This document summarizes new results from a study of proper motions in the optical jet of the galaxy M87 using over 13 years of Hubble Space Telescope imaging data. Key findings include:
1) Superluminal velocities (above the speed of light) were measured for knots as far out as knot C in the jet, suggesting these speeds persist over large distances.
2) Significant apparent accelerations both parallel and transverse to the jet axis were found, as well as evidence for stationary features in some knots.
3) Complex motions including differing velocities between nearby features and changes in velocity over time were observed throughout the jet, placing constraints on theoretical jet models.
Todo mundo sabe que os raios produzidos pela Estrela da Morte em Guerra nas Estrelas não pode existir na vida real, porém no universo existem fenômenos que as vezes conseguem superar até a mais surpreendente ficção.
A galáxia Pictor A, é um desses objetos que possuem fenômenos tão espetaculares quanto aqueles exibidos no cinema. Essa galáxia localiza-se a cerca de 500 milhões de anos-luz da Terra e possui um buraco negro supermassivo no seu centro. Uma grande quantidade de energia gravitacional é lançada, à medida que o material cai em direção ao horizonte de eventos, o ponto sem volta ao redor do buraco negro. Essa energia produz um enorme jato de partículas que viajam a uma velocidade próxima da velocidade da luz no espaço intergaláctico, chamado de jato relativístico.
Para obter imagens desse jato, os cientistas usaram o Observatório de Raios-X Chandra, da NASA várias vezes durante 15 anos. Os dados do Chandra, apresentados em azul nas imagens, foram combinados com os dados obtidos em ondas de rádio a partir do Australia Telescope Compact Array, e são aparesentados em vermelho nas imagens.
The Internal Structure of Asteroid (25143) Itokawa as Revealed by Detection o...WellingtonRodrigues2014
- The authors detected an acceleration in the rotation rate of asteroid (25143) Itokawa through photometric observations spanning 2001 to 2013.
- By measuring rotational phase offsets between observed and modeled lightcurves, they found a YORP acceleration of 3.54 ± 0.38 × 10−8 rad day−2, equivalent to a decrease in the asteroid's rotation period of about 45 ms per year.
- Thermophysical modeling of the detailed shape model from the Hayabusa spacecraft could not reconcile the observed YORP strength unless the asteroid's center of mass is shifted by about 21 m along its long axis. This suggests Itokawa has two components with different densities that merged, either from a
Imaging the dust_sublimation_front_of_a_circumbinary_diskSérgio Sacani
Aims. We present the first near-IR milli-arcsecond-scale image of a post-AGB binary that is surrounded by hot circumbinary dust.
Methods. A very rich interferometric data set in six spectral channels was acquired of IRAS 08544-4431 with the new RAPID camera
on the PIONIER beam combiner at the Very Large Telescope Interferometer (VLTI). A broadband image in the H-band was reconstructed
by combining the data of all spectral channels using the SPARCO method.
Results. We spatially separate all the building blocks of the IRAS 08544-4431 system in our milliarcsecond-resolution image. Our
dissection reveals a dust sublimation front that is strikingly similar to that expected in early-stage protoplanetary disks, as well as an
unexpected flux signal of 4% from the secondary star. The energy output from this companion indicates the presence of a compact
circum-companion accretion disk, which is likely the origin of the fast outflow detected in H.
Conclusions. Our image provides the most detailed view into the heart of a dusty circumstellar disk to date. Our results demonstrate
that binary evolution processes and circumstellar disk evolution can be studied in detail in space and over time.
Probing the jet_base_of_blazar_pks1830211_from_the_chromatic_variability_of_i...Sérgio Sacani
This document summarizes ALMA observations of the blazar PKS 1830-211 taken over multiple epochs in 2012. The blazar is lensed by a foreground galaxy, producing two resolved images (NE and SW) separated by 1". The observations were taken at frequencies corresponding to 350-1050 GHz in the blazar rest frame. Analysis of the flux ratio between the two images over time and frequency revealed a remarkable frequency-dependent behavior, implying a "chromatic structure" in the blazar jet. This is interpreted as evidence for a "core-shift effect" caused by plasmon ejection very near the base of the jet. The observations provide a unique probe of activity in the region where plasma acceleration occurs in blazar
The open cluster_ngc6520_and_the_nearby_dark_molecular_cloud_barnard_86Sérgio Sacani
This document presents optical photometry and CO observations of the open cluster NGC 6520 and nearby dark molecular cloud Barnard 86. Analysis of the optical data finds the cluster radius is 1.0±0.5 arcmin, smaller than previous estimates. The cluster age is estimated to be 150±50 Myr with reddening of EB−V =0.42±0.10. The distance from the Sun is estimated to be 1900±100 pc, larger than previous estimates. CO observations are used to derive basic properties of Barnard 86 under the assumption it lies at the same distance as the cluster.
The document describes measurements of the proper motion of the Andromeda Galaxy (M31) using Hubble Space Telescope imaging data from multiple fields observed at two epochs separated by 5-7 years. Background galaxies in the images are used as stationary reference objects to measure the displacement of thousands of M31 stars between epochs. This allows determining M31's absolute proper motion with an accuracy of 12 microarcseconds per year, providing crucial information about M31 and the Local Group's dynamics and future evolution.
This document summarizes research on determining temperatures, luminosities, and masses of the coldest known brown dwarfs. The key findings are:
1) Precise distances were measured for a sample of late-T and Y dwarfs using Spitzer Space Telescope astrometry, allowing accurate calculation of absolute fluxes, luminosities, and temperatures.
2) Y0 dwarfs were found to have temperatures of 400-450 K, significantly warmer than previous estimates, and masses of 5-20 times Jupiter's mass.
3) While having similar temperatures, Y dwarfs showed diverse spectral energy distributions, suggesting temperature alone does not determine spectra. Physical properties like gravity, clouds and chemistry also influence spectra.
This document summarizes a blind HI survey of the southern Milky Way zone of avoidance conducted with the Parkes radio telescope. The survey detected 883 galaxies at Galactic longitudes 212° < l < 36° and latitudes |b| < 5° to a sensitivity of 6 mJy per 27 km/s channel. Fifty-one percent of detections had known optical/near-infrared counterparts, while 27% had new counterparts identified. The survey delineated large-scale structures in the Puppis and Great Attractor regions for the first time. Several newly identified galaxy concentrations and clusters were revealed that help trace the Great Attractor Wall.
Todo mundo sabe que os raios produzidos pela Estrela da Morte em Guerra nas Estrelas não pode existir na vida real, porém no universo existem fenômenos que as vezes conseguem superar até a mais surpreendente ficção.
A galáxia Pictor A, é um desses objetos que possuem fenômenos tão espetaculares quanto aqueles exibidos no cinema. Essa galáxia localiza-se a cerca de 500 milhões de anos-luz da Terra e possui um buraco negro supermassivo no seu centro. Uma grande quantidade de energia gravitacional é lançada, à medida que o material cai em direção ao horizonte de eventos, o ponto sem volta ao redor do buraco negro. Essa energia produz um enorme jato de partículas que viajam a uma velocidade próxima da velocidade da luz no espaço intergaláctico, chamado de jato relativístico.
Para obter imagens desse jato, os cientistas usaram o Observatório de Raios-X Chandra, da NASA várias vezes durante 15 anos. Os dados do Chandra, apresentados em azul nas imagens, foram combinados com os dados obtidos em ondas de rádio a partir do Australia Telescope Compact Array, e são aparesentados em vermelho nas imagens.
The Internal Structure of Asteroid (25143) Itokawa as Revealed by Detection o...WellingtonRodrigues2014
- The authors detected an acceleration in the rotation rate of asteroid (25143) Itokawa through photometric observations spanning 2001 to 2013.
- By measuring rotational phase offsets between observed and modeled lightcurves, they found a YORP acceleration of 3.54 ± 0.38 × 10−8 rad day−2, equivalent to a decrease in the asteroid's rotation period of about 45 ms per year.
- Thermophysical modeling of the detailed shape model from the Hayabusa spacecraft could not reconcile the observed YORP strength unless the asteroid's center of mass is shifted by about 21 m along its long axis. This suggests Itokawa has two components with different densities that merged, either from a
Imaging the dust_sublimation_front_of_a_circumbinary_diskSérgio Sacani
Aims. We present the first near-IR milli-arcsecond-scale image of a post-AGB binary that is surrounded by hot circumbinary dust.
Methods. A very rich interferometric data set in six spectral channels was acquired of IRAS 08544-4431 with the new RAPID camera
on the PIONIER beam combiner at the Very Large Telescope Interferometer (VLTI). A broadband image in the H-band was reconstructed
by combining the data of all spectral channels using the SPARCO method.
Results. We spatially separate all the building blocks of the IRAS 08544-4431 system in our milliarcsecond-resolution image. Our
dissection reveals a dust sublimation front that is strikingly similar to that expected in early-stage protoplanetary disks, as well as an
unexpected flux signal of 4% from the secondary star. The energy output from this companion indicates the presence of a compact
circum-companion accretion disk, which is likely the origin of the fast outflow detected in H.
Conclusions. Our image provides the most detailed view into the heart of a dusty circumstellar disk to date. Our results demonstrate
that binary evolution processes and circumstellar disk evolution can be studied in detail in space and over time.
Probing the jet_base_of_blazar_pks1830211_from_the_chromatic_variability_of_i...Sérgio Sacani
This document summarizes ALMA observations of the blazar PKS 1830-211 taken over multiple epochs in 2012. The blazar is lensed by a foreground galaxy, producing two resolved images (NE and SW) separated by 1". The observations were taken at frequencies corresponding to 350-1050 GHz in the blazar rest frame. Analysis of the flux ratio between the two images over time and frequency revealed a remarkable frequency-dependent behavior, implying a "chromatic structure" in the blazar jet. This is interpreted as evidence for a "core-shift effect" caused by plasmon ejection very near the base of the jet. The observations provide a unique probe of activity in the region where plasma acceleration occurs in blazar
The open cluster_ngc6520_and_the_nearby_dark_molecular_cloud_barnard_86Sérgio Sacani
This document presents optical photometry and CO observations of the open cluster NGC 6520 and nearby dark molecular cloud Barnard 86. Analysis of the optical data finds the cluster radius is 1.0±0.5 arcmin, smaller than previous estimates. The cluster age is estimated to be 150±50 Myr with reddening of EB−V =0.42±0.10. The distance from the Sun is estimated to be 1900±100 pc, larger than previous estimates. CO observations are used to derive basic properties of Barnard 86 under the assumption it lies at the same distance as the cluster.
The document describes measurements of the proper motion of the Andromeda Galaxy (M31) using Hubble Space Telescope imaging data from multiple fields observed at two epochs separated by 5-7 years. Background galaxies in the images are used as stationary reference objects to measure the displacement of thousands of M31 stars between epochs. This allows determining M31's absolute proper motion with an accuracy of 12 microarcseconds per year, providing crucial information about M31 and the Local Group's dynamics and future evolution.
This document summarizes research on determining temperatures, luminosities, and masses of the coldest known brown dwarfs. The key findings are:
1) Precise distances were measured for a sample of late-T and Y dwarfs using Spitzer Space Telescope astrometry, allowing accurate calculation of absolute fluxes, luminosities, and temperatures.
2) Y0 dwarfs were found to have temperatures of 400-450 K, significantly warmer than previous estimates, and masses of 5-20 times Jupiter's mass.
3) While having similar temperatures, Y dwarfs showed diverse spectral energy distributions, suggesting temperature alone does not determine spectra. Physical properties like gravity, clouds and chemistry also influence spectra.
This document summarizes a blind HI survey of the southern Milky Way zone of avoidance conducted with the Parkes radio telescope. The survey detected 883 galaxies at Galactic longitudes 212° < l < 36° and latitudes |b| < 5° to a sensitivity of 6 mJy per 27 km/s channel. Fifty-one percent of detections had known optical/near-infrared counterparts, while 27% had new counterparts identified. The survey delineated large-scale structures in the Puppis and Great Attractor regions for the first time. Several newly identified galaxy concentrations and clusters were revealed that help trace the Great Attractor Wall.
A dust-enshrouded tidal disruption event with a resolved radio jet in a galax...Sérgio Sacani
Tidal disruption events (TDEs) are transient flares produced when a star is ripped apart by the
gravitational field of a supermassive black hole (SMBH). We have observed a transient source in the
western nucleus of the merging galaxy pair Arp 299 that radiated >1.5 × 1052 erg in the infrared and radio
but was not luminous at optical or x-ray wavelengths. We interpret this as a TDE with much of its emission
reradiated at infrared wavelengths by dust. Efficient reprocessing by dense gas and dust may explain the
difference between theoretical predictions and observed luminosities of TDEs. The radio observations
resolve an expanding and decelerating jet, probing the jet formation and evolution around a SMBH.
A nearby yoiung_m_dwarf_with_wide_possibly_planetary_m_ass_companionSérgio Sacani
This document summarizes the identification of two young objects, TYC 9486-927-1 and 2MASS J21265040−8140293, as a likely very wide binary system. It presents revised astrometry showing they have common proper motion. Spectroscopy of the secondary yields a radial velocity consistent with the primary. Analysis of lithium absorption and kinematics suggests an age range of 10-45 Myr, with the secondary having an estimated mass in the planetary mass regime. If confirmed, this would be the widest known exoplanet system at over 4500 AU separation.
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.
Water vapour absorption_in_the_clear_atmosphere_of_a_neptune_sized_exoplanetSérgio Sacani
This document summarizes research on the transmission spectrum of the exoplanet HAT-P-11b, a Neptune-sized planet. Observations from the Hubble Space Telescope and Spitzer Space Telescope detected water vapor absorption in the planet's atmosphere at a wavelength of 1.4 micrometers. Analysis of the spectrum indicates the atmosphere is predominantly clear down to 1 mbar and has a hydrogen abundance similar to solar values. Atmospheric modeling suggests a metallicity around 190 times that of the Sun's, in agreement with core accretion planet formation theories. This makes HAT-P-11b the smallest exoplanet to date with a detected molecular signature in its atmosphere, providing new insights into the composition and formation of Neptune-sized
The discovery of_lensed_radio_and_x-ray_sources_behind_the_frontier_fields_cl...Sérgio Sacani
We report on high-resolution JVLA and Chandra observations of the Hubble Space Telescope (HST) Frontier Cluster
MACSJ0717.5+3745. MACSJ0717.5+3745 offers the largest contiguous magnified area of any known cluster,
making it a promising target to search for lensed radio and X-ray sources. With the high-resolution 1.0–6.5 GHz
JVLA imaging in A and B configuration, we detect a total of 51 compact radio sources within the area covered by the
HST imaging. Within this sample, we find sevenlensed sources with amplification factors larger than two. None of
these sources are identified as multiply lensed. Based on the radio luminosities, the majority of these sources are
likely star-forming galaxies with star-formation rates (SFRs) of 10–50 M: yr−1 located at 1 1 z 1 2. Two of the
lensed radio sources are also detected in the Chandra image of the cluster. These two sources are likely active galactic
nuclei, given their 2–10 keV X-ray luminosities of ∼1043–44 erg s−1. From the derived radio luminosity function, we
find evidence for an increase in the number density of radio sources at 0.6 z 2.0, compared to a z 0.3 sample.
Our observations indicate that deep radio imaging of lensing clusters can be used to study star-forming galaxies, with
SFRs as low as ∼10Me yr−1, at the peak of cosmic star formation history.
Spectral and morphological_analysis_of_the_remnant_of_supernova_1987_a_with_a...Sérgio Sacani
The document provides a spectral and morphological analysis of the remnant of Supernova 1987A using data from the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/submillimeter Array (ALMA). ALMA images from 94 GHz to 672 GHz reveal non-thermal synchrotron and thermal dust emission components. The analysis shows a decreasing east-west asymmetry with frequency, attributed to shorter synchrotron lifetimes at high frequencies. Across the radio to far-infrared transition, excess emission is seen that could be due to a second synchrotron component, implying a pulsar wind nebula in the remnant interior.
This document describes observations of Cepheid variables in the host galaxies of two Type Ia supernovae, SN 1995al in NGC 3021 and SN 2002fk in NGC 1309, using the Hubble Space Telescope. The observations aim to increase the sample of reliably calibrated supernovae to improve the measurement of the Hubble constant. New Cepheids were discovered, including many with periods over 60 days. Metallicity measurements of the galaxies' H II regions were also consistent with solar metallicity. The new data on the supernovae and Cepheids will help strengthen the distance ladder and reduce systematic uncertainties in the determination of the Hubble constant.
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.
Alignment of th_angular_momentum_vectors_of_planetary_nebulae_in_the_galactic...Sérgio Sacani
This document analyzes the orientations of 130 planetary nebulae (PNe) in the Galactic Bulge to investigate whether there is a preferred alignment. It finds that while the full sample shows a uniform distribution, the bipolar PNe exhibit a non-uniform distribution with a mean orientation along the Galactic plane at a 90 degree position angle, significant at the 0.001 level. This indicates that the orbital planes of binary systems in old stars are oriented perpendicular to the Galactic plane, likely due to strong magnetic fields during star formation that influenced the angular momentum vectors.
Dissecting x ray_emitting_gas_around_the_center_of_our_galaxySérgio Sacani
1) The Chandra X-ray Observatory was used to observe the supermassive black hole at the center of the Milky Way, Sgr A*, for a total of 3 megaseconds.
2) The observations revealed extended X-ray emission around Sgr A* that aligns spatially with a surrounding disk of massive stars.
3) Spectral analysis ruled out low-mass stars as the origin of the X-ray emission and instead found evidence that the emission is from a radiatively inefficient accretion flow onto the black hole, with an outflow present.
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
A giant galaxy in the young Universe with a massive ringSérgio Sacani
In the local (redshift z ≈ 0) Universe, collisional ring galaxies make up only ~0.01% of galaxies1 and are formed by head-on galactic collisions that trigger radially propagating density waves2–4. These striking systems provide key snapshots for dissecting galactic disks and are studied extensively in the local Universe5–9. However, not much is known about distant (z > 0.1) collisional rings10–14. Here we present a detailed study of a ring galaxy at a look-back time of 10.8 Gyr (z = 2.19). Compared with our Milky Way, this galaxy has a similar stellar mass, but has a stellar half-light radius that is 1.5–2.2 times larger and is forming stars 50 times faster. The extended, dif- fuse stellar light outside the star-forming ring, combined with a radial velocity on the ring and an intruder galaxy nearby, provides evidence for this galaxy hosting a collisional ring. If the ring is secularly evolved15,16, the implied large bar in a giant disk would be inconsistent with the current understand- ing of the earliest formation of barred spirals17–21. Contrary to previous predictions10–12, this work suggests that massive col- lisional rings were as rare 11 Gyr ago as they are today. Our discovery offers a unique pathway for studying density waves in young galaxies, as well as constraining the cosmic evolution of spiral disks and galaxy groups.
This document summarizes the results of an MHD simulation coupled with a radiation transport model to simulate X-ray spectra from an accreting black hole. Key points:
- For the first time, the simulation is able to reproduce the main components seen in observed X-ray spectra, including a thermal peak, power-law tail, reflection hump, and iron line, by varying only the mass accretion rate.
- The temperature in the corona varies from 10 keV near the disk to over 100 keV in low-density regions, producing the hard X-ray emission through inverse-Compton scattering.
- Even as the disk's reflection edge varies from the horizon out to 6 gravitational radii with decreasing accretion
Discovery of rotational modulations in the planetary mass companion 2m1207b i...Sérgio Sacani
Rotational modulations of brown dwarfs have recently provided powerful constraints on the properties
of ultra-cool atmospheres, including longitudinal and vertical cloud structures and cloud evolution.
Furthermore, periodic light curves directly probe the rotational periods of ultra-cool objects. We
present here, for the first time, time-resolved high-precision photometric measurements of a planetarymass
companion, 2M1207b. We observed the binary system with HST/WFC3 in two bands and with
two spacecraft roll angles. Using point spread function-based photometry, we reach a nearly photonnoise
limited accuracy for both the primary and the secondary. While the primary is consistent with
a flat light curve, the secondary shows modulations that are clearly detected in the combined light
curve as well as in di↵erent subsets of the data. The amplitudes are 1.36% in the F125W and 0.78%
in the F160W filters, respectively. By fitting sine waves to the light curves, we find a consistent period
of 10.7+1.2
−0.6 hours and similar phases in both bands. The J- and H-band amplitude ratio of 2M1207b
is very similar to a field brown dwarf that has identical spectral type but di↵erent J-H color. Importantly,
our study also measures, for the first time, the rotation period for a directly imaged extra-solar
planetary-mass companion.
Mapping spiral structure on the far side of the Milky WaySérgio Sacani
Little is known about the portion of the Milky Way lying beyond the Galactic center at distances
of more than 9 kiloparsec from the Sun. These regions are opaque at optical wavelengths
because of absorption by interstellar dust, and distances are very large and hard to measure.
We report a direct trigonometric parallax distance of 20:4þ2:8
2:2 kiloparsec obtained with the Very
Long Baseline Array to a water maser source in a region of active star formation. These
measurements allow us to shed light on Galactic spiral structure by locating the ScutumCentaurus
spiral arm as it passes through the far side of the Milky Way and to validate a
kinematic method for determining distances in this region on the basis of transverse motions.
The document summarizes the history and current state of the post-Newtonian (PN) approximation for modeling compact binary systems and gravitational waves. It discusses how PN theory has achieved an "unreasonable accuracy" in describing binary pulsars and is now being used to construct initial data and compare waveforms for numerical relativity simulations.
Adaptive optics are used in ground-based telescopes to directly image extrasolar planets and overcome atmospheric turbulence. Atmospheric turbulence causes distortions that blur planetary images. Adaptive optics systems measure wavefront distortions using a wavefront sensor and correct for them using a deformable mirror in a closed-loop system. This results in sharper, diffraction-limited images that help verify exoplanets. Future extremely large telescopes will use many more actuators on deformable mirrors to provide substantial correction, aiding the search for Earth-like exoplanets.
Probing the innermost_regions_of_agn_jets_and_their_magnetic_fields_with_radi...Sérgio Sacani
Desde 1974, observações feitas com o chamado Long Baseline Interferometry, ou VLBI, combinaram sinais de um objeto cósmico recebidos em diferentes rádio telescópios espalhados pelo globo para criar uma antena com o tamanho equivalente à maior separação entre elas. Isso fez com que fosse possível fazer imagens com uma nitidez sem precedentes, com uma resolução 1000 vezes melhor do que Hubble consegue na luz visível. Agora, uma equipe internacional de astrônomos quebrou todos os recordes combinando 15 rádio telescópios na Terra e a antena de rádio da missão RadioAstron, da agência espacial russa, na órbita da Terra. O trabalho, liderado pelo Instituto de Astrofísica de Andalucía, o IAA-CSIC, forneceu novas ideias sobre a natureza das galáxias ativas, onde um buraco negro extremamente massivo engole a matéria ao redor enquanto simultaneamente emite um par de jatos de partículas de alta energia e campos magnéticos a velocidades próximas da velocidade da luz.
Observações feitas no comprimento de onda das micro-ondas são essenciais para explorar esses jatos, já que os elétrons de alta energia se movendo em campos magnéticos são mais proficientes em produzir micro-ondas. Mas a maioria das galáxias ativas com jatos brilhantes estão a bilhões de anos-luz de distância da Terra, de modo que esses jatos são minúsculos no céu. Desse modo a alta resolução é essencial para observar esses jatos em ação e então revelar fenômenos como as ondas de choque e a turbulência que controla o quanto de luz é produzida num dado tempo. “Combinando pela primeira vez rádio telescópios na Terra com rádio telescópios no espaço, operando na máxima resolução, tem permitido que a nossa equipe crie uma antena que tem um tamanho equivalente a 8 vezes o diâmetro da Terra, correspondendo a 20 micro arcos de segundo”, disse José L; Gómez, o líder da equipe no Instituto de Astrofísica de Andalucía, IAA-CSIC.
A new universal formula for atoms, planets, and galaxiesIOSR Journals
In this paper a new universal formula about the rotation velocity distribution of atoms, planets, and galaxies is presented. It is based on a new general formula based on the relativistic Schwarzschild/Minkowski metric, where it has been possible to obtain expressions for the rotation velocity - and mass distribution versus the distance to the atomic nucleus, planet system centre, and galactic centre. A mathematical proof of this new formula is also given. This formula is divided into a Keplerian(general relativity)-and a relativistic(special relativity) part. For the atomic-and planet systems the Keplerian distribution is followed, which is also in accordance with observations.
According to the rotation velocity distribution of the galaxies the rotation velocity increases very rapidly from the centre and reaches a plateau which is constant out to a great distance from the centre. This is in accordance with observations and is also in accordance with the main structure of rotation velocity versus distance from different galaxy measurements.
Computer simulations were also performed to establish and verify the rotation velocity distributions in the atomic – planetary- and galaxy system, according to this paper. These computer simulations are in accordance with observations in two and three dimensions. It was also possible to study the matching percentage in these calculations showing a much higher matching percentage between theoretical and observational values by this new formula.
One tenth solar_abundances_along_the_body_of-the_streamSérgio Sacani
This document summarizes a study that analyzed spectra from four background quasars to measure the chemical abundances along the Magellanic Stream. Two key findings are:
1) The sightlines toward RBS 144 and NGC 7714 yielded metallicities of around 0.1 times the solar value, indicating a uniform low abundance along the main body of the Stream. This supports models where the Stream was stripped from the SMC around 1-2.5 billion years ago when the SMC had a metallicity of around 0.1 solar.
2) A higher metallicity of around 0.5 solar was found in the inner Stream toward Fairall 9, sampling a filament traced to the LMC. This shows the bifurc
Abundance and isotopic_composition_of_gases_in_the_martian_atmosphere_from_th...Sérgio Sacani
The Curiosity rover measured the composition and isotopic ratios of gases in the Martian atmosphere using its Sample Analysis at Mars (SAM) instrument suite. Key findings include:
- Carbon dioxide makes up 96% of the atmosphere.
- Argon-40 and nitrogen levels are consistent with previous Viking measurements, but the 40Ar/36Ar ratio is lower and the 40Ar/N2 ratio is higher than Viking.
- Isotopic signatures of carbon and other gases support the hypothesis that Mars has lost a significant portion of its original atmosphere over geological time through atmospheric escape processes.
A dust-enshrouded tidal disruption event with a resolved radio jet in a galax...Sérgio Sacani
Tidal disruption events (TDEs) are transient flares produced when a star is ripped apart by the
gravitational field of a supermassive black hole (SMBH). We have observed a transient source in the
western nucleus of the merging galaxy pair Arp 299 that radiated >1.5 × 1052 erg in the infrared and radio
but was not luminous at optical or x-ray wavelengths. We interpret this as a TDE with much of its emission
reradiated at infrared wavelengths by dust. Efficient reprocessing by dense gas and dust may explain the
difference between theoretical predictions and observed luminosities of TDEs. The radio observations
resolve an expanding and decelerating jet, probing the jet formation and evolution around a SMBH.
A nearby yoiung_m_dwarf_with_wide_possibly_planetary_m_ass_companionSérgio Sacani
This document summarizes the identification of two young objects, TYC 9486-927-1 and 2MASS J21265040−8140293, as a likely very wide binary system. It presents revised astrometry showing they have common proper motion. Spectroscopy of the secondary yields a radial velocity consistent with the primary. Analysis of lithium absorption and kinematics suggests an age range of 10-45 Myr, with the secondary having an estimated mass in the planetary mass regime. If confirmed, this would be the widest known exoplanet system at over 4500 AU separation.
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.
Water vapour absorption_in_the_clear_atmosphere_of_a_neptune_sized_exoplanetSérgio Sacani
This document summarizes research on the transmission spectrum of the exoplanet HAT-P-11b, a Neptune-sized planet. Observations from the Hubble Space Telescope and Spitzer Space Telescope detected water vapor absorption in the planet's atmosphere at a wavelength of 1.4 micrometers. Analysis of the spectrum indicates the atmosphere is predominantly clear down to 1 mbar and has a hydrogen abundance similar to solar values. Atmospheric modeling suggests a metallicity around 190 times that of the Sun's, in agreement with core accretion planet formation theories. This makes HAT-P-11b the smallest exoplanet to date with a detected molecular signature in its atmosphere, providing new insights into the composition and formation of Neptune-sized
The discovery of_lensed_radio_and_x-ray_sources_behind_the_frontier_fields_cl...Sérgio Sacani
We report on high-resolution JVLA and Chandra observations of the Hubble Space Telescope (HST) Frontier Cluster
MACSJ0717.5+3745. MACSJ0717.5+3745 offers the largest contiguous magnified area of any known cluster,
making it a promising target to search for lensed radio and X-ray sources. With the high-resolution 1.0–6.5 GHz
JVLA imaging in A and B configuration, we detect a total of 51 compact radio sources within the area covered by the
HST imaging. Within this sample, we find sevenlensed sources with amplification factors larger than two. None of
these sources are identified as multiply lensed. Based on the radio luminosities, the majority of these sources are
likely star-forming galaxies with star-formation rates (SFRs) of 10–50 M: yr−1 located at 1 1 z 1 2. Two of the
lensed radio sources are also detected in the Chandra image of the cluster. These two sources are likely active galactic
nuclei, given their 2–10 keV X-ray luminosities of ∼1043–44 erg s−1. From the derived radio luminosity function, we
find evidence for an increase in the number density of radio sources at 0.6 z 2.0, compared to a z 0.3 sample.
Our observations indicate that deep radio imaging of lensing clusters can be used to study star-forming galaxies, with
SFRs as low as ∼10Me yr−1, at the peak of cosmic star formation history.
Spectral and morphological_analysis_of_the_remnant_of_supernova_1987_a_with_a...Sérgio Sacani
The document provides a spectral and morphological analysis of the remnant of Supernova 1987A using data from the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/submillimeter Array (ALMA). ALMA images from 94 GHz to 672 GHz reveal non-thermal synchrotron and thermal dust emission components. The analysis shows a decreasing east-west asymmetry with frequency, attributed to shorter synchrotron lifetimes at high frequencies. Across the radio to far-infrared transition, excess emission is seen that could be due to a second synchrotron component, implying a pulsar wind nebula in the remnant interior.
This document describes observations of Cepheid variables in the host galaxies of two Type Ia supernovae, SN 1995al in NGC 3021 and SN 2002fk in NGC 1309, using the Hubble Space Telescope. The observations aim to increase the sample of reliably calibrated supernovae to improve the measurement of the Hubble constant. New Cepheids were discovered, including many with periods over 60 days. Metallicity measurements of the galaxies' H II regions were also consistent with solar metallicity. The new data on the supernovae and Cepheids will help strengthen the distance ladder and reduce systematic uncertainties in the determination of the Hubble constant.
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.
Alignment of th_angular_momentum_vectors_of_planetary_nebulae_in_the_galactic...Sérgio Sacani
This document analyzes the orientations of 130 planetary nebulae (PNe) in the Galactic Bulge to investigate whether there is a preferred alignment. It finds that while the full sample shows a uniform distribution, the bipolar PNe exhibit a non-uniform distribution with a mean orientation along the Galactic plane at a 90 degree position angle, significant at the 0.001 level. This indicates that the orbital planes of binary systems in old stars are oriented perpendicular to the Galactic plane, likely due to strong magnetic fields during star formation that influenced the angular momentum vectors.
Dissecting x ray_emitting_gas_around_the_center_of_our_galaxySérgio Sacani
1) The Chandra X-ray Observatory was used to observe the supermassive black hole at the center of the Milky Way, Sgr A*, for a total of 3 megaseconds.
2) The observations revealed extended X-ray emission around Sgr A* that aligns spatially with a surrounding disk of massive stars.
3) Spectral analysis ruled out low-mass stars as the origin of the X-ray emission and instead found evidence that the emission is from a radiatively inefficient accretion flow onto the black hole, with an outflow present.
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
A giant galaxy in the young Universe with a massive ringSérgio Sacani
In the local (redshift z ≈ 0) Universe, collisional ring galaxies make up only ~0.01% of galaxies1 and are formed by head-on galactic collisions that trigger radially propagating density waves2–4. These striking systems provide key snapshots for dissecting galactic disks and are studied extensively in the local Universe5–9. However, not much is known about distant (z > 0.1) collisional rings10–14. Here we present a detailed study of a ring galaxy at a look-back time of 10.8 Gyr (z = 2.19). Compared with our Milky Way, this galaxy has a similar stellar mass, but has a stellar half-light radius that is 1.5–2.2 times larger and is forming stars 50 times faster. The extended, dif- fuse stellar light outside the star-forming ring, combined with a radial velocity on the ring and an intruder galaxy nearby, provides evidence for this galaxy hosting a collisional ring. If the ring is secularly evolved15,16, the implied large bar in a giant disk would be inconsistent with the current understand- ing of the earliest formation of barred spirals17–21. Contrary to previous predictions10–12, this work suggests that massive col- lisional rings were as rare 11 Gyr ago as they are today. Our discovery offers a unique pathway for studying density waves in young galaxies, as well as constraining the cosmic evolution of spiral disks and galaxy groups.
This document summarizes the results of an MHD simulation coupled with a radiation transport model to simulate X-ray spectra from an accreting black hole. Key points:
- For the first time, the simulation is able to reproduce the main components seen in observed X-ray spectra, including a thermal peak, power-law tail, reflection hump, and iron line, by varying only the mass accretion rate.
- The temperature in the corona varies from 10 keV near the disk to over 100 keV in low-density regions, producing the hard X-ray emission through inverse-Compton scattering.
- Even as the disk's reflection edge varies from the horizon out to 6 gravitational radii with decreasing accretion
Discovery of rotational modulations in the planetary mass companion 2m1207b i...Sérgio Sacani
Rotational modulations of brown dwarfs have recently provided powerful constraints on the properties
of ultra-cool atmospheres, including longitudinal and vertical cloud structures and cloud evolution.
Furthermore, periodic light curves directly probe the rotational periods of ultra-cool objects. We
present here, for the first time, time-resolved high-precision photometric measurements of a planetarymass
companion, 2M1207b. We observed the binary system with HST/WFC3 in two bands and with
two spacecraft roll angles. Using point spread function-based photometry, we reach a nearly photonnoise
limited accuracy for both the primary and the secondary. While the primary is consistent with
a flat light curve, the secondary shows modulations that are clearly detected in the combined light
curve as well as in di↵erent subsets of the data. The amplitudes are 1.36% in the F125W and 0.78%
in the F160W filters, respectively. By fitting sine waves to the light curves, we find a consistent period
of 10.7+1.2
−0.6 hours and similar phases in both bands. The J- and H-band amplitude ratio of 2M1207b
is very similar to a field brown dwarf that has identical spectral type but di↵erent J-H color. Importantly,
our study also measures, for the first time, the rotation period for a directly imaged extra-solar
planetary-mass companion.
Mapping spiral structure on the far side of the Milky WaySérgio Sacani
Little is known about the portion of the Milky Way lying beyond the Galactic center at distances
of more than 9 kiloparsec from the Sun. These regions are opaque at optical wavelengths
because of absorption by interstellar dust, and distances are very large and hard to measure.
We report a direct trigonometric parallax distance of 20:4þ2:8
2:2 kiloparsec obtained with the Very
Long Baseline Array to a water maser source in a region of active star formation. These
measurements allow us to shed light on Galactic spiral structure by locating the ScutumCentaurus
spiral arm as it passes through the far side of the Milky Way and to validate a
kinematic method for determining distances in this region on the basis of transverse motions.
The document summarizes the history and current state of the post-Newtonian (PN) approximation for modeling compact binary systems and gravitational waves. It discusses how PN theory has achieved an "unreasonable accuracy" in describing binary pulsars and is now being used to construct initial data and compare waveforms for numerical relativity simulations.
Adaptive optics are used in ground-based telescopes to directly image extrasolar planets and overcome atmospheric turbulence. Atmospheric turbulence causes distortions that blur planetary images. Adaptive optics systems measure wavefront distortions using a wavefront sensor and correct for them using a deformable mirror in a closed-loop system. This results in sharper, diffraction-limited images that help verify exoplanets. Future extremely large telescopes will use many more actuators on deformable mirrors to provide substantial correction, aiding the search for Earth-like exoplanets.
Probing the innermost_regions_of_agn_jets_and_their_magnetic_fields_with_radi...Sérgio Sacani
Desde 1974, observações feitas com o chamado Long Baseline Interferometry, ou VLBI, combinaram sinais de um objeto cósmico recebidos em diferentes rádio telescópios espalhados pelo globo para criar uma antena com o tamanho equivalente à maior separação entre elas. Isso fez com que fosse possível fazer imagens com uma nitidez sem precedentes, com uma resolução 1000 vezes melhor do que Hubble consegue na luz visível. Agora, uma equipe internacional de astrônomos quebrou todos os recordes combinando 15 rádio telescópios na Terra e a antena de rádio da missão RadioAstron, da agência espacial russa, na órbita da Terra. O trabalho, liderado pelo Instituto de Astrofísica de Andalucía, o IAA-CSIC, forneceu novas ideias sobre a natureza das galáxias ativas, onde um buraco negro extremamente massivo engole a matéria ao redor enquanto simultaneamente emite um par de jatos de partículas de alta energia e campos magnéticos a velocidades próximas da velocidade da luz.
Observações feitas no comprimento de onda das micro-ondas são essenciais para explorar esses jatos, já que os elétrons de alta energia se movendo em campos magnéticos são mais proficientes em produzir micro-ondas. Mas a maioria das galáxias ativas com jatos brilhantes estão a bilhões de anos-luz de distância da Terra, de modo que esses jatos são minúsculos no céu. Desse modo a alta resolução é essencial para observar esses jatos em ação e então revelar fenômenos como as ondas de choque e a turbulência que controla o quanto de luz é produzida num dado tempo. “Combinando pela primeira vez rádio telescópios na Terra com rádio telescópios no espaço, operando na máxima resolução, tem permitido que a nossa equipe crie uma antena que tem um tamanho equivalente a 8 vezes o diâmetro da Terra, correspondendo a 20 micro arcos de segundo”, disse José L; Gómez, o líder da equipe no Instituto de Astrofísica de Andalucía, IAA-CSIC.
A new universal formula for atoms, planets, and galaxiesIOSR Journals
In this paper a new universal formula about the rotation velocity distribution of atoms, planets, and galaxies is presented. It is based on a new general formula based on the relativistic Schwarzschild/Minkowski metric, where it has been possible to obtain expressions for the rotation velocity - and mass distribution versus the distance to the atomic nucleus, planet system centre, and galactic centre. A mathematical proof of this new formula is also given. This formula is divided into a Keplerian(general relativity)-and a relativistic(special relativity) part. For the atomic-and planet systems the Keplerian distribution is followed, which is also in accordance with observations.
According to the rotation velocity distribution of the galaxies the rotation velocity increases very rapidly from the centre and reaches a plateau which is constant out to a great distance from the centre. This is in accordance with observations and is also in accordance with the main structure of rotation velocity versus distance from different galaxy measurements.
Computer simulations were also performed to establish and verify the rotation velocity distributions in the atomic – planetary- and galaxy system, according to this paper. These computer simulations are in accordance with observations in two and three dimensions. It was also possible to study the matching percentage in these calculations showing a much higher matching percentage between theoretical and observational values by this new formula.
One tenth solar_abundances_along_the_body_of-the_streamSérgio Sacani
This document summarizes a study that analyzed spectra from four background quasars to measure the chemical abundances along the Magellanic Stream. Two key findings are:
1) The sightlines toward RBS 144 and NGC 7714 yielded metallicities of around 0.1 times the solar value, indicating a uniform low abundance along the main body of the Stream. This supports models where the Stream was stripped from the SMC around 1-2.5 billion years ago when the SMC had a metallicity of around 0.1 solar.
2) A higher metallicity of around 0.5 solar was found in the inner Stream toward Fairall 9, sampling a filament traced to the LMC. This shows the bifurc
Abundance and isotopic_composition_of_gases_in_the_martian_atmosphere_from_th...Sérgio Sacani
The Curiosity rover measured the composition and isotopic ratios of gases in the Martian atmosphere using its Sample Analysis at Mars (SAM) instrument suite. Key findings include:
- Carbon dioxide makes up 96% of the atmosphere.
- Argon-40 and nitrogen levels are consistent with previous Viking measurements, but the 40Ar/36Ar ratio is lower and the 40Ar/N2 ratio is higher than Viking.
- Isotopic signatures of carbon and other gases support the hypothesis that Mars has lost a significant portion of its original atmosphere over geological time through atmospheric escape processes.
Imaging of the_co_snow_line_in_a_solar_nebula_analogSérgio Sacani
This document summarizes research on observing the location of the carbon monoxide (CO) snow line in protoplanetary disks. Key points:
1) N2H+ emission is expected to trace the CO snow line as N2H+ forms most abundantly in gas where CO is frozen onto dust grains.
2) Observations of the protoplanetary disk around the young star TW Hya using ALMA revealed a ring-shaped distribution of N2H+ emission with an inner radius of 21-32 AU, indicating the location of the CO snow line.
3) Disk models suggest the N2H+ emission inner edge corresponds to a midplane temperature of 16-20K,
The stelar mass_growth_of_brightest_cluster_galaxies_in_the_irac_shallow_clus...Sérgio Sacani
This document describes a study of the stellar mass growth of brightest cluster galaxies (BCGs) between z=1.5 and z=0.5 using data from the Spitzer IRAC Shallow Cluster Survey (ISCS). The researchers developed a method to select high-redshift clusters as progenitors of lower-redshift clusters to study the evolution of BCG stellar masses. They find that between z=1.5 and z=0.5, the BCGs grew in stellar mass by a factor of 2.3, matching predictions from a semi-analytic galaxy formation model. Below z=0.5, there are hints of differences between the observed BCG growth and the model predictions.
Candels the correlation_between_galaxy_morphology_and_star_formation_activity...Sérgio Sacani
This document summarizes a study investigating the relationship between galaxy morphology and star formation activity at z ~ 2 using a sample of 1,671 galaxies from CANDELS images in the GOODS-South field. The sample separates into massive, red, passive galaxies and less massive, blue, star-forming galaxies, correlating well with morphological properties. Star-forming galaxies show a variety of morphologies including clumpy structures and bulges mixed with faint disks, while passive galaxies often have compact morphologies resembling local spheroids. Similar trends are seen in local massive galaxies, suggesting the Hubble sequence was in place by z ~ 2.
Grb 130606a as_a_probe_of_the_intergalactic_medium_and_the_interstelar_medium...Sérgio Sacani
This document summarizes observations of the gamma-ray burst GRB 130606A at a redshift of z=5.913 using spectroscopy from the MMT and Gemini telescopes. The high quality spectra exhibit a smooth near-infrared continuum that is sharply cut off by Lyman-alpha absorption at z=5.91, with some flux transmitted through the Lyman-alpha forest at lower redshifts. Metal absorption lines in the host galaxy are used to constrain its metallicity between -1.7 and -0.5 solar. Transmission in the Lyman-alpha forest is found to evolve consistently with previous quasar observations. An extended region at z=5.77 shows no Lyman-alpha transmission,
Allan Sandage devoted significant research efforts to determining the Hubble constant and calibrating the cosmic distance scale. In the 1950s, his work confirmed Baade's revision that galaxy distances were twice as large as previously thought. Over the following decades, through calibrating different distance indicators like Cepheid variables and tip of the red giant branch stars, Sandage lowered his estimate of the Hubble constant from 250 km/s/Mpc to around 60 km/s/Mpc. His landmark "Steps toward the Hubble Constant" series in the 1970s utilized galaxy properties to extend the distance scale and further refine the Hubble constant value.
3C 273 was one of the first quasars discovered in 1963. It remains one of the brightest and best studied quasars. It is located approximately 3 billion light years from Earth and radiates energy equivalent to 1014 times the luminosity of the Sun. 3C 273 plays a key role in understanding the nature of quasars as powered by accretion disks around supermassive black holes. It continues to be intensely observed across the electromagnetic spectrum to better understand the physics occurring in these energetic and distant cosmic objects.
A dwarf galaxy is colliding with the large spiral galaxy NGC 1232, as revealed by X-ray observations from Chandra. The collision is creating a large region (7.25 kpc in diameter) of shocked, hot gas with a temperature of around 5.8 million kelvin. The X-ray luminosity of this collisional aftermath is estimated to be 3.7x10^38 ergs/s. Based on the size and temperature of the X-ray emitting region, the collision likely involves a dwarf galaxy and represents a massive energy input into NGC 1232, far exceeding a typical supernova. Such collisions detected solely in X-rays may provide insights into the role of dwarf galaxy interactions in the evolution of
Alma observations of_the_hh46_47_molecular_outflowSérgio Sacani
ALMA observations of the HH 46/47 molecular outflow reveal striking differences between the blue and red lobes. The blue lobe morphology and kinematics are consistent with entrainment by a wide-angle wind, while the red lobe shows a more complex structure with evidence of entrainment by both a wide-angle wind and collimated episodic winds. Three major clumps along the red lobe axis have velocity distributions consistent with prompt entrainment by periodic mass ejection episodes occurring every few hundred years. Position-velocity cuts show velocity gradients increasing toward the outflow axis, inconsistent with outflow rotation.
Mass and motion_of_globulettes_in_the_rosette_nebulaSérgio Sacani
This document summarizes observations of globulettes (small molecular clumps) in the Rosette Nebula made using radio telescopes and infrared imaging. Radio observations of 16 globulettes detected molecular line emission from 12CO and 13CO, allowing masses to be estimated. Masses ranged from about 50 to 500 Jupiter masses. Infrared imaging found that several globulettes are very opaque and contain dense cores. Analysis of velocities found that globulettes and other nebula structures are expanding at about 22 km/s, with globulettes having only small velocity differences, suggesting they are moving with the general expansion. Some globulettes appear to be detaching from larger structures as they expand outwards.
The identification of_93_day_periodic_photometric_variability_for_yso_ylw_16aSérgio Sacani
This study identifies a 93 day periodic photometric variability in the Class I young stellar object (YSO) YLW 16A in the Rho Ophiuchus star forming region. Light curve analysis reveals variations of ~0.5 magnitudes in the Ks band over this period. The authors propose a triple system model consisting of an inner binary with a 93 day period eclipsed by a warped circumbinary disk, with a tertiary companion at ~40 AU responsible for warping the disk. This model is similar to one previously proposed for another YSO, WL 4, and may indicate such triple systems with eclipsing disks are common around young stars. Understanding these systems can provide insights into stellar and planetary formation and evolution.
Evidence for a_complex_enrichment_history_of_the_stream_from_fairall_9_sightlineSérgio Sacani
This study analyzes absorption spectra of the Magellanic Stream (MS) toward the quasar Fairall 9, obtained using the Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS) and the Very Large Telescope Ultraviolet and Visible Echelle Spectrograph (VLT/UVES). The spectra reveal absorption from multiple velocity components of the MS, indicating multiphase gas. Surprisingly, the sulfur abundance is found to be high ([S/H] = -0.30), five times higher than other MS sightlines, while the nitrogen abundance is lower ([N/H] = -1.15). This points to a complex enrichment history, where the gas toward Fair
The colision between_the_milky_way_and_andromedaSérgio Sacani
The document summarizes a simulation of the future collision between the Milky Way and Andromeda galaxies. It finds that given current observational constraints on their distance, velocity, and masses:
1) The Milky Way and Andromeda are likely to collide in a few billion years, within the lifetime of the Sun.
2) During the interaction, there is a chance the Sun could be pulled into an extended tidal tail between the galaxies.
3) Eventually, after the merger is complete, the Sun would most likely be scattered to the outer halo of the merged galaxy at a distance over 30 kpc.
A dynamical signature_of_multiple_stellar_populations_in_47_tucanaeSérgio Sacani
The document analyzes proper motion data from Hubble Space Telescope images of the globular cluster 47 Tucanae taken over 10 years. It finds differing proper motion anisotropies between the bluest and reddest main sequence stars in 47 Tucanae, suggesting different kinematic properties for the different stellar populations. The bluest stars also exhibit the strongest central concentration. These results provide dynamical evidence for multiple stellar populations in 47 Tucanae and implications for their formation scenarios.
Effect of a_high_opacity_on_the_light_curves_of_radioactively_powered_transie...Sérgio Sacani
This document discusses how higher opacities from lanthanide elements in the ejecta of neutron star mergers could dramatically affect the predicted light curves of electromagnetic counterparts. The key points are:
1) Ab initio calculations show r-process element opacities are orders of magnitude higher than previously assumed iron opacities, particularly from lanthanide elements.
2) With these higher opacities, radiation transport models predict light curves that are longer (lasting about a week), dimmer, and redder, with emission peaked in the infrared rather than optical/ultraviolet.
3) A two-component light curve may result if there is both lanthanide-rich ejecta and a secondary
The document reports measurements of isotope ratios in CO2 and H2O in the Martian atmosphere taken by the Curiosity rover. Isotope ratios of hydrogen, carbon, and oxygen can reveal information about planetary processes like atmospheric loss and interactions with the surface. The measurements imply that the Martian reservoirs of CO2 and H2O were largely established 4 billion years ago, but that some atmospheric loss or surface interaction may still be ongoing. Comparison to measurements of Martian meteorites provides information about these long-term planetary processes and the evolution of the Martian atmosphere and surface.
This document summarizes observations of the gas cloud G2 as it passes near the supermassive black hole at the center of the Milky Way galaxy. New observations in 2013 with the NACO and SINFONI instruments on the VLT show that G2 continues to be stretched out along its orbit due to tidal forces. The head of G2 is now stretched over 15,000 Schwarzschild radii. Some gas has passed the pericenter of the orbit and is seen blueshifted. The luminosity and line ratios of G2 remain constant, showing no evidence of heating as it interacts with ambient gas. The pericenter passage will occur over about a year as G2 is stretched out along its orbit.
The document summarizes new HI observations of Hoag's Object obtained with the Westerbork Synthesis Radio Telescope. The key findings are:
1) The HI is detected in a ring that coincides with and extends beyond the optical ring of Hoag's Object. The entire HI structure is twice as large as the optical ring and shows a mild warp in its outer regions.
2) The HI kinematics are regular with no disturbances, providing evidence against a recent interaction being the source of the HI.
3) Two additional faint HI sources are detected near Hoag's Object, approximately 0.3 and 1 Mpc away in projected distance. At least one does
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
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
This document reports the discovery of a newly discovered optical Einstein ring (ER) called the "Canarias Einstein Ring". It was discovered serendipitously in imaging data from the Dark Energy Camera. Follow-up spectroscopy with the Gran Telescopio CANARIAS confirmed the nature of the system, with the lens being an early-type galaxy at a redshift of z=0.581 and the source being a starburst galaxy at z=1.165. Analysis of the system determined the Einstein radius to be 2.16 arcseconds and the total enclosed mass producing the lensing effect to be 1.86 ± 0.23 × 1012 solar masses.
Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Gal...Sérgio Sacani
The three-dimensional intrinsic shape of a galaxy and the mass of the central supermassive black hole provide key
insight into the galaxy’s growth history over cosmic time. Standard assumptions of a spherical or axisymmetric
shape can be simplistic and can bias the black hole mass inferred from the motions of stars within a galaxy. Here,
we present spatially resolved stellar kinematics of M87 over a two-dimensional 250″ × 300″ contiguous field
covering a radial range of 50 pc–12 kpc from integral-field spectroscopic observations at the Keck II Telescope.
From about 5 kpc and outward, we detect a prominent 25 km s−1 rotational pattern, in which the kinematic axis
(connecting the maximal receding and approaching velocities) is 40° misaligned with the photometric major axis of
M87. The rotational amplitude and misalignment angle both decrease in the inner 5 kpc. Such misaligned and
twisted velocity fields are a hallmark of triaxiality, indicating that M87 is not an axisymmetrically shaped galaxy.
Triaxial Schwarzschild orbit modeling with more than 4000 observational constraints enabled us to determine
simultaneously the shape and mass parameters. The models incorporate a radially declining profile for the stellar
mass-to-light ratio suggested by stellar population studies. We find that M87 is strongly triaxial, with ratios of
p = 0.845 for the middle-to-long principal axes and q = 0.722 for the short-to-long principal axes, and determine
the black hole mass to be ( - ´) 5.37 0.22 10 +
0.25
0.37 9M , where the second error indicates the systematic uncertainty
associated with the distance to M87.
Intra cluster light_at_the_frontier_abell_2744Sérgio Sacani
This document summarizes a study of the intra-cluster light (ICL) in the galaxy cluster Abell 2744 using deep Hubble Space Telescope images. The study finds that the ICL has bluer colors than the main galaxy members, indicating a younger average age of 6 billion years and lower metallicity. The ICL likely formed from the disruption of infalling galaxies similar to the Milky Way in mass and metallicity. The ICL comprises at least 6% of the total stellar mass in the central region of the cluster.
MUSE sneaks a peek at extreme ram-pressure stripping events. I. A kinematic s...Sérgio Sacani
- MUSE observations of the galaxy ESO137-001 reveal an extended gaseous tail over 30 kpc long traced by H-alpha emission, providing evidence of an extreme ram pressure stripping event as the galaxy falls into the massive Norma galaxy cluster.
- Analysis of the H-alpha kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center, with gravitational interactions not appearing to be the main mechanism of gas removal.
- The stripped gas retains evidence of the disk's rotational velocity out to around 20 kpc downstream, indicating the galaxy is moving radially along the plane of the sky, while
This document describes observations of the galaxy ESO137-001 using the MUSE instrument on the VLT. The key points are:
1) MUSE observations reveal an extended gas tail stretching over 30 kpc from the galaxy, tracing ongoing ram pressure stripping as it falls into the Norma galaxy cluster.
2) Analysis of the gas kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center.
3) The stripped gas retains evidence of the disk's rotational velocity out to 20 kpc downstream, indicating the galaxy is moving radially through the cluster. Beyond this the gas shows greater turbulence,
ALMA Observations of the Extraordinary Carina Pillars: A Complementary SampleSérgio Sacani
We present a study of six dusty and gaseous pillars (containing the HH 1004 and HH 1010 objects)
and globules (that contain the HH 666, HH 900, HH 1006, and HH 1066 objects) localized in the Carina
nebula using sensitive and high angular resolution (∼0.3′′) Atacama Large Millimeter/Sub-millimeter
Array (ALMA) observations. This is a more extensive study that the one presented in Cortes-Rangel
et al. (2020). As in this former study, we also analyzed the 1.3 mm continuum emission and C18O(2−1),
N2D+(3−2) and 12CO(2−1) spectral lines. These new observations revealed the molecular outflows
emanating from the pillars, the dusty envelopes+disks that are exciting them, and the extended HH
objects far from their respective pillars. We reveal that the masses of the disks+envelopes are in a
range of 0.02 to 0.38 M⊙, and those for the molecular outflows are of the order of 10−3 M⊙, which
suggests that their exciting sources might be low- or intermediate-mass protostars as already revealed
in recent studies at infrared and submillimeter bands. In the regions associated with the objects HH
900 and HH 1004, we report multiple millimeter continuum sources, from where several molecular
outflows emanate.
This project uses computer simulations to model observations of the 2005 Deep Impact collision with comet Tempel 1. The simulations aim to understand the physics behind the light curves observed by Hubble Space Telescope. The simulations suggest the optically thick ejecta cloud was about 28 km in diameter 13 minutes after impact and expanding at around 36 m/s, constraining the cloud's mass to approximately 2x10^7 kg. This mass and expansion velocity are consistent with independent estimates from observations by different astronomy groups.
Orbital configurations of spaceborne interferometers for studying photon ring...Sérgio Sacani
Recent advances in technology coupled with the progress of observational
radio astronomy methods resulted in achieving a major milestone of astrophysics - a direct image of the shadow of a supermassive black hole, taken
by the Earth-based Event Horizon Telescope (EHT). The EHT was able to
achieve a resolution of ∼20 µas, enabling it to resolve the shadows of the
black holes in the centres of two celestial objects: the supergiant elliptical
galaxy M87 and the Milky Way Galaxy. The EHT results mark the start of a
new round of development of next generation Very Long Baseline Interferometers (VLBI) which will be able to operate at millimetre and sub-millimetre
wavelengths. The inclusion of baselines exceeding the diameter of the Earth
and observation at as short a wavelength as possible is imperative for further development of high resolution astronomical observations. This can be
achieved by a spaceborne VLBI system. We consider the preliminary mission
design of such a system, specifically focused on the detection and analysis
of photon rings, an intrinsic feature of supermassive black holes. Optimised
Earth, Sun-Earth L2 and Earth-Moon L2 orbit configurations for the space
interferometer system are presented, all of which provide an order of magnitude improvement in resolution compared to the EHT. Such a space-borne
The wonderful complexity_of_the_mira_ab_systemSérgio Sacani
The ALMA observations of the Mira AB binary system reveal an amazingly complex circumstellar environment shaped by multiple dynamical processes. In the blue wing of the CO emission line, opposing large arcs form a bubble structure around Mira A, possibly created by the wind from Mira B blowing into Mira A's expanding envelope. In the main line component, spiral arcs are seen around Mira A that appear relatively flat and oriented in the orbital plane. An accretion wake is also visible trailing Mira B. The companion is marginally resolved with a separation of 0.487 arcseconds from Mira A.
A highly magnetized twin-jet base pinpoints a supermassive black holeSérgio Sacani
Supermassive black holes (SMBH) are essential for the production of jets in radio-loud active galactic nuclei (AGN). Theoretical
models based on (Blandford & Znajek 1977, MNRAS, 179, 433) extract the rotational energy from a Kerr black hole, which could
be the case for NGC1052, to launch these jets. This requires magnetic fields on the order of 103 G to 104 G. We imaged the vicinity
of the SMBH of the AGN NGC1052 with the Global Millimetre VLBI Array and found a bright and compact central feature that is
smaller than 1.9 light days (100 Schwarzschild radii) in radius. Interpreting this as a blend of the unresolved jet bases, we derive the
magnetic field at 1 Schwarzschild radius to lie between 200 G and 8:3 104 G consistent with Blandford & Znajek models.
A multi wavelength_analysis_of_m8_insight_on_the_nature_of_arp_loopSérgio Sacani
This document presents a multi-wavelength analysis of M81 and Arp's loop, a peculiar ring-like structure around M81. Optical images reveal Arp's loop has a filamentary structure with many overlapping dust features. Infrared images show Arp's loop has infrared colors and emission properties similar to Galactic cirrus clouds in the region. The results suggest the light at optical wavelengths comes from recent star formation near M81, M81's extended disk, and scattered light from Galactic cirrus, while the infrared emission is dominated by cold dust from Galactic cirrus.
A thirty-four billion solar mass black hole in SMSS J2157–3602, the most lumi...Sérgio Sacani
From near-infrared spectroscopic measurements of the Mg II emission line doublet, we estimate the black hole (BH) mass of the quasar, SMSS J215728.21–360215.1, as being (3.4 ± 0.6) × 1010 M⊙ and refine the redshift of the quasar to be z = 4.692. SMSS J2157 is the most luminous known quasar, with a 3000 Å luminosity of (4.7 ± 0.5) × 1047 erg s−1 and an estimated bolometric luminosity of 1.6 × 1048 erg s−1 , yet its Eddington ratio is only ∼0.4. Thus, the high luminosity of this quasar is a consequence of its extremely large BH – one of the most massive BHs at z > 4.
The internal structure_of_asteroid_itokawa_as_revealed_by_detection_of_yorp_s...Sérgio Sacani
The study detected an acceleration in the rotation rate of asteroid (25143) Itokawa through long-term photometric monitoring between 2001-2013. By measuring rotational phase offsets between observed and modeled lightcurves, a YORP acceleration of 3.54 ± 0.38 × 10−8 rad day−2 was measured, equivalent to a decrease in the asteroid's rotation period of about 45 ms per year. Thermophysical analysis of the detailed shape model from the Hayabusa spacecraft found that the center-of-mass must be offset by about 21 m along the long axis to reconcile the observed and theoretical YORP strengths, suggesting Itokawa is composed of two separate bodies with densities of 1750 ± 110 kg m
Hubble Space Telescope observations of the globular cluster NGC 6752 reveal a broadened and asymmetric main sequence, indicative of a large binary population. Artificial star experiments show that photometric errors and chance star superpositions alone cannot account for the observed broadening. A Monte Carlo technique is used to estimate the binary fraction, which is likely 15-38% in the inner core but less than 16% beyond that radius. The discovery of a significant main-sequence binary population provides constraints on the dynamical evolution and stellar populations of globular clusters.
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.
Fleeting Small-scale Surface Magnetic Fields Build the Quiet-Sun CoronaSérgio Sacani
Arch-like loop structures filled with million Kelvin hot plasma form the building blocks of the quiet-Sun corona.
Both high-resolution observations and magnetoconvection simulations show the ubiquitous presence of magnetic
fields on the solar surface on small spatial scales of ∼100 km. However, the question of how exactly these quietSun coronal loops originate from the photosphere and how the magnetic energy from the surface is channeled to
heat the overlying atmosphere is a long-standing puzzle. Here we report high-resolution photospheric magnetic
field and coronal data acquired during the second science perihelion of Solar Orbiter that reveal a highly dynamic
magnetic landscape underlying the observed quiet-Sun corona. We found that coronal loops often connect to
surface regions that harbor fleeting weaker, mixed-polarity magnetic field patches structured on small spatial
scales, and that coronal disturbances could emerge from these areas. We suggest that weaker magnetic fields with
fluxes as low as 1015 Mx and/or those that evolve on timescales less than 5 minutes are crucial to understanding
the coronal structuring and dynamics.
Serendipitous discovery of an extended xray jet without a radio counterpart i...Sérgio Sacani
A recent Chandra observation of the nearby galaxy cluster Abell 585 has led to the discovery of
an extended X-ray jet associated with the high-redshift background quasar B3 0727+409, a luminous
radio source at redshift z = 2:5. This is one of only few examples of high-redshift X-ray jets known
to date. It has a clear extension of about 1200, corresponding to a projected length of 100 kpc, with
a possible hot spot located 3500 from the quasar. The archival high resolution VLA maps surprisingly
reveal no extended jet emission, except for one knot about 1:400 from the quasar. The high X-ray to
radio luminosity ratio for this source appears consistent with the / (1 + z)4 amplication expected
from the inverse Compton radiative model. This serendipitous discovery may signal the existence
of an entire population of similar systems with bright X-ray and faint radio jets at high redshift, a
selection bias which must be accounted for when drawing any conclusions about the redshift evolution
of jet properties and indeed about the cosmological evolution of supermassive black holes and active
galactic nuclei in general.
Students aged 12 to 18 observed the Big Bang using an 11-inch telescope. They measured redshifts of galaxies and deduced quantitative conclusions about the age of the universe and density of dark matter. Key findings included:
- Measuring significant redshifts of 0.0077 and 0.003 for galaxies NGC 3516 and M66, matching literature values.
- Interpreting the main emission line at 6590 Angstroms as hydrogen-alpha, indicating a redshift of 0.0077 for NGC 3516.
- Concluding the Big Bang observations were highly significant based on statistical analysis, despite limitations of the small telescope.
Similar to Optical proper motion_measurements_of_the_m87_jet_new_results_from_the_hubble_space_telescope (20)
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
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1. arXiv:1308.4633v1[astro-ph.CO]21Aug2013
Accepted for Publication in Astrophysical Journal Letters
Preprint typeset using LATEX style emulateapj v. 5/2/11
OPTICAL PROPER MOTION MEASUREMENTS OF THE M87 JET: NEW RESULTS FROM THE HUBBLE
SPACE TELESCOPE
Eileen T. Meyer1
, W. B. Sparks1
, J. A. Biretta1
, Jay Anderson1
, Sangmo Tony Sohn1
, Roeland P. van der
Marel1
, Colin Norman1,2
, and Masanori Nakamura3
Accepted for Publication in Astrophysical Journal Letters
ABSTRACT
We report new results from an HST archival program to study proper motions in the optical jet of
the nearby radio galaxy M87. Using over 13 years of archival imaging, we reach accuracies below 0.1c
in measuring the apparent velocities of individual knots in the jet. We confirm previous findings of
speeds up to 4.5c in the inner 6′′
of the jet, and report new speeds for optical components in the outer
part of the jet. We find evidence of significant motion transverse to the jet axis on the order of 0.6c
in the inner jet features, and superluminal velocities parallel and transverse to the jet in the outer
knot components, with an apparent ordering of velocity vectors possibly consistent with a helical jet
pattern. Previous results suggested a global deceleration over the length of the jet in the form of
decreasing maximum speeds of knot components from HST-1 outward, but our results suggest that
superluminal speeds persist out to knot C, with large differentials in very nearby features all along
the jet. We find significant apparent accelerations in directions parallel and transverse to the jet axis,
along with evidence for stationary features in knots D, E, and I. These results are expected to place
important constraints on detailed models of kpc-scale relativistic jets.
Subject headings: galaxies: jets — galaxies: individual(M87) — galaxies: active — astrometry
1. INTRODUCTION
The nearby radio galaxy M87, a giant elliptical near
the center of the Virgo cluster, hosts a striking opti-
cal jet extending 20′′
to the northwest of a blazar-like
core, as first observed by Curtis (1918). This source has
been extensively observed in the radio, infrared, optical,
and X-rays (e.g., Owen et al. 1989; Sparks et al. 1996;
Perlman et al. 2001; Walker et al. 2008; Marshall et al.
2002; Perlman & Wilson 2005). At a distance of only
16.7 Mpc (81 pc/′′
, Blakeslee et al. 2009), structures
on the order of parsecs can easily be resolved using
high-resolution instruments such as the Hubble Space
Telescope (HST). The bright knots of emission spread
along the 1.6 kpc (projected) jet in optical and X-
ray imaging correspond to features seen in the radio,
with a spectrum consistent with synchrotron emission
(Marshall et al. 2002).
Proper motion studies are integral to our understand-
ing of relativistic jets, as apparent velocities (βapp=v/c)
give lower limits to the bulk Lorentz factor and upper
limits on the angle to the line of sight, as well as detailed
kinematics for comparison to theoretical jet models. Al-
most all proper motion studies of jetted AGN have used
Very Long Baseline Interferometry (VLBI), and in the
case of M87 have revealed sub-relativistic speeds in small
components within a parsec of the core (Reid et al. 1989;
Junor & Biretta 1995; Kovalev et al. 2007). Superlumi-
nal motions have also been measured in the kpc-scale jet
with both the VLA (Biretta et al. 1995, hereafter B95),
and in the optical with HST (Biretta et al. 1999, here-
Email: meyer@stsci.edu
1 Space Telescope Science Institute, 3700 San Martin Drive,
Baltimore, MD 21218, USA
2 Department of Physics and Astronomy, Johns Hopkins Uni-
versity, Baltimore, MD 21218, USA
3 Institute of Astronomy and Astrophysics, Academia Sinica,
P.O. Box 23-141, Taipei 10617, Taiwan
after B99). The latter study measured only the inner
6′′
of the jet, and suffered from rather larger errors (on
the order of 0.3 - 1c). However, in comparison to radio
measurements, the optical jet emission traces higher en-
ergy electron populations more closely associated with
the sites of acceleration, leading to more compact fea-
tures which can be precisely measured.
In this letter we present the initial results of an archival
study of proper motions in the M87 jet with HST. The
aim of this work is to leverage 13.25 years of Hubble
observations of M87 to vastly improve on previous mea-
surements of apparent velocities in the jet, reaching ac-
curacies better than 0.1c in order to map the detailed
velocity field of the jet as it propagates from the core,
including transverse motions and accelerations.
2. OBSERVATIONS
2.1. Hubble Archival Data
Because jet components are known to differ in size, in-
tensity, and apparent location with wavelength, we used
archival images only in a single filter, F814W (wide I
band), which gives the longest possible baseline of 13.25
years and a dense sampling in time. The total dataset
is comprised of nearly all the ACS/HRC, ACS/WFC,
and WFPC2 (PC chip) archival images in this filter.
For ACS/HRC, we used 30 (48-50s) exposures spanning
November 2002 to November 2006. For ACS/WFC, we
used 217 dithered exposures (all 360s) taken in 2006. For
WFPC2, we used 161 exposures of 160-600s, spanning
1995 to 2008; several shorter exposures of 30-40s were
not used due to poor signal-to-noise ratio.
2.2. Astrometry Methods
The general method we have used is simi-
lar to that used (and described in detail) in
Anderson & van der Marel (2010) and Sohn et al.
2. 2 Meyer et al.
Figure 1. (Top Figure) The entire jet, from a stack of ACS/WFC F606W images taken in 2006 with galaxy subtracted. All other images
are taken from stacks of WFPC2 exposures in the F814W filter. (Lower Left) Within knot D, D-East appears to be nearly stationary, while
D-Middle appears to move at 4.27±0.30c along the jet. D-West is the only knot to show a strong deceleration in the jet-direction, apparent
when comparing the 2001 and 2007 epochs. The new component noted with an arrow appears to move at ∼2.4c (Vertical lines in all figures
are to guide the eye). (Lower Middle) Knot E appears complex, with a new extension to the East of the main knot (E-West) appearing
in 2008. (Lower Right) Knot F shows evidence of complex, even clumpy structure. F-Middle is moving at 0.36±0.14c and appears to be
fading over time.
(2012). The reference frame is based on the positions of
hundreds of bright globular clusters associated with the
host galaxy which are easily detected in the ACS/WFC
images and are effectively stationary to proper motions
over the time of this study. As cluster positions do
not change with filter, the reference frame was built
using 56 (500s) ACS/WFC exposures of the field in
the F606W filter, which has slightly better resolution
than F814W. The reference frame was created by first
detecting the positions of the globular clusters in each
flat-fielded, CTE-corrected ACS/WFC image4
using a
PSF-peak-fitting routine, then applying the standard
(filter-specific) geometric correction to those positions,
and then finding the best linear transformation for each
image which matches the positions in the individual
(geometrically-corrected) frames to a master reference
frame. This last step is done by a routine similar
to MultiDrizzle, but better optimized for astrometry.
The process of finding transformations for all frames
is iterated so that the master reference frame (super-
sampled to a pixel scale of 0.025′′
/pixel) effectively
gives the average position of each reference source in a
geometrically-corrected frame.
The final reference system consists of positions and
magnitudes for 1378 globular clusters within ∼100′′
of the
M87 core position. Among all clusters, the median one-
dimensional RMS residual relative to the mean position
4 ACS/HRC and WFPC2 data were not used due to inferior
in signal-to-noise quality to the longer ACS/WFC images, and to
avoid complications of combining different instruments.
was 0.05 (reference-frame) pixels (1.25 mas), correspond-
ing to a systematic astrometric accuracy (× 1/
√
56) of
0.17 mas; over the 13.25 year baseline this is equivalent
to 0.003c.
Astrometric solutions were then found for all the
ACS/HRC , ACS/WFC, and WFPC2 images in F814W,
except that the linear transformation solution between
the individual (corrected) images and the reference frame
was found once rather than iterated. Typical numbers of
globular clusters used to match the frames were ∼200-
500 for ACS/WFC, ∼15-30 for WFPC2 images, and
∼15-25 for ACS/HRC; corresponding systematic errors
were ∼0.006, ∼0.03, and ∼0.05 pixels, or 0.003c, 0.015c,
0.025c over 13.25 years, respectively.
2.3. Measuring the Jet Knot Positions
Because of the difficulty in measuring the dif-
fuse/complex knot structures particularly in the noisy
HRC images and shorter WFPC2 images, we chose to
first identify the peaks of interest using stacked images.
The image stacks include the 2006 ACS/WFC stack,
four WFPC2 stacks (epochs 1995-1996, 1998-1999, 2001,
and 2007-2008), and three stacks of ACS/HRC exposures
(November 2002 - November 2003, July 2004 - Septem-
ber 2005, November 2005 - November 2006). The host
galaxy was modeled using the ACS/WFC stacked image
with the IRAF/STSDAS tasks ellipse and bmodel and
then subtracted. Seven jet regions were cut out from
these images, corresponding to knots HST-1, D, E, F, I,
A+B, and C (see Figure 1).
3. M87 Jet Optical Proper Motions 3
Xposition[pixels]
156
157
158
159
160
3.9
3.95
4
Distance[arcseconds]
WFPC2
ACS/HRC
ACS/WFC
D−West, Radial
Year
Yposition[pixels]
−0.5
0
0.5
1
1996 1998 2000 2002 2004 2006 2008
−15
− 5
5
15
25
Distance[mas]
D−West, Transverse
Figure 2. (Upper Panel): Distance from the core versus time for
knot D-West. The blue points show the mean values for each time
bin with errors estimated from nearby globular clusters. This knot
shows a remarkable deceleration over time, from an initial speed
of ∼2.7c in 1996 to near zero by the end of the time series.(Lower
Panel) The rapid transverse velocity of knot D-West is apparent
in this plot of y-coordinate versus time, corresponding to −0.59c.
A two-dimensional continuous functional representa-
tion of the image cutouts was then created using the
Cosine Transform function (FourierDCT) in Mathemat-
ica, which allowed us to find prominent peaks, as well
as contours of constant flux level around those peaks.
In general, the number of interesting peaks was cho-
sen by hand, and the contour line levels were at 50%
of the flux of the peak, after a ‘background’ level was
subtracted, the latter estimated as the minimum flux
level between the particular peak and the next nearest
peak. The positions defining the contour were ‘reverse-
transformed’ from master frame coordinates into each
distorted, galaxy-subtracted image so that an intensity-
weighted centroid position from the pixels within the
contour could be calculated. These final positions were
then transformed back into the common reference frame,
so that each peak of interest was measured in every ex-
posure, resulting in hundreds of position measurements
spread over the 13 year baseline.
To measure the apparent motion of the jet components
over time, we define the x-direction as the line from the
core through the center of knot I (PA of 290◦
), with y-
direction perpendicular. Data were binned into 26 time
bins (depicted in Figure 2), and a linear model was fit
using standard weighted least squares. The weights were
taken to be the inverse of the variance for each time bin,
as measured from the 10 nearby globular cluster refer-
ence sources (discussed below). For each feature and in
each direction, we also attempted to fit the data with a
quadratic to look for accelerations. When the Analysis of
Variance (ANOVA) favored the quadratic over the linear
model at a 95% level or greater, the quadratic fit is noted
in Table 1 along with the linear fit. The apparent speed
(βapp) in each direction in units of c is also given; where
the quadratic fit is favored βapp corresponds to the speed
at the mean date of 2004.06.
2.4. The Globular Clusters as Controls
The method was tested using ten globular clusters near
to the jet, each of which was measured as described
above, with contour levels drawn at 50% of the peak
intensity. Each set of cluster positions was binned into
the 26 time bins spread between 1995 and 2008, and for
each bin the mean position for all ten clusters was sub-
tracted from the positions so that the variance in the es-
timates could be measured from all clusters as a function
of epoch for use in the weighted linear least squares fit.
The measured variance was essentially constant across
all epochs at ∼0.1 reference pixels. Linear fits to the x-
and y-direction positions versus time in all cases were
consistent with a slope of zero, with typical errors on the
order of 0.003 pixels yr−1
or 0.02c.
3. RESULTS
Starting from the core, the first well-detected features
in our dataset include a small narrow extension from the
core (out to ∼0.5′′
) probably corresponding to knot L
seen in VLBI images, as well as the famous variable fea-
ture, HST-1. Both the core and HST-1 are highly vari-
able in flux and frequently saturated in our images. Be-
cause special care must be taken with saturated images,
an analysis of the inner region of the M87 jet up to and
including HST-1 will be addressed in a follow-up to this
letter. For all the knots described below, the WFPC2 im-
age stacks (galaxy subtracted) described above are shown
in Figures 1 and 3.5
.
3.1. The Inner Jet: Knots D, E, F, and I
Knot D is the most consistently bright feature after
the knot A/B/C Complex, and significant proper mo-
tions were measured in both previous studies.6
As sug-
gested by the contours overlaid on Figure 1, D-Middle is
one of the fastest components with a speed of 4.27±0.30c
along the jet, while the brighter D-West shows evidence
of deceleration radially, slowing to a near stop by the fi-
nal epoch in 2008, while maintaining one of the largest
transverse speeds of −0.59±0.05c (see Figure 2). These
measurements are consistent with the results of B99
(5.26±0.92c and 2.77±0.98c for D-Middle and D-West,
respectively), where we compare with our estimated ve-
locity of D-West in 1996 of 2.73±0.40c from the quadratic
fit.
Previous results on knot D-East have been conflict-
ing: B95 found that it moved inward along the jet at
0.23±0.12c (possibly consistent with being stationary),
while B99 found a large outward apparent velocity of
3.12±0.29c; our result of 0.28±0.05 is more in line with
B95. It is possible that there is a stationary feature at
D-East, through which components emerge (analogous
to what is seen in HST-1). In that case, the higher-
resolution FOC was perhaps tracking an emerging bright
component, while over longer periods the global feature
at D-East is stationary.
5 Movies of the jet and knots are also available in the online
version of this paper.
6 It is important to note that B95 used data from 1985 through
1995, and so directly precedes the epoch of our dataset, while B99
overlaps with only the early part of it, spanning 1995-1998. All
βapp (including previous work) were computed with the conversion
factor 0.264c yr mas−1.
4. 4 Meyer et al.
Figure 3. (Upper Left) Knot I appears to fade and move backwards along the jet at 0.23±0.12c. (Lower Left) Knot A is shown with
a stretch to emphasize the fading of the knot over time. (Middle Panel) The knot A/B complex shows remarkable variability, with both
sub-relativistic and superluminal apparent motions. The white arrow is pointing to a ‘bar’ which appears in the last epoch. (Right Panel)
Knot C shows speeds on the order of 0.5-1c. (Bottom Panel) A depiction of velocities as vectors from their positions along the jet.
As shown in the central lower panel of Figure 1, the
main knot structure of knot E (E-West) is complex, with
a moderately superluminal speed of 1.91±0.14c, about
half of that found in B99 (4.07±0.85c). In addition to
the 50% intensity contrast contour line shown, a lower-
intensity contour at 30% has been drawn around this
area, to illustrate the morphological changes of this fea-
ture over time. To the west there appears a bright exten-
sion in the 1995 epoch which advances westward faster
than the brightest part, and rapidly fades in the later
epochs. Interestingly, a new component appears to the
East in 2008, suggesting again the possibility of a favored
location or stationary feature, which should be checked
with future observations.
Like knot E, the next feature in the jet, knot F, is dif-
fuse, faint, and apparently complex. We track two broad
features, F-East and F-Middle, as shown in the lower
right of Figure 1. As B99 were unable to measure proper
motions for anything beyond knot E, the only previous
measurement gives 0.90±0.23c in B95, for the entire dif-
fuse feature seen in the radio. This is slightly faster than
the value we measure for the most prominent component
F-Middle (0.36±0.14c), however, the epochs of observa-
tion are not contemporaneous and slight deceleration is
possible.
Finally, knot I has a slight negative velocity along the
jet axis, of −0.23±0.12c. The knot clearly fades steadily
with time, as shown in the upper left of Figure 3. This
knot is the clearest case of a possible stationary feature in
the jet outside of the upstream component HST-1d which
has been extensively observed with VLBI (βapp <0.25c;
Cheung et al. 2007).
3.2. The Outer Jet: Knots A, B, and C
5. M87 Jet Optical Proper Motions 5
The outer part of the jet looks very different from
the evenly spaced knots discussed previously. Knot A
is the brightest feature in the entire jet, excepting HST-
1 during its remarkable flare of 2002 - 2008 (Harris et al.
2006). It has been suggested that knot A is an oblique
shock which precipitates the break-up of the orderly
structure of the jet, thus resulting in the complex knot B
region downstream, and the final knot C feature which is
considerably off the main jet axis (Bicknell & Begelman
1996). Within the bright but extended knot A, we track
two features which appear on top of this more diffuse
emission (see Figure 3). For A1, we find a relativistic
velocity of 1.32±0.12c, however it is not clear that this
feature is really a single component, as the western side of
it appears to move slowly if at all. For A2, we measure
a much slower radial velocity of 0.31±0.06c, consistent
with the previous results of 0.4-0.6c from B95.
Qualitatively, the A/B complex is surprisingly ‘active’
with new features brightening up and moving with high
speeds relative to other nearby components. A good ex-
ample is pointed out by the arrow in the last epoch of
the central panel in Figure 3, where a ‘bar’ has formed
between B3 and B4. At the same time, within region B4
a separation is taking place, leaving a small knot behind
to the northeast. While B4 is probably a complex of at
least 2-3 ‘subknots’, we used the inner contour (at 80%
median flux), giving us an apparent speed of 1.66±0.11c
along the jet direction. B1,B2, and B3 as well as the
final knot C show significant apparent velocities in both
directions, on the order of 0.5-1.5c.
The final terminus of knot B is particularly interesting,
as a new distinct component (which we have labeled B5-
n) appears in the northern half in the 2001 epoch. Using
data from 2001 - 2008 only (the time when this com-
ponent was detected), we measure an apparent velocity
of 2.16±0.35c along the jet direction and 1.30±0.31c in
the transverse direction. Qualitatively, the northern end
of B5 seems to continuously brighten while the whole
feature stretches up towards the northwest. In knot B
generally there is a repeating motif of two bright regions
connected by a fainter ‘bar’; this is apparent between
knots B1 and B2, between B3 and the remnant of B4,
and the two halves of B5.
The most striking finding of the outer jet component
velocities is depicted in the lower panel of Figure 3, where
the velocity vectors are plotted from the center of each
knot. There is a conspicuous ‘tip-to-tail’ alignment of
almost all the vectors within the outer knot A/B/C com-
plex, strongly suggestive of a flattened view of a helical
motion which might result in such a ‘zig-zag’ pattern,
though this should be checked with theoretical model-
ing.
4. DISCUSSION AND CONCLUSIONS
We have presented new proper motion measurements
for the knots in the M87 optical jet, reaching accuracies
better than 0.1c. The speeds are largely in agreement
with previous results where they exist (see Figure 4);
some discrepancies are likely due to the higher resolu-
tion in the optical allowing us to track more compact
features than those measured in the radio, or changes
such as the observed deceleration of knot D-West. We
also find evidence of stationary features in knots D-East,
I, and possibly E (if the new extensions in 2008 is a recur-
Figure 4. Velocities along the jet (upper panel) and transverse to
the jet (lower panel) as a function of distance from the core. Pre-
vious measurements shown for comparison taken from B95, B99,
Cheung et al. 2007, and Kovalev et al. 2007.
rence at a preferred location), which should be checked
with future observations. Both D-Middle, and the small
component extending from D-East (labeled with an ar-
row in Figure 1) appear to steadily drop in intensity over
the 13 years of observation, a very similar behavior to
the western components of knot HST-1 (e.g., B99), and
both HST-1 and knot D are dominated by a transverse
magnetic field as noted by (Perlman et al. 1999), which
suggests a shock at these locations. It has been suggested
that at the eastern edge of HST-1 there is a recollimation
shock (Stawarz et al. 2006; Cheung et al. 2007; see also
Asada & Nakamura 2012), but the appearance of very
different speeds all along the jet might also be consistent
with pairs of forward/reverse fast-mode MHD shocks in
a strongly magnetized relativistic flow (Nakamura et al.
2010).
In the outer jet (from knot A), we find apparent ve-
locities that are still superluminal and velocity vectors
that appear to line up into a helical/side-to-side pattern.
However it is not clear that the measured speeds can be
identified with discrete moving components. It is possi-
ble that if the jet of M87 has a helical structure which is
broken up at knot A, we are seeing the ‘unwinding’ of the
coil in knot B. Thus the appearance of the bar noted with
an arrow in 2008 could be the result of a change in geom-
etry as the coil of the jet unwinds, bringing a length into
our line of sight. Sideways oscillation of components B1-
B5 may presumably follow a helical path of underlying
magnetic fluxes (Owen et al. 1989; Perlman et al. 1999)
in three dimensions. Thus, the knot A/B/C complex
could be seen as a consequence of the interplay between
6. 6 Meyer et al.
the slow-mode MHD shocks and growing helical kink in-
stability (Nakamura & Meier 2004).
This project is part of the HSTPROMO collaboration
(www.stsci.edu/ marel/hstpromo.html), a set of HST
projects aimed at improving our dynamical understand-
ing of stars, clusters, and galaxies in the nearby Universe
through measurement and interpretation of proper mo-
tions. Support for this work was provided by NASA
through a grant for archival program 12635 from the
Space Telescope Science Institute (STScI), which is op-
erated by the Association of Universities for Research in
Astronomy (AURA), Inc., under NASA contract NAS5-
26555. Facilities: HST (WFPC2, ACS).
7. M87 Jet Optical Proper Motions 7
Table 1
Linear Fit Quadratic Fit Speed
Knot Subknot Distance† µx µy µx ξx µy ξy βx βy
′′ kpc mas yr−1 mas yr−1 mas yr−1 mas yr−2 mas yr−1 mas yr−2 c c
D East 2.77 0.224 1.1±0.2 −0.2±0.1 0.28±0.05 −0.05±0.03
Middlea 3.61 0.292 16.2±1.1 −0.7±0.1 −1.3±0.2 −0.2±0.1 4.27±0.30 −0.35±0.05
West 3.97 0.321 5.7±0.5 −2.2±0.2 3.9±0.5 −0.80±0.2 1.03±0.14 −0.59±0.05
E East 5.86 0.473 9.6±1.2 −1.8±0.3 2.52±0.32 −0.48±0.08
West 6.21 0.502 7.2±0.5 0.0±0.2 1.91±0.14 −0.01±0.05
F East 8.23 0.666 7.0±0.9 −1.3±0.4 1.85±0.24 −0.35±0.12
Middle 8.68 0.702 1.4±0.5 0.7±0.5 2.2±0.5 0.6±0.2 0.36±0.14 0.58±0.14
I 11.01 0.890 −0.9±0.4 −0.1±0.2 −0.23±0.12 −0.02±0.07
A A1 12.28 0.993 5.0±0.4 2.4±0.3 3.1±0.3 0.3±0.1 1.32±0.12 0.82±0.09
A2 12.60 1.019 1.2±0.2 1.9±0.6 0.31±0.06 0.50±0.16
B B1 12.88 1.041 5.2±0.6 −0.6±0.9 2.0±1.0 1.1±0.3 1.37±0.16 0.53±0.26
B2 13.16 1.064 1.6±0.3 −1.4±0.2 −0.8±0.3 0.2±0.1 0.42±0.07 −0.22±0.08
B3 13.74 1.110 1.3±0.2 1.2±0.1 1.9±0.2 0.3±0.1 1.6±0.2 0.2±0.1 0.49±0.05 0.42±0.04
B4 14.29 1.155 6.3±0.4 −3.3±0.5 −1.7±0.3 0.7±0.1 1.66±0.11 −0.45±0.08
B5-s 15.18 1.227 7.2±0.3 2.8±0.3 1.8±0.3 −0.4±0.1 1.90±0.09 0.48±0.07
B5-n 15.18 1.227 8.2±1.3 4.9±1.2 2.16±0.35 1.30±0.31
C C1 17.48 1.413 3.3±0.4 −0.6±0.3 0.3±0.3 0.4±0.1 0.86±0.10 0.07±0.08
C2 17.83 1.441 2.4±0.3 −1.7±1.2 1.5±0.2 −0.4±0.1 −5.6±0.9 −1.6±0.3 0.41±0.06 −1.47±0.23
C3 17.90 1.447 2.2±0.5 0.7±0.6 −1.7±0.3 −1.0±0.1 0.57±0.13 −0.45±0.07
C2+C3 17.83 1.441 3.2±0.4 −2.1±0.3 0.83±0.12 −0.54±0.08
GCb (single) 0.0±0.22 0.31±0.15 0.00±0.06 0.08±0.04
(mean) 0.0±0.06 0.00±0.06 0.00±0.02 0.00±0.02
Note. — Quadratic fit given when preferred at >95% level, where β values in those cases correspond to the mean time
2004.06. No HRC data was used for knots D-Middle, F,A,B, and C due to poor signal-to-noise.
† Distance from the core as measured in the 1995 epoch WFPC2 stacked image.
a No data after 2007 used in fit due to feature fading.
b Examples of Globular Cluster (GC) fits, including a single faint GC near knot A and the ensemble average.
8. 8 Meyer et al.
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