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Thermal Instability with Anisotropic Thermal Conduction and Adiabatic
Cosmic Rays: Implications for Cold Filaments in Galaxy Clusters: Observations of the cores of nearby galaxy clusters show H$\alpha$ and
molecular emission line filaments. We argue that these are the result of {\em
local} thermal instability in a {\em globally} stable galaxy cluster core. We
present local, high resolution, two-dimensional magnetohydrodynamic simulations
of thermal instability for conditions appropriate to the intracluster medium
(ICM); the simulations include thermal conduction along magnetic field lines
and adiabatic cosmic rays. Thermal conduction suppresses thermal instability
along magnetic field lines on scales smaller than the Field length ($\gtrsim$10
kpc for the hot, diffuse ICM). We show that the Field length in the cold medium
must be resolved both along and perpendicular to the magnetic field in order to
obtain numerically converged results. Because of negligible conduction
perpendicular to the magnetic field, thermal instability leads to fine scale
structure in the perpendicular direction. Filaments of cold gas along magnetic
field lines are thus a natural consequence of thermal instability with
anisotropic thermal conduction. Nonlinearly, filaments of cold ($\sim 10^4$ K)
gas should have lengths (along the magnetic field) comparable to the Field
length in the cold medium $\sim 10^{-4}$ pc! Observations show, however, that
the atomic filaments in clusters are far more extended, $\sim 10$ kpc. Cosmic
ray pressure support (or a small scale turbulent magnetic pressure) may resolve
this discrepancy: even a small cosmic ray pressure in the diffuse ICM, $\sim
10^{-4}$ of the thermal pressure, can be adiabatically compressed to provide
significant pressure support in cold filaments. This is qualitatively
consistent with the large population of cosmic rays invoked to explain the
atomic and molecular line ratios observed in filaments. | astro-ph_GA |
Confirmation of Enhanced Long Wavelength Dust Emission in OMC 2/3: Previous continuum observations from the MUSTANG camera on the Green Bank
Telescope (GBT) of the nearby star-forming filament OMC 2/3 found elevated
emission at 3.3 mm relative to shorter wavelength data. As a consequence, the
inferred dust emissivity index obtained from modified black body dust spectra
was considerably lower than what is typically measured on $\sim 0.1 \, {\rm
pc}$ scales in nearby molecular clouds. Here we present new observations of OMC
2/3 collected with the MUSTANG-2 camera on the GBT which confirm this elevated
emission. We also present for the first time sensitive 1 cm observations made
with the Ka-band receiver on the GBT which also show higher than expected
emission. We use these observations--- along with Herschel, JCMT, Mambo, and
GISMO data--- to assemble spectral energy distributions (SEDs) of a variety of
structures in OMC 2/3 spanning the range $160 \, {\rm \mu m}$ to $1 \, {\rm
cm}$. The data at 2 mm and shorter are generally consistent with a modified
black body spectrum and a single value of $\beta \sim 1.6$. The 3 mm and 1 cm
data, however, lie well above such an SED. The spectrum of the long wavelength
excess is inconsistent with both free-free emission and standard "Spinning
Dust" models for Anomalous Microwave Emission (AME). The 3 mm and 1 cm data
could be explained by a flatter dust emissivity at wavelengths shorter than 2
mm, potentially in concert with AME in some regions. | astro-ph_GA |
Probing the interplay between jets, winds and multi-phase gas in 11
radio-quiet PG Quasars: A uGMRT-VLA study: We present polarization-sensitive images from the Karl G. Jansky Very Large
Array (VLA) at 5 GHz of 11 radio-quiet PG quasars. Based on the radio
morphology, spectral index and polarization properties from the VLA study,
coupled with the findings of our previous 685 MHz uGMRT data, we find the
presence of low-power jets on sub-arcsecond and arcsecond scales in 9 sources;
some show signatures of bent jets. The origin of radio emission remains unclear
in the remaining 2 sources. Of the 11 sources, linear polarization is detected
in four of them with fractional polarization ranging between 2% and 21%. In PG
1229+204, the inferred B-field direction is parallel to the local kpc-scale jet
direction. The inferred B-fields are transverse to the weak southward extension
in PG 0934+013. For PG 0050+124 and PG 0923+129, the relationship between the
B-field structure and radio outflow direction remains unclear. Localized or
small-scale jet-medium interactions can be inferred across the sample based on
the VLA jet kinetic power arguments and polarization data. These may have the
potential as a feedback mechanism. We find that the radio properties do not
show strong correlations with the star formation, [O III] and CO quantities
published in the literature. The lack of evidence of AGN feedback on the global
galaxy properties could be due to the relative time scales of AGN activity and
those over which any impact might be taking place. | astro-ph_GA |
Hubble-COS Observations of Galactic High-Velocity Clouds: Four AGN Sight
Lines through Complex C: We report ultraviolet spectra of Galactic high-velocity clouds (HVCs) in
Complex C, taken by the Cosmic Origins Spectrograph (COS) on the Hubble Space
Telescope (HST), together with new 21-cm spectra from the Green Bank Telescope.
The wide spectral coverage and higher S/N, compared to previous HST spectra,
provide better velocity definition of the HVC absorption, additional ionization
species, and improved abundances in this halo gas. Complex C has a metallicity
of 0.1-0.3 solar and a wide range of ions, suggesting dynamical and thermal
interactions with hot gas in the Galactic halo. Spectra in the COS
medium-resolution G130M (1133-1468 A) and G160M (1383-1796 A) gratings detect
ultraviolet absorption lines from 8 elements in low ionization stages (O I, N
I, C II, S II, Si II, Al II, Fe II, P II) and 3 elements in intermediate and
high-ionization states (Si III, Si IV, C IV, N V). Our four AGN sight lines
toward Mrk 817, Mrk 290, Mrk 876, and PG1259+593 have high-velocity H I and O
VI column densities, log N_HI = 19.39-20.05 and log N_OVI = 13.58-14.10, with
substantial amounts of kinematically associated photoionized gas. The high-ion
abundance ratios are consistent with cooling interfaces between photoionized
gas and collisionally ionized gas: N(C IV)/N(O VI) = 0.3-0.5, N(Si IV)/N(O VI)
= 0.05-0.11, N(N V)/N(O VI) = 0.07-0.13, and N(Si IV)/N(Si III) = 0.2. | astro-ph_GA |
Modeling Star Formation as a Markov Process in a Supersonic
Gravoturbulent Medium: Molecular clouds exhibit lognormal probability density functions (PDF) of
mass densities, which are thought to arise as a consequence of isothermal,
supersonic turbulence. Star formation is then widely assumed to occur in
perturbations in which gravitational collapse is faster than the rate of change
due to turbulent motions. Here we use direct numerical simulations to measure
this rate as a function of density for a range of turbulent Mach numbers, and
show it is faster at high densities than at low densities. Furthermore, we show
that both the density PDF and rate of change arise naturally in a simple model
of turbulence as a continuous Markov process. The one-dimensional Langevin
equation that describes this evolution depends on only two parameters, yet it
captures the full evolution seen in direct three-dimensional simulations. If it
is modified to include gravity, the Langevin equation also reproduces the rate
of material collapsing to high densities seen in turbulent simulations
including self-gravity. When generalized to include both temperature and
density, similar analyses are likely applicable throughout astrophysics. | astro-ph_GA |
Constraining stellar population parameters from narrow band photometric
surveys using convolutional neural networks: Upcoming large-area narrow band photometric surveys, such as J-PAS, will
enable us to observe a large number of galaxies simultaneously and efficiently.
However, it will be challenging to analyse the spatially-resolved stellar
populations of galaxies from such big data to investigate galaxy formation and
evolutionary history. We have applied a convolutional neural network (CNN)
technique, which is known to be computationally inexpensive once it is trained,
to retrieve the metallicity and age from J-PAS-like narrow band images. The CNN
was trained using mock J-PAS data created from the CALIFA IFU survey and the
age and metallicity at each data point, which are derived using full spectral
fitting to the CALIFA spectra. We demonstrate that our CNN model can
consistently recover age and metallicity from each J-PAS-like spectral energy
distribution. The radial gradients of the age and metallicity for galaxies are
also recovered accurately, irrespective of their morphology. However, it is
demonstrated that the diversity of the dataset used to train the neural
networks has a dramatic effect on the recovery of galactic stellar population
parameters. Hence, future applications of CNNs to constrain stellar populations
will rely on the availability of quality spectroscopic data from samples
covering a wide range of population parameters. | astro-ph_GA |
Collisional excitation of HC3N by para- and ortho-H2: New calculations for rotational excitation of cyanoacetylene by collisions
with hydrogen molecules are performed to include the lowest 38 rotational
levels of HC3N and kinetic temperatures to 300 K. Calculations are based on the
interaction potential of Wernli et al. A&A, 464, 1147 (2007) whose accuracy is
checked against spectroscopic measurements of the HC3N-H2 complex. The quantum
coupled-channel approach is employed and complemented by quasi-classical
trajectory calculations. Rate coefficients for ortho-H2 are provided for the
first time. Hyperfine resolved rate coefficients are also deduced. Collisional
propensity rules are discussed and comparisons between quantum and classical
rate coefficients are presented. This collisional data should prove useful in
interpreting HC3N observations in the cold and warm ISM, as well as in
protoplanetary disks. | astro-ph_GA |
GC-IRS13E - A puzzling association of three early-type stars: We present a detailed analysis of high resolution near-infrared imaging and
spectroscopy of the potential star cluster IRS13E very close to the massive
black hole in the Galactic Center. We detect 19 objects in IRS13E from Ks-band
images, 15 of which are also detected reliably in H-band. We derive consistent
proper motions for these objects from the two bands. Most objects share a
similar westward proper motion. We characterize the objects using spectroscopy
(1.45 to 2.45 micrometer) and (narrow-band) imaging from H- (1.66 mircrometer)
to L'-band (3.80 micrometer). Nine of the objects detected in both Ks- and
H-band are very red, and we find that they are all consistent with being warm
dust clumps. The dust emission may be caused by the colliding winds of the two
Wolf-Rayet stars in the cluster. Three of the six detected stars do not share
the motion or spectral properties of the three bright stars. This leaves only
the three bright, early-type stars as potential cluster members. It is unlikely
that these stars are a chance configuration. Assuming the presence of an IMBH,
a mass of about 14000 solar masses follows from the velocities and positions of
these three stars. However, our acceleration limits make such an IMBH nearly as
unlikely as a chance occurrence of such a star association. Furthermore, there
is no variable X-ray source in IRS13E despite the high density of dust and gas.
Therefore, we conclude that is unlikely that IRS13E hosts a black hole massive
enough to bind the three stars. | astro-ph_GA |
The Presence of Thermally Unstable X-ray Filaments and the Production of
Cold Gas in the NGC 5044 Group: We present the results of a deep Chandra observation of the X-ray bright,
moderate cooling flow group NGC 5044 along with the observed correlations
between the ionized, atomic, and molecular gas in this system. The Chandra
observation shows that the central AGN has undergone two outbursts in the past
100 Myrs, based on the presence of two pairs of nearly bipolar X-ray cavities.
The molecular gas and dust within the central 2kpc is aligned with the
orientation of the inner pair of bipolar X-ray cavities, suggesting that the
most recent AGN outburst had a dynamical impact on the molecular gas. NGC 5044
also hosts many X-ray filaments within the central 8kpc, but there are no
obvious connections between the X-ray and H$\alpha$ filaments and the more
extended X-ray cavities that were inflated during the prior AGN outburst. Using
the linewidth of the blended Fe-L line complex as a diagnostic for multiphase
gas, we find that the majority of the multiphase, thermally unstable gas in NGC
5044 is confined within the X-ray filaments. While the cooling time and entropy
of the gas within the X-ray filaments are very similar, not all filaments show
evidence of gas cooling or an association with Ha emission. We suggest that the
various observed properties of the X-ray filaments are suggestive of an
evolutionary sequence where thermally unstable gas begins to cool, becomes
multiphased, develops Ha emitting plasma, and finally produces cold gas. | astro-ph_GA |
What does the first highly-redshifted 21-cm detection tell us about
early galaxies?: The Experiment to Detect the Global Epoch of Reionization Signature (EDGES)
recently reported a strong 21-cm absorption signal relative to the cosmic
microwave background at $z \sim 18$. While its anomalous amplitude may indicate
new physics, in this work we focus on the timing of the signal, as it alone
provides an important constraint on galaxy formation models. Whereas rest-frame
ultraviolet luminosity functions (UVLFs) over a broad range of redshifts are
well fit by simple models in which galaxy star formation histories track the
assembly of dark matter halos, we find that these same models, with reasonable
assumptions about X-ray production in star-forming galaxies, cannot generate a
narrow absorption trough at $z \sim 18$. If verified, the EDGES signal
therefore requires the fundamental inputs of galaxy formation models to evolve
rapidly at $z \gtrsim 10$. Unless extremely faint sources residing in halos
below the atomic cooling threshold are responsible for the EDGES signal, star
formation in $\sim 10^8$-$10^{10} \ M_{\odot}$ halos must be more efficient
than expected, implying that the faint-end of the UVLF at $M_{\mathrm{UV}}
\lesssim -12$ must steepen at the highest redshifts. This steepening provides a
concrete test for future galaxy surveys with the James Webb Space Telescope and
ongoing efforts in lensed fields, and is required regardless of whether the
amplitude of the EDGES signal is due to new cooling channels or a strong radio
background in the early Universe. However, the radio background solution
requires that galaxies at $z > 15$ emit 1-2 GHz photons with an efficiency
$\sim 10^3$ times greater than local star-forming galaxies, posing a challenge
for models of low-frequency photon production in the early Universe. | astro-ph_GA |
The Effect of Noise on the Dust Temperature - Spectral Index Correlation: We investigate how uncertainties in flux measurements affect the results from
modified blackbody SED fits. We show that an inverse correlation between the
dust temperature T and spectral index (beta) naturally arises from least
squares fits due to the uncertainties, even for sources with a single T and
beta. Fitting SEDs to noisy fluxes solely in the Rayleigh-Jeans regime produces
unreliable T and beta estimates. Thus, for long wavelength observations (lambda
>~ 200 micron), or for warm sources (T >~ 60 K), it becomes difficult to
distinguish sources with different temperatures. We assess the role of noise in
recent observational results that indicate an inverse and continuously varying
T - beta relation. Though an inverse and continuous T - beta correlation may be
a physical property of dust in the ISM, we find that the observed inverse
correlation may be primarily due to noise. | astro-ph_GA |
Exploring the interstellar medium of NGC 891 at millimeter wavelengths
using the NIKA2 camera: In the framework of the IMEGIN Large Program, we used the NIKA2 camera on the
IRAM 30-m telescope to observe the edge-on galaxy NGC 891 at 1.15 mm and 2 mm
and at a FWHM of 11.1" and 17.6", respectively. Multiwavelength data enriched
with the new NIKA2 observations fitted by the HerBIE SED code (coupled with the
THEMIS dust model) were used to constrain the physical properties of the ISM.
Emission originating from the diffuse dust disk is detected at all wavelengths
from mid-IR to mm, while mid-IR observations reveal warm dust emission from
compact HII regions. Indications of mm excess emission have also been found in
the outer parts of the galactic disk. Furthermore, our SED fitting analysis
constrained the mass fraction of the small (< 15 Angstrom) dust grains. We
found that small grains constitute 9.5% of the total dust mass in the galactic
plane, but this fraction increases up to ~ 20% at large distances (|z| > 3 kpc)
from the galactic plane. | astro-ph_GA |
Quenching in Cosmic Sheets: Tracing the Impact of Large Scale Structure
Collapse on the Evolution of Dwarf Galaxies: Dwarf galaxies are thought to quench primarily due to environmental processes
most typically occurring in galaxy groups and clusters or around single,
massive galaxies. However, at earlier epochs, ($5 < z < 2$), the collapse of
large scale structure (forming Zel'dovich sheets and subsequently filaments of
the cosmic web) can produce volume-filling accretion shocks which elevate large
swaths of the intergalactic medium (IGM) in these structures to a hot ($T>10^6$
K) phase. We study the impact of such an event on the evolution of central
dwarf galaxies ($5.5 < \log M_* < 8.5$) in the field using a spatially large,
high resolution cosmological zoom simulation which covers the cosmic web
environment between two protoclusters. We find that the shock-heated sheet acts
as an environmental quencher much like clusters and filaments at lower
redshift, creating a population of quenched, central dwarf galaxies. Even
massive dwarfs which do not quench are affected by the shock, with reductions
to their sSFR and gas accretion. This process can potentially explain the
presence of isolated quenched dwarf galaxies, and represents an avenue of
pre-processing, via which quenched satellites of bound systems quench before
infall. | astro-ph_GA |
ALMA observations of molecular tori around massive black holes: We report ALMA observations of CO(3-2) emission in a sample of 7
Seyfert/LINER galaxies at the unprecedented spatial resolution of 0.1'' = 4-9
pc. Our aim is to explore the close environment of AGN, and the dynamical
structures leading to its fueling. The selected galaxies host low-luminosity
AGN, and have a wide range of activity types, and barred or ringed
morphologies. The observed maps reveal the existence of circum-nuclear disk
structures, defined by their morphology and decoupled kinematics. We call these
structures "molecular tori", even though they appear often as disks, without
holes in the center. They have varied orientations, unaligned with their host
galaxy. The radius of the tori ranges from 6 to 27 pc, and their mass from 0.7
10$^7$ to 3.9 10$^7$ Msun. At larger scale, the gas is always piled up in a few
100~pc scale resonant rings, that play the role of a reservoir to fuel the
nucleus. In some cases, a trailing spiral is observed inside the ring,
providing evidence for feeding processes. Most frequently, the torus and the
AGN are slightly off-centered, with respect to the bar-resonant ring position,
implying that the black hole is wandering by a few 10~pc amplitude around the
center of mass of the galaxy. Our spatial resolution allows us to measure gas
velocities inside the sphere of influence of the central black holes. By
fitting the observations with different simulated cubes, varying the torus
inclination and the black hole mass, it is possible to estimate the mass of the
central black hole, which is in general difficult for such late-type galaxies,
with only a pseudo-bulge. | astro-ph_GA |
Investigating the Baryon Cycle in Interacting Dwarfs with the Very Large
Array and Pan-STARRS: We present resolved HI synthesis maps from the Very Large Array (VLA) of
three interacting dwarf systems: the NGC 3664 dwarf pair, the NGC 3264 dwarf
pair, and the UGC 4638 dwarf triplet. All three dwarf systems are captured at
various stages of interaction and span a range of environments. We detect clear
hallmarks of tidal interactions through the presence of HI bridges, and diffuse
HI extensions that surround the dwarfs. We overlay the HI data on Pan-STARRS
r-band images and find further evidence of tidal interactions through
coincident distorted HI and tidal stellar features in NGC 3264 and UGC 4638,
and an unwound spiral arm pointing towards its smaller companion in NGC 3264.
In UGC 4638, both the gas and diffuse stars are extended to similar radii east
of the primary, which could indicate that the smaller dwarf in the system has
already completed one pass through the primary. We additionally find that our
three systems, and those from the Local Volume TiNy Titans survey, are not HI
deficient and thus the interaction has not resulted in a loss of gas from the
systems. A comparison with non-interacting dwarf galaxies shows that the
interactions have a significant impact on the kinematics of the systems. Our
new resolved HI kinematics, combined with detailed stellar and HI morphologies,
provide crucial constraints for future dynamical modelling of hierarchical
mergers and the baryon cycle at the low-mass scale. | astro-ph_GA |
Comparisons of Different Fitting Methods for the Physical Parameters of
A Star Cluster Sample of M33 with Spectroscopy and Photometry: Star clusters are good tracers for formation and evolution of galaxies. We
compared different fitting methods by using spectra (or by combining
photometry) to determine the physical parameters. We choose a sample of 17 star
clusters in M33, which previously lacked spectroscopic observations. The
low-resolution spectra were taken with the Xinglong 2.16-m reflector of NAOC.
The photometry used in the fitting includes $\rm u_{SC}$ and $\rm v_{SAGE}$
bands from the SAGE survey, as well as the published $UBVRI$ and $ugriz$
photometry. We firstly derived ages and metallicities with the {\sc ULySS}
(Vazdekis et al. and {\sc pegase-hr}) SSP model and the Bruzual \& Charlot
(2003) (BC03) stellar population synthesis models for the full-spectrum
fitting. The fitting results of both the BC03 and {\sc ULySS} models seem
consistent with those of previous works as well. Then we add the SAGE $\rm
u_{SC}$ and $\rm v_{SAGE}$ photometry in the spectroscopic fitting with the
BC03 models. It seems the results become much better, especially for the Padova
2000+Chabrier IMF set. Finally we add more photometry data, $UBVRI$ and
$ugriz$, in the fitting and we found that the results do not improve
significantly. Therefore, we conclude that the photometry is useful for
improving the fitting results, especially for the blue bands ($\lambda <4000$
{\AA}), e.g., $\rm u_{SC}$ and $\rm v_{SAGE}$ band. At last, we discuss the
"UV-excess" for the star clusters and we find five star clusters have
UV-excess, based on the $GALEX$ FUV, NUV photometry. | astro-ph_GA |
The impact of baryonic discs on the shapes and profiles of
self-interacting dark matter halos: We employ isolated N-body simulations to study the response of
self-interacting dark matter (SIDM) halos in the presence of the baryonic
potentials. Dark matter self-interactions lead to kinematic thermalization in
the inner halo, resulting in a tight correlation between the dark matter and
baryon distributions. A deep baryonic potential shortens the phase of SIDM core
expansion and triggers core contraction. This effect can be further enhanced by
a large self-scattering cross section. We find the final SIDM density profile
is sensitive to the baryonic concentration and the strength of dark matter
self-interactions. Assuming a spherical initial halo, we also study evolution
of the SIDM halo shape together with the density profile. The halo shape at
later epochs deviates from spherical symmetry due to the influence of the
non-spherical disc potential, and its significance depends on the baryonic
contribution to the total gravitational potential, relative to the dark matter
one. In addition, we construct a multi-component model for the Milky Way,
including an SIDM halo, a stellar disc and a bulge, and show it is consistent
with observations from stellar kinematics and streams. | astro-ph_GA |
BAL effect in quasars due to source orientation: We investigated a scenario where the presence of a broad absorption line
(BAL) feature in quasars (QSOs) is contingent upon the line of sight being
situated within an outflow cone emanating from the source. We examined the
mechanism of dust-driven winds based on the failed radiatively accelerated
dusty outflow (FRADO) model proposed by Czerny & Hryniewicz, letting it be
responsible for the formation of massive outflow. We calculated the probability
of observing the BAL effect from the geometry of outflow which is a function of
global parameters of black hole mass (M$_{BH}$), Eddington ratio
($\alpha_{Edd}$), and metallicity (Z). We then compared the results with
prevalence of BAL QSOs in a sample of observational data from SDSS. The
consistency of our model with the data supports the interpretation of the BAL
phenomenon as a result of source orientation, rather than a transitory stage in
AGN evolution | astro-ph_GA |
An Isolated Compact Galaxy Triplet: We report the discovery of an isolated compact galaxy triplet SDSS
J084843.45+164417.3, which is first detected by the LAMOST spectral survey and
then confirmed by the spectroscopic observation of the BFOSC of the 2.16 meter
telescope. It is found that this triplet is an isolated and extremely compact
system, which has an aligned configuration and very small radial velocity
dispersion. The member galaxies have similar colors and show marginal star
formation activities. These results enhance the opinion that the compact
triplets are well-evolved systems rather than the hierarchically forming
structures. This occasional discovery reveals the limitations of the fiber
spectral redshift surveys in studying such compact system, and declares the
necessity of additional observations to complete the current redshift sample. | astro-ph_GA |
High Galactic latitude runaway stars as tracers of the spiral arms: A direct observation of the spiral structure of the Galaxy is hindered by our
position in the middle of the Galactic plane. We propose a method based on the
analysis of the birthplaces of high Galactic latitude runaway stars to map the
spiral arms and determine their dynamics. As a proof of concept, the method is
applied to a local sample of early-type stars and a sample of runaways stars to
obtain estimates of the pattern speed and the spiral arm's phase angle. We also
estimate the performance of this method once the data gathered by Gaia, in
particular for runaway stars observed on the other side of the Galaxy, is
available. | astro-ph_GA |
The Effects of Inhomogeneities within Colliding Flows on the Formation
and Evolution of Molecular Clouds: Observational evidence from local star-forming regions mandates that star
formation occurs shortly after, or even during, molecular cloud formation.
Models of the formation of molecular clouds in large-scale converging flows
have identified the physical mechanisms driving the necessary rapid
fragmentation. They also point to global gravitational collapse driving
supersonic turbulence in molecular clouds. Previous cloud formation models have
focused on turbulence generation, gravitational collapse, magnetic fields, and
feedback. Here, we explore the effect of structure in the flow on the resulting
clouds and the ensuing gravitational collapse. We compare two extreme cases,
one with a collision between two smooth streams, and one with streams
containing small clumps. We find that structured converging flows lead to a
delay of local gravitational collapse ("star formation"). Thus, more gas has
time to accumulate, eventually leading to a strong global collapse, and thus to
a high star formation rate. Uniform converging flows fragment hydrodynamically
early on, leading to the rapid onset of local gravitational collapse and an
overall low sink formation rate. | astro-ph_GA |
Characteristics of remnant radio galaxies detected in the deep radio
continuum observations from the SKA pathfinders: The cessation of AGN activity in radio galaxies leads to a remnant phase
during which jets are no longer sustained, but lobes can be detected for a
period of time before they fade away due to radiative and dynamical energy
losses. The time-scale of the remnant phase and AGN duty cycle are vital to
understanding the evolution of radio galaxies. In this paper, we report new
band-3 observations with the upgraded Giant Meterwave Radio Telescope (uGMRT)
for five remnant radio galaxies. Our uGMRT observations reveal emission of
low-surface-brightness in all five remnants with 400 MHz surface brightness in
the range of 36$-$201 mJy arcmin$^{-2}$. With band-3 uGMRT observations, we
discover wing-shaped radio morphology in one of our sample sources. Using radio
observations at 150 MHz, 325 MHz, 400 MHz, and 1.5 GHz, we model the radio
spectral energy distributions (SEDs) of our sample sources with the continuous
injection-off model (CI$_{\rm OFF}$), that assumes an active phase with
continuous injection followed by a remnant phase. We obtain total source ages
($t_{\rm s}$) in the range of 20.3 Myr to 41.4 Myr with $t_{\rm OFF}$/$t_{\rm
s}$ distributed in the range of 0.16 to 0.63, which in turn suggests them to
belong to different evolutionary phases. We note that, in comparison to the
remnants reported in the literature, our sample sources tend to show lower
spectral ages that can be explained by the combined effects of more dominant
inverse Compton losses for our sources present at the relatively higher
redshifts and possible rapid expansion of lobes in their less dense
environments. | astro-ph_GA |
Clocking the Evolution of Post-Starburst Galaxies: Methods and First
Results: Detailed modeling of the recent star formation histories (SFHs) of
post-starburst (or "E+A") galaxies is impeded by the degeneracy between the
time elapsed since the starburst ended (post-burst age), the fraction of
stellar mass produced in the burst (burst strength), and the burst duration. To
resolve this issue, we combine GALEX ultraviolet photometry, SDSS photometry
and spectra, and new stellar population synthesis models to fit the SFHs of 532
post-starburst galaxies. In addition to an old stellar population and a recent
starburst, 48% of the galaxies are best fit with a second recent burst. Lower
stellar mass galaxies (log M$_\star$/M$_\odot<10.5$) are more likely to
experience two recent bursts, and the fraction of their young stellar mass is
more strongly anti-correlated with their total stellar mass. Applying our
methodology to other, younger post-starburst samples, we identify likely
progenitors to our sample and examine the evolutionary trends of molecular gas
and dust content with post-burst age. We discover a significant (4$\sigma$)
decline, with a 117-230 Myr characteristic depletion time, in the molecular gas
to stellar mass fraction with the post-burst age. The implied rapid gas
depletion rate of 2-150 M$_\odot$yr$^{-1}$ cannot be due to current star
formation, given the upper limits on the current SFRs in these post-starbursts.
Nor are stellar winds or SNe feedback likely to explain this decline. Instead,
the decline points to the expulsion or destruction of molecular gas in
outflows, a possible smoking gun for AGN feedback. | astro-ph_GA |
The Host Galaxies of Hybrid Morphology Radio Sources: Based on their differing radio morphologies, powerful radio galaxies can be
separated into the Fanaroff-Riley I (FR-I) and II (FR-II) classes. Hybrid
morphology radio sources (HyMoRS) contain morphologies consistent with each
type of jet on either side: a powerful, highly relativistic FR-II-like jet
terminating in a hotspot on one side and an FRI-like plume on the other. HyMoRS
present a unique opportunity to study the conditions which give rise to the
dichotomy. Using host galaxy properties, we conduct the first multiwavelength
investigation into whether orientation can explain HyMoRS morphology. Through
optical spectroscopy and mid-infrared photometry, we analyze the emission
characteristics, and evaluate the broad characteristics of five HyMoRS host
galaxies at intermediate redshifts (0.4 < z < 1.5). The HyMoRS host galaxies in
our sample have properties consistent with typical host galaxies of FR-II
sources, suggesting that the observed hybrid morphologies may be caused by a
dense, cluster-like environment bending FR-II jets combined with a favorable
orientation which can make one side appear similar to an FR-I jet. Our results
thus support the hypothesis that HyMoRS are mainly caused by environment and
orientation. | astro-ph_GA |
Numerical Models for the Diffuse Ionized Gas in Galaxies. II.
Three-dimensional radiative transfer in inhomogeneous interstellar structures
as a tool for analyzing the diffuse ionized gas: Aims: We systematically explore a plausible subset of the parameter space
involving effective temperatures and metallicities of the ionizing stellar
sources, the effects of the hardening of their radiation by surrounding leaky
HII regions with different escape fractions, as well as different scenarios for
the clumpiness of the DIG, and compute the resulting line strength ratios for a
number of diagnostic optical emission lines.
Methods: For the ionizing fluxes we compute a grid of stellar spectral energy
distributions (SEDs) from detailed, fully non-LTE model atmospheres that
include the effects of stellar winds and line blocking and blanketing. To
calculate the ionization and temperature structure in the HII regions and the
diffuse ionized gas we use spherically symmetric photoionization models as well
as state-of-the-art three-dimensional (3D) non-LTE radiative transfer
simulations, considering hydrogen, helium, and the most abundant metals.
Results: We provide quantitative predictions of how the line ratios from HII
regions and the DIG vary as a function of metallicity, stellar effective
temperature, and escape fraction from the HII region. The range of predicted
line ratios reinforces the hypothesis that the DIG is ionized by (filtered)
radiation from hot stars; however, comparison of observed and predicted line
ratios indicates that the DIG is typically ionized with a softer SED than
predicted by the chosen stellar population synthesis model. Even small changes
in simulation parameters like the clumping factor can lead to considerable
variation in the ionized volume. Both for a more homogeneous gas and a very
inhomogeneous gas containing both dense clumps and channels with low gas
density, the ionized region in the dilute gas above the galactic plane can
cease to be radiation-bounded, allowing the ionizing radiation to leak into the
intergalactic medium. | astro-ph_GA |
Herschel observations of Extra-Ordinary Sources: H2S as a Probe of Dense
Gas and Possibly Hidden Luminosity Toward the Orion KL Hot Core: We present Herschel/HIFI observations of the light hydride H$_{2}$S obtained
from the full spectral scan of the Orion Kleinmann-Low nebula (Orion KL) taken
as part of the HEXOS GT key program. In total, we observe 52, 24, and 8
unblended or slightly blended features from H$_{2}$$^{32}$S, H$_{2}$$^{34}$S,
and H$_{2}$$^{33}$S, respectively. We only analyze emission from the so called
hot core, but emission from the plateau, extended ridge, and/or compact ridge
are also detected. Rotation diagrams for ortho and para H$_{2}$S follow
straight lines given the uncertainties and yield T$_{\rm rot}$=141$\pm$12 K.
This indicates H$_{2}$S is in LTE and is well characterized by a single kinetic
temperature or an intense far-IR radiation field is redistributing the
population to produce the observed trend. We argue the latter scenario is more
probable and find that the most highly excited states (E$_{\rm up}$>1000 K) are
likely populated primarily by radiation pumping. We derive an H$_{2}$$^{32}$S
column density, N$_{\rm tot}$(H$_{2}$$^{32}$S)=9.5$\pm$1.9$\times$10$^{17}$
cm$^{-2}$, gas kinetic temperature, T$_{\rm kin}$=120$\pm^{13}_{10}$ K, and
constrain the H$_{2}$ volume density, n$_{H2}$>9$\times$10$^{7}$ cm$^{-3}$, for
the H$_{2}$S emitting gas. These results point to an H$_{2}$S origin in
markedly dense, heavily embedded gas, possibly in close proximity to a hidden
self-luminous source (or sources), which are conceivably responsible for Orion
KL's high luminosity. We also derive an H$_{2}$S ortho/para ratio of
1.7$\pm$0.8 and set an upper limit for HDS/H2S of <4.9$\times$10$^{-3}$. | astro-ph_GA |
On Synthetic Absorption Line Profiles of Thermally Driven Winds from
Active Galactic Nuclei: The warm absorbers observed in more than half of all nearby active galactic
nuclei (AGN) are tracers of ionized outflows located at parsec scale distances
from the central engine. If the smallest inferred ionization parameters
correspond to plasma at a few $10^4$~K, then the gas undergoes a transition
from being bound to unbound provided it is further heated to $\sim 10^6$~K at
larger radii. Dannen et al. recently discovered that under these circumstances,
thermally driven wind solutions are unsteady and even show very dense clumps
due to thermal instability. To explore the observational consequences of these
new wind solutions, we compute line profiles based on the one-dimensional
simulations of Dannen et al. We show how the line profiles from even a simple
steady state wind solution depend on the ionization energy (IE) of absorbing
ions, which is a reflection of the wind ionization stratification. To organize
the diversity of the line shapes, we group them into four categories: weak
Gaussians, saturated boxy profiles with and without an extended blue wing, and
broad weak profiles. The lines with profiles in the last two categories are
produced by ions with the highest IE that probe the fastest regions. Their
maximum blueshifts agree with the highest flow velocities in thermally unstable
models, both steady state and clumpy versions. In contrast, the maximum
blueshifts of the most high IE lines in thermally stable models can be less
than half of the actual solution velocities. Clumpy solutions can additionally
imprint distinguishable absorption troughs at widely separated velocities. | astro-ph_GA |
Cosmicflows 4: The Calibration of Optical and Infrared Tully-Fisher
Relations: This study is a part of the Cosmicflows-4 project with the aim of measuring
the distances of more than ~10,000 spiral galaxies in the local universe up to
~15,000 km/s. New HI linewidth information has come primarily from the Arecibo
Legacy Fast ALFA Survey. Photometry of our sample galaxies has been carried out
in optical (SDSS u, g, r, i, z) and infrared (WISE W1 and W2) bands.
Inclinations have been determined using an online graphical interface
accessible to a collaboration of citizen scientists. Galaxy distances are
measured based on the correlation between the rotation rate of spirals and
their absolute luminosity, known as the Tully-Fisher Relation (TFR). In this
study, we present the calibration of the TFR using a subsample of ~600 spirals
located in 20 galaxy clusters. Correlations among such observables as color,
surface brightness, and relative HI content are explored in an attempt to
reduce the scatter about the TFR with the goal of obtaining more accurate
distances. A preliminary determination of the Hubble constant from the
distances and velocities of the calibrator clusters is
H0=76.0+-1.1(stat.)+-2.3(sys.) km/s/Mpc. | astro-ph_GA |
CHORUS. III. Photometric and Spectroscopic Properties of Ly$α$
Blobs at $z=4.9-7.0$: We report the Subaru Hyper Suprime-Cam (HSC) discovery of two Ly$\alpha$
blobs (LABs), dubbed z70-1 and z49-1 at $z=6.965$ and $z=4.888$ respectively,
that are Ly$\alpha$ emitters with a bright ($\log L_{\rm Ly\alpha}/{\rm [erg\
s^{-1}]}>43.4$) and spatially-extended Ly$\alpha$ emission, and present the
photometric and spectroscopic properties of a total of seven LABs; the two new
LABs and five previously-known LABs at $z=5.7-6.6$. The z70-1 LAB shows the
extended Ly$\alpha$ emission with a scale length of $1.4\pm 0.2$ kpc, about
three times larger than the UV continuum emission, making z70-1 the most
distant LAB identified to date. All of the 7 LABs, except z49-1, exhibit no AGN
signatures such as X-ray emission, {\sc Nv}$\lambda$1240 emission, or
Ly$\alpha$ line broadening, while z49-1 has a strong {\sc Civ}$\lambda$1548
emission line indicating an AGN on the basis of the UV-line ratio diagnostics.
We carefully model the point-spread functions of the HSC images, and conduct
two-component exponential profile fitting to the extended Ly$\alpha$ emission
of the LABs. The Ly$\alpha$ scale lengths of the core (star-forming region) and
the halo components are $r_{\rm c}=0.6-1.2$ kpc and $r_{\rm h}=2.0-13.8$ kpc,
respectively. The average $r_{\rm h}$ of the LABs falls on the extrapolation of
the $r_{\rm h}$-Ly$\alpha$ luminosity relation of the Ly$\alpha$ halos around
VLT/MUSE star-forming galaxies at the similar redshifts, suggesting that
typical LABs at $z\gtrsim5$ are not special objects, but star-forming galaxies
at the bright end. | astro-ph_GA |
The Subaru high-z quasar survey: discovery of faint z~6 quasars: We present the discovery of one or two extremely faint z~6 quasars in 6.5
deg^2 utilizing a unique capability of the wide-field imaging of the
Subaru/Suprime-Cam. The quasar selection was made in (i'-z_B) and (z_B-z_R)
colors, where z_B and z_R are bandpasses with central wavelengths of 8842A and
9841A, respectively. The color selection can effectively isolate quasars at z~6
from M/L/T dwarfs without the J-band photometry down to z_R<24.0, which is 3.5
mag. deeper than SDSS. We have selected 17 promising quasar candidates. The
follow-up spectroscopy for seven targets identified one apparent quasar at
z=6.156 with M_1450=-23.10. We also identified one possible quasar at z=6.041
with a faint continuum of M_1450=-22.58 and a narrow Lyman-alpha emission with
HWHM=427 km/s, which cannot be distinguished from Lyman-alpha emitters. We
derive the quasar luminosity function at z~6 by combining our faint quasar
sample with the bright quasar samples by SDSS and CFHQS. Including our data
points invokes a higher number density in the faintest bin of the quasar
luminosity function than the previous estimate employed. This suggests a
steeper faint-end slope than lower-z, though it is yet uncertain based on a
small number of spectroscopically identified faint quasars and several quasar
candidates are still remain to be diagnosed. The steepening of the quasar
luminosity function at the faint-end does increase the expected emission rate
of the ionizing photon, however, it only changes by a factor of ~2-6. This was
found to be still insufficient for the required photon budget of reionization
at z~6. | astro-ph_GA |
ALMACAL VI: Molecular gas mass density across cosmic time via a blind
search for intervening molecular absorbers: We are just starting to understand the physical processes driving the
dramatic change in cosmic star-formation rate between $z\sim 2$ and the present
day. A quantity directly linked to star formation is the molecular gas density,
which should be measured through independent methods to explore variations due
to cosmic variance and systematic uncertainties. We use intervening CO
absorption lines in the spectra of mm-bright background sources to provide a
census of the molecular gas mass density of the Universe. The data used in this
work are taken from ALMACAL, a wide and deep survey utilizing the ALMA
calibrator archive. While we report multiple Galactic absorption lines and one
intrinsic absorber, no extragalactic intervening molecular absorbers are
detected. However, thanks to the large redshift path surveyed ($\Delta z=182$),
we provide constraints on the molecular column density distribution function
beyond $z\sim 0$. In addition, we probe column densities of N(H$_2$) >
10$^{16}$ atoms~cm$^{-2}$, five orders of magnitude lower than in previous
studies. We use the cosmological hydrodynamical simulation IllustrisTNG to show
that our upper limits of $\rho ({\rm H}_2)\lesssim 10^{8.3} \text{M}_{\odot}
\text{Mpc}^{-3}$ at $0 < z \leq 1.7$ already provide new constraints on current
theoretical predictions of the cold molecular phase of the gas. These results
are in agreement with recent CO emission-line surveys and are complementary to
those studies. The combined constraints indicate that the present decrease of
the cosmic star-formation rate history is consistent with an increasing
depletion of molecular gas in galaxies compared to $z\sim 2$. | astro-ph_GA |
HI-to-H$_2$ Transitions in Dust-Free Interstellar Gas: We present numerical computations and analysis of atomic to molecular
(HI-to-H$_2$) transitions in cool ($\sim$100 K) low-metallicity dust-free
(primordial) gas, in which molecule formation occurs via cosmic-ray driven
negative ion chemistry, and removal is by a combination of far-UV
photodissociation and cosmic-ray ionization and dissociation. For any gas
temperature, the behavior depends on the ratio of the Lyman-Werner (LW) band
FUV intensity to gas density, $I_{\rm LW}/n$, and the ratio of the cosmic-ray
ionization rate to the gas density, $\zeta/n$. We present sets of HI-to-H$_2$
abundance profiles for a wide range of $\zeta/n$ and $I_{\rm LW}/n$, for
dust-free gas. We determine the conditions for which H$_2$ absorption line
self-shielding in optically thick clouds enables a transition from atomic to
molecular form for ionization-driven chemistry. We also examine the effects of
cosmic-ray energy losses on the atomic and molecular density profiles and
transition points. For a unit Galactic interstellar FUV field intensity
($I_{\rm LW}=1$) with LW flux $2.07\times 10^7$ photons cm$^{-2}$ s$^{-1}$, and
a uniform cosmic-ray ionization rate $\zeta=10^{-16}$ s$^{-1}$, an HI-to-H$_2$
transition occurs at a total hydrogen gas column density of $4\times 10^{21}$
cm$^{-2}$, within $3\times 10^7$ yr, for a gas volume density of $n=10^6$
cm$^{-3}$ at 100 K. For these parameters, the dust-free limit obtains for a
dust-to-gas ratio Z$^\prime_d \lesssim 10^{-5}$, which may be reached for
overall metallicities $Z^\prime\lesssim 0.01$ relative to Galactic solar
values. | astro-ph_GA |
Neutral Hydrogen Observations of Low Surface Brightness Galaxies around
M101 and NGC 5485: We present atomic hydrogen (HI) observations using the Robert C. Byrd Green
Bank Telescope along the lines-of-sight to 27 low surface brightness (LSB)
dwarf galaxy candidates discovered in optical searches around M101. We detect
HI reservoirs in 5 targets and place stringent upper limits on the remaining
22, implying that they are gas poor. The distances to our HI detections range
from 7 Mpc --150 Mpc, demonstrating the utility of wide-bandpass HI
observations as a follow-up tool. The systemic velocities of 3 detections are
consistent with that of the NGC~5485 group behind M101, and we suggest that our
15 non-detections with lower distance limits from the optical are associated
with and have been stripped by that group. We find that the gas richnesses of
confirmed M101 satellites are broadly consistent with those of the Milky Way
satellites, as well as with those of satellites around other hosts of
comparable mass, when survey completeness is taken into account. This suggests
that satellite quenching and gas stripping proceeds similarly around halos of
similar mass, in line with theoretical expectations. | astro-ph_GA |
Evolution of virial clouds-I: from surface of last scattering up to the
formation of population-III stars: The analysis of WMAP and Planck CMB data has shown the presence of
temperature asymmetries towards the halos of several galaxies, which is
probably due to the rotation of clouds present in these halos about the
rotational axis of the galaxies. It had been proposed that these are hydrogen
clouds that {\it should} be in equilibrium with the CMB. However, standard
theory did not allow equilibrium of such clouds at the very low CMB
temperature, but it was recently shown that the equilibrium {\it could} be
stable. This still does not prove that the cloud concentration and that the
observed temperature asymmetry is due to clouds in equilibrium with the CMB. To
investigate the matter further, it would be necessary to trace the evolution of
such clouds, which we call "virial clouds", from their formation epoch to the
present, so as to confront the model with the observational data. The task is
to be done in two steps: (1) from the cloud formation before the formation of
first generation of stars; (2) from that time to the present. In this paper we
deal with the first step leaving the second one to a subsequent analysis. | astro-ph_GA |
Genetically modified halos: towards controlled experiments in
$Λ$CDM galaxy formation: We propose a method to generate `genetically-modified' (GM) initial
conditions for high-resolution simulations of galaxy formation in a
cosmological context. Building on the Hoffman-Ribak algorithm, we start from a
reference simulation with fully random initial conditions, then make controlled
changes to specific properties of a single halo (such as its mass and merger
history). The algorithm demonstrably makes minimal changes to other properties
of the halo and its environment, allowing us to isolate the impact of a given
modification. As a significant improvement over previous work, we are able to
calculate the abundance of the resulting objects relative to the reference
simulation. Our approach can be applied to a wide range of cosmic structures
and epochs; here we study two problems as a proof-of-concept. First, we
investigate the change in density profile and concentration as the collapse
time of three individual halos are varied at fixed final mass, showing good
agreement with previous statistical studies using large simulation suites.
Second, we modify the $z=0$ mass of halos to show that our theoretical
abundance calculations correctly recover the halo mass function. The results
demonstrate that the technique is robust, opening the way to controlled
experiments in galaxy formation using hydrodynamic zoom simulations. | astro-ph_GA |
Measuring the dust attenuation law of galaxies using photometric data: Fitting model spectral energy distributions (SED) to galaxy photometric data
is a widely used method to recover galaxy parameters from galaxy surveys.
However, the parameter space used to describe galaxies is wide and
interdependent, and distinctions between real and spurious correlations that
are found between these parameters can be difficult to discern. In this work,
we use the SED fitting code BAGPIPES to investigate degeneracies between galaxy
parameters and the effect of the choice of different sets of photometric bands.
In particular, we focus on optical to infrared wavelength coverage, and on two
parameters describing the galaxies' dust attenuation law: $A_V$ and $\delta$,
which characterize dust column density and the slope of a flexible dust
attenuation law, respectively. We demonstrate that 1) a degeneracy between the
residual (the difference between truth and recovered value) $A_V$ and star
formation rate exists, but this is lifted when WISE bands are included; 2)
BAGPIPES is able to accurately recover the input $A_V$ and $\delta$
distributions and relations (differences in slope of less than 1.7$\sigma$ for
a flat relation, less than 1.2$\sigma$ for an observationally-motivated
relation from Salim et al. 2018) and is not introducing spurious correlations
between these parameters. Our findings suggest that the information needed to
constrain $A_V$ and $\delta$ well enough individually exists in the data,
especially when IR is added. This indicates that recent works finding a
correlation between $A_V$ and $\delta$ are not being misled by fitting
degeneracies from their SED fitting code. | astro-ph_GA |
The OTELO survey: Nature and mass-metallicity relation for H$α$
emitters at $z\sim\,0.4$: A sample of low-mass H$\alpha$ emission line sources (ELS) at $z\,\sim\,0.4$
was studied in the context of the mass-metallicty relation (MZR) and its
possible evolution. We drew our sample from the OSIRIS Tunable Emission Line
Object (OTELO) survey, which exploits the red tunable filter of OSIRIS at the
Gran Telescopio Canarias to perform a blind narrow-band spectral scan in a
selected field of the Extended Groth Strip. We were able to directly measure
emission line fluxes and equivalent widths from the analysis of OTELO
pseudo-spectra. This study aims to explore the MZR in the very low-mass regime.
Our sample reaches stellar masses ($M_*$) as low as $10^{6.8}\,M_\odot$, where
63\% of the sample have $M_*\,<10^9\,M_\odot$. We also explore the relation of
the star formation rate (SFR) and specific SFR (sSFR) with $M_*$ and gas-phase
oxygen abundances, as well as the $M_*$-size relation and the morphological
classification. The $M_*$ were estimated using synthetic rest-frame colours.
Using an $\chi^2$ minimization method, we separated the contribution of
\Nii$\lambda$6583 to the H$\alpha$ emission lines. Using the N2 index, we
separated active galactic nuclei from star-forming galaxies (SFGs) and
estimated the gas metallicity. We studied the morphology of the sampled
galaxies qualitatively (visually) and quantitatively (automatically) using
high-resolution data from the \textit{Hubble Space Telescope}-ACS. The physical
size of the galaxies was derived from the morphological analysis using
\texttt{GALAPAGOS2/GALFIT}, where we fit a single-S\'ersic 2D model to each
source. | astro-ph_GA |
Detecting Low-Mass Perturbers in Cluster Lenses using Curved Arc Bases: Strong gravitationally lensed arcs produced by galaxy clusters have been
observationally detected for several decades now. These strong lensing
constraints provided high-fidelity mass models for cluster lenses that include
substructure down to $10^{9-10}\,\mathrm{M}_\odot$. Optimizing lens models,
where the cluster mass distribution is modeled by a smooth component and
subhalos associated with the locations of individual cluster galaxies, has
enabled deriving the subhalo mass function, providing important constraints on
the nature and granularity of dark matter. In this work, we explore and present
a novel method to detect and measure individual perturbers (subhalos,
line-of-sight halos, and wandering supermassive black holes) by exploiting
their proximity to highly distorted lensed arcs in galaxy clusters, and by
modeling the local lensing distortions with curved arc bases. This method
offers the possibility of detecting individual low-mass perturber subhalos in
clusters and halos along the line-of-sight down to a mass resolution of
$10^8\,\mathrm{M}_\odot$. We quantify our sensitivity to low-mass perturbers
($M\sim 10^{7-9}\,\mathrm{M}_\odot$) in clusters ($M\sim
10^{14-15}\mathrm{M}_\odot$), by creating realistic mock data. Using three
lensed images of a background galaxy in the cluster SMACS J0723, taken by the
$\textit{James Webb Space Telescope}$, we study the retrieval of the properties
of potential perturbers with masses $M=10^{7-9}\,\mathrm{M}_\odot$. From the
derived posterior probability distributions for the perturber, we constrain its
concentration, redshift, and ellipticity. By allowing us to probe lower-mass
substructures, the use of curved arc bases can lead to powerful constraints on
the nature of dark matter as discrimination between dark matter models appears
on smaller scales. | astro-ph_GA |
The formation and physical origin of highly ionized cooling gas: We present a simple model that explains the origin of warm diffuse gas seen
primarily as highly ionized absorption line systems in the spectra of
background sources. We predict the observed column densities of several highly
ionized transitions such as OVI, OVIII, NeVIII, NV, and MgX; and present a
unified comparison of the model predictions with absorption lines seen in the
Milky Way disk, Milky Way halo,starburst galaxies, the circumgalactic medium
and the intergalactic medium at low and high redshifts. We show that diffuse
gas seen in such diverse environments can be simultaneously explained by a
simple model of radiatively cooling gas. We show that most of such absorption
line systems are consistent with being collisionally ionized, and estimate the
maximum likelihood temperature of the gas in each observation. This model
satisfactorily explains why OVI is regularly observed around star-forming low-z
L* galaxies, and why NV is rarely seen around the same galaxies. We further
present some consequences of this model in quantifying the dynamics of the
cooling gas around galaxies and predict the shock velocities associated with
such flows. A unique strength of this model is that while it has only one free
(but physically well-constrained) parameter, it nevertheless successfully
reproduces the available data on O VI absorbers in the interstellar,
circumgalactic, intra-group, and intergalactic media, as well as the available
data on other absorption-line from highly ionized species. | astro-ph_GA |
The X-SHOOTER Lyman-$α$ survey at z=2 (XLS-z2) I: What makes a
galaxy a Lyman-$α$ emitter?: We present the first results from the X-SHOOTER Lyman-$\alpha$ survey at
$z=2$ (XLS-$z2$). XLS-$z2$ is a deep spectroscopic survey of 35 Lyman-$\alpha$
emitters (LAEs) utilising $\approx90$ hours of exposure time with VLT/X-SHOOTER
and covers rest-frame Ly$\alpha$ to H$\alpha$ emission with R$\approx4000$. We
present the sample selection, the observations and the data reduction. Systemic
redshifts are measured from rest-frame optical lines for 33/35 sources. In the
stacked spectrum, our LAEs are characterised by an interstellar medium with
little dust, a low metallicity and a high ionisation state. The ionising
sources are young hot stars that power strong emission-lines in the optical and
high ionisation lines in the UV. The LAEs exhibit clumpy UV morphologies and
have outflowing kinematics with blue-shifted SiII absorption, a broad [OIII]
component and a red-skewed Ly$\alpha$ line. Typically 30 % of the Ly$\alpha$
photons escape, of which one quarter on the blue side of the systemic velocity.
A fraction of Ly$\alpha$ photons escapes directly at the systemic suggesting
clear channels enabling a $\approx10$ % escape of ionising photons, consistent
with an inference based on MgII. A combination of a low effective HI column
density, a low dust content and young star-burst determine whether a star
forming galaxy is observed as a LAE. The first is possibly related to outflows
and/or a fortunate viewing angle, while we find that the latter two in LAEs are
typical for their stellar mass of 10$^9$ M$_{\odot}$. | astro-ph_GA |
Early Science with the Large Millimeter Telescope: discovery of the
12CO(1-0) emission line in the ring galaxy, VIIZw466: We report an early science discovery of the CO(1-0) emission line in the
collisional ring galaxy, VII Zw466, using the Redshift Search Receiver
instrument on the Large Millimeter Telescope Alfonso Serrano.The apparent
molecular-to-atomic gas ratio either places the ISM of VII Zw466 in the
HI-dominated regime or implies a large quantity of CO-dark molecular gas, given
its high star formation rate. The molecular gas densities and star formation
rate densities of VII Zw466 are consistent with the standard Kennicutt-Schmidt
star formation law even though we find this galaxy to be H2-deficient. The
choice of CO-to-H2 conversion factors cannot explain the apparent H2 deficiency
in its entirety. Hence, we find that the collisional ring galaxy, VII Zw466, is
either largely deficient in both H2 and HI or contains a large mass of CO-dark
gas. A low molecular gas fraction could be due to the enhancement of feedback
processes from previous episodes of star formation as a result of the
star-forming ISM being confined to the ring. We conclude that collisional ring
galaxy formation is an extreme form of galaxy interaction that triggers a
strong galactic-wide burst of star formation that may provide immediate
negative feedback towards subsequent episodes of star formation---resulting in
a short-lived star formation history or, at least, the appearance of a
molecular gas deficit. | astro-ph_GA |
Host Galaxy Properties and Black Hole Mass of Swift J164449.3+573451
from Multi-Wavelength Long-Term Monitoring and HST Data: We study the host galaxy properties of the tidal disruption object, Swift
J164449.3+573451 using long-term optical to near-infrared (NIR) data. First, we
decompose the galaxy surface brightness distribution and analyze the morphology
of the host galaxy using high resolution \emph{HST} WFC3 images. We conclude
that the host galaxy is a bulge-dominant galaxy that is well described by a
single S\'{e}rsic model with S\'{e}rsic index $n=3.43\pm0.05$. Adding a disk
component, the bulge to total host galaxy flux ratio (B/T) is $0.83\pm0.03$,
which still indicates a bulge-dominant galaxy. Second, we estimate multi-band
fluxes of the host galaxy through long-term light curves. Our long-term NIR
light curves reveal the pure host galaxy fluxes $\sim500$ days after the burst.
We fit spectral energy distribution (SED) models to the multi-band fluxes from
the optical to NIR of the host galaxy and determine its properties. The stellar
mass, the star formation rate, and the age of stellar population are
$\log(M_{\star}/M_{\odot}) = 9.14^{+0.13}_{-0.10}$, $0.03^{+0.28}_{-0.03}\,
M_{\odot}$/yr, and $0.63^{+0.95}_{-0.43}$ Gyr. Finally, we estimate the mass of
the central super massive black hole which is responsible for the tidal
disruption event. The black hole mass is estimated to be $10^{6.7\pm0.4}\,
M_{\odot}$ from $M_{\mathrm{BH}}$ - $M_{\star,\mathrm{bul}}$ and
$M_{\mathrm{BH}}$ - $L_{\mathrm{bul}}$ relations for the $K$ band, although a
smaller value of $\sim10^5\, M_{\odot}$ cannot be excluded convincingly if the
host galaxy harbors a pseudobulge. | astro-ph_GA |
Interactions of the Infrared bubble N4 with the surroundings: The physical mechanisms that induce the transformation of a certain mass of
gas in new stars are far from being well understood. Infrared bubbles
associated with HII regions have been considered to be good samples of
investigating triggered star formation. In this paper we report on the
investigation of the dust properties of the infrared bubble N4 around the HII
region G11.898+0.747, analyzing its interaction with its surroundings and star
formation histories therein, with the aim of determining the possibility of
star formation triggered by the expansion of the bubble. Using Herschel PACS
and SPIRE images with a wide wavelength coverage, we reveal the dust properties
over the entire bubble. Meanwhile, we are able to identify six dust clumps
surrounding the bubble, with a mean size of 0.50 pc, temperature of about 22 K,
mean column density of 1.7 $\times10^{22}$ cm$^{-2}$, mean volume density of
about 4.4 $\times10^{4}$ cm$^{-3}$, and a mean mass of 320 $M_{\odot}$. In
addition, from PAH emission seen at 8 $\mu$m, free-free emission detected at 20
cm and a probability density function in special regions, we could identify
clear signatures of the influence of the HII region on the surroundings. There
are hints of star formation, though further investigation is required to
demonstrate that N4 is the triggering source. | astro-ph_GA |
The Dust Properties of Bubble HII Regions as seen by Herschel: Because of their relatively simple morphology, "bubble" HII regions have been
instrumental to our understanding of star formation triggered by HII regions.
With the far-infrared (FIR) spectral coverage of the Herschel satellite, we can
access the wavelengths where these regions emit the majority of their energy
through their dust emission. At Herschel wavelengths 70 micron to 500 micron,
the emission associated with HII regions is dominated by the cool dust in their
photodissociation regions (PDRs). We find average dust temperatures of 26K
along the PDRs, with little variation between the HII regions in the sample,
while local filaments and infrared dark clouds average 19K and 15K
respectively. Higher temperatures lead to higher values of the Jeans mass,
which may affect future star formation. The mass of the material in the PDR,
collected through the expansion of the HII region, is between ~300 and ~10,000
Solar masses for the HII regions studied here. These masses are in rough
agreement with the expected masses swept up during the expansion of the \hii\
regions. Approximately 20% of the total FIR emission is from the direction of
the bubble central regions. This suggests that we are detecting emission from
the "near-side" and "far-side" PDRs along the line of sight and that bubbles
are three-dimensional structures. We find only weak support for a relationship
between dust temperature and beta, of a form similar to that caused by noise
and calibration uncertainties alone. | astro-ph_GA |
The Mechanical Alignment of Dust (MAD) I: On the spin-up process of
fractal grains by a gas-dust drift: Context: Aligned dust grains are commonly exploited to probe the magnetic
field orientation. However, the exact physical processes that result in a
coherent large-scale grain alignment are far from being constrained. Aims: In
this work, we aim to investigate the impact of a gas-dust drift leading to a
mechanical alignment of dust (MAD) and to dust polarization. Methods: We
explore fractal dust aggregates to statistically analyze the average alignment
behavior of distinct grain ensembles. The spin-up efficiencies for individual
aggregates are determined utilizing MC simulations. These efficiencies are
analyzed to identify stable points for the grain alignment in direction of the
gas-dust drift and along the magnetic field lines. Finally, the net dust
polarization is calculated per grain ensemble. Results: The mechanical spin-up
within the CNM is sufficient to drive grains to a stable alignment. A likely
mechanical grain alignment is parallel to the drift direction. All grains can
align at subsonic conditions. Here, we predict a polarization efficiency in the
order of unity for the MAD. A supersonic drift may result in a rapid rotation
where dust grains may become rotationally disrupted and the polarization
becomes drastically reduced. In the presence of a magnetic field, the drift
required for the alignment of elongated grains is roughly one order of
magnitude higher compared to the pure MAD. Here, the dust polarization
efficiency is 0.6-0.9 indicating that a drift can provide the prerequisites to
probe the magnetic field. The alignment is inefficient when the direction of
the drift and the field lines are perpendicular. Conclusions: We find that MAD
has to be taken into consideration as an alternative driving mechanism where
the standard RAT alignment theory fails to account for the full spectrum of
available dust polarization observations. | astro-ph_GA |
Neutral carbon and CO in 76 (U)LIRGs and starburst galaxy centers A
method to determine molecular gas properties in luminous galaxies: We present fluxes in both neutral carbon [CI] lines at the centers of 76
galaxies with FIR luminosities between 10^{9} and 10^{12} L(o) obtained with
Herschel-SPIRE and with ground-based facilities, along with the J=7-6, J=4-3,
J=2-1 12CO and J=2-1 13CO line fluxes. We investigate whether these lines can
be used to characterize the molecular ISM of the parent galaxies in simple ways
and how the molecular gas properties define the model results. In most
starburst galaxies, the [CI]/13CO flux ratio is much higher than in Galactic
star-forming regions, and it is correlated to the total FIR luminosity. The
[CI](1-0)/CO(4-3), the [CI](2-1) (2-1)/CO(7-6), and the [CI] (2-1)/(1-0) flux
ratios are also correlated, and trace the excitation of the molecular gas. In
the most luminous infrared galaxies (LIRGs), the ISM is fully dominated by
dense and moderately warm gas clouds that appear to have low [C]/[CO] and
[13CO]/[12CO] abundances. In less luminous galaxies, emission from gas clouds
at lower densities becomes progressively more important, and a multiple-phase
analysis is required to determine consistent physical characteristics. Neither
the CO nor the [CI] velocity-integrated line fluxes are good predictors of H2
column densities in individual galaxies, and X(CI) conversion factors are not
superior to X(CO) factors. The methods and diagnostic diagrams outlined in this
paper also provide a new and relatively straightforward means of deriving the
physical characteristics of molecular gas in high-redshift galaxies up to z=5,
which are otherwise hard to determine. | astro-ph_GA |
H2CO ortho-to-para ratio in the protoplanetary disk HD 163296: Ortho-to-para (o/p) ratios of species like water, ammonia and formaldehyde
(H2CO) are believed to encode information about the formation history of the
molecule. Measurements of o/p ratios in protoplanetary disks could thus be used
to constrain their physical and chemical histories. We present the first
measurement of the H2CO o/p ratio in a protoplanetary disk, using three ortho
and two para lines observed with the Sub-millimeter Array (SMA) combined with
one highly resolved measurement of a single H2CO line with ALMA toward the disk
around Herbig Ae star HD 163296. We find a disk-averaged H2CO o/p ratio of
1.8-2.8 (depending on the assumed disk structure), corresponding to a spin
temperature of 11-22 K. We also derive a rotational temperature of 24 K from
the flux ratio of the three ortho lines. The observed spatial distribution, as
seen by ALMA, as well as the rotational temperature and the o/p ratio, at the
large scales the SMA is most sensitive to, are consistent with a
low-temperature formation pathway, most likely grain surface chemistry, of H2CO
in this disk. | astro-ph_GA |
The Star Formation Reference Survey. II. Activity demographics and
host-galaxy properties for Infrared-selected galaxies: We present activity demographics and host-galaxy properties of
infrared-selected galaxies in the local Universe, using the representative Star
Formation Reference Survey (SFRS). Our classification scheme is based on a
combination of optical emission-line diagrams (BPT) and IR-color diagnostics.
Using the weights assigned to the SFRS galaxies based on its parent sample, a
far-infrared-selected sample comprises 71\% H\,\textsc{ii} galaxies, 13\%
Seyferts, 3\% Transition Objects (TOs), and 13\% Low-Ionization Nuclear
Emission-Line Regions (LINERs). For the SFRS H\,\textsc{ii} galaxies we derive
nuclear star-formation rates and gas-phase metallicities. We measure
host-galaxy metallicities for all galaxies with available long-slit
spectroscopy and abundance gradients for a subset of 12 face-on galaxies. The
majority of H\,\textsc{ii} galaxies show a narrow range of metallicities, close
to solar, and flat metallicity profiles. Based on their host-galaxy and nuclear
properties, the dominant ionizing source in the far-infrared selected TOs is
star-forming activity. LINERs are found mostly in massive hosts (median of
$10^{10.5}$ M$_{\odot} $), median $L(60\mu m) = 10^{9}$ L$_{\odot}$, median
dust temperatures of $ F60/F100 = 0.36 $, and median $L_{\textrm{H}\alpha}$
surface density of $ 10^{40.2} $ erg s$ ^{-1} $kpc$ ^{-2} $, indicating older
stellar populations as their main ionizing source rather than AGN activity. | astro-ph_GA |
Galaxy evolution within the Kilo-Degree Survey: The ESO Public Kilo-Degree Survey (KiDS) is an optical wide-field imaging
survey carried out with the VLT Survey Telescope and the OmegaCAM camera. KiDS
will scan 1500 square degrees in four optical filters (u, g, r, i). Designed to
be a weak lensing survey, it is ideal for galaxy evolution studies, thanks to
the high spatial resolution of VST, the good seeing and the photometric depth.
The surface photometry have provided with structural parameters (e.g. size and
S\'ersic index), aperture and total magnitudes have been used to derive
photometric redshifts from Machine learning methods and stellar
masses/luminositites from stellar population synthesis. Our project aimed at
investigating the evolution of the colour and structural properties of galaxies
with mass and environment up to redshift $z \sim 0.5$ and more, to put
constraints on galaxy evolution processes, as galaxy mergers. | astro-ph_GA |
A flux-ratio anomaly in the CO spectral line emission from
gravitationally-lensed quasar MG J0414+0534: We present an analysis of archival observations with the Atacama Large
(sub-)Millimetre Array (ALMA) of the gravitationally lensed quasar MG
J0414+0534, which show four compact images of the quasar and an Einstein ring
from the dust associated with the quasar host galaxy. We confirm that the
flux-ratio anomalies observed in the mid-infrared and radio persists into the
sub-mm for the continuum images of the quasar. We report the detection of CO
(11-10) spectral line emission, which traces a region of compact gas around the
quasar nucleus. This line emission also shows evidence of a flux-ratio anomaly
between the merging lensed images that is consistent with those observed at
other wavelengths, suggesting high-excitation CO can also provide a useful
probe of substructures that is unaffected by microlensing or dust extinction.
However, we do not detect the candidate dusty dwarf galaxy that was previously
reported with this dataset, which we conclude is due to a noise artefact. Thus,
the cause of the flux-ratio anomaly between the merging lensed images is still
unknown. The composite compact and diffuse emission in this system suggest
lensed quasar-starbursts will make excellent targets for detecting dark
sub-haloes and testing models for dark matter. | astro-ph_GA |
HH 80/81: Structure and Kinematics of the Fastest Protostellar Outflow: Hubble Space Telescope images obtained in 2018 are combined with archival HST
data taken in 1995 to detect changes and measure proper motions in the HH 80/81
shock complex which is powered by the fastest known jet driven by a forming
star, the massive object IRAS 18162-2048. Some persistent features close to the
radio jet axis have proper motions grater than 1,000 km/s away from IRAS
18162-2048. About 3 to 5 parsecs downstream from the IRAS source and beyond HH
80/81, H-alpha emission traces the rim of a parsec-scale bubble blown by the
jet. Lower speed motions are seen in [Sii] away from the jet axis; these
features have a large component of motion at right-angles to the jet. We
identify new HH objects and H2 shocks in the counterflow opposite HH 80/81. The
northeastern counterflow to HH 80/81 exhibits an extended but faint complex of
2.12 um H2 shocks. The inner portion of the outflow is traced by dim 1.64 um
[Feii] emission. The full extent of this outflow is at least 1,500" (about 10
pc in projection at a distance of 1.4 kpc). We speculate about the conditions
responsible for the production of the ultra-fast jet and the absence of
prominent large-scale molecular outflow lobes. | astro-ph_GA |
Rapid Chemical Enrichment by Intermittent Star Formation in GN-z11: We interpret the peculiar super-solar nitrogen abundance recently reported by
the James Webb Space Telescope observations for GN-z11 ($z=10.6$) using our
state-of-the-art chemical evolution models. The observed CNO ratios can be
successfully reproduced -- independently of the adopted initial mass function,
nucleosynthesis yields, and presence of supermassive ($>$1000$M_\odot$) stars
-- if the galaxy has undergone an intermittent star formation history with a
quiescent phase lasting $\sim$100 Myr, separating two strong starbursts.
Immediately after the second burst, Wolf--Rayet stars (up to $120M_\odot$)
become the dominant enrichment source, also temporarily ($<$1 Myr) enhancing
particular elements (N, F, Na, and Al) and isotopes ($^{13}$C and $^{18}$O).
Alternative explanations involving (i) single burst models, also including very
massive stars and/or pair-instability supernovae, or (ii) pre-enrichment
scenarios fail to match the data. Feedback-regulated, intermittent star
formation might be common in early systems. Elemental abundances can be used to
test this hypothesis and to get new insights on nuclear and stellar
astrophysics. | astro-ph_GA |
An All-Sky Sample of Intermediate-Mass Star-Forming Regions: We present an all-sky sample of 984 candidate intermediate-mass Galactic
star-forming regions color-selected from the Infrared Astronomical Satellite
(IRAS) Point Source Catalog and morphologically classify each object using
mid-infrared Wide-field Infrared Survey Explorer (WISE) images. Of the 984
candidates, 616 are probable star-forming regions (62.6%), 128 are filamentary
structures (13.0%), 39 are point-like objects of unknown nature (4.0%), and 201
are galaxies (20.4%). We conduct a study of four of these regions, IRAS
00259+5625, IRAS 00420+5530, IRAS 01080+5717, and IRAS 05380+2020, at Galactic
latitudes |b| > 5 degrees using optical spectroscopy from the Wyoming Infrared
Observatory along with near-infrared photometry from the Two-Micron All Sky
Survey to investigate their stellar content. New optical spectra,
color-magnitude diagrams, and color-color diagrams reveal their extinctions,
spectrophotometric distances, and the presence of small stellar clusters
containing 20-78 solar masses of stars. These low-mass diffuse star clusters
contain 65-250 stars for a typical initial mass function, including one or more
mid-B stars as their most massive constituents. Using infrared spectral energy
distributions we identify young stellar objects near each region and assign
probable masses and evolutionary stages to the protostars. The total infrared
luminosity lies in the range 190 to 960 solar luminosities, consistent with the
sum of the luminosities of the individually identified young stellar objects. | astro-ph_GA |
The Spitzer Local Volume Legacy (LVL) Global Optical Photometry: We present the global optical photometry of 246 galaxies in the Local Volume
Legacy (LVL) survey. The full volume-limited sample consists of 258 nearby (D <
11 Mpc) galaxies whose absolute B-band magnitude span a range of -9.6 < M_B <
-20.7 mag. A composite optical (UBVR) data set is constructed from observed
UBVR and SDSS ugriz imaging, where the ugriz magnitudes are transformed into
UBVR. We present photometry within three galaxy apertures defined at UV,
optical, and IR wavelengths. Flux comparisons between these apertures reveal
that the traditional optical R25 galaxy apertures do not fully encompass
extended sources. Using the larger IR apertures we find color-color
relationships where later-type spiral and irregular galaxies tend to be bluer
than earlier-type galaxies. These data provide the missing optical emission
from which future LVL studies can construct the full panchromatic
(UV-optical-IR) spectral energy distributions. | astro-ph_GA |
A VLT/FLAMES study of the peculiar intermediate-age Large Magellanic
Cloud star cluster NGC 1846 - I. Kinematics: In this paper we present high resolution VLT/FLAMES observations of red giant
stars in the massive intermediate-age Large Magellanic Cloud star cluster NGC
1846, which, on the basis of its extended main-sequence turn-off (EMSTO),
possesses an internal age spread of ~300 Myr. We describe in detail our target
selection and data reduction procedures, and construct a sample of 21 stars
possessing radial velocities indicating their membership of NGC 1846 at high
confidence. We consider high-resolution spectra of the planetary nebula Mo-17,
and conclude that this object is also a member of the cluster. Our measured
radial velocities allow us to conduct a detailed investigation of the internal
kinematics of NGC 1846, the first time this has been done for an EMSTO system.
The key result of this work is that the cluster exhibits a significant degree
of systemic rotation, of a magnitude comparable to the mean velocity
dispersion. Using an extensive suite of Monte Carlo models we demonstrate that,
despite our relatively small sample size and the substantial fraction of
unresolved binary stars in the cluster, the rotation signal we detect is very
likely to be genuine. Our observations are in qualitative agreement with the
predictions of simulations modeling the formation of multiple populations of
stars in globular clusters, where a dynamically cold, rapidly rotating second
generation is a common feature. NGC 1846 is less than one relaxation time old,
so any dynamical signatures encoded during its formation ought to remain
present. | astro-ph_GA |
Identification of Ambient Molecular Clouds Associated with Galactic
Supernova Remnant IC443: The Galactic supernova remnant (SNR) IC443 is one of the most studied
core-collapse SNRs for its interaction with molecular clouds. However, the
ambient molecular clouds with which IC443 is interacting have not been
thoroughly studied and remain poorly understood. Using Five College Radio
Astronomy Observatory 14m telescope, we obtained fully sampled maps of ~
1{\deg} \times 1{\deg} region toward IC443 in the 12CO J=1-0 and HCO+ J=1-0
lines. In addition to the previously known molecular clouds in the velocity
range v_lsr = -6 to -1 km/s (-3 km/s clouds), our observations reveal two new
ambient molecular cloud components: small (~ 1') bright clouds in v_lsr = -8 to
-3 km/s (SCs), and diffuse clouds in v_lsr = +3 to +10 km/s (+5 km/s clouds).
Our data also reveal the detailed kinematics of the shocked molecular gas in
IC443, however the focus of this paper is the physical relationship between the
shocked clumps and the ambient cloud components. We find strong evidence that
the SCs are associated with the shocked clumps. This is supported by the
positional coincidence of the SCs with shocked clumps and other tracers of
shocks. Furthermore, the kinematic features of some shocked clumps suggest that
these are the ablated material from the SCs upon the impact of the SNR shock.
The SCs are interpreted as dense cores of parental molecular clouds that
survived the destruction by the pre-supernova evolution of the progenitor star
or its nearby stars. We propose that the expanding SNR shock is now impacting
some of the remaining cores and the gas is being ablated and accelerated
producing the shocked molecular gas. The morphology of the +5 km/s clouds
suggests an association with IC443. On the other hand, the -3 km/s clouds show
no evidence for interaction. | astro-ph_GA |
Analysis of the interstellar matter at the periphery of the supershell
surrounding the CYG OB1 association in 2.12 micron molecular hydrogen line: We present observations of the vdB 130 cluster vicinity in a narrow-band
filter centered at a $2.12\,\mu$m molecular hydrogen line performed at the
Caucasus Mountain Observatory of the Lomonosov Moscow State University. The
observations reveal an H$_2$ emission shell around vdB 130, coincident with a
bright infrared shell, visible in all \textit{Spitzer} bands. Also, numerous
H$_{2}$ emission features are detected around infrared Blobs E and W and in the
vicinity of a protocluster located to the east of the shell, in a tail of a
cometary molecular cloud. H$_2$ emission in the vicinity of the vdB~130 cluster
is mostly generated in well-developed \HII\ regions and is of fluorescent
nature. In the protocluster area, isolated spots are observed, where H$_2$
emission is collisionally excited and is probably related to shocks in
protostellar outflows. Obtained results are discussed in the context of
possible sequential star formation in the vicinity of the vdB 130 cluster,
triggered by the interaction of the expanding supershell surrounding the Cyg
OB1 association with the molecular cloud and an associated molecular filament. | astro-ph_GA |
Magnetic Field of Molecular Gas Measured with the Velocity Gradient
Technique I. Orion A: Magnetic fields play an important role in the evolution of molecular clouds
and star formation. Using the Velocity Gradient Technique (VGT) model, we
measured the magnetic field in Orion A using the 12CO, 13CO, and C18O (1-0)
emission lines at a scale of 0.07 pc. The measured B-field shows an east-west
orientation that is perpendicular to the integral shaped filament of Orion A at
large scale. The VGT magnetic fields obtained from 13CO and C18O are in
agreement with the B-field that is measured from the Planck 353 GHz dust
polarization at a scale of 0.55 pc. Removal of density effects by using a
Velocity Decomposition Algorithm can significantly improve the accuracy of the
VGT in tracing magnetic fields with the 12CO (1-0) line. The magnetic field
strength of seven sub-clouds, OMC-1, OMC-2, OMC-3, OMC-4, OMC-5, L 1641-N, and
NGC 1999 has also been estimated with the Davis-Chandrasekhar-Fermi (DCF) and
MM2 technique, and these are found to be in agreement with previous results
obtained from dust polarization at far-infrared and sub-millimeter wavelengths.
At smaller scales, the VGT proves a good method to measure magnetic fields. | astro-ph_GA |
Gas morphology and energetics at the surface of PDRs: new insights with
Herschel observations of NGC 7023: We investigate the physics and chemistry of the gas and dust in dense
photon-dominated regions (PDRs), along with their dependence on the
illuminating UV field. Using Herschel-HIFI observations, we study the gas
energetics in NGC 7023 in relation to the morphology of this nebula. NGC 7023
is the prototype of a PDR illuminated by a B2V star and is one of the key
targets of Herschel. Our approach consists in determining the energetics of the
region by combining the information carried by the mid-IR spectrum (extinction
by classical grains, emission from very small dust particles) with that of the
main gas coolant lines. In this letter, we discuss more specifically the
intensity and line profile of the 158 micron (1901 GHz) [CII] line measured by
HIFI and provide information on the emitting gas. We show that both the [CII]
emission and the mid-IR emission from polycyclic aromatic hydrocarbons (PAHs)
arise from the regions located in the transition zone between atomic and
molecular gas. Using the Meudon PDR code and a simple transfer model, we find
good agreement between the calculated and observed [CII] intensities. HIFI
observations of NGC 7023 provide the opportunity to constrain the energetics at
the surface of PDRs. Future work will include analysis of the main coolant line
[OI] and use of a new PDR model that includes PAH-related species. | astro-ph_GA |
UVIT view of dwarf irregular galaxy IC 2574 : Is the star formation
triggered due to expanding H$~$I shells?: Star forming dwarf galaxies in the local volume are diverse and are ideal
test beds to understand details of star formation in a variety of environments.
Here, we present a deep FUV imaging study of a nearby dwarf irregular galaxy IC
2574 using the Ultraviolet Imaging Telescope (UVIT). We identified 419 FUV
bright regions with radii between 15 - 285 pc in the galaxy and found that
28.6\% of them to be located in H~I shells, 12.6\% inside holes and 60.1\% to
be away from the holes. The H~I column density is found to be more than
$10^{21} cm^{-2}$ for 82.3\% of the identified regions. 30 out of the 48 H~I
holes show triggered star formation in their shells while 16 holes do not show
any related FUV emission. Cross-matching with H$\alpha$ emission, we found that
23 holes have both FUV and H$\alpha$ emission in their shells signifying very
recent trigger. Therefore, star formation in the galaxy has been partly
triggered due to the expanding H~I holes whereas in majority of the sites it is
driven by other mechanisms. Irrespective of the location, larger star forming
complexes were found to have multiple sub-structures. We report two resolved
components for the remnant cluster of the super giant shell and estimated their
masses. The star formation rate of IC 2574 is found to be 0.57 $M_{\odot}$/yr,
which is slightly higher compared to the average value of other nearby dwarf
irregular galaxies. | astro-ph_GA |
The star formation history in the solar neighborhood as told by massive
white dwarfs: White dwarfs are the remnants of low and intermediate mass stars. Because of
electron degeneracy, their evolution is just a simple gravothermal process of
cooling. Recently, thanks to Gaia data, it has been possible to construct the
luminosity function of massive (0.9 < M/Msun < 1.1) white dwarfs in the solar
neighborhood (d < 100 pc). Since the lifetime of their progenitors is very
short, the birth times of both, parents and daughters, are very close and allow
to reconstruct the (effective) star formation rate. This rate started growing
from zero during the early Galaxy and reached a maximum 6-7 Gyr ago. It
declined and ~5 Gyr ago started to climb once more reaching a maximum 2 - 3 Gyr
in the past and decreased since then. There are some traces of a recent star
formation burst, but the method used here is not appropriate for recently born
white dwarfs. | astro-ph_GA |
Still at Odds with Conventional Galaxy Evolution: The Star Formation
History of Ultra-Diffuse Galaxy Dragonfly 44: We study the star formation history (SFH) of the ultra-diffuse galaxy (UDG)
Dragonfly 44 (DF44) based on the simultaneous fit to near-ultraviolet to
near-infrared photometry and high signal-to-noise optical spectroscopy. In
fitting the observations we adopt an advanced physical model with a flexible
SFH, and we discuss the results in the context of the degeneracies between
stellar population parameters. Through reconstructing the mass-assembly history
with a prior for extended star formation (akin to methods in the literature) we
find that DF44 formed 90 per cent of its stellar mass by $z\sim 0.9$ ($\sim
7.2$ Gyr ago). In comparison, using a prior that prefers concentrated star
formation (as informed by previous studies of DF44's stellar populations)
suggests that DF44 formed as early as $z\sim 8$ ($\sim 12.9$ Gyr ago).
Regardless of whether DF44 is old or very old, the SFHs imply early star
formation and rapid quenching. This result, together with DF44's large size and
evidence that it is on its first infall into the Coma cluster, challenges UDG
formation scenarios from simulations that treat all UDGs as contiguous with the
canonical dwarf population. While our results cannot confirm any particular
formation scenario, we can conclude from this that DF44 experienced a rare
quenching event. | astro-ph_GA |
DNC/HNC and N2D+/N2H+ ratios in high-mass star forming cores: Chemical models predict that the deuterated fraction (the column density
ratio between a molecule containing D and its counterpart containing H) of
N2H+, Dfrac(N2H+), is high in massive pre-protostellar cores and rapidly drops
of an order of magnitude after the protostar birth, while that of HNC,
Dfrac(HNC), remains constant for much longer. We tested these predictions by
deriving Dfrac(HNC) in 22 high-mass star forming cores divided in three
different evolutionary stages, from high-mass starless core candidates (HMSCs,
8) to high-mass protostellar objects (HMPOs, 7) to Ultracompact HII regions
(UCHIIs, 7). For all of them, Dfrac (N2H+) was already determined through
IRAM-30m Telescope observations, which confirmed the theoretical rapid decrease
of Dfrac(N2H+) after protostar birth (Fontani et al. 2011). Therefore our
comparative study is not affected by biases introduced by the source selection.
We have found average Dfrac(HNC) of 0.012, 0.009 and 0.008 in HMSCs, HMPOs and
UCHIIs, respectively, with no statistically significant differences among the
three evolutionary groups. These findings confirm the predictions of the
chemical models, and indicate that large values of Dfrac(N2H+) are more
suitable than large values of Dfrac(HNC) to identify cores on the verge of
forming high-mass stars, likewise what found in the low-mass regime. | astro-ph_GA |
The Einasto model for dark matter haloes: Context: The Einasto model has become one of the most popular models for
describing the density profile of dark matter haloes. There have been
relatively few comprehensive studies on the dynamical structure of the Einasto
model, mainly because only a limited number of properties can be calculated
analytically. Aims: We want to systematically investigate the photometric and
dynamical structure of the family of Einasto models over the entire model
parameter space. Methods: We used the SpheCow code to explore the properties of
the Einasto model. We systematically investigated how the most important
properties change as a function of the Einasto index $n$. We considered both
isotropic models and radially anisotropic models with an Osipkov-Merritt
orbital structure. Results: We find that all Einasto models with $n<\tfrac12$
have a formal isotropic or Osipkov-Merritt distribution function that is
negative in parts of phase space, and hence cannot be supported by such orbital
structures. On the other hand, all models with larger values of $n$ can be
supported by an isotropic orbital structure, or by an Osipkov-Merritt
anisotropy, as long as the anisotropy radius is larger than a critical value.
This critical anisotropy radius is a decreasing function of $n$, indicating
that less centrally concentrated models allow for a larger degree of radial
anisotropy. Conclusions: Studies of the structure and dynamics of models for
galaxies and dark matter haloes should not be restricted to completely
analytical models. Numerical codes such as SpheCow can help open up the range
of models that are systematically investigated. This applies to the Einasto
model discussed here, but also to other proposed models for dark matter haloes,
including different extensions to the Einasto model. | astro-ph_GA |
Warm Molecular Gas in the Central Parsecs of the Buried Nucleus of NGC
4418 Traced with the Fundamental CO Ro-vibrational Absorptions: We investigated the inner buried nucleus of a nearby luminous infrared galaxy
NGC 4418 using high-resolution spectroscopy of fundamental carbon monoxide (CO)
ro-vibrational absorptions around $4.67 \mu$m for the first time. This method
allowed us to examine the physical and kinematical properties in the hot inner
region of this nucleus. We detected a series of both very deep (partly
saturated) $^{12}$CO and moderately deep (optically thin) $^{13}$CO absorption
lines and inferred a large column density ($N_\mathrm{H2}=(5\pm3)\times10^{23}$
cm$^{-2}$ in front of the $5 \mu$m photosphere) of warm
($T_\mathrm{ex}\simeq170$ K) molecular gas by assuming an isothermal
plane-parallel slab illuminated by a compact background MIR-emitting source. We
modeled that the warm CO absorber almost covers the central heating source and
that it is an inner layer around the $5 \mu$m photosphere (at $r=$several pc)
of a compact shroud of gas and dust ($d\sim100$ pc). The width of the
absorption lines ($110$ km s$^{-1}$) and their small deviation from the
systemic velocity ($<10$ km s$^{-1}$) are consistent with a warm and turbulent
layer with little bulk motion in the radial direction. | astro-ph_GA |
Dynamical masses of brightest cluster galaxies II: constraints on the
stellar IMF: We use stellar and dynamical mass profiles, combined with a stellar
population analysis, of 32 brightest cluster galaxies (BCGs) at redshifts of
0.05 $\leq z \leq$ 0.30, to place constraints on their stellar Initial Mass
Function (IMF). We measure the spatially-resolved stellar population properties
of the BCGs, and use it to derive their stellar mass-to-light ratios
($\Upsilon_{\star \rm POP}$). We find young stellar populations ($<$200 Myr) in
the centres of 22 per cent of the sample, and constant $\Upsilon_{\star \rm
POP}$ within 15 kpc for 60 per cent of the sample. We further use the stellar
mass-to-light ratio from the dynamical mass profiles of the BCGs
($\Upsilon_{\star \rm DYN}$), modelled using a Multi-Gaussian Expansion (MGE)
and Jeans Anisotropic Method (JAM), with the dark matter contribution
explicitly constrained from weak gravitational lensing measurements. We
directly compare the stellar mass-to-light ratios derived from the two
independent methods, $\Upsilon_{\star \rm POP}$ (assuming some IMF) to
$\Upsilon_{\star \rm DYN}$ for the subsample of BCGs with no young stellar
populations and constant $\Upsilon_{\star \rm POP}$. We find that for the
majority of these BCGs, a Salpeter (or even more bottom-heavy) IMF is needed to
reconcile the stellar population and dynamical modelling results although for a
small number of BCGs, a Kroupa (or even lighter) IMF is preferred. For those
BCGs better fit with a Salpeter IMF, we find that the mass-excess factor
against velocity dispersion falls on an extrapolation (towards higher masses)
of known literature correlations. We conclude that there is substantial scatter
in the IMF amongst the highest-mass galaxies. | astro-ph_GA |
A population of dust-enshrouded objects orbiting the Galactic black hole: The central 0.1 parsecs of the Milky Way host a supermassive black hole
identified with the position of the radio and infrared source Sagittarius A*, a
cluster of young, massive stars (the S stars) and various gaseous features.
Recently, two unusual objects have been found to be closely orbiting
Sagittarius A*: the so-called G sources, G1 and G2. These objects are
unresolved (having a size of the order of 100 astronomical units, except at
periapse, where the tidal interaction with the black hole stretches them along
the orbit) and they show both thermal dust emission and line emission from
ionized gas. G1 and G2 have generated attention because they appear to be
tidally interacting with the supermassive Galactic black hole, possibly
enhancing its accretion activity. No broad consensus has yet been reached
concerning their nature: the G objects show the characteristics of gas and dust
clouds but display the dynamical properties of stellar-mass objects. Here we
report observations of four additional G objects, all lying within 0.04 parsecs
of the black hole and forming a class that is probably unique to this
environment. The widely varying orbits derived for the six G objects
demonstrate that they were commonly but separately formed. | astro-ph_GA |
ISM properties of a Massive Dusty Star-Forming Galaxy discovered at z ~
7: We report the discovery and constrain the physical conditions of the
interstellar medium of the highest-redshift millimeter-selected dusty
star-forming galaxy (DSFG) to date, SPT-S J031132-5823.4 (hereafter
SPT0311-58), at $z=6.900 +/- 0.002$. SPT0311-58 was discovered via its 1.4mm
thermal dust continuum emission in the South Pole Telescope (SPT)-SZ survey.
The spectroscopic redshift was determined through an ALMA 3mm frequency scan
that detected CO(6-5), CO(7-6) and [CI](2-1), and subsequently confirmed by
detections of CO(3-2) with ATCA and [CII] with APEX. We constrain the
properties of the ISM in SPT0311-58 with a radiative transfer analysis of the
dust continuum photometry and the CO and [CI] line emission. This allows us to
determine the gas content without ad hoc assumptions about gas mass scaling
factors. SPT0311-58 is extremely massive, with an intrinsic gas mass of $M_{\rm
gas} = 3.3 \pm 1.9 \times10^{11}\,M_{\odot}$. Its large mass and intense star
formation is very rare for a source well into the Epoch of Reionization. | astro-ph_GA |
Orbital tori for non-axisymmetric galaxies: Our Galaxy's bar makes the Galaxy's potential distinctly non-axisymmetric.
All orbits are affected by non-axisymmetry, and significant numbers are
qualitatively changed by being trapped at a resonance with the bar. Orbital
tori are used to compute these effects. Thick-disc orbits are no less likely to
be trapped by corotation or a Lindblad resonance than thin-disc orbits.
Perturbation theory is used to create non-axisymmetric orbital tori from
standard axisymmetric tori, and both trapped and untrapped orbits are recovered
to surprising accuracy. Code is added to the TorusModeller library that makes
it as easy to manipulate non-axisymmetric tori as axisymmetric ones. The
augmented TorusModeller is used to compute the velocity structure of the solar
neighbourhood for bars of different pattern speeds and a simple action-based
distribution function. The technique developed here can be applied to any
non-axisymmetric potential that is stationary in a rotating from - hence also
to classical spiral structure. | astro-ph_GA |
Discovery of the Magellanic Stellar Stream Out to 100 Kiloparsecs: The Magellanic Stream (MS) - an enormous ribbon of gas spanning $140^\circ$
of the southern sky trailing the Magellanic Clouds - has been exquisitely
mapped in the five decades since its discovery. However, despite concerted
efforts, no stellar counterpart to the MS has been conclusively identified.
This stellar stream would reveal the distance and 6D kinematics of the MS,
constraining its formation and the past orbital history of the Clouds. We have
been conducting a spectroscopic survey of the most distant and luminous red
giant stars in the Galactic outskirts. From this dataset, we have discovered a
prominent population of 13 stars matching the extreme angular momentum of the
Clouds, spanning up to $100^\circ$ along the MS at distances of $60-120$ kpc.
Furthermore, these kinemetically-selected stars lie along a
[$\alpha$/Fe]-deficient track in chemical space from $-2.5 < \mathrm{[Fe/H]} <
-0.5$, consistent with their formation in the Clouds themselves. We identify
these stars as high-confidence members of the Magellanic Stellar Stream. Half
of these stars are metal-rich and closely follow the gaseous MS, whereas the
other half are more scattered and metal-poor. We argue that the metal-rich
stream is the recently-formed tidal counterpart to the MS, and speculate that
the metal-poor population was thrown out of the SMC outskirts during an earlier
interaction between the Clouds. The Magellanic Stellar Stream provides a strong
set of constraints - distances, 6D kinematics, and birth locations - that will
guide future simulations towards unveiling the detailed history of the Clouds. | astro-ph_GA |
History-independent tracers: Forgetful molecular probes of the physical
conditions of the dense interstellar medium: Molecular line emission is a powerful probe of the physical conditions of
astrophysical objects but can be complex to model, and it is often unclear
which transitions would be the best targets for observers who wish to constrain
a given parameter. We therefore produce a list of molecular species for which
the gas history can be ignored, removing a major modelling complexity. We then
determine the best of these species to observe when attempting to constrain
various physical parameters. To achieve this, we use a large set of chemical
models with different chemical histories to determine which species have
abundances at 1 MYr that are insensitive to the initial conditions. We then use
radiative transfer modelling to produce the intensity of every transition of
these molecules. We finally compute the mutual information between the physical
parameters and all transitions and transition ratios in order to rank their
usefulness in determining the value of a given parameter.
We find 48 species that are insensitive to the chemical history of the gas,
23 of which have collisional data available. We produce a ranked list of all
the transitions and ratios of these species using their mutual information with
various gas properties. We show mutual information is an adequate measure of
how well a transition can constrain a physical parameter by recovering known
probes and demonstrating that random forest regression models become more
accurate predictors when high-scoring features are included. Therefore, this
list can be used to select target transitions for observations in order to
maximize knowledge about those physical parameters. | astro-ph_GA |
The black hole and host galaxy growth in an isolated $z\sim 6$ QSO
observed with ALMA: The outstanding mass growth of supermassive black holes (SMBHs) at the
Reionisation Epoch and how it is related to the concurrent growth of their host
galaxies, poses challenges to theoretical models aimed at explaining how these
systems formed in short timescales (<1 Gyr). To trace the average evolutionary
paths of quasi-stellar objects (QSOs) and their host galaxies in the BH
mass-host mass ($M_{\rm dyn}$) plane, we compare the star formation rate (SFR),
derived from the accurate estimate of the dust temperature and the dust mass
($T_{\rm dust}, M_{\rm dust}$), with the BH accretion rate. To this aim, we
analysed a deep, $900$ pc resolution ALMA observation of the sub-mm continuum,
[CII] and H$_2$O of the $z\sim 6$ QSO J2310+1855, enabling a detailed study of
dust properties and cold gas kinematics. We performed an accurate SED analysis
obtaining a dust temperature of $T_{\rm dust} = 71$ K and a dust mass of
$M_{\rm dust}= 4.4 \times 10^8\ \rm M_{\odot}$. The implied AGN-corrected SFR
is $1240 \ \rm M_{\odot}yr^{-1}$, a factor of 2 smaller than previously
reported for this QSO. We derived the best estimate of the dynamical mass
$M_{\rm dyn} = 5.2\times 10^{10}\ \rm M_{\odot}$ within $r = 1.7$ kpc, based on
a dynamical model of the system. We found that ${\rm SFR}/M_{\rm dyn}>\dot
M_{\rm BH}/M_{\rm BH}$, suggesting that AGN feedback might be efficiently
acting to slow down the SMBH accretion, while the stellar mass assembly is
still vigorously taking place in the host galaxy. In addition, we were also
able to detect high-velocity emission on the red and blue sides of the [CII]
emission line, that traces a gaseous outflow, and for the first time, we mapped
a spatially-resolved water vapour disk through the H$_2$O v=0
$3_{(2,2)}-3_{(1,3)}$ emission line detected at $\nu_{\rm obs} = 274.074$ GHz,
whose kinematic properties and size are broadly consistent with those of the
[CII] disk. | astro-ph_GA |
MMT Spectroscopy of Lyman-alpha at z$\simeq$7: Evidence for Accelerated
Reionization Around Massive Galaxies: Reionization-era galaxies tend to exhibit weak Ly$\alpha$ emission, likely
reflecting attenuation from an increasingly neutral IGM. Recent observations
have begun to reveal exceptions to this picture, with strong Ly$\alpha$
emission now known in four of the most massive z=7$-$9 galaxies in the CANDELS
fields, all of which also exhibit intense [OIII]$+$H$\beta$ emission (EW$>$800
$\mathrm{\mathring{A}}$). To better understand why Ly$\alpha$ is anonymously
strong in a subset of massive z$\simeq$7$-$9 galaxies, we have initiated an
MMT/Binospec survey targeting a larger sample (N=22) of similarly luminous
($\simeq$1$-$6 L$^{\ast}_{\mathrm{UV}}$) z$\simeq$7 galaxies selected over very
wide-area fields ($\sim$3 deg$^2$). We confidently ($>$7$\sigma$) detect
Ly$\alpha$ in 78% (7/9) of galaxies with strong [OIII]$+$H$\beta$ emission
(EW$>$800 $\mathrm{\mathring{A}}$) as opposed to only 8% (1/12) of galaxies
with more moderate (EW=200$-$800 $\mathrm{\mathring{A}}$) [OIII]$+$H$\beta$. We
argue that the higher Ly$\alpha$ EWs of the strong [OIII]$+$H$\beta$ population
likely reflect enhanced ionizing photon production efficiency owing to their
large sSFRs ($\gtrsim$30 Gyr$^{-1}$). We also find evidence that Ly$\alpha$
transmission from massive galaxies declines less rapidly over $6<z<7$ than in
low-mass lensed systems. In particular, our data suggest no strong evolution in
Ly$\alpha$ transmission, consistent with a picture wherein massive z$\simeq$7
galaxies often reside in large ionized regions. We detect three
closely-separated ($R$ = 1.7 physical Mpc) z$\simeq$7 Ly$\alpha$ emitters in
our sample, conceivably tracing a large ionized structure that is consistent
with this picture. We detect tentative evidence for an overdensity in this
region, implying a large ionizing photon budget in the surrounding volume. | astro-ph_GA |
Dark-ages Reionization & Galaxy Formation Simulation I: The dynamical
lives of high redshift galaxies: We present the Dark-ages Reionization and Galaxy-formation Observables from
Numerical Simulations (DRAGONS) program and Tiamat, the collisionless N-body
simulation program upon which DRAGONS is built. The primary trait
distinguishing Tiamat from other large simulation programs is its density of
outputs at high redshift (100 from z=35 to z=5; roughly one every 10 Myr)
enabling the construction of very accurate merger trees at an epoch when galaxy
formation is rapid and mergers extremely frequent. We find that the
friends-of-friends halo mass function agrees well with the prediction of Watson
et al. at high masses, but deviates at low masses, perhaps due to our use of a
different halo finder or perhaps indicating a break from "universal" behaviour.
We then analyse the dynamical evolution of galaxies during the Epoch of
Reionization finding that only a small fraction (~20%) of galactic halos are
relaxed. We illustrate this using standard relaxation metrics to establish two
dynamical recovery time-scales: i) halos need ~1.5 dynamical times following
formation, and ii) ~2 dynamical times following a major (3:1) or minor (10:1)
merger to be relaxed. This is remarkably consistent across a wide mass range.
Lastly, we use a phase-space halo finder to illustrate that major mergers drive
long-lived massive phase-space structures which take many dynamical times to
dissipate. This can yield significant differences in the inferred mass build-up
of galactic halos and we suggest that care must be taken to ensure a physically
meaningful match between the galaxy-formation physics of semi-analytic models
and the halo finders supplying their input. | astro-ph_GA |
Galaxy And Mass Assembly (GAMA): Accurate Panchromatic Photometry from
Optical Priors using LAMBDAR: We present the Lambda Adaptive Multi-Band Deblending Algorithm in R
(LAMBDAR), a novel code for calculating matched aperture photometry across
images that are neither pixel- nor PSF-matched, using prior aperture
definitions derived from high resolution optical imaging. The development of
this program is motivated by the desire for consistent photometry and
uncertainties across large ranges of photometric imaging, for use in
calculating spectral energy distributions. We describe the program,
specifically key features required for robust determination of panchromatic
photometry: propagation of apertures to images with arbitrary resolution, local
background estimation, aperture normalisation, uncertainty determination and
propagation, and object deblending. Using simulated images, we demonstrate that
the program is able to recover accurate photometric measurements in both
high-resolution, low-confusion, and low-resolution, high-confusion, regimes. We
apply the program to the 21-band photometric dataset from the Galaxy And Mass
Assembly (GAMA) Panchromatic Data Release (PDR; Driver et al. 2016), which
contains imaging spanning the far-UV to the far-IR. We compare photometry
derived from LAMBDAR with that presented in Driver et al. (2016), finding broad
agreement between the datasets. Nonetheless, we demonstrate that the photometry
from LAMBDAR is superior to that from the GAMA PDR, as determined by a
reduction in the outlier rate and intrinsic scatter of colours in the LAMBDAR
dataset. We similarly find a decrease in the outlier rate of stellar masses and
star formation rates using LAMBDAR photometry. Finally, we note an exceptional
increase in the number of UV and mid-IR sources able to be constrained, which
is accompanied by a significant increase in the mid-IR colour-colour
parameter-space able to be explored. | astro-ph_GA |
Quantifying the Significance of the Magnetic Field from Large-Scale
Cloud to Collapsing Core: Self-Similarity, Mass-to-Flux Ratio and Star
Formation Efficiency: Dust polarization observational results are analyzed for the high-mass star
formation region W51 from the largest parent cloud ($\sim$ 2~pc, JCMT) to the
large-scale envelope ($\sim$ 0.5~pc, BIMA) down to the collapsing core e2
($\sim$ 60~mpc, SMA). Magnetic field and dust emission gradient orientations
reveal a correlation which becomes increasingly more tight with higher
resolution. The previously developed polarization - intensity gradient method
(Koch et al. 2012) is applied in order to quantify the magnetic field
significance. This technique provides a way to estimate the local magnetic
field force compared to gravity without the need of any mass or field strength
measurements, solely making use of measured angles which reflect the
geometrical imprint of the various forces. All three data sets clearly show
regions with distinct features in the field-to-gravity force ratio. Azimuthally
averaged radial profiles of this force ratio reveal a transition from a field
dominance at larger distances to a gravity dominance closer to the emission
peaks. Normalizing these profiles to a characteristic core scale points toward
self-similarity. Furthermore, the polarization intensity-gradient method is
linked to the mass-to-flux ratio, providing a new approach to estimate the
latter one without mass and field strength inputs. A transition from a
magnetically supercritical to a subcritical state as a function of distance
from the emission peak is found for the e2 core. Finally, based on the measured
radius-dependent field-to-gravity force ratio we derive a modified star
formation efficiency with a diluted gravity force. Compared to a standard
(free-fall) efficiency, the observed field is capable of reducing the
efficiency down to 10\% or less. | astro-ph_GA |
The impact of JWST broad-band filter choice on photometric redshift
estimation: The determination of galaxy redshifts in James Webb Space Telescope (JWST)'s
blank-field surveys will mostly rely on photometric estimates, based on the
data provided by JWST's Near-Infrared Camera (NIRCam) at 0.6-5.0 {\mu}m and Mid
Infrared Instrument (MIRI) at {\lambda}>5.0 {\mu}m. In this work we analyse the
impact of choosing different combinations of NIRCam and MIRI broad-band filters
(F070W to F770W), as well as having ancillary data at {\lambda}<0.6 {\mu}m, on
the derived photometric redshifts (zphot) of a total of 5921 real and simulated
galaxies, with known input redshifts z=0-10. We found that observations at
{\lambda}<0.6 {\mu}m are necessary to control the contamination of high-z
samples by low-z interlopers. Adding MIRI (F560W and F770W) photometry to the
NIRCam data mitigates the absence of ancillary observations at {\lambda}<0.6
{\mu}m and improves the redshift estimation. At z=7-10, accurate zphot can be
obtained with the NIRCam broad bands alone when S/N>=10, but the zphot quality
significantly degrades at S/N<=5. Adding MIRI photometry with one magnitude
brighter depth than the NIRCam depth allows for a redshift recovery of 83-99%,
depending on SED type, and its effect is particularly noteworthy for galaxies
with nebular emission. The vast majority of NIRCam galaxies with [F150W]=29 AB
mag at z=7-10 will be detected with MIRI at [F560W, F770W]<28 mag if these
sources are at least mildly evolved or have spectra with emission lines
boosting the mid-infrared fluxes. | astro-ph_GA |
High redshift JWST predictions from IllustrisTNG: III. Infrared
luminosity functions, obscured star formation and dust temperature of
high-redshift galaxies: We post-process galaxies in the IllustrisTNG simulations with SKIRT radiative
transfer calculations to make predictions for the rest-frame near-infrared
(NIR) and far-infrared (FIR) properties of galaxies at $z\geq 4$. The
rest-frame $K$- and $z$-band galaxy luminosity functions from TNG are overall
consistent with observations, despite a $\sim 0.5\,\mathrm{dex}$
underprediction at $z=4$ for $M_{\rm K}\lesssim -25$ and $M_{\rm z}\lesssim
-24$. Predictions for the JWST MIRI observed galaxy luminosity functions and
number counts are given. Based on theoretical estimations, we show that the
next-generation survey conducted by JWST can detect 500 (30) galaxies in F1000W
in a survey area of $500\,{\rm arcmin}^{2}$ at $z=6$ ($z=8$). As opposed to the
consistency in the UV, optical and NIR, we find that TNG, combined with our
dust modelling choices, significantly underpredicts the abundance of most
dust-obscured and thus most luminous FIR galaxies. As a result, the obscured
cosmic star formation rate density (SFRD) and the SFRD contributed by
optical/NIR dark objects are underpredicted. The discrepancies discovered here
could provide new constraints on the sub-grid feedback models, or the dust
contents, of simulations. Meanwhile, although the TNG predicted dust
temperature and its relations with IR luminosity and redshift are qualitatively
consistent with observations, the peak dust temperature of $z\geq 6$ galaxies
are overestimated by about $20\,{\rm K}$. This could be related to the limited
mass resolution of our simulations to fully resolve the porosity of the
interstellar medium (or specifically its dust content) at these redshifts. | astro-ph_GA |
Formation of the first galaxies in the aftermath of the first supernovae: We perform high-resolution cosmological hydrodynamic simulations to study the
formation of the first galaxies that reach the masses of
$10^{8-9}~h^{-1}~M_\odot$ at $z=9$. The resolution of the simulations is high
enough to resolve minihaloes and allow us to successfully pursue the formation
of multiple Population (Pop) III stars, their supernova (SN) explosions,
resultant metal-enrichment of the inter-galactic medium (IGM) in the course of
the build-up of the system. Metals are ejected into the IGM by multiple Pop III
SNe, but some of the metal-enriched gas falls back onto the halo after $\gtrsim
100~\rm Myr$. The star formation history of the first galaxy depends
sensitively on the initial mass function (IMF) of Pop III stars. The dominant
stellar population transits from Pop III to Pop II at $z\sim 12-15$ in the case
of power-law Pop III IMF, ${\rm d}n/{\rm d}M \propto M^{-2.35}$ with the mass
range $10-500~M_\odot$. At $z\lesssim 12$, stars are stably formed in the first
galaxies with a star formation rate of $\sim 10^{-3}$-$10^{-1}~M_\odot/{\rm
yr}$. In contrast, for the case with a flat IMF, gas-deprived first galaxies
form due to frequent Pop III pair-instability SNe, resulting in the suppression
of subsequent Pop II star formation. In addition, we calculate UV continuum,
Ly$\alpha$- and H$\alpha$-line fluxes from the first galaxies. We show that the
James Webb Space Telescope will be able to detect both UV continuum, Ly$\alpha$
and H$\alpha$ line emission from first galaxies with halo mass $\gtrsim
10^{9}~M_\odot$ at $z \gtrsim 10$. | astro-ph_GA |
Application of Convolutional Neural Networks to Predict Magnetic Fields
Directions in Turbulent Clouds: We adopt the deep learning method CASI-3D (Convolutional Approach to
Structure Identification-3D) to infer the orientation of magnetic fields in
sub-/trans- Alfvenic turbulent clouds from molecular line emission. We carry
out magnetohydrodynamic simulations with different magnetic field strengths and
use these to generate synthetic observations. We apply the 3D radiation
transfer code RADMC-3d to model 12CO and 13CO (J = 1-0) line emission from the
simulated clouds and then train a CASI-3D model on these line emission data
cubes to predict magnetic field morphology at the pixel level. The trained
CASI-3D model is able to infer magnetic field directions with low error (<
10deg for sub-Alfvenic samples and <30deg for trans-Alfvenic samples). We
furthermore test the performance of CASI-3D on a real sub-/trans- Alfvenic
region in Taurus. The CASI-3D prediction is consistent with the magnetic field
direction inferred from Planck dust polarization measurements. We use our
developed methods to produce a new magnetic field map of Taurus that has a
three-times higher angular resolution than the Planck map. | astro-ph_GA |
The Extremely Luminous Quasar Survey in the Pan-STARRS 1 Footprint
(PS-ELQS): We present the results of the Extremely Luminous Quasar Survey in the $3\pi$
survey of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS;
PS1). This effort applies the successful quasar selection strategy of the
Extremely Luminous Survey in the Sloan Digital Sky Survey footprint
($\sim12,000\,\rm{deg}^2$) to a much larger area
($\sim\rm{21486}\,\rm{deg}^2$). This spectroscopic survey targets the most
luminous quasars ($M_{1450}\le-26.5$; $m_{i}\le18.5$) at intermediate redshifts
($z\ge2.8$). Candidates are selected based on a near-infrared JKW2 color cut
using WISE AllWISE and 2MASS photometry to mainly reject stellar contaminants.
Photometric redshifts ($z_{\rm{reg}}$) and star-quasar classifications for each
candidate are calculated from near-infrared and optical photometry using the
supervised machine learning technique random forests. We select 806 quasar
candidates at $z_{\rm{reg}}\ge2.8$ from a parent sample of 74318 sources. After
exclusion of known sources and rejection of candidates with unreliable
photometry, we have taken optical identification spectra for 290 of our 334
good PS-ELQS candidates. We report the discovery of 190 new $z\ge2.8$ quasars
and an additional 28 quasars at lower redshifts. A total of 44 good PS-ELQS
candidates remain unobserved. Including all known quasars at $z\ge2.8$, our
quasar selection method has a selection efficiency of at least $77\%$. At lower
declinations $-30\le\rm{Decl.}\le0$ we approximately triple the known
population of extremely luminous quasars. We provide the PS-ELQS quasar catalog
with a total of 592 luminous quasars ($m_{i}\le18.5$, $z\ge2.8$). This unique
sample will not only be able to provide constraints on the volume density and
quasar clustering of extremely luminous quasars, but also offers valuable
targets for studies of the intergalactic medium. | astro-ph_GA |
A gas cloud on its way towards the super-massive black hole in the
Galactic Centre: Measurements of stellar orbits provide compelling evidence that the compact
radio source Sagittarius A* at the Galactic Centre is a black hole four million
times the mass of the Sun. With the exception of modest X-ray and infrared
flares, Sgr A* is surprisingly faint, suggesting that the accretion rate and
radiation efficiency near the event horizon are currently very low. Here we
report the presence of a dense gas cloud approximately three times the mass of
Earth that is falling into the accretion zone of Sgr A*. Our observations
tightly constrain the cloud's orbit to be highly eccentric, with an innermost
radius of approach of only ~3,100 times the event horizon that will be reached
in 2013. Over the past three years the cloud has begun to disrupt, probably
mainly through tidal shearing arising from the black hole's gravitational
force. The cloud's dynamic evolution and radiation in the next few years will
probe the properties of the accretion flow and the feeding processes of the
super-massive black hole. The kilo-electronvolt X-ray emission of Sgr A* may
brighten significantly when the cloud reaches pericentre. There may also be a
giant radiation flare several years from now if the cloud breaks up and its
fragments feed gas into the central accretion zone. | astro-ph_GA |
Spectropolarimetry of the changing-look active galactic nucleus Mrk 1018: We have obtained new spectropolarimetric observations at visible wavelengths
of the changing-look active galactic nucleus (AGN) Mrk 1018. The AGN direct
spectrum shows an extremely weak continuum with faint broad H$\beta$ and
H$\alpha$ emission lines. Both lines can be fit with a single very broad
emission line component of full width at half maximum FWHM $\simeq$ 7200 km
s$^{-1}$, with no evidence of the additional 3000 km s$^{-1}$-wide component
that was previously detected. While this is in agreement with line formation in
a Keplerian disk, the line profile variability suggests that the broad emission
line region is likely more complex. The continuum polarization of Mrk 1018 is
low; it is not higher in the current faint state compared to the past bright
state, confirming that dust obscuration is not the mechanism at the origin of
the change of look. The polarization profile of the H$\alpha$ line is
asymmetric with no rotation of the polarization angle, which possibly reveals
line formation in a polar outflow. Alternatively, the polarization profile may
be the consequence of a time delay between the direct and the polarized light.
Interestingly, the polarization signatures predicted for broad lines emitted
around supermassive binary black holes are not observed. | astro-ph_GA |
Implications of the SPEAR FUV Maps on Our Understanding of the ISM: The distribution of a low-density transition temperature (10^4.5 - 10^5.5 K)
gas in the interstellar medium conveys the character and evolution of diffuse
matter in the Galaxy. This difficult to observe component of the ISM emits
mainly in the far-ultraviolet (FUV) (912-1800 {\AA}) band. We describe spectral
maps of FUV emission lines from the highly ionized species CIV and OVI likely
to be the dominant cooling mechanisms of transition temperature gas in the ISM.
The maps were obtained using an orbital spectrometer, SPEAR, that was launched
in 2003 and has observed the FUV sky with a spectral resolution of \sim 550 and
an angular resolution of 10'. We compare distribution of flux in these maps
with three basic models of the distribution of transition temperature gas. We
find that the median distribution of CIV and OVI emission is consistent with
the spatial distribution and line ratios expected from a McKee-Ostriker (MO)
type model of evaporative interfaces. However, the intensities are a factor of
three higher than would be expected at the MO preferred parameters. Some high
intensity regions are clearly associated with supernova remnants and
superbubble structures. Others may indicate regions where gas is cooling
through the transition temperature. | astro-ph_GA |
Galactic Wind in the Nearby Starburst Galaxy NGC 253 Observed with the
Kyoto3DII Fabry-Perot Mode: We have observed the central region of the nearby starburst galaxy NGC 253
with the Kyoto Tridimensional Spectrograph II (Kyoto3DII) Fabry-Perot mode in
order to investigate the properties of its galactic wind. Since this galaxy has
a large inclination, it is easy to observe its galactic wind. We produced the
Ha, [N II]6583, and [S II]6716,6731 images, as well as those line ratio maps.
The [N II]/Ha ratio in the galactic wind region is larger than those in H II
regions in the galactic disk. The [N II]/Ha ratio in the southeastern filament,
a part of the galactic wind, is the largest and reaches about 1.5. These large
[N II]/Ha ratios are explained by shock ionization/excitation. Using the [S
II]/Ha ratio map, we spatially separate the galactic wind region from the
starburst region. The kinetic energy of the galactic wind can be sufficiently
supplied by supernovae in a starburst region in the galactic center. The shape
of the galactic wind and the line ratio maps are non-axisymmetric about the
galactic minor axis, which is also seen in M82. In the [N II]6583/[S
II]6716,6731 map, the positions with large ratios coincide with the positions
of star clusters found in the Hubble Space Telescope (HST) observation. This
means that intense star formation causes strong nitrogen enrichment in these
regions. Our unique data of the line ratio maps including [S II] lines have
demonstrated their effectiveness for clearly distinguishing between shocked gas
regions and starburst regions, determining the extent of galactic wind and its
mass and kinetic energy, and discovering regions with enhanced nitrogen
abundance. | astro-ph_GA |
The AGORA High-Resolution Galaxy Simulations Comparison Project: We introduce the AGORA project, a comprehensive numerical study of
well-resolved galaxies within the LCDM cosmology. Cosmological hydrodynamic
simulations with force resolutions of ~100 proper pc or better will be run with
a variety of code platforms to follow the hierarchical growth, star formation
history, morphological transformation, and the cycle of baryons in and out of 8
galaxies with halo masses M_vir ~= 1e10, 1e11, 1e12, and 1e13 Msun at z=0 and
two different ("violent" and "quiescent") assembly histories. The numerical
techniques and implementations used in this project include the smoothed
particle hydrodynamics codes GADGET and GASOLINE, and the adaptive mesh
refinement codes ART, ENZO, and RAMSES. The codes will share common initial
conditions and common astrophysics packages including UV background,
metal-dependent radiative cooling, metal and energy yields of supernovae, and
stellar initial mass function. These are described in detail in the present
paper. Subgrid star formation and feedback prescriptions will be tuned to
provide a realistic interstellar and circumgalactic medium using a
non-cosmological disk galaxy simulation. Cosmological runs will be
systematically compared with each other using a common analysis toolkit, and
validated against observations to verify that the solutions are robust - i.e.,
that the astrophysical assumptions are responsible for any success, rather than
artifacts of particular implementations. The goals of the AGORA project are,
broadly speaking, to raise the realism and predictive power of galaxy
simulations and the understanding of the feedback processes that regulate
galaxy "metabolism." The proof-of-concept dark matter-only test of the
formation of a galactic halo with a z=0 mass of M_vir ~= 1.7e11 Msun by 9
different versions of the participating codes is also presented to validate the
infrastructure of the project. | astro-ph_GA |
Strong suppression of star formation and spiral arm formation in disk
galaxies with counter-rotating gas disks: Galaxy-wide star formation can be quenched by a number of physical processes
such as environmental effects (e.g., ram pressure stripping) and supernova
feedback. Using numerical simulations, we here demonstrate that star formation
can be severely suppressed in disk galaxies with their gas disks
counter-rotating with respect to their stellar disks. This new mechanism of
star formation suppression (or quenching) does not depend so strongly on model
parameters of disk galaxies, such as bulge-to-disk- ratios and gas mass
fractions. Such severe suppression of star formation is due largely to the
suppression of the gas density enhancing mechanism i.e spiral arm formation in
disk galaxies with counter-rotating gas. Our simulations also show that
molecular hydrogen and dust can be rather slowly consumed by star formation in
disk galaxies with counter-rotating gas disks (i.e., long gas depletion
timescale). Based on these results, we suggest that spiral and S0 galaxies with
counter-rotation can have rather low star formation rate for their gas
densities. Also we suggest that a minor fraction of S0 galaxies have no
prominent spiral arms, because they have a higher fraction of counter-rotating
gas. We predict that poststarburst E+A disk galaxies with cold gas could have
counter-rotating gas. | astro-ph_GA |
Comparisons of Different Fitting Methods for the Physical Parameters of
A Star Cluster Sample of M33 with Spectroscopy and Photometry: Star clusters are good tracers for formation and evolution of galaxies. We
compared different fitting methods by using spectra (or by combining
photometry) to determine the physical parameters. We choose a sample of 17 star
clusters in M33, which previously lacked spectroscopic observations. The
low-resolution spectra were taken with the Xinglong 2.16-m reflector of NAOC.
The photometry used in the fitting includes $\rm u_{SC}$ and $\rm v_{SAGE}$
bands from the SAGE survey, as well as the published $UBVRI$ and $ugriz$
photometry. We firstly derived ages and metallicities with the {\sc ULySS}
(Vazdekis et al. and {\sc pegase-hr}) SSP model and the Bruzual \& Charlot
(2003) (BC03) stellar population synthesis models for the full-spectrum
fitting. The fitting results of both the BC03 and {\sc ULySS} models seem
consistent with those of previous works as well. Then we add the SAGE $\rm
u_{SC}$ and $\rm v_{SAGE}$ photometry in the spectroscopic fitting with the
BC03 models. It seems the results become much better, especially for the Padova
2000+Chabrier IMF set. Finally we add more photometry data, $UBVRI$ and
$ugriz$, in the fitting and we found that the results do not improve
significantly. Therefore, we conclude that the photometry is useful for
improving the fitting results, especially for the blue bands ($\lambda <4000$
{\AA}), e.g., $\rm u_{SC}$ and $\rm v_{SAGE}$ band. At last, we discuss the
"UV-excess" for the star clusters and we find five star clusters have
UV-excess, based on the $GALEX$ FUV, NUV photometry. | astro-ph_GA |
Testing Galaxy Formation Simulations with Damped Lyman-$α$
Abundance and Metallicity Evolution: We examine the properties of damped Lyman-$\alpha$ absorbers (DLAs) emerging
from a single set of cosmological initial conditions in two state-of-the-art
cosmological hydrodynamic simulations: {\sc Simba} and {\sc Technicolor Dawn}.
The former includes star formation and black hole feedback treatments that
yield a good match with low-redshift galaxy properties, while the latter uses
multi-frequency radiative transfer to model an inhomogeneous ultraviolet
background (UVB) self-consistently and is calibrated to match the Thomson
scattering optical depth, UVB amplitude, and Ly-$\alpha$ forest mean
transmission at $z>5$. Both simulations are in reasonable agreement with the
measured stellar mass and star formation rate functions at $z\geq 3$, and both
reproduce the observed neutral hydrogen cosmological mass density, $\Omega_{\rm
HI}(z)$. However, the DLA abundance and metallicity distribution are sensitive
to the galactic outflows' feedback and the UVB amplitude. Adopting a strong UVB
and/or slow outflows under-produces the observed DLA abundance, but yields
broad agreement with the observed DLA metallicity distribution. By contrast,
faster outflows eject metals to larger distances, yielding more metal-rich DLAs
whose observational selection may be more sensitive to dust bias. The DLA
metallicity distribution in models adopting an ${\rm H}_2$-regulated star
formation recipe includes a tail extending to $[M/H] \ll -3$, lower than any
DLA observed to date, owing to curtailed star formation in low-metallicity
galaxies. Our results show that DLA observations play an imporant role in
constraining key physical ingredients in galaxy formation models, complementing
traditional ensemble statistics such as the stellar mass and star formation
rate functions. | astro-ph_GA |
Image Stacking Analysis of SDSS Galaxies with AKARI Far-Infrared
Surveyor Maps at 65μm, 90μm, and 140μm: We perform image stacking analysis of Sloan Digital Sky Survey (SDSS)
photometric galaxies over the AKARI Far-Infrared Surveyor (FIS) maps at
65{\mu}m, 90{\mu}m, and 140{\mu}m. The resulting image profiles are decomposed
into the central galaxy component (single term) and the nearby galaxy component
(clustering term), as a function of the r-band magnitude, m_r of the central
galaxy. We find that the mean far-infrared (FIR) flux of a galaxy with
magnitude m_r is well fitted with f^s_{90{\mu}m}=13*10^{0.306(18-m_r)}[mJy].
The FIR amplitude of the clustering term is consistent with that expected from
the angular-correlation function of the SDSS galaxies, but galaxy morphology
dependence needs to be taken into account for a more quantitative conclusion.
We also fit the spectral energy distribution of stacked galaxies at 65{\mu}m,
90{\mu}m, and 140{\mu}m, and derive a mean dust temperature of ~30K. This is
consistent with the typical dust temperature of galaxies that are FIR luminous
and individually detected. | astro-ph_GA |
Lyman continuum leakage in faint star-forming galaxies at redshift
z=3-3.5 probed by gamma-ray bursts: We present the observations of Lyman continuum (LyC) emission in the
afterglow spectra of GRB 191004B at $z=3.5055$, together with those of the
other two previously known LyC-emitting long gamma-ray bursts (LGRB) (GRB
050908 at $z=3.3467$, and GRB 060607A at $z=3.0749$), to determine their LyC
escape fraction and compare their properties. From the afterglow spectrum of
GRB 191004B we determine a neutral hydrogen column density at the LGRB redshift
of $\log(N_{\rm HI}/cm^{-2})= 17.2 \pm 0.15$, and negligible extinction
($A_{\rm V}=0.03 \pm 0.02$ mag). The only metal absorption lines detected are
CIV and SiIV. In contrast to GRB 050908 and GRB 060607A, the host galaxy of GRB
191004B displays significant Ly$\alpha$ emission. From its Ly$\alpha$ emission
and the non-detection of Balmer emission lines we constrain its star-formation
rate (SFR) to $1 \leq$ SFR $\leq 4.7$ M$_{\odot}\ yr^{-1}$. We fit the
Ly$\alpha$ emission with a shell model and find parameters values consistent
with the observed ones. The absolute LyC escape fractions we find for GRB
191004B, GRB 050908 and GRB 060607A are of $0.35^{+0.10}_{-0.11}$,
$0.08^{+0.05}_{-0.04}$ and $0.20^{+0.05}_{-0.05}$, respectively. We compare the
LyC escape fraction of LGRBs to the values of other LyC emitters found from the
literature, showing that LGRB afterglows can be powerful tools to study LyC
escape for faint high-redshift star-forming galaxies. Indeed we could push LyC
leakage studies to much higher absolute magnitudes. The host galaxies of the
three LGRB presented here have all $M_{\rm 1600} > -19.5$ mag, with the GRB
060607A host at $M_{\rm 1600} > -16$ mag. LGRB hosts may therefore be
particularly suitable for exploring the ionizing escape fraction in galaxies
that are too faint or distant for conventional techniques. Furthermore the time
investment is very small compared to galaxy studies. [Abridged] | astro-ph_GA |
PACS photometry of the Herschel Reference Survey -
Far-infrared/sub-millimeter colours as tracers of dust properties in nearby
galaxies: We present Herschel/PACS 100 and 160 micron integrated photometry for the 323
galaxies in the Herschel Reference Survey (HRS), a K-band-, volume-limited
sample of galaxies in the local Universe. Once combined with the Herschel/SPIRE
observations already available, these data make the HRS the largest
representative sample of nearby galaxies with homogeneous coverage across the
100-500 micron wavelength range. In this paper, we take advantage of this
unique dataset to investigate the properties and shape of the
far-infrared/sub-millimeter spectral energy distribution in nearby galaxies. We
show that, in the stellar mass range covered by the HRS (8<log(M*/Msun)<12),
the far-infrared/sub-millimeter colours are inconsistent with a single modified
black-body having the same dust emissivity index beta for all galaxies. In
particular, either beta decreases, or multiple temperature components are
needed, when moving from metal-rich/gas-poor to metal-poor/gas-rich galaxies.
We thus investigate how the dust temperature and mass obtained from a single
modified black-body depend on the assumptions made on beta. We show that, while
the correlations between dust temperature, galaxy structure and star formation
rate are strongly model dependent, the dust mass scaling relations are much
more reliable, and variations of beta only change the strength of the observed
trends. | astro-ph_GA |
On the Tremaine-Weinberg method: how much can we trust gas tracers to
measure pattern speeds?: Pattern speeds are a fundamental parameter of the dynamical features (e.g.
bars, spiral arms) of a galaxy, setting resonance locations. Pattern speeds are
not directly observable, so the Tremaine-Weinberg (TW) method has become the
most common method used to measure them in galaxies. However, it has not been
tested properly whether this method can straightforwardly be applied to gas
tracers, despite this being widely done in the literature. When applied to
observations, the TW method may return invalid results, which are difficult to
diagnose due to a lack of ground truth for comparison. Although some works
applying the TW method to simulated galaxies exist, only stellar populations
have been tested. Therefore, here we explore the applicability of the TW method
for gas gracers, by applying it to hydrodynamical simulations of galaxies,
where we know the true value of the bar pattern speed. We perform some simple
tests to see if the TW method has a physically reasonable output. We add
different kinds of uncertainties (e.g. in position angle or flux) to the data
to mock observational errors based on the magnitude of uncertainty present in
the observations. Second, we test the method on 3D simulations with chemical
networks. We show that in general, applying TW to observations of gas will not
recover the true pattern speed. These results have implications for many
"pattern speeds" reported in the literature, and based on these tests we also
give some best practices for measuring pattern speeds using gas tracers going
forwards. | astro-ph_GA |
Interacting Galactic Neutral Hydrogen Filaments and Associated
High-Frequency Continuum Emission: Galactic HI emission profiles in an area where several large-scale filaments
at velocities ranging from -46 km/s to 0 km/s overlap were decomposed into
Gaussian components. Eighteen families of components defined by similarities of
center velocity and line width were identified and related to small-scale
structure in the high-frequency continuum emission observed by the WMAP
spacecraft, as evidenced in the Internal Linear Combination (ILC) map of
Hinshaw et al. (2007). When the center velocities of the Gaussian families,
which summarize the properties of all the HI along the lines-of-sight in a
given area, are used to focus on HI channel maps the phenomenon of close
associations between HI and ILC peaks reported in previous papers is
dramatically highlighted. Of particular interest, each of two pairs of HI peaks
straddles a continuum peak. The previously hypothesized model for producing the
continuum radiation (Verschuur, 2010) involving free-free emission from
electrons is re-examined in the light of the new data. By choosing reasonable
values for the parameters required to evaluate the model, the distance for
associated HI-ILC features is of order 30 to 100 pc. No associated H-alpha
radiation is expected because the electrons involved exist throughout the Milky
Way. The mechanism for clumping and separation of neutrals and electrons needs
to be explored. | astro-ph_GA |
Seeds of Life in Space SOLIS. IX. Chemical segregation of $\rm SO_2$ and
SO toward the low-mass protostellar shocked region of L1157: We present observations of SO and $\rm SO_2$ lines toward the shocked regions
along the L1157 chemically rich outflow, taken in the context of the Seeds Of
Life In Space IRAM-NOrthern Extended Millimeter Array Large Program, and
supported by data from Submillimeter Array and IRAM-30 m telescope at 1.1--3.6
mm wavelengths. We simultaneously analyze, for the first time, all of the
brightest shocks in the blueshifted lobe, namely, B0, B1, and B2. We found the
following. (1) SO and $\rm SO_2$ may trace different gas, given that the
large(-scale) velocity gradient analysis indicates for $\rm SO_2$ a volume
density ($\rm 10^5\text{--}10^6\,cm^{-3}$) denser than that of the gas emitting
in SO by a factor up to an order of magnitude. (2) Investigating the 0.1 pc
scale field of view, we note a tentative gradient along the path of the
precessing jet. More specifically, $\rm \chi({SO/SO_2})$ decreases from the
B0-B1 shocks to the older B2. (3) At a linear resolution of 500--1400 au, a
tentative spatial displacement between the two emitting molecules is detected,
with the SO peak closer (with respect to $\rm SO_2$) to the position where the
recent jet is impinging on the B1 cavity wall. Our astrochemical modeling shows
that the SO and $\rm SO_2$ abundances evolve on timescales less than about 1000
years. Furthermore, the modeling requires high abundances ($2\times10^{-6}$) of
both $\rm H_2S/H$ and S/H injected in the gas phase due to the shock
occurrence, so pre-frozen OCS only is not enough to reproduce our new
observations. | astro-ph_GA |
A new method for unveiling Open Clusters in Gaia: new nearby Open
Clusters confirmed by DR2: The publication of the Gaia Data Release 2 (Gaia DR2) opens a new era in
Astronomy. It includes precise astrometric data (positions, proper motions and
parallaxes) for more than $1.3$ billion sources, mostly stars. To analyse such
a vast amount of new data, the use of data mining techniques and machine
learning algorithms are mandatory. The search for Open Clusters, groups of
stars that were born and move together, located in the disk, is a great example
for the application of these techniques. Our aim is to develop a method to
automatically explore the data space, requiring minimal manual intervention. We
explore the performance of a density based clustering algorithm, DBSCAN, to
find clusters in the data together with a supervised learning method such as an
Artificial Neural Network (ANN) to automatically distinguish between real Open
Clusters and statistical clusters. The development and implementation of this
method to a $5$-Dimensional space ($l$, $b$, $\varpi$, $\mu_{\alpha^*}$,
$\mu_\delta$) to the Tycho-Gaia Astrometric Solution (TGAS) data, and a
posterior validation using Gaia DR2 data, lead to the proposal of a set of new
nearby Open Clusters. We have developed a method to find OCs in astrometric
data, designed to be applied to the full Gaia DR2 archive. | astro-ph_GA |
The clumpiness of molecular clouds: HCO+ (3--2) survey near Herbig-Haro
objects: Some well-studied Herbig Haro objects have associated with them one or more
cold, dense, and quiescent clumps of gas. We propose that such clumps near an
HH object can be used as a general measure of clumpiness in the molecular cloud
that contains that HH object. Our aim is to make a survey of clumps around a
sample of HH objects, and to use the results to make an estimate of the
clumpiness in molecular clouds. All known cold, dense, and quiescent clumps
near HH objects are anomalously strong HCO+ emitters. Our method is, therefore,
to search for strong HCO+ emission as an indicator of a clump near to an HH
object. The searches were made using JCMT and SEST in the HCO+ 3-2 and also
H13CO+ 1-0 lines, with some additional searches for methanol and sulphur
monoxide lines. The sources selected were a sample of 22 HH objects in which no
previous HCO+ emission had been detected. We find that half of the HH objects
have clumps detected in the HCO+ 3-2 line and that all searches in H13CO$+ 1-0
lines show evidence of clumpiness. All condensations have narrow linewidths and
are evidently unaffected dynamically by the HH jet shock. We conclude that the
molecular clouds in which these HH objects are found must be highly
heterogeneous on scales of less than 0.1 pc. An approximate calculation based
on these results suggests that the area filling factor of clumps affected by HH
objects is on the order of 10%. These clumps have gas number densities larger
than 3e4 cm-2. | astro-ph_GA |
JADES: A large population of obscured, narrow line AGN at high redshift: We present the identification of 42 narrow-line active galactic nuclei
(type-2 AGN) candidates in the two deepest observations of the JADES
spectroscopic survey with JWST/NIRSpec. The spectral coverage and the depth of
our observations allow us to select narrow-line AGNs based on both rest-frame
optical and UV emission lines up to z=10. Due to the metallicity decrease of
galaxies, at $z>3$ the standard optical diagnostic diagrams (N2-BPT or S2-VO87)
become unable to distinguish many AGN from other sources of photoionisation.
Therefore, we also use high ionisation lines, such as HeII$\lambda$4686,
HeII$\lambda$1640, NeIV$\lambda$2422, NeV$\lambda$3420, and NV$\lambda$1240,
also in combination with other UV transitions, to trace the presence of AGN.
Out of a parent sample of 209 galaxies, we identify 42 type-2 AGN (although 10
of them are tentative), giving a fraction of galaxies in JADES hosting type-2
AGN of about $20\pm3$\%, which does not evolve significantly in the redshift
range between 2 and 10. The selected type-2 AGN have estimated bolometric
luminosities of $10^{41.3-44.9}$ erg s$^{-1}$ and host-galaxy stellar masses of
$10^{7.2-9.3}$ M$_{\odot}$. The star formation rates of the selected AGN host
galaxies are consistent with those of the star-forming main sequence. The AGN
host galaxies at z=4-6 contribute $\sim$8-30 \% to the UV luminosity function,
slightly increasing with UV luminosity. | astro-ph_GA |
An Active Galactic Nucleus Recognition Model based on Deep Neural
Network: To understand the cosmic accretion history of supermassive black holes,
separating the radiation from active galactic nuclei (AGNs) and star-forming
galaxies (SFGs) is critical. However, a reliable solution on photometrically
recognising AGNs still remains unsolved. In this work, we present a novel AGN
recognition method based on Deep Neural Network (Neural Net; NN). The main
goals of this work are (i) to test if the AGN recognition problem in the North
Ecliptic Pole Wide (NEPW) field could be solved by NN; (ii) to shows that NN
exhibits an improvement in the performance compared with the traditional,
standard spectral energy distribution (SED) fitting method in our testing
samples; and (iii) to publicly release a reliable AGN/SFG catalogue to the
astronomical community using the best available NEPW data, and propose a better
method that helps future researchers plan an advanced NEPW database. Finally,
according to our experimental result, the NN recognition accuracy is around
80.29% - 85.15%, with AGN completeness around 85.42% - 88.53% and SFG
completeness around 81.17% - 85.09%. | astro-ph_GA |
Evidence for a Rotational Component in the Circumgalactic Medium of
Nearby Galaxies: We present results of a study comparing the relative velocity of $\rm
Ly\alpha$ absorbers to the rotation velocity of nearby galaxy disks in the
local universe ($z \leq 0.03$). We have obtained rotation curves via long-slit
spectroscopy of eight galaxies with the Southern African Large Telescope, and
combine this dataset with an additional 16 galaxies with data from the
literature. Each galaxy appears within $3R_{\rm vir}$ of a QSO sightline with
archival Cosmic Origin Spectrograph (COS) spectra. We study the velocity
orientation of absorbers with respect to nearby galaxy's rotation, and compare
with results from both the Steidel et al. (2002) monolithic halo model and a
new cylindrical Navarro-Frenk-White galaxy halo model to interpret these data
in the context of probing 3D galaxy halos via 1D QSO absorption-line
spectroscopy. Relative to these models we find that up to $59\pm5\%$ of $\rm
Ly\alpha$ absorbers have velocities consistent with co-rotation. We find the
$\rm Ly\alpha$ co-rotation fraction to decrease with galaxy luminosity ($L^*$)
and impact parameter in a model-independent fashion. We report that both
anti-rotating absorbers and those found near luminous galaxies ($L \gtrsim 0.5
L^*$) mostly have low Doppler $b$-parameters ($b \lesssim 50$ km $\rm s^{-1}$).
Absorbers consistent with co-rotation show a wide range of Doppler
$b$-parameters. Finally, we find a strong anticorrelation between co-rotation
fraction and galaxy inclination, which is at odds with recent metal-line
kinematic studies and suggests the kinematic and geometric distribution of the
circumgalactic medium is complex and multiphase. | astro-ph_GA |
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