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 canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
We report the discovery of an optical Einstein Ring in the Sculptor constellation,
IAC J010127-334319, in the vicinity of the Sculptor Dwarf Spheroidal Galaxy. It is
an almost complete ring ( 300◦) with a diameter of 4.5 arcsec. The discovery was
made serendipitously from inspecting Dark Energy Camera (DECam) archive imaging
data. Confirmation of the object nature has been obtained by deriving spectroscopic
redshifts for both components, lens and source, from observations at the 10.4 m Gran
Telescopio CANARIAS (GTC) with the spectrograph OSIRIS. The lens, a massive
early-type galaxy, has a redshift of z = 0.581 while the source is a starburst galaxy
with redshift of z = 1.165. The total enclosed mass that produces the lensing effect
has been estimated to be Mtot = (1.86 ± 0.23) · 1012M⊙.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
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
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest f...Sérgio Sacani
Aims. We present the first public release of photometric redshifts, galaxy rest frame properties and associated magnification values
in the cluster and parallel pointings of the first two Frontier Fields, Abell-2744 and MACS-J0416. The released catalogues aim to
provide a reference for future investigations of extragalactic populations in these legacy fields: from lensed high-redshift galaxies to
cluster members themselves.
Methods.We exploit a multiwavelength catalogue, ranging from Hubble Space Telescope (HST) to ground-based K and Spitzer IRAC,
which is specifically designed to enable detection and measurement of accurate fluxes in crowded cluster regions. The multiband
information is used to derive photometric redshifts and physical properties of sources detected either in the H-band image alone, or
from a stack of four WFC3 bands. To minimize systematics, median photometric redshifts are assembled from six dierent approaches
to photo-z estimates. Their reliability is assessed through a comparison with available spectroscopic samples. State-of-the-art lensing
models are used to derive magnification values on an object-by-object basis by taking into account sources positions and redshifts.
Results. We show that photometric redshifts reach a remarkable 3–5% accuracy. After accounting for magnification, the H-band
number counts are found to be in agreement at bright magnitudes with number counts from the CANDELS fields, while extending
the presently available samples to galaxies that, intrinsically, are as faint as H 32 33, thanks to strong gravitational lensing. The
Frontier Fields allow the galaxy stellar mass distribution to be probed, depending on magnification, at 0.5–1.5 dex lower masses with
respect to extragalactic wide fields, including sources at Mstar 107–108 M at z > 5. Similarly, they allow the detection of objects
with intrinsic star formation rates (SFRs) >1 dex lower than in the CANDELS fields reaching 0.1–1 M=yr at z 6–10.
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
We report the discovery of an optical Einstein Ring in the Sculptor constellation,
IAC J010127-334319, in the vicinity of the Sculptor Dwarf Spheroidal Galaxy. It is
an almost complete ring ( 300◦) with a diameter of 4.5 arcsec. The discovery was
made serendipitously from inspecting Dark Energy Camera (DECam) archive imaging
data. Confirmation of the object nature has been obtained by deriving spectroscopic
redshifts for both components, lens and source, from observations at the 10.4 m Gran
Telescopio CANARIAS (GTC) with the spectrograph OSIRIS. The lens, a massive
early-type galaxy, has a redshift of z = 0.581 while the source is a starburst galaxy
with redshift of z = 1.165. The total enclosed mass that produces the lensing effect
has been estimated to be Mtot = (1.86 ± 0.23) · 1012M⊙.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
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
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest f...Sérgio Sacani
Aims. We present the first public release of photometric redshifts, galaxy rest frame properties and associated magnification values
in the cluster and parallel pointings of the first two Frontier Fields, Abell-2744 and MACS-J0416. The released catalogues aim to
provide a reference for future investigations of extragalactic populations in these legacy fields: from lensed high-redshift galaxies to
cluster members themselves.
Methods.We exploit a multiwavelength catalogue, ranging from Hubble Space Telescope (HST) to ground-based K and Spitzer IRAC,
which is specifically designed to enable detection and measurement of accurate fluxes in crowded cluster regions. The multiband
information is used to derive photometric redshifts and physical properties of sources detected either in the H-band image alone, or
from a stack of four WFC3 bands. To minimize systematics, median photometric redshifts are assembled from six dierent approaches
to photo-z estimates. Their reliability is assessed through a comparison with available spectroscopic samples. State-of-the-art lensing
models are used to derive magnification values on an object-by-object basis by taking into account sources positions and redshifts.
Results. We show that photometric redshifts reach a remarkable 3–5% accuracy. After accounting for magnification, the H-band
number counts are found to be in agreement at bright magnitudes with number counts from the CANDELS fields, while extending
the presently available samples to galaxies that, intrinsically, are as faint as H 32 33, thanks to strong gravitational lensing. The
Frontier Fields allow the galaxy stellar mass distribution to be probed, depending on magnification, at 0.5–1.5 dex lower masses with
respect to extragalactic wide fields, including sources at Mstar 107–108 M at z > 5. Similarly, they allow the detection of objects
with intrinsic star formation rates (SFRs) >1 dex lower than in the CANDELS fields reaching 0.1–1 M=yr at z 6–10.
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
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.
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
The importance of comets for the origin of life on Earth has been advocated for many decades. Amino acids are
key ingredients in chemistry, leading to life as we know it. Many primitive meteorites contain amino acids, and it
is generally believed that these are formed by aqueous alterations. In the collector aerogel and foil samples of the
Stardust mission after the flyby at comet Wild 2, the simplest form of amino acids, glycine, has been found
together with precursor molecules methylamine and ethylamine. Because of contamination issues of the samples,
a cometary origin was deduced from the 13C isotopic signature. We report the presence of volatile glycine
accompanied by methylamine and ethylamine in the coma of 67P/Churyumov-Gerasimenko measured by
the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) mass spectrometer, confirming the
Stardust results. Together with the detection of phosphorus and a multitude of organic molecules, this result
demonstrates that comets could have played a crucial role in the emergence of life on Earth.
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.
Magnetic interaction of_a_super_cme_with_the_earths_magnetosphere_scenario_fo...Sérgio Sacani
Solar eruptions, known as Coronal Mass Ejections (CMEs), are
frequently observed on our Sun. Recent Kepler observations of super
ares
on G-type stars have implied that so called super-CMEs, possessing kinetic
energies 10 times of the most powerful CME event ever observed on the Sun,
could be produced with a frequency of 1 event per 800-2000 yr on solar-
like slowly rotating stars. We have performed a 3D time-dependent global
magnetohydrodynamic simulation of the magnetic interaction of such a CME
cloud with the Earth's magnetosphere. We calculated the global structure
of the perturbed magnetosphere and derive the latitude of the open-closed
magnetic eld boundary. We also estimated energy
uxes penetrating the
Earth's ionosphere and discuss the consequences of energetic particle
uxes
on biological systems on early Earth.
Detection of lyman_alpha_emission_from_a_triply_imaged_z_6_85_galaxy_behind_m...Sérgio Sacani
We report the detection of Ly emission at 9538A
in the Keck/DEIMOS and HST WFC3
G102 grism data from a triply-imaged galaxy at z = 6:846 0:001 behind galaxy cluster MACS
J2129.4 0741. Combining the emission line wavelength with broadband photometry, line ratio upper
limits, and lens modeling, we rule out the scenario that this emission line is [O II] at z = 1:57. After
accounting for magnication, we calculate the weighted average of the intrinsic Ly luminosity to be
1:31042 erg s 1 and Ly equivalent width to be 7415A. Its intrinsic UV absolute magnitude at
1600A
is 18:60:2 mag and stellar mass (1:50:3)107 M, making it one of the faintest (intrinsic
LUV 0:14 L
UV) galaxies with Ly detection at z 7 to date. Its stellar mass is in the typical range
for the galaxies thought to dominate the reionization photon budget at z & 7; the inferred Ly escape
fraction is high (& 10%), which could be common for sub-L z & 7 galaxies with Ly emission. This
galaxy oers a glimpse of the galaxy population that is thought to drive reionization, and it shows
that gravitational lensing is an important avenue to probe the sub-L galaxy population.
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
The 19 Feb. 2016 Outburst of Comet 67P/CG: An ESA Rosetta Multi-Instrument StudySérgio Sacani
On 19 Feb. 2016 nine Rosetta instruments serendipitously observed an outburst of gas and dust
from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras
and spectrometers ranging from UV over visible to microwave wavelengths, in-situ gas, dust and
plasma instruments, and one dust collector. At 9:40 a dust cloud developed at the edge of an image
in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature
of the outburst that signicantly exceeded the background. The enhancement ranged from 50% of
the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus.
Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest
enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3
and consequently the spacecraft potential changed from 16V to 20V during the outburst. A
clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15
minutes the Star Tracker camera detected fast particles ( 25 ms 1) while 100 m radius particles
were detected by the GIADA dust instrument 1 hour later at a speed of 6 ms 1. The slowest
were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst
originated just outside the FOV of the instruments, the source region and the magnitude of the
outburst could be determined.
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
Galaxy growth in a massive halo in the first billion years of cosmic historySérgio Sacani
According to the current understanding of cosmic structure formation, the precursors of the most massive structures in the Universe began to form shortly after the Big Bang, in regions corresponding to the largest fluctuations in the cosmic density field1–3. Observing these structures during their period of active growth and assembly—the first few hundred million years of the Universe—is challenging because it requires surveys that are sensitive enough to detect the distant galaxies that act as signposts for these structures and wide enough to capture the rarest objects. As a result, very few such objects have been detected so far4,5. Here we report observations of a far-infrared-luminous object at redshift 6.900 (less than 800 million years after the Big Bang) that was discovered in a wide-field survey6. High-resolution imaging shows it to be a pair of extremely massive star-forming galaxies. The larger is forming stars at a rate of 2,900 solar masses per year, contains 270 billion solar masses of gas and 2.5 billion solar masses of dust, and is more massive than any other known object at a redshift of more than 6. Its rapid star formation is probably triggered by its companion galaxy at a projected separation of 8 kiloparsecs. This merging companion hosts 35 billion solar masses of stars and has a star-formation rate of 540 solar masses per year, but has an order of magnitude less gas and dust than its neighbour and physical conditions akin to those observed in lower-metallicity galaxies in the nearby Universe7. These objects suggest the presence of a dark-matter halo with a mass of more than 100 billion solar masses, making it among the rarest dark-matter haloes that should exist in the Universe at this epoch.
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
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.
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
The importance of comets for the origin of life on Earth has been advocated for many decades. Amino acids are
key ingredients in chemistry, leading to life as we know it. Many primitive meteorites contain amino acids, and it
is generally believed that these are formed by aqueous alterations. In the collector aerogel and foil samples of the
Stardust mission after the flyby at comet Wild 2, the simplest form of amino acids, glycine, has been found
together with precursor molecules methylamine and ethylamine. Because of contamination issues of the samples,
a cometary origin was deduced from the 13C isotopic signature. We report the presence of volatile glycine
accompanied by methylamine and ethylamine in the coma of 67P/Churyumov-Gerasimenko measured by
the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) mass spectrometer, confirming the
Stardust results. Together with the detection of phosphorus and a multitude of organic molecules, this result
demonstrates that comets could have played a crucial role in the emergence of life on Earth.
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.
Magnetic interaction of_a_super_cme_with_the_earths_magnetosphere_scenario_fo...Sérgio Sacani
Solar eruptions, known as Coronal Mass Ejections (CMEs), are
frequently observed on our Sun. Recent Kepler observations of super
ares
on G-type stars have implied that so called super-CMEs, possessing kinetic
energies 10 times of the most powerful CME event ever observed on the Sun,
could be produced with a frequency of 1 event per 800-2000 yr on solar-
like slowly rotating stars. We have performed a 3D time-dependent global
magnetohydrodynamic simulation of the magnetic interaction of such a CME
cloud with the Earth's magnetosphere. We calculated the global structure
of the perturbed magnetosphere and derive the latitude of the open-closed
magnetic eld boundary. We also estimated energy
uxes penetrating the
Earth's ionosphere and discuss the consequences of energetic particle
uxes
on biological systems on early Earth.
Detection of lyman_alpha_emission_from_a_triply_imaged_z_6_85_galaxy_behind_m...Sérgio Sacani
We report the detection of Ly emission at 9538A
in the Keck/DEIMOS and HST WFC3
G102 grism data from a triply-imaged galaxy at z = 6:846 0:001 behind galaxy cluster MACS
J2129.4 0741. Combining the emission line wavelength with broadband photometry, line ratio upper
limits, and lens modeling, we rule out the scenario that this emission line is [O II] at z = 1:57. After
accounting for magnication, we calculate the weighted average of the intrinsic Ly luminosity to be
1:31042 erg s 1 and Ly equivalent width to be 7415A. Its intrinsic UV absolute magnitude at
1600A
is 18:60:2 mag and stellar mass (1:50:3)107 M, making it one of the faintest (intrinsic
LUV 0:14 L
UV) galaxies with Ly detection at z 7 to date. Its stellar mass is in the typical range
for the galaxies thought to dominate the reionization photon budget at z & 7; the inferred Ly escape
fraction is high (& 10%), which could be common for sub-L z & 7 galaxies with Ly emission. This
galaxy oers a glimpse of the galaxy population that is thought to drive reionization, and it shows
that gravitational lensing is an important avenue to probe the sub-L galaxy population.
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
The 19 Feb. 2016 Outburst of Comet 67P/CG: An ESA Rosetta Multi-Instrument StudySérgio Sacani
On 19 Feb. 2016 nine Rosetta instruments serendipitously observed an outburst of gas and dust
from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras
and spectrometers ranging from UV over visible to microwave wavelengths, in-situ gas, dust and
plasma instruments, and one dust collector. At 9:40 a dust cloud developed at the edge of an image
in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature
of the outburst that signicantly exceeded the background. The enhancement ranged from 50% of
the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus.
Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest
enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3
and consequently the spacecraft potential changed from 16V to 20V during the outburst. A
clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15
minutes the Star Tracker camera detected fast particles ( 25 ms 1) while 100 m radius particles
were detected by the GIADA dust instrument 1 hour later at a speed of 6 ms 1. The slowest
were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst
originated just outside the FOV of the instruments, the source region and the magnitude of the
outburst could be determined.
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
Galaxy growth in a massive halo in the first billion years of cosmic historySérgio Sacani
According to the current understanding of cosmic structure formation, the precursors of the most massive structures in the Universe began to form shortly after the Big Bang, in regions corresponding to the largest fluctuations in the cosmic density field1–3. Observing these structures during their period of active growth and assembly—the first few hundred million years of the Universe—is challenging because it requires surveys that are sensitive enough to detect the distant galaxies that act as signposts for these structures and wide enough to capture the rarest objects. As a result, very few such objects have been detected so far4,5. Here we report observations of a far-infrared-luminous object at redshift 6.900 (less than 800 million years after the Big Bang) that was discovered in a wide-field survey6. High-resolution imaging shows it to be a pair of extremely massive star-forming galaxies. The larger is forming stars at a rate of 2,900 solar masses per year, contains 270 billion solar masses of gas and 2.5 billion solar masses of dust, and is more massive than any other known object at a redshift of more than 6. Its rapid star formation is probably triggered by its companion galaxy at a projected separation of 8 kiloparsecs. This merging companion hosts 35 billion solar masses of stars and has a star-formation rate of 540 solar masses per year, but has an order of magnitude less gas and dust than its neighbour and physical conditions akin to those observed in lower-metallicity galaxies in the nearby Universe7. These objects suggest the presence of a dark-matter halo with a mass of more than 100 billion solar masses, making it among the rarest dark-matter haloes that should exist in the Universe at this epoch.
M82 X-2 is the first pulsating ultraluminous X-ray source discovered. The luminosity of these extreme pulsars, if
isotropic, implies an extreme mass transfer rate. An alternative is to assume a much lower mass transfer rate, but
with an apparent luminosity boosted by geometrical beaming. Only an independent measurement of the mass
transfer rate can help discriminate between these two scenarios. In this paper, we follow the orbit of the neutron star
for 7 yr, measure the decay of the orbit (P P orb orb 8 10 yr 6 1 · » - - - ), and argue that this orbital decay is driven by
extreme mass transfer of more than 150 times the mass transfer limit set by the Eddington luminosity. If this is true,
the mass available to the accretor is more than enough to justify its luminosity, with no need for beaming. This also
strongly favors models where the accretor is a highly magnetized neutron star.
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.
A density cusp of quiescent X-ray binaries in the central parsec of the GalaxySérgio Sacani
The existence of a ‘density cusp’1,2—a localized increase in
number—of stellar-mass black holes near a supermassive black
hole is a fundamental prediction of galactic stellar dynamics3
. The
best place to detect such a cusp is in the Galactic Centre, where
the nearest supermassive black hole, Sagittarius A*, resides. As
many as 20,000 black holes are predicted to settle into the central
parsec of the Galaxy as a result of dynamical friction3–5; however,
so far no density cusp of black holes has been detected. Low-mass
X-ray binary systems that contain a stellar-mass black hole are
natural tracers of isolated black holes. Here we report observations
of a dozen quiescent X-ray binaries in a density cusp within one
parsec of Sagittarius A*. The lower-energy emission spectra that
we observed in these binaries is distinct from the higher-energy
spectra associated with the population of accreting white dwarfs that
dominates the central eight parsecs of the Galaxy6
. The properties
of these X-ray binaries, in particular their spatial distribution and
luminosity function, suggest the existence of hundreds of binary
systems in the central parsec of the Galaxy and many more isolated
black holes. We cannot rule out a contribution to the observed
emission from a population (of up to about one-half the number of
X-ray binaries) of rotationally powered, millisecond pulsars. The
spatial distribution of the binary systems is a relic of their formation
history, either in the stellar disk around Sagittarius A* (ref. 7) or
through in-fall from globular clusters, and constrains the number
density of sources in the modelling of gravitational waves from
massive stellar remnants8,9
, such as neutron stars and black holes.
Millimetre-wave emission from an intermediatemass black hole candidate in the...Sérgio Sacani
It is widely accepted that black holes with masses greater
than a million solar masses (M⊙) lurk at the centres of massive
galaxies. The origins of such ‘supermassive’ black holes
(SMBHs) remain unknown1, although those of stellar-mass
black holes are well understood. One possible scenario is that
intermediate-mass black holes (IMBHs), which are formed
by the runaway coalescence of stars in young compact star
clusters2, merge at the centre of a galaxy to form a SMBH3.
Although many candidates for IMBHs have been proposed,
none is accepted as definitive. Recently, we discovered a
peculiar molecular cloud, CO–0.40–0.22, with an extremely
broad velocity width, near the centre of our Milky Way galaxy.
Based on the careful analysis of gas kinematics, we concluded
that a compact object with a mass of about 105M⊙ is lurking
in this cloud4. Here we report the detection of a point-like
continuum source as well as a compact gas clump near the
centre of CO–0.40–0.22. This point-like continuum source
(CO–0.40–0.22*) has a wide-band spectrum consistent with
1/500 of the Galactic SMBH (Sgr A*) in luminosity. Numerical
simulations around a point-like massive object reproduce the
kinematics of dense molecular gas well, which suggests that
CO–0.40–0.22* is one of the most promising candidates for
an intermediate-mass black hole.
Galaxy and mass_assembly_gama_panchromatic_data_release_and__the_low_energy_b...Sérgio Sacani
Uma equipe internacional de astrônomos estudou mais de 200 000 galáxias e mediu a energia gerada numa enorme região do espaço com a maior precisão até hoje. Este estudo representa a estimativa mais completa de produção de energia no Universo próximo. A equipe confirmou que a energia produzida nesta região do Universo de hoje é apenas cerca de metade da produzida há dois bilhões de anos atrás e descobriu que este enfraquecimento ocorre em todos os comprimentos de onda que vão desde o ultravioleta ao infravermelho longínquo. O Universo está morrendo lentamente.
O estudo envolve muitos dos telescópios mais poderosos do mundo, incluindo o VISTA e o VST — os telescópios de rastreio do ESO, instalados no Observatório do Paranal, no Chile. Observações de suporte foram obtidas por dois telescópios espaciais operados pela NASA (GALEX e WISE) e por um outro pertencente à Agência Espacial Europeia (Herschel) [1].
Este trabalho realizou-se no âmbito do projeto Galaxy And Mass Assembly (GAMA), o maior rastreio já realizado em múltiplos comprimentos de onda.
“Usamos tantos telescópios terrestres e espaciais quanto nos foi possível para medir a produção de energia de cerca de 200 000 galáxias ao longo do maior intervalo de comprimentos de onda possível,” disse Simon Driver (ICRAR, The University of Western Australia), que lidera a enorme equipe GAMA.
The xmm newton-view_of_the_central_degrees_of_the_milk_waySérgio Sacani
Novas imagens do Observatório de Raios-X XMM-Newton da ESA revelaram alguns dos processos mais intensos que acontecem no coração da nossa Via Láctea.
As fontes brilhantes e pontuais que se destacam por toda imagem indicam os sistemas estelares binários onde uma das estrelas atingiu o final de sua vida, desenvolvendo para um objeto compacto e denso – uma estrela de nêutrons ou um buraco negro.
A região central da Via Láctea também contém jovens estrelas e aglomerados estelares e algumas dessas fontes são visíveis como pontos brancos e vermelhos brilhando na imagem, que se espalha por 1000 anos-luz.
A maior parte da ação ocorre no centro, onde nuvens difusas de gás estão sendo cavadas por ventos poderosos soprados por estrelas jovens, bem como por supernovas.
Observational constraints on mergers creating magnetism in massive starsSérgio Sacani
Massive stars (those ≥8 solar masses at birth) have radiative envelopes that cannot sustain the dynamos that produce magnetic fields in lower mass stars. Despite this, ∼7% of massive stars have observed magnetic fields. We use multi-epoch interferometric and spectroscopic observations to characterise a magnetic binary system formed of two massive stars. We find that only one star of the binary is magnetic. Using the non-magnetic star as an independent reference clock to estimate the age of the system, we show that the magnetic star appears younger than its companion. The system properties, and a surrounding bipolar nebula, can be reproduced by a model in which this system was originally a triple within which two of the stars merged, producing the magnetic massive star. Thus, our results provide observational evidence that magnetic fields form in at least some massive stars through stellar mergers.
A supermassive black_hole_in_a_ultra_compact_dwarf_galaxySérgio Sacani
Hubble e Gemini observam a galáxia ultra compacta M60-UCD1 e por meio de imagens e medidas de espectrometria descobrem buraco negro que representa 15% da massa da galáxia. Um buraco negro gigante em uma galáxia anã.
Similar to Cold clumpy accretion_toward_an_active_supermasive_black_hole (20)
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.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
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
Comparing Evolved Extractive Text Summary Scores of Bidirectional Encoder Rep...University of Maribor
Slides from:
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Track: Artificial Intelligence
https://www.etran.rs/2024/en/home-english/
This presentation explores a brief idea about the structural and functional attributes of nucleotides, the structure and function of genetic materials along with the impact of UV rays and pH upon them.
Deep Behavioral Phenotyping in Systems Neuroscience for Functional Atlasing a...Ana Luísa Pinho
Functional Magnetic Resonance Imaging (fMRI) provides means to characterize brain activations in response to behavior. However, cognitive neuroscience has been limited to group-level effects referring to the performance of specific tasks. To obtain the functional profile of elementary cognitive mechanisms, the combination of brain responses to many tasks is required. Yet, to date, both structural atlases and parcellation-based activations do not fully account for cognitive function and still present several limitations. Further, they do not adapt overall to individual characteristics. In this talk, I will give an account of deep-behavioral phenotyping strategies, namely data-driven methods in large task-fMRI datasets, to optimize functional brain-data collection and improve inference of effects-of-interest related to mental processes. Key to this approach is the employment of fast multi-functional paradigms rich on features that can be well parametrized and, consequently, facilitate the creation of psycho-physiological constructs to be modelled with imaging data. Particular emphasis will be given to music stimuli when studying high-order cognitive mechanisms, due to their ecological nature and quality to enable complex behavior compounded by discrete entities. I will also discuss how deep-behavioral phenotyping and individualized models applied to neuroimaging data can better account for the subject-specific organization of domain-general cognitive systems in the human brain. Finally, the accumulation of functional brain signatures brings the possibility to clarify relationships among tasks and create a univocal link between brain systems and mental functions through: (1) the development of ontologies proposing an organization of cognitive processes; and (2) brain-network taxonomies describing functional specialization. To this end, tools to improve commensurability in cognitive science are necessary, such as public repositories, ontology-based platforms and automated meta-analysis tools. I will thus discuss some brain-atlasing resources currently under development, and their applicability in cognitive as well as clinical neuroscience.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
Salas, V. (2024) "John of St. Thomas (Poinsot) on the Science of Sacred Theol...Studia Poinsotiana
I Introduction
II Subalternation and Theology
III Theology and Dogmatic Declarations
IV The Mixed Principles of Theology
V Virtual Revelation: The Unity of Theology
VI Theology as a Natural Science
VII Theology’s Certitude
VIII Conclusion
Notes
Bibliography
All the contents are fully attributable to the author, Doctor Victor Salas. Should you wish to get this text republished, get in touch with the author or the editorial committee of the Studia Poinsotiana. Insofar as possible, we will be happy to broker your contact.
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,
and analysis methods, numerous infrastructure platforms have been developed for phenotyping.
The ability to recreate computational results with minimal effort and actionable metrics provides a solid foundation for scientific research and software development. When people can replicate an analysis at the touch of a button using open-source software, open data, and methods to assess and compare proposals, it significantly eases verification of results, engagement with a diverse range of contributors, and progress. However, we have yet to fully achieve this; there are still many sociotechnical frictions.
Inspired by David Donoho's vision, this talk aims to revisit the three crucial pillars of frictionless reproducibility (data sharing, code sharing, and competitive challenges) with the perspective of deep software variability.
Our observation is that multiple layers — hardware, operating systems, third-party libraries, software versions, input data, compile-time options, and parameters — are subject to variability that exacerbates frictions but is also essential for achieving robust, generalizable results and fostering innovation. I will first review the literature, providing evidence of how the complex variability interactions across these layers affect qualitative and quantitative software properties, thereby complicating the reproduction and replication of scientific studies in various fields.
I will then present some software engineering and AI techniques that can support the strategic exploration of variability spaces. These include the use of abstractions and models (e.g., feature models), sampling strategies (e.g., uniform, random), cost-effective measurements (e.g., incremental build of software configurations), and dimensionality reduction methods (e.g., transfer learning, feature selection, software debloating).
I will finally argue that deep variability is both the problem and solution of frictionless reproducibility, calling the software science community to develop new methods and tools to manage variability and foster reproducibility in software systems.
Exposé invité Journées Nationales du GDR GPL 2024
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Toxic effects of heavy metals : Lead and Arsenicsanjana502982
Heavy metals are naturally occuring metallic chemical elements that have relatively high density, and are toxic at even low concentrations. All toxic metals are termed as heavy metals irrespective of their atomic mass and density, eg. arsenic, lead, mercury, cadmium, thallium, chromium, etc.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
1. LETTER
Cold, clumpy accretion toward an active
supermassive black hole
Grant R. Tremblay1,2,†, J. B. Raymond Oonk3,4, Franc¸oise Combes5, Philippe Salom´e5, Christopher O’Dea6,7, Stefi A. Baum6,8,
G. Mark Voit9, Megan Donahue9, Brian R. McNamara10, Timothy A. Davis11,2,‡, Michael A. McDonald12, Alastair C. Edge13,
Tracy E. Clarke14, Roberto Galv´an-Madrid15,2, Malcolm N. Bremer16, Louise O. V. Edwards1, Andrew C. Fabian17, Stephen
Hamer5, Yuan Li18, Ana¨elle Maury19, Helen Russell17, Alice C. Quillen20, C. Megan Urry1, Jeremy S. Sanders21, Michael Wise3
Supermassive black holes in galaxy centres can grow by the ac-
cretion 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 never-
theless largely unconstrained by observations, and is instead rou-
tinely 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 re-
mains elusive. Here we show observational evidence for a cold,
clumpy accretion flow toward a supermassive black hole fuel reser-
voir in the nucleus of the Abell 2597 Brightest Cluster Galaxy
(BCG), a nearby (zzz === 000...000888222111) 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 in-
habits 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 ∼∼∼ 333000000
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 geome-
try and probability, indicates that these clouds are within the inner-
most hundred parsecs of the black hole, and falling closer toward
it.
1Yale Center for Astronomy & Astrophysics, Yale University, 52 Hillhouse Ave., New Haven,
CT 06511, USA 2European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748, Garching-bei-
M¨unchen, Germany 3ASTRON, Netherlands Institute for Radio Astronomy, P.O. Box 2, 7990 AA
Dwingeloo, The Netherlands 4Leiden Observatory, Leiden University, Niels Borhweg 2, NL-2333 CA
Leiden, The Netherlands 5LERMA, Observatoire de Paris, PSL Research Univ., College de France,
CNRS, Sorbonne Univ., Paris, France 6Department of Physics & Astronomy, University of Manitoba,
Winnipeg, MB R3T 2N2, Canada 7School of Physics & Astronomy, Rochester Institute of Technol-
ogy, 84 Lomb Memorial Dr., Rochester, NY 14623, USA 8Chester F. Carlson Center for Imaging
Science, Rochester Institute of Technology, 84 Lomb Memorial Dr., Rochester, NY 14623, USA
9Physics & Astronomy Department, Michigan State University, East Lansing, MI 48824-2320, USA
10Physics & Astronomy Department, Waterloo University, 200 University Ave. W., Waterloo, ON,
N2L, 2GL, Canada 11School of Physics & Astronomy, Cardiff University, The Parade, Cardiff CF24
3AA, United Kingdom 12Kavli Institute for Astrophysics & Space Research, MIT, 77 Massachusetts
Ave., Cambridge, MA 02139, USA 13Department of Physics, Durham University, Durham, DHL 3LE,
United Kingdom 14Naval Research Laboratory Remote Sensing Division, Code 7213 4555 Overlook
Ave. SW, Washington, DC 20375, USA 15Instituto de Radioastronom´ıa y Astrof´ısica, UNAM, Apdo.
Postal 3-72 (Xangari), 58089 Morelia, Michoac´an, M´exico 16H. W. Wills Physics Laboratory, Uni-
versity of Bristol, Tyndall Avenue, Bristol, BS8 1TL, United Kingdom 17Institute of Astronomy, Cam-
bridge University, Madingly Rd., Cambridge, CB3 0HA, United Kingdom 18Department of Astronomy,
University of Michigan, 1085 S. University Avenue, Ann Arbor, MI 48109, USA 19Laboratoire AIM-
Paris-Saclay, CEA/DSM/Irfu CNRS ? Univ. Paris Diderot, CE-Saclay, F-91191 Gif-sur-Yvette, France
20Department of Physics & Astronomy, University of Rochester, Rochester, NY 14627, USA 21Max
Planck Institut f¨ur Extraterrestrische Physik, 85748 Garching bei M¨unchen, Germany
We observed the Abell 2597 Brightest Cluster Galaxy (Fig. 1) with
the Atacama Large Millimeter/submillimeter Array (ALMA), enabling
us to create a three-dimensional map of both the location and motions
of cold gas at uniquely high sensitivity and spatial resolution. The
ALMA receivers were sensitive to emission from the J = 2 − 1 rota-
tional line of the carbon monoxide (CO) molecule. CO(2-1) emission
is used as a tracer of cold (∼ 10−30 K) molecular hydrogen, which is
vastly more abundant, but not directly observable at these low temper-
atures.
The continuum-subtracted CO(2-1) images (Fig. 2) reveal that the
filamentary emission line nebula that spans the galaxy’s innermost ∼ 30
kpc (Fig. 1b) consists not only of warm ionised gas18–20
, but cold
molecular gas as well. In projection, the optical emission line neb-
ula is cospatial and morphologically matched with CO(2-1) emission
detected at a significance between >∼ 3σ (in the outer filaments) and
>∼ 20σ (in the nuclear region) above the background noise level. The
warm ionised nebula is therefore likely to have a substantial molecu-
lar component, consistent with results for other similar galaxies21
. The
total measured CO(2-1) line flux corresponds to a molecular hydrogen
gas mass of MH2
= (1.8±0.2) × 109 M , where M is the mass of
the sun. The critical (minimum) density for CO(2-1) emission requires
that the volume filling factor of this gas be very low, of order a few
percent. The projected spatial coincidence of both the warm ionised
and cold molecular nebulae therefore supports the long-envisaged hy-
pothesis that the ionised gas is merely the warm “skin” surrounding
far colder and more massive molecular cores22,23
, whose outer regions
are heated by intense radiation from the environment in which they re-
side. Rather than a monolithic, kiloparsec-scale slab of cold gas, we
are more likely observing a projected superposition of many smaller,
isolated clouds and filaments.
The data unambiguously show that cold molecular gas is falling in-
ward along a line of sight that intersects the galaxy centre. We know
this because the ALMA beam cospatial with the millimetre continuum
source, the radio core, and the isophotal centre of the galaxy reveals
strong, redshifted continuum absorption (Fig. 3b), found by extract-
ing the CO(2-1) spectrum from this central beam. This reveals at least
three deep and narrow absorption lines (Fig. 3c), with redshifted line
centres at +240, +275, and +335 km s−1 relative to the systemic (stel-
lar) velocity of the galaxy, all within an angular (physical) region of
0. 715×0. 533 (1 kpc×0.8 kpc).
These absorption features arise from cold molecular clouds mov-
ing toward the centre of the galaxy, either via radial or inspiralling tra-
jectories. They manifest as continuum absorption because they cast
“shadows” along the line of sight as the clouds eclipse or attenuate
about 20% (or about 2 mJy) of the millimetre synchrotron continuum
† Einstein Fellow ‡ Rutherford Fellow
1
2. Abell 2597 (z=0.082)
Rapidly cooling
X-ray atmosphere Buoyant X-ray Bubbles
B: X-ray
Y: Optical
R: H-alpha
30 kpc (20’’)
Ly-alpha
8.4 GHz Contours
FUV cont.(unsharp mask)
8.4 GHz Contours
5 kpc (3.3’’)
Brightest Cluster Galaxy
and surrounding environment
Cool Gas Young Stars
(a)
(b) (c)
Figure 1 | A multiwavelength view of the Abell 2597 BCG. (a) Chandra X-ray, HST and DSS optical, and Magellan Hα+[NII] emission is shown in blue, yellow, and
red, respectively (Credit: X-ray: NASA / CXC / Michigan State Univ / G.Voit et al; Optical: NASA/STScI & DSS; Hα: Carnegie Obs. / Magellan / W.Baade Telescope
/ U.Maryland / M.McDonald). (b) HST image of Lyα emission associated with the ionised gas nebula13. (c) Unsharp mask of the HST far-ultraviolet continuum image
of the central regions of the nebula13. Very Large Array (VLA) radio contours of the 8.4 GHz source are overlaid in red.
2
3. source, which serves as a bright backlight (13.6 mJy at rest-frame 230
GHz). The synchrotron continuum is emitted by jets launched from
the accreting supermassive (∼ 3×108 M )13
black hole in the galaxy’s
active nucleus (Fig. 4). The absorbers must therefore be located some-
where between the observer and the galaxy centre, falling deeper into
the galaxy at ∼ +300 km s−1 toward the black hole at its core. This ra-
dial speed is roughly equal to the expected circular velocity24
in the nu-
cleus, consistent either with a nearly radial orbit, or highly non-circular
motions in close proximity to the galaxy’s core.
Gaussian fits to the spectral absorption features reveal narrow
linewidths of σ <∼ 6 km s−1, which means the absorbers are more
likely spatially compact, with sizes that span tens (rather than hundreds
or thousands) of parsecs. The shapes of the absorption lines remain
roughly the same regardless of how finely the spectra are binned, sug-
gesting that the absorbers are likely coherent structures, rather than a
superposition of many smaller absorbers unresolved in velocity space.
If each absorption feature corresponds to one coherent cloud, and if
those clouds roughly obey size-linewidth relations25,26
for giant molec-
ular clouds in the Milky Way, they should have diameters not larger
than ∼ 40 pc. If in virial equilibrium, molecular clouds this size would
have masses of order 105−6 M , and if in rough pressure equilibrium
with their ambient multiphase 103−7 K environment13
, they must have
high column densities of order NH2
≈ 1022−24 cm−2 so as to main-
tain pressure support. The thermal pressure in the core of Abell 2597
is nearly three thousand times11
greater than that for the Milky Way,
however, which means the absorbing clouds may be much smaller.
The absorbers have optical depths that range from 0.1 <∼
τCO(2−1) <∼ 0.3. The physical resolution of the ALMA data is larger
than the synchrotron background source, which means that the optical
depth is likely contaminated by an unresolved, additive superposition
of both emission and absorption within the beam. Compact, dense cold
clouds are nevertheless likely to be optically thick, which may mean
they eclipse the continuum source with an optical depth of unity but
a small covering factor of roughly 0.2. Especially when considering
beam contamination by emission, the covering factor cannot be known
with certainty, as this depends on the unknown geometry of the absorb-
ing and emitting regions within the ALMA beam.
This geometry can be constrained, however, given existing Very
Long Baseline Array (VLBA) radio observations at extremely high
spatial resolution15
. These data resolve the 1.3 and 5 GHz radio con-
tinuum source down to scales of 25 parsecs, revealing a highly sym-
metric, 100 pc-scale jet about a bright radio core (Fig. 4c). Just as we
have found in cold molecular gas, inflowing warmer atomic hydrogen
gas (HI) has previously been found in absorption against this pc-scale
jet, corroborating prior reports of inflowing atomic gas at lower spatial
resolutions14
. The inflow velocity of this gas matches that seen in our
ALMA data. Remarkably, both the optical depth and linewidth of the
warm atomic absorption signal varies dramatically across the jet, with
a broad (σ ≈ 310 km s−1) component cospatial with the core that is
absent just ∼ 20 pc to the northeast, where only a narrow (σ ≈ 50 km
s−1) HI line is found at the same redshift. This effectively requires the
inflowing atomic gas to be confined within the innermost ∼ 100 pc of
the black hole, as gas further out would give rise to an unchanging ab-
sorption signal across the compact jet. The infall velocity is the same
as that for the cold molecular clouds seen in CO(2-1) absorption, which
means they most likely stem from the same spatial region, within tens
of parsecs of the accreting black hole.
This is further supported by the ALMA data itself. In emission, all
gas around ∼ +300 km s−1 that is conceivably available to attenuate
the continuum signal is confined to the innermost 2 kpc about the nu-
cleus (Fig. 4a,b). The radial dependence of molecular cloud volume
number density within this region is uncertain, but probably steeper
than r−1, and likely closer to r−2 (Fig. 4b). This means that the chances
of a random line of sight crossing will drop with increasing distance
from the black hole. If the gas volume density goes as r−2, a cloud
100 pc from the black hole is ten times more likely to cross our line
of sight than a cloud at a galactocentric distance of 1 kpc. It would be
exceedingly unlikely for three such clouds to cross our line of sight to
the black hole were they spread over several kiloparsecs throughout the
galaxy’s outskirts.
The data therefore serve as strong observational evidence for an
inward-moving, clumpy distribution of molecular clouds within a few
hundred parsecs of an accreting supermassive black hole. The infalling
clouds are likely a few to tens of parsecs across and therefore mas-
sive (perhaps 105−6 M each). If they are falling directly toward the
black hole, rather than bound in a non-circular orbit that tightly winds
around it, they could supply an upper-limit accretion rate on the order
of ∼ 0.1 to a few M yr−1, depending on the three dimensional distri-
bution of infalling clouds. If most of the clouds are instead locked in
non-circular orbits around the black hole, the fuelling rate would de-
pend on the gas angular momentum, and the local supply of torques
that might lessen it. Simulations suggest7,12
that such torques may be
plentiful, as they predict a stochastic “rain” of thermal instabilities that
condense from all directions around the black hole, promoting angu-
lar momentum cancellation via tidal stress and cloud-cloud collisions.
Even highly elliptical cloud orbits should therefore be associated with
significant inward radial motions. The clouds might fall onto the ac-
cretion disc itself, or into a clumpy rotating ring akin to the “torus”
invoked in AGN unification models27
.
Cold accretion onto black holes has long been predicted by both
theory and simulations5–10
, but it has not been definitively observed
in a manner so stripped of ambiguity regarding the clouds’ proximity
to a black hole. While no observation of a single galaxy can prove
this theoretical prediction to be definitively true, the combined ALMA
and VLBA dataset for Abell 2597 enable a uniquely unambiguous ob-
servation of molecular clouds that are either directly associated with
black hole growth, or are soon about to be. The result augments a
small but growing set of previously published molecular absorption
systems28–30
in which black hole proximity is less well constrained.
These could nevertheless be used to inform future systematic searches
for cold black hole accretion across larger samples. Multi-epoch ob-
servations with ALMA might reveal shifts in the absorption lines, con-
firming their close proximity, and resolving cold black hole accretion
as it evolves through time.
Received 17 December 2015; accepted 16 March 2016.
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3
4. 0.1 0.5 0.9
ALMA Integrated >3σ CO(2-1) emission
(Jy / beam × km / s)
7.5 kpc (5’’)
Hα contours
Radio
contours
Figure 2 | ALMA observation of continuum-subtracted CO(2-1) emission in the Abell 2597 BCG. Emission is integrated from −600 to +600 km s−1 relative to
the galaxy’s systemic velocity. Channels are binned to 40 km s−1. 40 km s−1. Only ≥ 3σ emission is shown. 8.4 GHz VLA radio contours are overlaid in black,
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4
5. Velocity (km / sec)
0 +500 +1000-500
0
12.5%
25%
Percentfluxrelativetoaveragecontinuum
-12.5%
-25%
Blue spot is
radio and mm core,
centre of galaxy, &
location of black hole
Redshifted continuum absorption
at +240, +275, +335 km/s
Continuum
absorption
on nucleus
0
-0.1
0.1
Jy/beamkm/s
Beam size
(1 kpc by 0.8 kpc)
0 +200 +400-200-400
Velocity (km/s)
Total CO(2-1)
profile
(c)
(b)(a)
Figure 3 | “Shadows” cast by molecular clouds moving toward the supermassive black hole. (a) Continuum-subtracted ALMA CO(2-1) spectrum extracted from a
central 10 kpc region. Brackets mark CO(2-1) emission shown in panel (b), where 8.4 GHz radio contours are overlaid. The central radio contours have been removed
to aid viewing of the continuum absorption, seen as the blue/black spot of “negative” emission. (c) Continuum-subtracted CO(2-1) spectrum extracted from this region
cospatial with the mm and radio core. Absorption lines are indicated in red.
5
6. 0
-4
mJy/beam
50 pc
VLBA 1.3 GHz (Taylor+99)
0
-6
0 +250 +6000-400
CO(2-1) at 300 km/s
-250 0 +250
Velocity (km / s)
0.02-0.01 Jy/bm x km/s
CO(2-1) from Galaxy Centre
Narrow HI
absorption
Broad HI
absorption
FluxDensity(mJy)
-2
0
2
+500
2 kpc
Core
0 +250 +6000-400
Velocity (km / s)
(a) (b) (c)
(d) (e)
Molecular
absorption 16 mas x 7 mas
Figure 4 | Corroborating evidence that the inflowing molecular clouds must be in close proximity to the black hole. (a) CO(2-1) absorption spectrum from
Fig. 3, with a region of emission at ∼ +300 km s−1 marked in yellow. (b) Integrated emission from this region, showing that gas at ∼ +300 km s−1 is confined to
the innermost ∼ 2 kpc of the galaxy. (c) 1.4 GHz radio continuum source from an archival VLBA observation17 with an extremely high physical resolution of ∼ 25
parsecs by ∼ 10 parsecs. (d,e) HI 21 cm absorption observed against this synchrotron jet. The signal varies dramatically over tens of parsec scales.
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Acknowledgements This paper makes use of the following ALMA data:
ADS/JAO.ALMA#2012.1.00988.S. ALMA is a partnership of ESO (represent-
ing 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. We are grateful to the European ALMA Regional Centres, particularly
those in Garching and Manchester, for their dedicated end-to-end support
of data associated with this paper. We thank Prof. Richard Larson for dis-
cussions. G.R.T. acknowledges support from the National Aeronautics and
Space Administration (NASA) through Einstein Postdoctoral Fellowship Award
Number PF-150128, issued by the Chandra X-ray Observatory Center, which
is operated by the Smithsonian Astrophysical Observatory for and on behalf
6
7. of NASA under contract NAS8-03060. F.C. acknowledges the European Re-
search Council (ERC) for the Advanced Grant Program #267399-Momentum.
B.R.M. is supported by a generous grant from the Natural Sciences and
Engineering Research Council of Canada. T.A.D. acknowledges support
from a Science and Technology Facilities Council (STFC) Ernest Rutherford
Fellowship. A.C.E. acknowledges support from STFC grant ST/L00075X/1.
A.C.F. and H.R.R. acknowledge support from ERC Advanced Grant Program
#340442-Feedback. M.N.B. acknowledges funding from the STFC. Basic re-
search in radio astronomy at the Naval Research Laboratory is supported by
6.1 Base funding.
Author Contributions G.R.T. was principal investigator on the original pro-
posal, performed the data analysis, and wrote the paper. J.B.R.O., T.A.D.,
R.G.M., and A.M. were substantially involved in planning both scientific and
technical aspects of the proposal, while T.A.D. and R.G.M. contributed ALMA
data reduction and analysis expertise once the data were obtained. J.B.R.O.,
F.C., and P.S. invested substantial time in analysis of the data. Substantial
scientific feedback was also provided over many months by F.C., J.B.R.O.,
C.P.O., S.A.B., G.M.V., M.D., B.R.M., M.A.M., T.E.C., H.R., A.C.E. and A.C.F.,
while all other co-authors discussed the results and commented on the
manuscript.
Author Information Reprints and permissions information is available at
www.nature.com/reprints. The authors declare no competing financial inter-
ests. Readers are welcome to comment on the online version of this ar-
ticle. Correspondence and requests for materials should be addressed to
G.R.T. (email: grant.tremblay@yale.edu).
METHODS
Observations, Data Reduction, and Analysis. The new ALMA data
presented in this paper were obtained in Cycle 1 with the use of 29
operational antennae in the 12m Array. ALMA’s Band 6 heterodyne
receivers were tuned to a frequency of 213 GHz, sensitive to the J = 2 − 1
rotational line transition of carbon monoxide at the redshift of the Abell
2597 BCG (z = 0.0821). The ALMA correlator, set to Frequency Division
Mode (FDM), delivered a bandwidth of 1875 MHz (per baseband) with a
0.488 MHz channel spacing, for a maximum spectral resolution of ∼ 2 km
s−1. One baseband was centered on the CO(2-1) line, while the other three
sampled the local continuum. Maximum antenna baselines extended to ∼ 1
km, delivering an angular resolution at 213 GHz of ∼ 0. 7 within a ∼ 28
primary beam (field of view). ALMA observed the Abell 2597 BCG for a
total of ∼ 3 hours over three separate scheduling blocks executed between
17-19 November 2013. The planet Neptune and quasars J2258-2758 and
J2331-1556 were used for amplitude, flux, and phase calibration. The data
were reduced using CASA version 4.2 with calibration and imaging scripts
kindly provided by the ALMA Regional Centres (ARCs) in both Garching,
Germany, and Manchester, UK. Beyond the standard application of the
phase calibrator solution, we iteratively performed self-calibration of the
data using the galaxy’s own continuum, yielding a ∼ 14% decrease in RMS
noise to a final value of 0.16 mJy per 0. 715 × 0. 533 beam per 40 km s−1
channel. There is effectively no difference in CO(2-1) morphology between
the self-calibrated and non-self-calibrated cubes. Measurement sets were
imaged using “natural” visibility weighting and binning to either 5 km s−1,
10 km s−1or 40 km s−1, as indicated in the figure captions. The figures
presented in this paper show only continuum-subtracted, pure CO(2-1) line
emission. The rest-frame 230 GHz continuum observation is dominated
by a bright (13.6 mJy) point source associated with the AGN (detected at
>∼ 400σ), serving as the bright “backlight” against which the continuum
absorption features presented in this Letter were observed. The continuum
data also features compact (∼ 5 kpc) extended emission at ∼ 10σ that
extends along the galaxy’s dust lane, to be discussed in a forthcoming paper.
Adoption of a systemic velocity. Interpretation of gas motions relative to
the stellar component of a galaxy requires adoption of a systemic (stellar)
velocity to be used as a “zero point” marking the transition from blue-
to redshift. All CO(2-1) line velocities discussed in this Letter are set
relative to 213.04685 GHz, where observed CO(2-1) emission peaks. This
frequency corresponds to 12CO(2-1) (rest-frame 230.538001 GHz) at a
redshift of z = 0.0821. This redshift is consistent, conservatively within ±60
km s−1, with every other available multiwavelength tracer of the galaxy’s
systemic velocity, including prominent Ca II H, K, and G-band absorption
features16
that directly trace the galaxy stellar component, the redshift of
all optical emission lines31
, as well as a broad (FWHM ∼ 412 km s−1) HI
absorption component16
at the optical emission and absorption line redshift.
It is also consistent, within ±60 km s−1, with a cross-correlation of emission
and absorption lines using galaxy template spectra15
, as well as with all
other published reports of the galaxy’s systemic velocity (found, e.g., within
the HyperLeda database). We are therefore certain that the reported redshift
of the absorption features discussed in this letter indeed corresponds to
real motion relative to the galaxy]s stellar component. Without caveat or
ambiguity, the absorbing cold clouds are moving into the galaxy at roughly
∼ +300 km s−1.
Mass Estimates. All molecular gas masses estimated in this letter adopt the
following relation32
:
Mmol =
1.05×104
3.2
XCO
2×1020 cm−2
K km s−1
1
1+z
SCO∆v
Jy km s−1
DL
Mpc
2
M ,
(1)
where SCO∆v is the emission integral for CO(1-0) (effectively the total
CO(1-0) flux over the region of interest), z is the galaxy redshift (z = 0.0821),
and DL its luminosity distance (373.3 Mpc), for which we assume a flat
ΛCDM model wherein H0 = 70 km s−1 Mpc−1, ΩM = 0.3, and ΩΛ = 0.7.
This mass estimate most critically relies on an assumption of the CO-to-H2
conversion factor32
XCO. In this Letter we assume the average Milky Way
value of XCO = 2 × 1020 cm−2 K km s−1 −1
and a CO(2-1) to CO(1-0)
flux density ratio of 3.2. Other authors have provided extensive discussion
of these assumptions as they pertain to cool core BCGs30,33,34
. Scientific
conclusions in this paper are largely insensitive to choice of XCO.
A single gaussian fit to the CO(2-1) spectrum extracted from an
aperture containing all detected emission yields an emission integral
of SCO∆v = 4.2 ± 0.4 Jy km s−1 with a line FWHM of 252 ± 14 km
s−1, corresponding to a total molecular hydrogen (H2) gas mass of
MH2 = (1.80±0.19) × 109 M . This is very close to the previously
reported13
mass, based on an IRAM 30m CO(2-1) observation, of
(1.8±0.3)×109 M . This comparison is not one-to-one, as the mass from
the IRAM 30m observation was computed within a beam size of 11 (rather
than 28 for the ALMA data), and used a CO(2-1)/CO(1-0) flux ratio of 4
(rather than 3.2, as we use here). These differences are minor, particularly
because nearly all of the CO(2-1) emission detected by ALMA is found
within the central 11 size of the IRAM 30m beam. It is therefore safe
to say that our ALMA observation has detected nearly all emission that
was detected in the single-dish IRAM 30m observation, and that very little
extended emission has been “resolved out”.
Estimating physical properties of the redshifted absorbing gas. We have
estimated a rough upper-limit size of the absorbing clouds assuming the
widely-adopted Larson et al.25
and Solomon et al.26
size-linewidth relation
for molecular clouds in the Milky Way (namely, the Solomon et al. 1987 fit),
σ = (1.0±0.1)S0.5±0.05
km s−1
, (2)
where σ is the velocity line-width of the cloud and S is the diameter of the
cloud in parsecs.
A measured absorber linewidth of σ ∼ 6 km s−1 would then correspond
to a size of ∼ 36 pc. As noted in the main text of the Letter, the thermal
pressure in the Abell 2597 Brightest Cluster Galaxy is likely up to three
orders of magnitude higher than that for the Milky Way, so it is likely that
the above relation does not apply. A higher ambient pressure implies higher
7
8. compression and therefore smaller cloud size, so the above estimate should,
at best, be considered a very rough upper-limit. The main lesson to take
away from this excersize is that the absorbing clouds are likely physically
compact (i.e. a few to tens of parsecs in diameter, rather than hundreds of
pc).
The three clouds are separated from one another by ∼ 45−60 km s−1 in
velocity space, which means they are unlikely to be closely bound satellites
of one another. Instead, it is more likely that they represent three random
points along a radial distribution of clouds.
If the absorbers are in virial equilibrium, their masses Mcloud can be
roughly estimated by applying the virial relation,
Mcloud ≈
Rcloudσ2
G
≈
20 pc×(6 km/s)2
4.302×10−3 pc M−1
(km/s)2
≈ 1.7×105
M , (3)
where Rcloud is the cloud radius (as roughly estimated above) and σ is its
velocity dispersion (also as above).
CO(2-1) optical depths for the absorbers were estimated by assuming
that
Itotal = Icontinuume−τCO(2−1) , (4)
where Itotal and Icontinuum are the integrated intensities of the total (line plus
continuum) and continuum-only signals, respectively, and τCO(2−1) is the
optical depth of the CO(2-1) absorption feature.
The stellar velocity dispersion of the BCG?
is σ = 220 ± 19 km s−1.
Under the assumption of an isothermal sphere, the circular velocity should be
∼ 300 km s−1, (i.e.,
√
2σ) which is roughly the line of sight velocity of the
absorption features. The redshift of the absorption features is a significant
fraction of this, which means they could be on a purely radial orbit (though
their transverse velocity cannot be known with this single observation).
If our line of sight is representative, and therefore a “pencil beam” sam-
ple of a three-dimensional spherical distribution of clouds, the total mass of
cold gas contained within this distribution should go roughly as
M ≈ 109
M × fc ×
r
1 kpc
2
×
NH
1022 cm−2
(5)
where fc is the covering factor and r is the radius of an imaginary thin
spherical shell of molecular gas with column density NH. If such a shell
had a covering factor of 1, a radius of 1 kpc, and a column density of
1022 cm−2, then the total mass of molecular hydrogen contained within
that shell would be roughly one billion solar masses. A column density in
excess of 1022 requires this distribution to be contained within a sphere
of radius << 1 kpc, lest the total mass of molecular hydrogen in the
galaxy be violated. If the characteristic column density is 1023 cm−2, for
example, this mass must be contained within a sphere of radius 300 pc,
or else its total mass would exceed the ∼ 1.8×109 M present in the system.
Code, software, and data availability. The raw ALMA data used in this
Letter are publicly available at the ALMA Science Archive (search for
project code 2012.1.00988.S). Codes that we have written to both reduce
and analyse the ALMA data have been made publicly available here. Reduc-
tion of the data as well as some simple modeling (e.g., fitting of Gaussians to
lines) was performed using routines included in CASA version 4.2, available
here.
8