. Likewise, reactions with C/C+
drive
NS into CS and CN. In star forming regions the radia-
tion field can keep a significant amount of C and O in
non-molecular form. As such, standard gas-phase models
predict NS cannot not attain abundances above X(NS)
⇠ 10 11
(e.g., McGonagle & Irvine 1997, McElroy et al.
2013). In the inner nuclear disk we observe NS abun-
dances in the range of 1 – 6⇥10 9
, at least two orders of
magnitude larger than the maximum gas-phase models
can accommodate. NS/SO abundances ratios are also
high, reaching 0.2 - 0.5 (the exact values are uncertain
due to non-matched array configurations). These ele-
vated abundances are consistent with that determined
from single-dish measurements toward NGC 253 (Mart´ın
et al. 2003, 2005), except the present observations further
demonstrate that the high abundances are attained to-
ward the same inner disk GMCs where PDR conditions
are pronounced.
To explain the similar (high) abundances of CS, SO
and NS toward the same region requires non-standard
chemistry. The atomic abundances of species like O must
be kept very low, despite the PDR conditions. Two pos-
sible scenarios appear feasible. The first, introduced by
Viti et al. (2001) (see also Charnley 1997, Harada et al.
2010 and Izumi et al. 2013), invokes a high tempera-
ture gas phase chemistry due to the passage of a shock.
This high temperature gas drives O into the more inert
H2O form so it does not destroy NS as rapidly. A sec-
ond possibility is that in the pre-starburst phase of NGC
253’s nucleus, much of the atomic species condensed onto
the dust grains where they are converted into their sat-
urated form (e.g., Brown et al. 1988). At a later time
shocks liberated the saturated species (e.g., CH4, NH3,
H2O and possibly H2S). The gas-phase chemistry then
evolved from molecular initial conditions, keeping atomic
C and O low. Both of the scenarios invoke the presence
of shocks, and so are consistent with the tight morpho-
logical connection between the sulfur species and SiO.
We observe both ortho-H2CS at 101 GHz and a mix
16. 16 Meier, Walter, Bolatto et al.
of para transitions at 103 GHz. The ortho-to-para ra-
tio of H2CS, the sulfur analog to formaldehyde H2CO, is
useful for constraining the formation conditions of H2CS
(Minh et al. 1991). Under optically thin, high-T (>15 K
in the case of H2CS), LTE case, the ratio of the ortho
species of H2CS (those with Ka [K 1] even, see Tab. 1)
to the para (those with Ka odd) should be 3.0. If the
temperature at the time of formation is 15 K then the
two forms of H2CS with not be thermalized to their sta-
tistical weights and hence have an abundance ratio less
than 3 — approaching unity at T=0 K. The intensity
ratio of the two types of transitions (Fig. 9) is approxi-
mately constant across the disc at a value of ⇠1.4. For
Tex = 75 K the measured ratio implies an ortho-to-para
ratio of 2.9. Therefore every position is consistent with
standard LTE, high temperature limit. Thus, at least
in the case of H2CS, this suggests that H2CS formed in
the high temperature gas phase after evaporation, or if
it was formed on the grain surfaces in an earlier epoch,
those surfaces were still significantly warmer than 15 K.
4.6. Millimeter Recombination Lines
We have detected three hydrogen recombination lines
in our observations (H40↵, H50 and H52 ). The mor-
phology of these recombination lines is very di↵erent
from all the molecular gas tracers (e.g., Figs. 1 and 3):
The emission is centrally concentrated, coincident with
the location of the underlying continuum emission (L14).
H radio recombination lines are reported outside the
Local Group for the first time here. The error bars are
significant for the lines, but the global H40↵/H50 ra-
tio is around 3.5, in good agreement with the LTE value
of 3.5 (=1/0.285) for ne = 104
cm 3
and Te = 104
K.
The lines would be fainter than the line by a factor of
2.3. Indeed, we do not clearly detect any lines. We also
do not detect any He↵ lines. Other radio/mm recombi-
nation lines mapped in NGC 253 have been discussed ex-
tensively elsewhere (e.g., Anantharamaiah & Goss 1996,
Mohan et al. 2002, 2005, Rodriguez-Rico et al. 2006,
Kepley et al. 2011). The morphology of both the ↵ and
lines mapped here are in excellent agreement with the
ones reported previously.
4.7. Tentatively Identified Species
We here briefly comment on other selected species de-
tected in our observations.
A large number of tentatively identified lines can
be attributed to carbon-rich complex species (e.g.,
CH3CH2CN, CH3CH2OH, CH2CN, CH2CO, CH3CHO
and NH2CHO (Tab. 1). These species represent the
next step in complexity beyond the molecules detected
in external galaxies up until now, and suggest that these
molecules may be fairly extended in NGC 253.
One unidentified feature detected is of particular inter-
est. This is the feature U-114.22 at ⇠114.218 GHz. This
spectral feature is within <4 MHz (<11 km s 1
) of both
C4H(N=12–11; J=23/2–21/2; F=12–11) and the v = 1
transition of CO(1–0). The upper energy state of the
CO(1–0; v = 1) line is 3089 K above ground, so the exci-
tation temperature of the gas must be >450 K in order to
explain the observed line ratio. The morphology of this
transition is very similar to the RRLs (accounting for
resolution di↵erences), as would be expected if it is trac-
ing molecular gas not associated with the cold molecular
phase. The C4H transition has a much lower upper en-
ergy level of 35.6 K, typical of the other transitions seen
here. Moreover, it is plausible to expect that the C4H
might trace PDR emission (like C2H), which are also con-
centrated towards the inner disk, though why it would be
significantly more compact than C2H is unexplained. We
consider C4H as the most likely identification, however
the observed morphology indicates that the possibility
this feature could be vibrationally excited CO deserves
further investigation.
5. SUMMARY AND CONCLUSIONS
We present the detection of a total of 50 molecular lines
in the nearby starburst galaxy NGC 253, based on early
science (cycle 0) observations taken with the Atacama
Large (Sub–)Millimeter Array (ALMA). For 27 lines we
have an unambiguous identification, and 13 lines have
tentative IDs (no plausible line identification was possible
in 10 cases).
We here describe a schematic picture of the central
starburst region of NGC 253 mapped by ALMA (Fig. 10):
As described in Sec. 3.1, the nucleus of NGC 253 is char-
acterized by the inner portion of NGC 253’s large–scale
bar. The outer part of the nuclear disk (the ‘outer nu-
clear disk’), likely represents the location where the gas
is flowing radially inward along the large-scale bar. In-
side this is a compact region exhibiting a large quantity of
high density gas and intense star formation, as evidenced
by the presence of dense gas (Sec. 4.2), PDR (Sec. 4.3)
and shock tracers (Sec. 4.4). This component (the ‘in-
ner nuclear disk’), dominates the morphology of most of
the spectral lines detected by the observations. We de-
tect high density molecular gas tracers (HCN, HCO+
and
CN) at the base of the molecular outflow first detected
in the 12
CO emission (B13).
In detail, we find moderate 12
CO opacities of ⇠2–5,
despite the large column density towards NGC 253’s nu-
cleus. This may be due to increased line–widths due
to turbulence, non–circular motions and/or elevated gas
temperatures that reduce the CO opacity per unit veloc-
ity. Comparing HCN(1–0) and HCO+
(1–0) with their
13
C–substituted isotopologues yields that the HCN(1–
0) and HCO+
(1–0) are also optically thick, with similar
(moderate) opacities to CO. These high HCN and HCO+
opacities imply that the main isotopologue HCN/HCO+
(and HCN/HNC) line ratios have less diagnostic power in
this starburst environment. Using the isotopically sub-
stituted versions of these high density tracers we measure
much more robust values for the popular ”HCO+
/HCN”,
”HNC/HCN” and ”HNC/HCO+
” ratios. All five of the
isotopic dense gas tracer ratios can be well fit by LVG
models with nH2
= 104.75
cm 3
, Tkin = 80 K and
X(HCN) ⇠ 5X(HCO+
) ⇠ 5X(HNC).
The weak shock tracer/ice mantle species HNCO has
the most distinctive morphology of all the bright lines be-
ing completely dominated by the outer locations of the
disk. This is at odds with what is seen in the strong
shock tracer, SiO. Attributing the dramatic variation in
the HNCO and SiO maps across the nucleus to chang-
ing shock strength is unsatisfactory because SiO is en-
hanced across the nucleus at a level that should imply
shocks are strong throughout the inner disk. A possible
explanation for the faintness of HNCO is that because
of its higher photodissociation rate relative to SiO, the
17. ALMA Multi–line Imaging of the Nearby Starburst Galaxy NGC 253 17
Fig. 10.— A schematic picture of the central starburst region of NGC 253 (see discussion in Sec. 5). The morphology is based on Figure
1 of (B13) with the chemistry added.
ice mantle evaporation shock signatures are being pref-
erentially erased in the presence of the intense central
radiation fields. This is consistent with the presence of
an enhanced PDR fraction towards the region of HNCO’s
dramatic decrease as determined form the CN/C17
O and
C2H/H13
CN ratios. The sulfureted species appear also
to be (indirectly) connected to the presence of shocks
across the inner disk.
We have detected three hydrogen recombination lines
(H40↵, H50 and H52 ) that show a centrally concen-
trated morphology (similar to the underlying continuum
emission) that is distinctly di↵erent from all molecular
gas tracers.
Finally, we report some tentative identifications, in-
cluding the aldehydes CH3CHO and NH2CHO, cyanides
CH2CN and CH3CH2CN and a number of organics of
similar complexity, CH2CO, HCOOH and CH3CH2OH.
The first vibrational state of the 12
CO(1–0) line is also
possibly detected. If follow–up, multi-line studies con-
firm these IDs then they would represent the first extra-
galactic detections of the above species.
DSM acknowledges partial support by the National
Science Foundation through grant AST-1009620. ADB
acknowledges support by the Alexander von Humboldt
Foundation and the Federal Ministry for Education and
Research through a Humboldt Fellowship, support by the
National Science Foundation through CAREER grant
AST-0955836 and AST-1412419, as well as a Cottrell
Scholar award from the Research Corporation for Sci-
ence Advancement. We thank the anonymous referee
for a thorough and helpful review. This paper makes
use of the following ALMA data: ADS/JAO.ALMA
#2011.0.00172.S. ALMA is a partnership of ESO (rep-
resenting its member states), NSF (USA) and NINS
(Japan), together with NRC (Canada) and NSC and
ASIAA (Taiwan), in cooperation with the Republic of
Chile. The Joint ALMA Observatory is operated by
ESO, AUI/NRAO and NAOJ. The National Radio As-
tronomy Observatory is a facility of the National Sci-
ence Foundation operated under cooperative agreement
by Associated Universities , Inc.
Facilities: ALMA
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