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Photometry and Kinematics of Self-Gravitating Eccentric Nuclear Disks: The Andromeda Galaxy hosts an elongated nucleus with (at least) two distinct
brightness peaks. The double nucleus can be explained by the projection of a
thick, apsidally-aligned eccentric nuclear disk of stars in orbit about the
central black hole. Several nearby early-type galaxies have similar asymmetric
nuclear features, indicating the possible presence of eccentric nuclear disks.
We create simulated photometric (surface density) and kinematic (line-of-sight
velocity) maps of eccentric nuclear disks using N-body simulations. We image
our simulations from various lines of sight in order to classify them as double
nuclei, offset nuclei, and centered nuclei. We explore the effects of mass
segregation on the photometric maps, finding that heavier stars are
concentrated in the brighter peak. The average line-of-sight velocity values
are lower in an eccentric nuclear disk than for a circular ring about the
supermassive black hole. The velocity dispersion values are higher and peak at
the position of the supermassive black hole, which does not typically match the
peak in photometry. | astro-ph_GA |
Infrared Contributions of X-Ray Selected Active Galactic Nuclei in Dusty
Star-Forming Galaxies: We investigate the infrared contribution from supermassive black hole
activity versus host galaxy emission in the mid to far-infrared (IR) spectrum
for a large sample of X-ray bright active galactic nuclei (AGN) residing in
dusty, star-forming host galaxies. We select 703 AGN with L_X = 10^42-46 ergs/s
at 0.1 < z < 5 from the Chandra XBootes X-ray Survey with rich multi-band
observations in the optical to far-IR. This is the largest sample to date of
X-ray AGN with mid and far-IR detections that uses spectral energy distribution
(SED) decomposition to determine intrinsic AGN and host galaxy infrared
luminosities. We determine weak or nonexistent relationships when averaging
star-formation activity as a function of AGN activity, but see stronger
positive trends when averaging L_X in bins of star-forming activity for AGN at
low redshifts. We estimate an average dust covering factor of 33% based on
infrared SEDs and bolometric AGN luminosity, corresponding to a Type 2 AGN
population of roughly a third. We also see a population of AGN that challenge
the inclination based unification model with individual dust covering factors
that contradict the nuclear obscuration expected from observed X-ray hardness
ratios. We see no strong connection between AGN fractions in the IR and
corresponding total infrared, 24 um, or X-ray luminosities. The average
rest-frame AGN contribution as a function of IR wavelength shows significant
(~80%) contributions in the mid-IR that trail off at lambda > 30 um.
Additionally, we provide a relation between observed L_X and pure AGN IR output
for high-z AGN allowing future studies to estimate AGN infrared contribution
using only observed X-ray flux density estimates. | astro-ph_GA |
Photoemission of spin-polarized electrons from aligned grains and chiral
symmetry breaking: The unique biosignature of life on Earth is the homochirality of organic
compounds such as amino acids, proteins, and sugars. The origin of this
homochirality has remained a mystery for over a century. While high-energy
spin-polarized (spin-up or spin-down) electrons (SPEs) from the $\beta$ decay
of radioactive nuclei discovered by Lee and Yang (1956) and Wu et al. (1957)
have been proposed as a potential source of symmetry breaking, their exact role
on homochirality is much debated. Here we suggest magnetically aligned dust
grains as a new source of SPEs due to photoemission of electrons having aligned
spins by the Barnett effect. For the interstellar UV radiation field of
strength $G_{\rm UV}$, we found that the SPE emission rate is $\Gamma_{\rm
pe}^{\rm SPE}\sim 10^{-14}G_{\rm UV}$ electrons per second per H, the fraction
of spin-polarized to total photoelectrons is $\sim 10\%$, and the SPE yield
(photoelectron number per UV photon) can reach $\sim 1\%$, using the modern
theory of grain alignment. Low-energy SPEs from aligned grains would cause
chiral symmetry breaking of interstellar chiral molecules due to spin-selective
(dipole-dipole) interactions. Finally, we suggest magnetically aligned grains
as chiral agents that facilitate and enrich the chiral asymmetry of chiral
molecules. Our proposed mechanism might explain the detection of chiral
asymmetry in the ISM, comets, and meteorites due to the ubiquitous UV radiation
and magnetically aligned grains, paving the way for understanding the origin
and distribution of life in the universe. This mechanism based on magnetic
grain alignment implies the role of magnetic fields on chirality symmetry
breaking. | astro-ph_GA |
Direct $N$-body simulations of globular clusters - II. Palomar 4: We use direct $N$-body calculations to study the evolution of the unusually
extended outer halo globular cluster Palomar 4 (Pal~4) over its entire lifetime
in order to reproduce its observed mass, half-light radius, velocity dispersion
and mass function slope at different radii.
We find that models evolving on circular orbits, and starting from a non-mass
segregated, canonical initial mass function (IMF) can reproduce neither Pal 4's
overall mass function slope nor the observed amount of mass segregation.
Including either primordial mass segregation or initially flattened IMFs does
not reproduce the observed amount of mass segregation and mass function
flattening simultaneously. Unresolved binaries cannot reconcile this
discrepancy either. We find that only models with both a flattened IMF and
primordial segregation are able to fit the observations. The initial (i.e.
after gas expulsion) mass and half-mass radius of Pal~4 in this case are about
57000 M${\odot}$ and 10 pc, respectively. This configuration is more extended
than most globular clusters we observe, showing that the conditions under which
Pal~4 formed must have been significantly different from that of the majority
of globular clusters. We discuss possible scenarios for such an unusual
configuration of Pal~4 in its early years. | astro-ph_GA |
Profiling filaments: comparing near-infrared extinction and
submillimetre data in TMC-1: Interstellar filaments are an important part of star formation. To understand
the structure of filaments, cross-section profiles are often fitted with
Plummer profiles. This profiling is often done with submm studies, such as
Herschel. It would be convenient if filament properties could also be studied
using groundbased NIR data. We compare the filament profiles obtained by NIR
extinction and submm observations to find out if reliable profiles can be
derived using NIR data. We use J-, H-, and K-band data of a filament north of
TMC-1 to derive an extinction map from colour excesses of background stars. We
compare the Plummer profiles obtained from extinction maps with Herschel dust
emission maps. We present 2 methods to estimate profiles from NIR: Plummer
profile fits to median Av of stars or directly to the Av of individual stars.
We compare the methods by simulations. In simulations extinction maps and the
new methods give correct results to within ~10-20 for modest densities. Direct
fit to data on individual stars gives more accurate results than extinction
map, and can work in higher density. In profile fits to real observations,
values of Plummer parameters are generally similar to within a factor of ~2.
Although parameter values can vary significantly, estimates of filament mass
usually remain accurate to within some tens of per cent. Our results for TMC-1
are in agreement with earlier results. High resolution NIR data give more
details, but 2MASS data can be used to estimate profiles. NIR extinction can be
used as an alternative to submm observations to profile filaments. Direct fits
of stars can also be a valuable tool. Plummer profile parameters are not always
well constrained, and caution should be taken when making fits. In the
evaluation of Plummer parameters, one can use the independence of dust emission
and NIR data and the difference in the shapes of the confidence regions. | astro-ph_GA |
A photometric and astrometric study of the open clusters NGC 1664 and
NGC 6939: This study calculated astrophysical parameters, as well as kinematic and
galactic orbital parameters, of the open clusters NGC 1664 and NGC 6939. The
work is based on CCD UBV and Gaia photometric and astrometric data from ground
and space-based observations. Considering Gaia Early Data Release 3 (EDR3)
astrometric data, we determined membership probabilities of stars located in
both of the clusters. We used two-color diagrams to determine $E(B-V)$ color
excesses for NGC 1664 and NGC 6939 as $0.190 \pm 0.018$ and $0.380 \pm 0.025$
mag, respectively. Photometric metallicities for the two clusters were
estimated as [Fe/H] = $-0.10 \pm 0.02$ dex for NGC 1664 and as [Fe/H] = $-0.06
\pm 0.01$ dex for NGC 6939. Using the reddening and metallicity calculated in
the study, we obtained distance moduli and ages of the clusters by fitting
PARSEC isochrones to the color-magnitude diagrams based on the most likely
member stars. Isochrone fitting distances are $1289 \pm 47$ pc and $1716 \pm
87$ pc, which coincide with ages of $675 \pm 50$ Myr and $1.5 \pm 0.2$ Gyr for
NGC 1664 and NGC 6939, respectively. We also derived the distances to the
clusters using Gaia trigonometric parallaxes and compared these estimates with
the literature. We concluded that the results are in good agreement with those
given by the current study. Present day mass function slopes were calculated as
$\Gamma=-1.22\pm0.33$ and $\Gamma=-1.18\pm0.21$ for NGC 1664 and NGC 6939,
respectively, which are compatible with the Salpeter (1955) slope. Analyses
showed that both of clusters are dynamically relaxed. The kinematic and dynamic
orbital parameters of the clusters were calculated, indicating that the
birthplaces of the clusters are outside the solar circle. | astro-ph_GA |
COOL-LAMPS I. An Extraordinarily Bright Lensed Galaxy at Redshift 5.04: We report the discovery of COOL J1241+2219, a strongly-lensed galaxy at
redshift $z$=5.043$\pm$0.002 with observed magnitude $z_{AB}=20.47$, lensed by
a moderate-mass galaxy cluster at $z$=1.001$\pm$0.001. COOL J1241+2219 is the
brightest lensed galaxy currently known at optical and near-infrared
wavelengths at $z$ $\gtrsim$ 5; it is $\sim$5 times brighter than the prior
record-holder lensed galaxy, and several magnitudes brighter than the brightest
unlensed galaxies known at these redshifts. It was discovered as part of
COOL-LAMPS, a collaboration initiated to find strongly lensed systems in recent
public optical imaging data. We characterise the lensed galaxy, as well as the
central galaxy of the lensing cluster using ground-based $griz$JH imaging and
optical spectroscopy. We report model-based magnitudes, and derive stellar
masses, dust content, metallicity and star-formation rates via
stellar-population synthesis modeling. Our lens mass modeling, based on
ground-based imaging, implies a median source magnification of $\sim$30, which
puts the stellar mass and star formation rate (in the youngest age bin, closest
to the epoch of observation) at logM$_{*}$ = $10.11^{+0.21}_{-0.26}$ and SFR =
$27^{+13}_{-9}$ M$_{\odot}$/yr, respectively. We constrain a star formation
history for COOL J1241+2219 consistent with constant star formation across
$\sim$1 Gyr of cosmic time, and that places this galaxy on the high-mass end of
the star-forming main sequence. COOL J1241+2219 is 2-4 times more luminous than
a galaxy with the characteristic UV luminosity at these redshifts. The UV
continuum slope $\beta$= -2.2$\pm$0.2 places this galaxy on the blue side of
the observed distribution of galaxies at $z$=5, although the lack of Ly$\alpha$
emission indicates dust sufficient to suppress this emission. | astro-ph_GA |
Alignment of dense molecular core morphology and velocity gradients with
ambient magnetic fields: Studies of dense core morphologies and their orientations with respect to gas
flows and the local magnetic field have been limited to only a small sample of
cores with spectroscopic data. Leveraging the Green Bank Ammonia Survey
alongside existing sub-millimeter continuum observations and Planck dust
polarization, we produce a cross-matched catalogue of 399 dense cores with
estimates of core morphology, size, mass, specific angular momentum, and
magnetic field orientation. Of the 399 cores, 329 exhibit 2D
$\mathrm{v}_\mathrm{LSR}$ maps that are well fit with a linear gradient,
consistent with rotation projected on the sky. We find a best-fit specific
angular momentum and core size relationship of $J/M \propto R^{1.82 \pm 0.10}$,
suggesting that core velocity gradients originate from a combination of solid
body rotation and turbulent motions. Most cores have no preferred orientation
between the axis of core elongation, velocity gradient direction, and the
ambient magnetic field orientation, favouring a triaxial and weakly magnetized
origin. We find, however, strong evidence for a preferred anti-alignment
between the core elongation axis and magnetic field for protostellar cores,
revealing a change in orientation from starless and prestellar populations that
may result from gravitational contraction in a magnetically-regulated (but not
dominant) environment. We also find marginal evidence for anti-alignment
between the core velocity gradient and magnetic field orientation in the L1228
and L1251 regions of Cepheus, suggesting a preferred orientation with respect
to magnetic fields may be more prevalent in regions with locally ordered
fields. | astro-ph_GA |
Variability-selected Active Galactic Nuclei in the VST-SUDARE/VOICE
Survey of the COSMOS Field: Optical variability has proven to be an effective way of detecting AGNs in
imaging surveys, lasting from weeks to years. In the present work we test its
use as a tool to identify AGNs in the VST multi-epoch survey of the COSMOS
field, originally tailored to detect supernova events. We make use of the
multi-wavelength data provided by other COSMOS surveys to discuss the
reliability of the method and the nature of our AGN candidates. Our selection
returns a sample of 83 AGN candidates; based on a number of diagnostics, we
conclude that 67 of them are confirmed AGNs (81% purity), 12 are classified as
supernovae, while the nature of the remaining 4 is unknown. For the subsample
of AGNs with some spectroscopic classification, we find that Type 1 are
prevalent (89%) compared to Type 2 AGNs (11%). Overall, our approach is able to
retrieve on average 15% of all AGNs in the field identified by means of
spectroscopic or X-ray classification, with a strong dependence on the source
apparent magnitude. In particular, the completeness for Type 1 AGNs is 25%,
while it drops to 6% for Type 2 AGNs. The rest of the X-ray selected AGN
population presents on average a larger r.m.s. variability than the bulk of non
variable sources, indicating that variability detection for at least some of
these objects is prevented only by the photometric accuracy of the data. We
show how a longer observing baseline would return a larger sample of AGN
candidates. Our results allow us to assess the usefulness of this AGN selection
technique in view of future wide-field surveys. | astro-ph_GA |
Gaseous Spiral Structure and Mass Drift in Spiral Galaxies: We use hydrodynamic simulations to investigate nonlinear gas responses to an
imposed stellar spiral potential in disk galaxies. The gaseous medium is
assumed to be infinitesimally thin, isothermal, and unmagnetized. We consider
various spiral-arm models with differing strength and pattern speed. We find
that the extent and shapes of gaseous arms as well as the related mass drift
rate depend rather sensitively on the arm pattern speed. In models where the
arm pattern is rotating slow, the gaseous arms extend across the corotation
resonance (CR) all the way to the outer boundary, with a pitch angle slightly
smaller than that of the stellar counterpart. In models with a fast rotating
pattern, on the other hand, spiral shocks are much more tightly wound than the
stellar arms, and cease to exist in the regions near and outside the CR where
$\mathcal{M}_\perp/{\rm sin} p_* \ge 25-40$, with $\mathcal{M}_\perp$ denoting
the perpendicular Mach number of a rotating gas relative to the arms with pitch
angle $p_*$. Inside the CR, the arms drive mass inflows at a rate of $\sim
0.05-3.0 {\rm M}_\odot {\rm yr}^{-1}$ to the central region, with larger values
corresponding to stronger and slower arms. The contribution of the shock
dissipation, external torque, and self-gravitational torque to the mass inflow
is roughly 50%, 40%, and 10%, respectively. We demonstrate that the
distributions of line-of-sight velocities and spiral-arm densities can be a
useful diagnostic tool to distinguish if the spiral pattern is rotating fast or
slow. | astro-ph_GA |
Following the Cosmic Evolution of Pristine Gas II: The search for Pop
III-Bright Galaxies: Direct observational searches for Population III (Pop III) stars at high
redshift are faced with the question of how to select the most promising
targets for spectroscopic follow-up. To help answer this, we use a large-scale
cosmological simulation, augmented with a new subgrid model that tracks the
fraction of pristine gas, to follow the evolution of high-redshift galaxies and
the Pop III stars they contain. We generate rest-frame ultraviolet (UV)
luminosity functions for our galaxies and find that they are consistent with
current $z \ge 7 $ observations. Throughout the redshift range $7 \le z \le 15$
we identify "Pop III-bright" galaxies as those with at least 75% of their flux
coming from Pop III stars. While less than 1% of galaxies brighter than $m_{\rm
UV, AB} = 31.4$ mag are Pop III--bright in the range $7\leq z \leq8$, roughly
17% of such galaxies are Pop III--bright at $z=9$, immediately before
reionization occurs in our simulation. Moving to $z=10$, $m_{\rm UV, AB} =
31.4$ mag corresponds to larger, more luminous galaxies and the Pop III-bright
fraction falls off to 5%. Finally, at the highest redshifts, a large fraction
(29% at $z=14$ and 41% at $z=15)$ of all galaxies are Pop III-bright regardless
of magnitude. While $m_{\rm UV, AB} = 31.4$ mag galaxies are extremely rare
during this epoch, we find that 13% of galaxies at $z = 14$ are Pop III-bright
with $m_{\rm UV, AB} \le 33$ mag, an intrisic magnitude within reach of the
James Webb Space Telescope using lensing. Thus, we predict that the best
redshift to search for luminous Pop III--bright galaxies is just before
reionization, while lensing surveys for fainter galaxies should push to the
highest redshifts possible. | astro-ph_GA |
High-precision astrometry with VVV -- II. A near-infrared extension of
Gaia into the Galactic plane: Aims. We use near-infrared, ground-based data from the VISTA Variables in the
Via Lactea (VVV) survey to indirectly extend the astrometry provided by the
Gaia catalog to objects in heavily-extincted regions towards the Galactic bulge
and plane that are beyond Gaia's reach. Methods. We make use of the
state-of-the-art techniques developed for high-precision astrometry and
photometry with the Hubble Space Telescope to process the VVV data. We employ
empirical, spatially-variable, effective point-spread functions and local
transformations to mitigate the effects of systematic errors, like residual
geometric distortion and image motion, and to improve measurements in crowded
fields and for faint stars. We also anchor our astrometry to the absolute
reference frame of the Gaia Data Release 3. Results. We measure between 20 and
60 times more sources than Gaia in the region surrounding the Galactic center,
obtaining an single-exposure precision of about 12 mas and a proper-motion
precision of better than 1 mas yr$^{-1}$ for bright, unsaturated sources. Our
astrometry provides an extension of Gaia into the Galactic center. We publicly
release the astro-photometric catalogs of the two VVV fields considered in this
work, which contain a total of $\sim$ 3.5 million sources. Our catalogs cover
$\sim$ 3 sq. degrees, about 0.5% of the entire VVV survey area. | astro-ph_GA |
What Makes Quadruply Lensed Quasars Quadruple?: Among known strongly lensed quasar systems, ~25% have gravitational
potentials sufficiently flat (and sources sufficiently well aligned) to produce
four images rather than two. The projected flattening of the lensing galaxy and
tides from neighboring galaxies both contribute to the potential's quadrupole.
Witt's hyperbola and Wynne's ellipse permit determination of the overall
quadrupole from the positions of the quasar images. The position of the lensing
galaxy resolves the distinct contributions of intrinsic ellipticity and tidal
shear to that quadrupole. Among 31 quadruply lensed quasars systems with
statistically significant decompositions, 15 are either reliably ($2\sigma$) or
provisionally ($1\sigma$) shear-dominated and 11 are either reliably or
provisionally ellipticity-dominated. For the remaining 8, the two effects make
roughly equal contributions to the combined cross section (newly derived here)
for quadruple lensing. This observational result is strongly at variance with
the ellipticity-dominated forecast of Oguri & Marshall (2010). | astro-ph_GA |
Formation and Evolution of the Disk System of the Milky Way: [alpha/Fe]
Ratios and Kinematics of the SEGUE G-Dwarf Sample: We employ measurements of the [alpha/Fe] ratio derived from low-resolution
(R~2000) spectra of 17,277 G-type dwarfs from the SEGUE survey to separate them
into likely thin- and thick-disk subsamples. Both subsamples exhibit strong
gradients of orbital rotational velocity with metallicity, of opposite signs,
-20 to -30 km/s/dex for the thin-disk and +40 to +50 km/s/dex for the
thick-disk population. The rotational velocity is uncorrelated with
Galactocentric distance for the thin-disk subsample, and exhibits a small trend
for the thick-disk subsample. The rotational velocity decreases with distance
from the plane for both disk components, with similar slopes (-9.0 {\pm} 1.0
km/s/kpc). Thick-disk stars exhibit a strong trend of orbital eccentricity with
metallicity (about -0.2/dex), while the eccentricity does not change with
metallicity for the thin-disk subsample. The eccentricity is almost independent
of Galactocentric radius for the thin-disk population, while a marginal
gradient of the eccentricity with radius exists for the thick-disk population.
Both subsamples possess similar positive gradients of eccentricity with
distance from the Galactic plane. The shapes of the eccentricity distributions
for the thin- and thick-disk populations are independent of distance from the
plane, and include no significant numbers of stars with eccentricity above 0.6.
Among several contemporary models of disk evolution we consider, radial
migration appears to have played an important role in the evolution of the
thin-disk population, but possibly less so for the thick disk, relative to the
gas-rich merger or disk heating scenarios. We emphasize that more physically
realistic models and simulations need to be constructed in order to carry out
the detailed quantitative comparisons that our new data enable. | astro-ph_GA |
HSCO$^+$ and DSCO$^+$: a multi-technique approach in the laboratory for
the spectroscopy of interstellar ions: Protonated molecular species have been proven to be abundant in the
interstellar gas. This class of molecules is also pivotal for the determination
of important physical parameters for the ISM evolution (e.g. gas ionisation
fraction) or as tracers of non-polar, hence not directly observable, species.
The identification of these molecular species through radioastronomical
observations is directly linked to a precise laboratory spectral
characterisation. The goal of the present work is to extend the laboratory
measurements of the pure rotational spectrum of the ground electronic state of
protonated carbonyl sulfide (HSCO$^+$) and its deuterium substituted isotopomer
(DSCO$^+$). At the same time, we show how implementing different laboratory
techniques allows the determination of different spectroscopical properties of
asymmetric-top protonated species. Three different high-resolution experiments
were involved to detected for the first time the $b-$type rotational spectrum
of HSCO$^+$, and to extend, well into the sub-millimeter region, the $a-$type
spectrum of the same molecular species and DSCO$^+$. The electronic
ground-state of both ions have been investigated in the 273-405 GHz frequency
range, allowing the detection of 60 and 50 new rotational transitions for
HSCO$^+$ and DSCO$^+$, respectively. The combination of our new measurements
with the three rotational transitions previously observed in the microwave
region permits the rest frequencies of the astronomically most relevant
transitions to be predicted to better than 100 kHz for both HSCO$^+$ and
DSCO$^+$ up to 500 GHz, equivalent to better than 60 m/s in terms of equivalent
radial velocity. The present work illustrates the importance of using different
laboratory techniques to spectroscopically characterise a protonated species at
high frequency, and how a similar approach can be adopted when dealing with
reactive species. | astro-ph_GA |
Photoinduced polycyclic aromatic hydrocarbon dehydrogenation: The
competition between H- and H2-loss: PAHs constitute a major component of the interstellar medium carbon budget,
locking up to 10--20% of the elemental carbon. Sequential fragmentation induced
by energetic photons leads to the formation of new species, including
fullerenes. However, the exact chemical routes involved in this process remain
largely unexplored. In this work, we focus on the first photofragmentation
steps, which involve the dehydrogenation of these molecules. For this, we
consider a multidisciplinary approach, taking into account the results from
experiments, DFT calculations, and modeling using dedicated Monte-Carlo
simulations. By considering the simplest isomerization pathways --- i.e.,
hydrogen roaming along the edges of the molecule --- we are able to
characterize the most likely photodissociation pathways for the molecules
studied here. These comprise nine PAHs with clearly different structural
properties. The formation of aliphatic-like side groups is found to be critical
in the first fragmentation step and, furthermore, sets the balance of the
competition between H- and H2-loss. We show that the presence of trio
hydrogens, especially in combination with bay regions in small PAHs plays an
important part in the experimentally established variations in the odd-to-even
H-atom loss ratios. In addition, we find that, as PAH size increases, H2
formation becomes dominant, and sequential hydrogen loss only plays a marginal
role. We also find disagreements between experiments and calculations for
large, solo containing PAHs, which need to be accounted for. In order to match
theoretical and experimental results, we have modified the energy barriers and
restricted the H-hopping to tertiary atoms. The formation of H2 in large PAHs
upon irradiation appears to be the dominant fragmentation channel, suggesting
an efficient formation path for molecular hydrogen in PDRs. | astro-ph_GA |
The local standard of rest and the well in the velocity distribution: It is now recognised that the traditional method of calculating the LSR
fails. We find an improved estimate of the LSR by making use of the larger and
more accurate database provided by XHIP and repeating our preferred analysis
from Francis & Anderson (2009a). We confirm an unexpected high value of $U_0$
by calculating the mean for stars with orbits sufficiently inclined to the
Galactic plane that they do not participate in bulk streaming motions. Our best
estimate of the solar motion with respect to the LSR $(U_0, V_0, W_0) = (14.1
\pm 1.1, 14.6 \pm 0.4, 6.9 \pm 0.1)$ km\ s$^{-1}$. | astro-ph_GA |
Environmental Quenching of Low Surface Brightness Galaxies near Milky
Way mass Hosts: Low Surface Brightness Galaxies (LSBGs) are excellent probes of quenching and
other environmental processes near massive galaxies. We study an extensive
sample of LSBGs near massive hosts in the local universe that are distributed
across a diverse range of environments. The LSBGs with surface-brightness
$\mu_{\rm eff,g}> $24.2 mag arcsec$^{-2}$ are drawn from the Dark Energy Survey
Year 3 catalog while the hosts with masses $9.0< log(M_{\star}/M_{\odot})<
11.0$ comparable to the Milky Way and the Large Magellanic Cloud are selected
from the z0MGS sample. We study the projected radial density profiles of LSBGs
as a function of their color and surface brightness around hosts in both the
rich Fornax-Eridanus cluster environment and the low-density field. We detect
an overdensity with respect to the background density, out to 2.5 times the
virial radius for both hosts in the cluster environment and the isolated field
galaxies. When the LSBG sample is split by $g-i$ color or surface brightness
$\mu_{\rm eff,g}$, we find the LSBGs closer to their hosts are significantly
redder and brighter, like their high surface-brightness counterparts. The LSBGs
form a clear 'red sequence' in both the cluster and isolated environments that
is visible beyond the virial radius of the hosts. This suggests a
pre-processing of infalling LSBGs and a quenched backsplash population around
both host samples. However, the relative prominence of the 'blue cloud' feature
implies that pre-processing is ongoing near the isolated hosts compared to the
cluster hosts. | astro-ph_GA |
Hot gas in massive halos drives both mass quenching and environment
quenching: Observations indicate that galaxies with high stellar masses or in dense
environments have low specific star formation rates, i.e. they are quenched.
Based on cosmological hydrodynamic simulations that include a prescription
where quenching occurs in regions dominated by hot (>10^5 K) gas, we argue that
this hot gas quenching in halos >10^12 Msun drives both mass quenching (i.e.
central quenching) and environment quenching (i.e. satellite quenching). These
simulations reproduce a broad range of locally observed trends among quenching,
halo mass, stellar mass, environment, and distance to halo center. We show that
mass quenching is independent of environment because 10^12-10^13 Msun
"quenching halos" -- those where most mass quenching occurs -- inhabit a large
range of environments. On the other hand, environment quenching is independent
of stellar mass because galaxies of all stellar masses may live in dense
environments as satellites of groups and clusters. Furthermore, satellite
galaxies show signs of mass quenching independent of halo mass because massive
satellites at z=0 have typically been mass quenched as centrals in their own
hot halos at higher z -- a kind of pre-processing. As in observations, the
fraction of quenched satellites increases with halo mass and decreases with
distance to the center of the group or cluster. We investigate quenched
centrals in low-mass halos (<10^12 Msun), and show that most of these are
ejected former satellites of groups or clusters, while about 20 per cent were
never satellites but are enveloped in hot gas that extends up to 3 Rvir from
the centers of clusters. The agreement of our model with key observational
trends suggests that hot gas in massive halos plays a leading role in quenching
low-redshift galaxies. | astro-ph_GA |
OH 18 cm Transition as a Thermometer for Molecular Clouds: We have observed the four hyperfine components of the 18 cm OH transition
toward the translucent cloud eastward of Heiles Cloud 2 (HCL2E), the cold dark
cloud L134N, and the photodissociation region of the $\rho$-Ophiuchi molecular
cloud with the Effelsberg 100 m telescope. We have found intensity anomalies
amongst the hyperfine components in all three regions. In particular, an
absorption feature of the 1612 MHz satellite line against the cosmic microwave
background has been detected toward HCL2E and two positions of the
$\rho$-Ophiuchi molecular cloud. On the basis of statistical equilibrium
calculations, we find that the hyperfine anomalies originate from the non-LTE
population of the hyperfine levels, and can be used to determine the kinetic
temperature of the gas over a wide range of H$_2$ density (10$^2$ - 10$^7$
cm$^{-3}$). Toward the center of HCL2E, the gas kinetic temperature is
determined to be 53$\pm$1 K, and it increases toward the cloud peripheries
($\sim$ 60 K). The ortho-to-para ratio of H$_2$ is determined to be 3.5 $\pm$
0.9 from the averaged spectrum for the 8 positions. In L134N, a similar
increase of the temperature is also seen toward the periphery. In the
$\rho$-Ophiuchi molecular cloud, the gas kinetic temperature decreases as a
function of the distance from the exciting star HD147889. These results
demonstrate a new aspect of the OH 18 cm line as a good thermometer of
molecular cloud envelopes. The OH 18 cm line can be used to trace a new class
of warm molecular gas surrounding a molecular cloud, which is not well traced
by emission of CO and its isotopologues. | astro-ph_GA |
A New Concept of Transonic Galactic Outflows in a Cold Dark Matter Halo
with a Central Super-Massive Black Hole: We study fundamental properties of isothermal, steady and spherically
symmetric galactic outflow in the gravitational potential of a cold dark matter
halo and a central super-massive black hole. We find that there are two
transonic solutions having different properties: each solution is mainly
produced by the dark matter halo and the super-massive black hole,
respectively. Furthermore, we apply our model to the Sombrero galaxy. In this
galaxy, Chandra X-ray observatory detected the diffuse hot gas as the trace of
galactic outflows while the star-formation rate is low and the observed gas
density distribution presumably indicates the hydrostatic equilibrium. To solve
this discrepancy, we propose a solution that this galaxy has a transonic
outflow, however, the transonic point forms in a very distant region from the
galactic center (?$\sim$ 127 kpc). In this slowly accelerated transonic
outflow, the outflow velocity is less than the sound velocity for most of the
galactic halo. Since the gas density distribution in this subsonic region is
similar to the hydrostatic one, it is difficult to distinguish the wide
subsonic region from hydrostatic state. Such galactic outflows are dfferent
from the conventional supersonic outflows observed in star-forming galaxies. | astro-ph_GA |
LBT/MODS spectroscopy of globular clusters in the irregular galaxy NGC
4449: We present intermediate-resolution (R$\sim$1000) spectra in the
$\sim$3500-10,000 A range of 14 globular clusters in the magellanic irregular
galaxy NGC 4449 acquired with the Multi Object Double Spectrograph on the Large
Binocular Telescope. We derived Lick indices in the optical and the
CaII-triplet index in the near-infrared in order to infer the clusters' stellar
population properties. The inferred cluster ages are typically older than
$\sim$9 Gyr, although ages are derived with large uncertainties. The clusters
exhibit intermediate metallicities, in the range
$-1.2\lesssim$[Fe/H]$\lesssim-0.7$, and typically sub-solar [$\alpha/Fe$]
ratios, with a peak at $\sim-0.4$. These properties suggest that i) during the
first few Gyrs NGC 4449 formed stars slowly and inefficiently, with galactic
winds having possibly contributed to the expulsion of the $\alpha$-elements,
and ii) globular clusters in NGC 4449 formed relatively "late", from a medium
already enriched in the products of type Ia supernovae. The majority of
clusters appear also under-abundant in CN compared to Milky Way halo globular
clusters, perhaps because of the lack of a conspicuous N-enriched,
second-generation of stars like that observed in Galactic globular clusters.
Using the cluster velocities, we infer the dynamical mass of NGC 4449 inside
2.88 kpc to be M($<$2.88 kpc)=$3.15^{+3.16}_{-0.75} \times 10^9~M_\odot$. We
also report the serendipitous discovery of a planetary nebula within one of the
targeted clusters, a rather rare event. | astro-ph_GA |
Stellar Over-densities in the Outer Halo of the Milky Way: This study presents a tomographic survey of a subset of the outer halo (10-40
kpc) drawn from the Sloan Digital Sky Survey Data Release 6. Halo substructure
on spatial scales of $>3$ degrees is revealed as an excess in the local density
of sub-giant stars. With an appropriate assumption of a model stellar isochrone
it is possible for us to then derive distances to the sub-giant population. We
describe three new candidate halo substructures; the 160- and 180-degree
over-densities (at distances of 17 and 19 kpc respectively and radii of 1.3 and
1.5 kpc respectively) and an extended feature at 28 kpc that covers at least
162 square degrees, the Virgo Equatorial Stream. In addition, we recover the
Sagittarius dwarf galaxy (Sgr) leading arm material and the Virgo Over-density.
The derived distances, together with the number of sub-giant stars associated
with each substructure, enables us to derive the integrated luminosity for the
features. The tenuous, low surface brightness of the features strongly suggests
an origin from the tidal disruption of an accreted galaxy or galaxies. Given
the dominance of the tidal debris of Sgr in this region of the sky we
investigate if our observations can be accommodated by tidal disruption models
for Sgr. The clear discordance between observations and model predictions for
known Sgr features means it is difficult to tell unambiguously if the new
substructures are related to Sgr or not. Radial velocities in the stellar
over-densities will be critical in establishing their origins. | astro-ph_GA |
An HI study of NGC 3521 - a galaxy with a slow-rotating halo: A study is presented of HI line observations of the nearby spiral galaxy NGC
3521 observed with the VLA as part of The HI Nearby Galaxy Survey. Clearly
evident in the HI data cube is the presence of an anomalous HI component that
is both diffuse and slow-rotating. The data cube is dynamically decomposed into
regular and anomalous HI components. A mass of M_HI=1.5 x 10^9 Msun is
estimated for the anomalous HI - 20 per cent of the total HI mass. Standard HI
data products and rotation curves are produced for each dynamical component. In
terms of circular rotation speed, the anomalous HI is found to lag the regular
HI by ~25 - 125 km/s. Three-dimensional models are generated and used to
determine the possible location of the anomalous HI. The results strongly
suggest it to be distributed in a thick disc with a scale-height of a few kpc
(~3.5 kpc). It is concluded that the anomalous HI in NGC 3521 constitutes a
slow-rotating halo gas component, consistent with similar findings for other
nearby galaxies. A study of the radial distribution of the anomalous HI shows
it to be spatially coincident with the inner regions of the stellar disc where
the star formation rate is highest. It is most likely a galactic fountain that
has deposited gas from the disc of the galaxy into the halo. | astro-ph_GA |
SiO maser emission from red supergiants across the Galaxy: I. Targets in
massive star clusters: Aims. Red supergiants (RSGs) are among the most luminous of all stars, easily
detectable in external galaxies, and may ideally serve as kinematic tracers of
Galactic structure. Some RSGs are surrounded by circumstellar envelopes
detectable by their dust and molecular and, in particular, maser emission. This
study consists of a search for maser emission from silicon monoxide (SiO)
toward a significant number of RSGs that are members of massive stellar
clusters, many of which have only recently been discovered. Further, we aim to
relate the occurrence of maser action to properties of the host stars.
Methods. Using the IRAM 30 meter telescope, we searched for maser emission in
the J = 2 - 1 rotational transition within the first vibrationally excited
state of SiO toward a sample of 88 RSGs.
Results. With an average rms noise level of 0.25 Jy, we detected maser
emission in 15% of the sample, toward most of the sources for the first time in
this transition. The peak of the emission provides accurate radial velocities
for the RSGs. The dependence of the detection rate on infrared colors supports
a radiative pumping mechanism for the SiO masers. | astro-ph_GA |
Constraints on the Shape of the Milky Way Dark Matter Halo from Jeans
Equations Applied to SDSS Data: We search for evidence of dark matter in the Milky Way by utilizing the
stellar number density distribution and kinematics measured by the Sloan
Digital Sky Survey (SDSS) to heliocentric distances exceeding ~10 kpc. We
employ the cylindrically symmetric form of Jeans equations and focus on the
morphology of the resulting acceleration maps, rather than the normalization of
the total mass as done in previous, mostly local, studies. Jeans equations are
first applied to a mock catalog based on a cosmologically derived N-body + SPH
simulation, and the known acceleration (gradient of gravitational potential) is
successfully recovered. The same simulation is also used to quantify the impact
of dark matter on the total acceleration. We use Galfast, a code designed to
quantitatively reproduce SDSS measurements and selection effects, to generate a
synthetic stellar catalog. We apply Jeans equations to this catalog and produce
two-dimensional maps of stellar acceleration. These maps reveal that in a
Newtonian framework, the implied gravitational potential cannot be explained by
visible matter alone. The acceleration experienced by stars at galactocentric
distances of ~20 kpc is three times larger than what can be explained by purely
visible matter. The application of an analytic method for estimating the dark
matter halo axis ratio to SDSS data implies an oblate halo with q_DM = 0.47 +/-
0.14 within the same distance range. These techniques can be used to map the
dark matter halo to much larger distances from the Galactic center using
upcoming deep optical surveys, such as LSST. | astro-ph_GA |
One hundred SMUDGes in S-PLUS: ultra-diffuse galaxies flourish in the
field: We present the first systematic study of the stellar populations of
ultra-diffuse galaxies (UDGs) in the field, integrating the large area search
and characterization of UDGs by the SMUDGes survey with the twelve-band optical
photometry of the S-PLUS survey. Based on Bayesian modeling of the optical
colors of UDGs, we determine the ages, metallicities and stellar masses of 100
UDGs distributed in an area of $\sim 330$ deg$^2$ in the Stripe 82 region. We
find that the stellar masses and metallicities of field UDGs are similar to
those observed in clusters and follow the trends previously defined in studies
of dwarf and giant galaxies. However, field UDGs have younger
luminosity-weighted ages than do UDGs in clusters. We interpret this result to
mean that field UDGs have more extended star formation histories, including
some that continue to form stars at low levels to the present time. Finally, we
examine stellar population scaling relations that show that UDGs are, as a
population, similar to other low-surface brightness galaxies. | astro-ph_GA |
Distances to PHANGS Galaxies: New Tip of the Red Giant Branch
Measurements and Adopted Distances: PHANGS-HST is an ultraviolet-optical imaging survey of 38 spiral galaxies
within ~20 Mpc. Combined with the PHANGS-ALMA, PHANGS-MUSE surveys and other
multiwavelength data, the dataset will provide an unprecedented look into the
connections between young stars, HII regions, and cold molecular gas in these
nearby star-forming galaxies. Accurate distances are needed to transform
measured observables into physical parameters (e.g., brightness to luminosity,
angular to physical sizes of molecular clouds, star clusters and associations).
PHANGS-HST has obtained parallel ACS imaging of the galaxy halos in the F606W
and F814W bands. Where possible, we use these parallel fields to derive tip of
the red giant branch (TRGB) distances to these galaxies. In this paper, we
present TRGB distances for 11 galaxies from ~4 to ~15 Mpc, based on the first
year of PHANGS-HST observations. Five of these represent the first published
TRGB distance measurements (IC 5332, NGC 2835, NGC 4298, NGC 4321, and NGC
4328), and eight of which are the best available distances to these targets. We
also provide a compilation of distances for the 118 galaxies in the full PHANGS
sample, which have been adopted for the first PHANGS-ALMA public data release. | astro-ph_GA |
Nebular spectroscopy: A guide on H II regions and planetary nebulae: We present a tutorial on the determination of the physical conditions and
chemical abundances in gaseous nebulae. We also include a brief review of
recent results on the study of gaseous nebulae, their relevance for the study
of stellar evolution, galactic chemical evolution, and the evolution of the
universe. One of the most important problems in abundance determinations is the
existence of a discrepancy between the abundances determined with collisionally
excited lines and those determined by recombination lines, this is called the
ADF (abundance discrepancy factor) problem; we review results related to this
problem. Finally, we discuss possible reasons for the large t$^2$ values
observed in gaseous nebulae. | astro-ph_GA |
The oldest stars of the bulge: new information on the ancient Galaxy: Recently the search for the oldest stars have started to focus on the Bulge
region. The Galactic bulge hosts extremely old stars, with ages compatible with
the ages of the oldest halo stars. The data coming from these recent
observations present new chemical signatures and therefore provide
complementary constraints to those already found in the halo. So, the study of
the oldest bulge stars can improve dramatically the constraints on the nature
of first stars and how they polluted the pristine ISM of our Galaxy. We present
our first results regarding the light elements (CNO) and the neutron capture
elements. Our findings in the oldest bulge stars support the scenario where the
first stellar generations have been fast rotators. | astro-ph_GA |
Tidal Limit of Stellar Systems in Two-Power Density Models: As the generalization of gravitational effects on the point mass systems, we
want to study the tidal effect exerted on an extended stellar system using
spherical and axisymmetric elliptical models. Considering the Isochrone and
Plummer models for a passing extended stellar system, the tidal distance and
the equipotential surface are calculated. The corresponding critical surfaces
and maps are plotted in different cases. There are different results some of
them may be used in describing stellar systems deformation | astro-ph_GA |
Supernova enhanced cosmic ray ionization and induced chemistry in a
molecular cloud of W51C: Cosmic rays pervade the Galaxy and are thought to be accelerated in supernova
shocks. The interaction of cosmic rays with dense interstellar matter has two
important effects: 1) high energy (>1 GeV) protons produce {\gamma}-rays by
{\pi}0-meson decay; 2) low energy (< 1 GeV) cosmic rays (protons and electrons)
ionize the gas. We present here new observations towards a molecular cloud
close to the W51C supernova remnant and associated with a recently discovered
TeV {\gamma}-ray source. Our observations show that the cloud ionization degree
is highly enhanced, implying a cosmic ray ionization rate ~ 10-15 s-1, i.e. 100
times larger than the standard value in molecular clouds. This is consistent
with the idea that the cloud is irradiated by an enhanced flux of freshly
accelerated low-energy cosmic rays. In addition, the observed high cosmic ray
ionization rate leads to an instability in the chemistry of the cloud, which
keeps the electron fraction high, ~ 10-5, in a large fraction (Av \geq 6mag) of
the cloud and low, ~ 10-7, in the interior. The two states have been predicted
in the literature as high- and low-ionization phases (HIP and LIP). This is the
observational evidence of their simultaneous presence in a cloud. | astro-ph_GA |
Cosmic evolution of supermassive black holes: A view into the next two
decades: The discoveries made over the past 20 years by Chandra and XMM-Newton surveys
in conjunction with multiwavelength imaging and spectroscopic data available in
the same fields have significantly changed the view of the supermassive black
hole (SMBH) and galaxy connection. These discoveries have opened up several
exciting questions that are beyond the capabilities of current X-ray telescopes
and will need to be addressed by observatories in the next two decades. As new
observatories peer into the early Universe, we will begin to understand the
physics and demographics of SMBH infancy (at $z>6$) and investigate the
influence of their accretion on the formation of the first galaxies ($\S$ 2.1).
We will also be able to understand the accretion and evolution over the cosmic
history (at $z\sim$1-6) of the full population of black holes in galaxies,
including low accretion rate, heavily obscured AGNs at luminosities beyond the
reach of current X-ray surveys ($\S$2.2 and $\S$2.3), enabling us to resolve
the connection between SMBH growth and their environment. | astro-ph_GA |
HST and Ground-Based Spectroscopy of Quasar Outflows: From Mini-BALs to
BALs: Quasar outflows have been posited as a mechanism to couple super-massive
black holes to evolution in their host galaxies. We use multi-epoch spectra
from the Hubble Space Telescope and ground-based observatories to study the
outflows in seven quasars that have CIV outflow lines ranging from a classic
BAL to weaker/narrower "mini-BALs" across rest wavelengths of at least 850
$\AA$ to 1650 $\AA$. The CIV outflow lines all varied within a time frame of
$\leq$ 1.9 yrs (rest). This includes equal occurrences of strengthening and
weakening plus the emergence of a new BAL system at $-$38,800 km/s accompanied
by dramatic strengthening in a mini-BAL at $-$22,800 km/s. We infer from
$\sim$1:1 doublet ratios in PV and other lines that the BAL system is highly
saturated with line-of-sight covering fractions ranging from 0.27 to 0.80 in
the highest to lowest column density regions, respectively. Three of the
mini-BALs also provide evidence for saturation and partial covering based on
$\sim$1:1 doublet ratios. We speculate that the BALs and mini-BALs form in
similar clumpy/filamentary outflows, with mini-BALs identifying smaller or
fewer clumps along our lines of sight. If we attribute the line variabilities
to clumps crossing our lines of sight at roughly Keplerian speeds, then a
typical variability time in our study, $\sim$1.1 yrs, corresponds to a distance
$\sim$2 pc from the central black hole. Combining this with the speed and
minimum total column density inferred from the PV BAL, $N_H \gtrsim$
2.5$\times$10$^{22}$ cm$^{-2}$, suggests that the BAL outflow kinetic energy is
in the range believed to be sufficient for feedback to galaxy evolution. | astro-ph_GA |
Cold gas in the early Universe. Survey for neutral atomic-carbon in GRB
host galaxies at 1 < z < 6 from optical afterglow spectroscopy: We present a survey for neutral atomic-carbon (CI) along gamma-ray burst
(GRB) sightlines, which probes the shielded neutral gas-phase in the
interstellar medium (ISM) of GRB host galaxies at high redshift. We compile a
sample of 29 medium- to high-resolution GRB optical afterglow spectra spanning
a redshift range through most of cosmic time from $1 < z < 6$. We find that
seven ($\approx 25\%$) of the GRBs entering our statistical sample have CI
detected in absorption. It is evident that there is a strong excess of cold gas
in GRB hosts compared to absorbers in quasar sightlines. We investigate the
dust properties of the GRB CI absorbers and find that the amount of neutral
carbon is positively correlated with the visual extinction, $A_V$, and the
strength of the 2175 \AA\ dust extinction feature, $A_{\mathrm{bump}}$. GRBs
with CI detected in absorption are all observed above a certain threshold of
$\log N$(HI)$/\mathrm{cm}^{-2}$ + [X/H] > 20.7 and a dust-phase iron column
density of $\log N$(Fe)$_{\mathrm{dust}}/\mathrm{cm}^{-2}$ > 16.2. In contrast
to the SED-derived dust properties, the strength of the CI absorption does not
correlate with the depletion-derived dust properties. This indicates that the
GRB CI absorbers trace dusty systems where the dust composition is dominated by
carbon-rich dust grains. The observed higher metal and dust column densities of
the GRB CI absorbers compared to H$_2$- and CI-bearing quasar absorbers is
mainly a consequence of how the two absorber populations are selected, but is
also required in the presence of intense UV radiation fields in actively
star-forming galaxies. | astro-ph_GA |
MCMC-based Voigt Profile fitting to a Mini-BAL System in the Quasar
UM675: We introduce a Bayesian approach coupled with a Markov Chain Monte Carlo
(MCMC) method and the maximum likelihood statistic for fitting the profiles of
narrow absorption lines (NALs) in quasar spectra. This method also incorporates
overlap between different absorbers. We illustrate and test this method by
fitting models to a "mini-broad" (mini-BAL) and six NAL profiles in four
spectra of the quasar UM675 taken over a rest-frame interval of 4.24 years. Our
fitting results are consistent with past results for the mini-BAL system in
this quasar by Hamann et al. (1997b). We also measure covering factors ($C_{\rm
f}$) for two narrow components in the CIV and NV mini-BALs and their overlap
covering factor with the broad component. We find that $C_{\rm f}$(NV) is
always larger than $C_{\rm f}$(CIV) for the broad component, while the opposite
is true for the narrow components in the mini-BAL system. This could be
explained if the broad and narrow components originated in gas at different
radial distances, but it seems more likely to be due to them produced by gas at
the same distance but with different gas densities (i.e., ionization states).
The variability detected only in the broad absorption component in the mini-BAL
system is probably due to gas motion since both $C_{\rm f}$(CIV) and $C_{\rm
f}$(NV) vary. We determine for the first time that multiple absorbing clouds
(i.e., a broad and two narrow components) overlap along our line of sight. We
conclude that the new method improves fitting results considerably compared to
previous methods. | astro-ph_GA |
History of the gas fuelling star formation in eagle galaxies: Theory predicts that cosmological gas accretion plays a fundamental role
fuelling star formation in galaxies. However, a detailed description of the
accretion process to be used when interpreting observations is still lacking.
Using the state-of-the-art cosmological hydrodynamical simulation eagle, we
work out the chemical inhomogeneities arising in the disk of galaxies due to
the randomness of the accretion process. In low-mass systems and outskirts of
massive galaxies, low metallicity regions are associated with enhanced
star-formation, a trend that reverses in the centers of massive galaxies. These
predictions agree with the relation between surface density of star formation
rate and metallicity observed in the local spiral galaxies from the MaNGA
survey. Then, we analyse the origin of the gas that produces stars at two key
epochs, z simeq 0 and z simeq 2. The main contribution comes from gas already
in the galaxy about 1 Gyr before stars are formed, with a share from external
gas that is larger at high redshift. The accreted gas may come from major and
minor mergers, but also as gravitationally unbound gas and from mergers with
dark galaxies (i.e., haloes where more than 95 % of the baryon mass is in gas).
We give the relative contribution of these sources of gas as a function of
stellar mass (8 < log Mstar < 11). Even at z = 0, some low-mass galaxies form a
significant fraction of their total stellar mass during the last Gyr from
mergers with dark galaxies. | astro-ph_GA |
Witnessing a Galaxy Cluster Merger with JWST and a Chandra X-ray
Temperature Map: The first James Webb Space Telescope (JWST) image released was of galaxy
cluster SMACSJ0723.3- 7327, a lensing cluster at z=0.39 showing detail only
JWST can provide. While the majority of the focus has been on the brilliantly
lensed galaxies at redshifts far beyond it, there is more to the story than it
being just a lensing cluster. The Chandra X-ray temperature map tells a tale of
a merging cluster with a significant subcluster leaving a wake in the
intracluster medium (ICM). This paper presents a high fidelity temperature map
of SMACSJ0723.3-7327 using adaptive circular binning, overlaid with the JWST
image, showing clear signs of merger activity. As the ICM extends well past the
boundaries of the JWST imagery, and no low-frequency radio observations are yet
published, a fuller story of this cluster remains to be told. This new X-ray
temperature map reveals new details of a moderately distant actively merging
cluster. | astro-ph_GA |
LoCuSS: Exploring the selection of faint blue background galaxies for
cluster weak-lensing: Cosmological constraints from galaxy clusters rely on accurate measurements
of the mass and internal structure of clusters. An important source of
systematic uncertainty in cluster mass and structure measurements is the secure
selection of background galaxies that are gravitationally lensed by clusters.
This issue has been shown to be particular severe for faint blue galaxies. We
therefore explore the selection of faint blue background galaxies, by reference
to photometric redshift catalogs derived from the COSMOS survey and our own
observations of massive galaxy clusters at z~0.2. We show that methods relying
on photometric redshifts of galaxies in/behind clusters based on observations
through five filters, and on deep 30-band COSMOS photometric redshifts are both
inadequate to identify safely faint blue background galaxies. This is due to
the small number of filters used by the former, and absence of massive galaxy
clusters at redshifts of interest in the latter. We therefore develop a
pragmatic method to combine both sets of photometric redshifts to select a
population of blue galaxies based purely on photometric analysis. This sample
yields stacked weak-lensing results consistent with our previously published
results based on red galaxies. We also show that the stacked clustercentric
number density profile of these faint blue galaxies is consistent with
expectations from consideration of the lens magnification signal of the
clusters. Indeed, the observed number density of blue background galaxies
changes by ~10-30 per cent across the radial range over which other surveys
assume it to be flat. | astro-ph_GA |
Cold galaxies: We use 350 mu angular diameter estimates from Planck to test the idea that
some galaxies contain exceptionally cold (10-13 K) dust, since colder dust
implies a lower surface brightness radiation field illuminating the dust, and
hence a greater physical extent for a given luminosity. The galaxies identified
from their spectral energy distributions as containing cold dust do indeed show
the expected larger 350 mu diameters. For a few cold dust galaxies where
Herschel data are available we are able to use submillimetre maps or surface
brightness profiles to locate the cold dust, which as expected generally lies
outside the optical galaxy. | astro-ph_GA |
Potential Importance of Binary Evolution in UV-Optical Spectral Fitting
of Early-Type Galaxies: Binaries are very common in galaxies, and more than half of Galactic hot
subdwarf stars, which are thought as a possible origin of UV-upturn of old
stellar populations, are found in binaries. Previous works showed that binary
evolution can make the spectra of binary star populations significantly
different from those of single star populations. However, the effect of binary
evolution has not been taken into account in most works of spectral fitting of
galaxies. This paper studies the role of binary evolution in spectral fitting
of early-type galaxies, via a stellar population synthesis model including both
single and binary star populations. Spectra from ultraviolet to optical band
are fitted to determine a few parameters of galaxies. The results show that the
inclusion of binaries in stellar population models may lead to obvious change
in the determination of some galaxy parameters and therefore it is potentially
important for spectral studies. In particular, the ages of young components of
composite stellar populations become much older when using binary star
population models instead of single star population models. This implies that
binary star population models will measure significantly different star
formation histories (SFHs) for galaxies compared to single star population
models. In addition, stellar population models with binary interactions measure
larger dust extinctions than single star population models on average. It
suggests that when using binary star population models instead of single star
population models, negative extinctions are possibly unnecessary in spectral
fitting of early-type galaxies. | astro-ph_GA |
The Far-Infrared-Radio Correlation in MS0451-03: We present a multi-wavelength analysis of star-forming galaxies in the
massive cluster MS0451.6-0305 at z $\sim$ 0.54 to shed new light on the
evolution of the far-infrared-radio relationship in distant rich clusters. We
have derived total infrared luminosities for a spectroscopically confirmed
sample of cluster and field galaxies through an empirical relation based on
$Spitzer$ MIPS 24 $\mu$m photometry. The radio flux densities were measured
from deep Very Large Array 1.4 GHz radio continuum observations. We find the
ratio of far-infrared to radio luminosity for galaxies in an intermediate
redshift cluster to be $q_{\rm FIR}$ = 1.80$\pm$0.15 with a dispersion of 0.53.
Due to the large intrinsic dispersion, we do not find any observable change in
this value with either redshift or environment. However, a higher percentage of
galaxies in this cluster show an excess in their radio fluxes when compared to
low redshift clusters ($27^{+23}_{-13}\%$ to $11\%$), suggestive of a cluster
enhancement of radio-excess sources at this earlier epoch. In addition, the
far-infrared-radio relationship for blue galaxies, where $q_{\rm FIR}$ =
2.01$\pm$0.14 with a dispersion of 0.35, is consistent with the predicted value
from the field relationship, although these results are based on a sample from
a single cluster. | astro-ph_GA |
Extremely metal-poor galaxies with HST/COS: laboratories for models of
low-metallicity massive stars and high-redshift galaxies: Ultraviolet (UV) observations of local star-forming galaxies have begun to
establish an empirical baseline for interpreting the rest-UV spectra of
reionization-era galaxies. However, existing high-ionization emission line
measurements at $z>6$ ($\mathrm{W_{C IV, 0}} \gtrsim 20$ {\AA}) are uniformly
stronger than observed locally ($\mathrm{W_{C IV, 0}} \lesssim 2$ {\AA}),
likely due to the relatively high metallicities ($Z/Z_\odot > 0.1$) typically
probed by UV surveys of nearby galaxies. We present new HST/COS spectra of six
nearby ($z<0.01$) extremely metal-poor galaxies (XMPs, $Z/Z_\odot \lesssim
0.1$) targeted to address this limitation and provide constraints on the
highly-uncertain ionizing spectra powered by low-metallicity massive stars. Our
data reveal a range of spectral features, including one of the most prominent
nebular C IV doublets yet observed in local star-forming systems and strong He
II emission. Using all published UV observations of local XMPs to-date, we find
that nebular C IV emission is ubiquitous in very high specific star formation
rate systems at low metallicity, but still find equivalent widths smaller than
those measured in individual lensed systems at $z>6$. Our moderate-resolution
HST/COS data allow us to conduct an analysis of the stellar winds in a local
nebular C IV emitter, which suggests that some of the tension with $z>6$ data
may be due to existing local samples not yet probing sufficiently high
$\mathrm{\alpha/Fe}$ abundance ratios. Our results indicate that C IV emission
can play a crucial role in the JWST and ELT era by acting as an accessible
signpost of very low metallicity ($Z/Z_\odot < 0.1$) massive stars in
assembling reionization-era systems. | astro-ph_GA |
Generating Images of the M87* Black Hole Using GANs: In this paper, we introduce a novel data augmentation methodology based on
Conditional Progressive Generative Adversarial Networks (CPGAN) to generate
diverse black hole (BH) images, accounting for variations in spin and electron
temperature prescriptions. These generated images are valuable resources for
training deep learning algorithms to accurately estimate black hole parameters
from observational data. Our model can generate BH images for any spin value
within the range of [-1, 1], given an electron temperature distribution. To
validate the effectiveness of our approach, we employ a convolutional neural
network to predict the BH spin using both the GRMHD images and the images
generated by our proposed model. Our results demonstrate a significant
performance improvement when training is conducted with the augmented dataset
while testing is performed using GRMHD simulated data, as indicated by the high
R2 score. Consequently, we propose that GANs can be employed as cost effective
models for black hole image generation and reliably augment training datasets
for other parameterization algorithms. | astro-ph_GA |
CARMA CO Observations of Three Extremely Metal-Poor, Star-Forming
Galaxies: We present sensitive CO (J = 1 - 0) emission line observations of three
metal-poor dwarf irregular galaxies Leo P (Z ~ 3% Z_Solar), Sextans A (Z ~ 7.5%
Z_Solar), and Sextans B (Z ~ 7.5% Z_Solar), all obtained with the Combined
Array for Millimeter-wave Astronomy (CARMA) interferometer. While no CO
emission was detected, the proximity of the three systems allows us to place
very stringent (4 sigma) upper limits on the CO luminosity (L_CO) in these
metal-poor galaxies. We find the CO luminosities to be L_CO < 2900 K km/s pc^2
for Leo P, L_CO < 12400 K km/s pc^2 for Sextans A, and L_CO < 9700 K km/s pc^2
for Sextans B. Comparison of our results with recent observational estimates of
the factor for converting between L_CO and the mass of molecular hydrogen, as
well as theoretical models, provides further evidence that either the CO-to-H_2
conversion factor increases sharply as metallicity decreases, or that stars are
forming in these three galaxies very efficiently, requiring little molecular
hydrogen. | astro-ph_GA |
Globular clusters in the stellar stream surrounding the Milky Way analog
NGC 5907: We study the globular clusters (GCs) in the spiral galaxy NGC~5907 well-known
for its spectacular stellar stream -- to better understand its origin. Using
wide-field Subaru/Suprime-Cam $gri$ images and deep Keck/DEIMOS multi-object
spectroscopy, we identify and obtain the kinematics of several GCs superimposed
on the stellar stream and the galaxy disk. We estimate the total number of
globular clusters in NGC 5907 to be $154\pm44$, with a specific frequency of
$0.73\pm0.21$. Our analysis also reveals a significant, new population of young
star cluster candidates found mostly along the outskirts of the stellar disk.
Using the properties of the stream GCs, we estimate that the disrupted galaxy
has a stellar mass similar to the Sagittarius dwarf galaxy accreted by the
Milky Way, i.e. $\sim10^8~M_\odot$. | astro-ph_GA |
Two-component outer ring and the Galactic spiral structure: Model of the Galaxy with the ring R1R2' can explain some large-scale
morphological features of the Galactic spiral structure. The Carina-Sagittarius
arm can consist of two ascending segments of the outer rings R1 and R2 which
almost touch each other near the Carina region. The Perseus and Crux arms can
be partially identified with the descending segments of the ring R2. Model of
the two-component outer ring can also explain the existence of some maxima in
diagrams (l, VLSR) which are supposed to correspond to the directions
tangential to the spiral arms. On the basis of numerical simulations we propose
two sketches of the ring structure of the Galaxy which include the bar, two
outer rings, the inner ring, and the nuclear gas condensation, that may be a
nuclear ring. Both sketches can explain the position of the Carina-Sagittarius
arm with respect to the Sun. | astro-ph_GA |
The structure of molecular gas associated with NGC2264: wide-field 12CO
and H2 imaging: We present wide-field, high-resolution imaging observations in 12CO 3-2 and
H2 1-0 S(1) towards a ~1 square degree region of NGC2264. We identify 46 H2
emission objects, of which 35 are new discoveries. We characterize several
cores as protostellar, reducing the previously observed ratio of
prestellar/protostellar cores in the NGC2264 clusters. The length of H2 jets
increases the previously reported spatial extent of the clusters. In each
cluster, <0.5% of cloud material has been perturbed by outflow activity. A
principal component analysis of the 12CO data suggests that turbulence is
driven on scales >2.6 pc, which is larger than the extent of the outflows. We
obtain an exponent alpha=0.74 for the size-linewidth relation, possibly due to
the high surface density of NGC2264. In this very active, mixed-mass star
forming region, our observations suggest that protostellar outflow activity is
not injecting energy and momentum on a large enough scale to be the dominant
source of turbulence. | astro-ph_GA |
Dynamic role of dust in formation of molecular clouds: Dust is the usual minor component of the interstellar medium. Its dynamic
role in the contraction of the diffuse gas into molecular clouds is commonly
assumed to be negligible because of the small mass fraction, $f \simeq 0.01$.
However, as shown in this study, the collective motion of dust grains with
respect to the gas may considerably contribute to the destabilisation of the
medium on scales $\lambda \lesssim \lambda_J$, where $\lambda_J$ is the Jeans
length-scale. The linear perturbations of the uniform self-gravitating gas at
rest are marginally stable at $\lambda \simeq \lambda_J$, but as soon as the
drift of grains is taken into account, they begin growing at a rate
approximately equal to $(f \tau)^{1/3} t^{-1}_{ff}$, where $\tau$ is the
stopping time of grains expressed in units of the free fall time of the cloud,
$t_{ff}$. The physical mechanism responsible for such a weak dependence of the
growth rate on $f$ is the resonance of heavy sound waves stopped by the
self-gravity of gas with weak gravitational attraction caused by perturbations
of the dust fraction. Once there is stationary subsonic bulk drift of the dust,
the growing gas-dust perturbations at $\lambda < \lambda_J$ become waves
propagating with the drift velocity projected onto the wavevector. Their growth
has a resonant nature as well and the growth rate is substantially larger than
that of the recently discovered resonant instability of gas-dust mixture in the
absence of self-gravity. The new instabilities can facilitate gravitational
contraction of cold interstellar gas into clouds and additionally produce dusty
domains of sub-Jeans size at different stages of molecular cloud formation and
evolution. | astro-ph_GA |
A New Challenge for Dark Matter Models: Cold dark matter (CDM) has faced a number of challenges mainly at small
scales, such as the too-big-to-fail problem, and core-cusp density profile of
dwarf galaxies. Such problems were argued to have a solution either in the
baryonic physics sector or in modifying the nature of dark matter to be
self-interacting, or self-annihilating, or ultra-light. Here we present a new
challenge for CDM by showing that two of Milky Way's satellites (Horologium I,
and Tucana II) are too dense, requiring the formation masses and redshifts of
halos in CDM not compatible with being a satellite. These
too-dense-to-be-satellite systems are dominated by dark matter and exhibit a
surface density above mean dark energy cosmic surface density
$\sim\Omega_{\Lambda} \rho_c c/H_0\approx 600~\rm M_{\odot}/pc^2$. This value
corresponds to dark matter pressure of $\approx 10^{-9}{\rm erg/cm^3}$. Along
with the recently reported excess in small-scale substructures found in
cluster-lenses, this problem, unlike other issues facing CDM, has no solution
in the baryonic sector and none of the current alternatives of dark matter can
account for it. The too-dense-to-be-satellite problem presented in this work
provides a new clue for the nature of dark matter, never accounted for before.
We note that Horologium I and Tucana II have only been discovered in the past
$\sim6$ years with DES, and future surveys (such as those done by Vera C. Rubin
Observatory) may uncover a broader population of such galaxies. Moreover, we
find that a number of MW's satellite require formation halo masses below the
atomic cooling limit which by itself is another challenging observation to
account for in CDM. | astro-ph_GA |
Infrared appearance of wind-blown bubbles around young massive stars: Thousands of ring-like bubbles appear on infrared images of the Galaxy plane.
Most of these infrared bubbles form during expansion of HII regions around
massive stars. However, the physical effects that determine their morphology
are still under debate. Namely, the absence of the infrared emission toward the
centres of the bubbles can be explained by pushing the dust grains by stellar
radiation pressure. At the same time, small graphite grains and PAHs are not
strongly affected by the radiation pressure and must be removed by another
process. Stellar ultraviolet emission can destroy the smallest PAHs but the
photodestruction is ineffective for the large PAHs. Meanwhile, the stellar wind
can evacuate all types of grains from HII regions. In the frame of our
chemo-dynamical model we vary parameters of the stellar wind and illustrate
their influence on the morphology and synthetic infrared images of the bubbles. | astro-ph_GA |
A Long Time Ago in a Galaxy Far, Far Away: A Candidate z ~ 12 Galaxy in
Early JWST CEERS Imaging: We report the discovery of a candidate galaxy with a photo-z of z~12 in the
first epoch of the JWST Cosmic Evolution Early Release Science (CEERS) Survey.
Following conservative selection criteria we identify a source with a robust
z_phot = 11.8^+0.3_-0.2 (1-sigma uncertainty) with m_F200W=27.3, and >7-sigma
detections in five filters. The source is not detected at lambda < 1.4um in
deep imaging from both HST and JWST, and has faint ~3-sigma detections in JWST
F150W and HST F160W, which signal a Ly-alpha break near the red edge of both
filters, implying z~12. This object (Maisie's Galaxy) exhibits F115W-F200W >
1.9 mag (2-sigma lower limit) with a blue continuum slope, resulting in 99.6%
of the photo-z PDF favoring z > 11. All data quality images show no artifacts
at the candidate's position, and independent analyses consistently find a
strong preference for z > 11. Its colors are inconsistent with Galactic stars,
and it is resolved (r_h = 340 +/- 14 pc). Maisie's Galaxy has log M*/Msol ~ 8.5
and is highly star-forming (log sSFR ~ -8.2 yr^-1), with a blue rest-UV color
(beta ~ -2.5) indicating little dust though not extremely low metallicity.
While the presence of this source is in tension with most predictions, it
agrees with empirical extrapolations assuming UV luminosity functions which
smoothly decline with increasing redshift. Should followup spectroscopy
validate this redshift, our Universe was already aglow with galaxies less than
400 Myr after the Big Bang. | astro-ph_GA |
Ultra-diffuse galaxies: the high-spin tail of the abundant dwarf galaxy
population: Recent observations have revealed the existence of an abundant population of
faint, low surface brightness (SB) galaxies, which appear to be numerous and
ubiquitous in nearby galaxy clusters, including the Virgo, Coma and Fornax
clusters. With median stellar masses of dwarf galaxies, these ultra-diffuse
galaxies (UDGs) have unexpectedly large sizes, corresponding to a mean SB of
$24\lesssim\langle\mu_e\rangle_r\ {\rm mag}^{-1} {\rm arcsec}^2\lesssim27$
within the effective radius. We show that the UDG population represents the
tail of galaxies formed in dwarf-sized haloes with higher-than-average angular
momentum. By adopting the standard model of disk formation -- in which the size
of galaxies is set by the spin of the halo -- we recover both the abundance of
UDGs as a function of the host cluster mass and the distribution of sizes
within the UDG population. According to this model, UDGs are not failed $L_*$
galaxies, but genuine dwarfs, and their low SB is not uniquely connected to the
harsh cluster environment. We therefore expect a correspondingly abundant
population of UDGs in the field, with likely different morphologies and
colours. | astro-ph_GA |
The Physical Properties of Galaxies with Unusually Red Mid-Infrared
Colours: The goal of this paper is to investigate the physical nature of galaxies in
the redshift range $0.02<z<0.15$ that have strong excess emission at mid-IR
wavelengths and to determine whether they host a population of accreting black
holes that cannot be identified using optical emission lines. We show that at
fixed stellar mass $M_*$ and $D_n(4000)$, the distribution of [3.4]-[4.6]
$\mu$m (WISE W1-W2 band) colours is sharply peaked, with a long tail to much
redder W1-W2 colours. We introduce a procedure to pull out the red outlier
population based on a combination of three stellar population diagnostics. When
compared with optically-selected AGN, red outliers are more likely to be found
in massive galaxies, and they tend to have lower stellar mass densities,
younger stellar ages and higher dust content than optically-selected AGN hosts.
They are twice as likely to be detected at radio wavelengths. We examine W1-W2
colour profiles for a subset of the nearest, reddest outliers and find that
most are not centrally peaked, indicating that the hot dust emission is spread
throughout the galaxy. We find that radio luminosity is the quantity that is
most predictive of a redder central W1-W2 colour. Radio-loud galaxies with
centrally concentrated hot dust emission are almost always morphologically
disturbed, with compact, unresolved emission at 1.4 Ghz. Eighty percent of such
systems are identifiable as AGN using optical emission line diagnostics. | astro-ph_GA |
Peering into the Milky Way by FAST: I. Exquisite HI structures in the
inner Galactic disk from the piggyback line observations of the FAST GPPS
survey: Neutral hydrogen (HI) is the fundamental component of the interstellar
medium. The Galactic Plane Pulsar Snapshot (GPPS) survey is designed for
hunting pulsars by using the Five-hundred-meter Aperture Spherical radio
Telescope (FAST) from the visible Galactic plane within $|b| \leq 10^{\circ}$.
The survey observations are conducted with the L-band 19-beam receiver in the
frequency range of 1.0 $-$ 1.5 GHz, and each pointing has an integration time
of 5 minutes. The piggyback spectral data simultaneously recorded during the
FAST GPPS survey are great resources for studies on the Galactic HI
distribution and ionized gas. We process the piggyback HI data of the FAST GPPS
survey in the region of $33^{\circ} \leq l \leq 55^{\circ}$ and $|b| \leq
2^{\circ}$. The rms of the data cube is found to be approximately 40 mK at a
velocity resolution of $0.1$ km s$^{-1}$, placing it the most sensitive
observations of the Galactic HI by far. The high velocity resolution and high
sensitivity of the FAST GPPS HI data enable us to detect weak exquisite HI
structures in the interstellar medium. HI absorption line with great details
can be obtained against bright continuum sources. The FAST GPPS survey
piggyback HI data cube will be released and updated on the web:
http://zmtt.bao.ac.cn/MilkyWayFAST/. | astro-ph_GA |
X-ray properties of two complementary samples of intermediate Seyfert
galaxies: We present the X-ray spectral analysis of two complementary sets of
intermediate Seyfert galaxies (ISs). Analyzing X-ray data, we estimate the
hydrogen abundance $N_H$ and test its connection with the [O III] luminosity
acquired from optical observations. The results confirm the conclusions drawn
in a previous study concerning the lack of a direct correlation between the
obscuration measure ($N_H$) and the intrinsic characteristics of the active
nuclei ([O III] luminosity). Instead, we validate the existence of a
correlation between the Seyfert type and the $N_H$ parameter, employing a
separation threshold of approximately 10$^{22}$ atoms cm$^{-2}$.
Simultaneously, our findings align with prior research, corroborating the
relationship between X-ray luminosity and the [O III] luminosity. | astro-ph_GA |
Disentangling star formation and AGN activity in powerful infrared
luminous radio galaxies at 1<z<4: High-redshift radio galaxies present signs of both star formation and AGN
activity, making them ideal candidates to investigate the connection and
coevolution of AGN and star formation in the progenitors of present-day massive
galaxies. We make use of a sample of 11 powerful radio galaxies spanning 1<z<4
which have complete coverage of their spectral energy distribution (SED) from
UV to FIR wavelengths. Using Herschel data, we disentangle the relative
contribution of the AGN and star formation by combining the
galaxyevolutioncodePEGASE.3 with an AGN torus model. We find that three
components are necessary to reproduce the observed SEDs: an evolved and massive
stellar component, a submm bright young starburst, and an AGN torus. We find
that powerful radio galaxies form at very high-redshift, but experience
episodic and important growth at 1<z<4 as the mass of the associated starburst
varies from 5 to 50% of the total mass of the system. The properties of star
formation differ from source to source, indicating no general trend of the star
formation properties in the most infrared luminous high-redshift radio galaxies
and no correlation with the AGN bolometric luminosity. Moreover, we find that
AGN scattered light have a very limited impact on broad-band SED fitting on our
sample. Finally, our analysis also suggests a wide range in origins for the
observed star formation,which we partially constrain for some sources. | astro-ph_GA |
Supermassive black hole pairs in clumpy galaxies at high redshift:
delayed binary formation and concurrent mass growth: Massive gas-rich galaxy discs at $z \sim 1-3$ host massive star-forming
clumps with typical baryonic masses in the range $10^7-10^8$~M$_{\odot}$ which
can affect the orbital decay and concurrent growth of supermassive black hole
(BH) pairs. Using a set of high-resolution simulations of isolated clumpy
galaxies hosting a pair of unequal-mass BHs, we study the interaction between
massive clumps and a BH pair at kpc scales, during the early phase of the
orbital decay. We find that both the interaction with massive clumps and the
heating of the cold gas layer of the disc by BH feedback tend to delay
significantly the orbital decay of the secondary, which in many cases is
ejected and then hovers for a whole Gyr around a separation of 1--2 kpc. In the
envelope, dynamical friction is weak and there is no contribution of disc
torques: these lead to the fastest decay once the orbit of the secondary BH has
circularised in the disc midplane. In runs with larger eccentricities the delay
is stronger, although there are some exceptions. We also show that, even in
discs with very sporadic transient clump formation, a strong spiral pattern
affects the decay time-scale for BHs on eccentric orbits. We conclude that,
contrary to previous belief, a gas-rich background is not necessarily conducive
to a fast BH decay and binary formation, which prompts more extensive
investigations aimed at calibrating event-rate forecasts for ongoing and future
gravitational-wave searches, such as with Pulsar Timing Arrays and the future
evolved Laser Interferometer Space Antenna. | astro-ph_GA |
The PAU Survey: Classifying low-z SEDs using Machine Learning clustering: We present an application of unsupervised Machine Learning Clustering to the
PAU Survey of galaxy spectral energy distribution (SED) within the COSMOS
field. The clustering algorithm is implemented and optimized to get the
relevant groups in the data SEDs. We find 12 groups from a total number of
5,234 targets in the survey at $0.01 <$ z $< 0.28$. Among the groups, 3,545
galaxies (68\%) show emission lines in the SEDs. These groups also include
1,689 old galaxies with no active star formation. We have fitted the SED to
every single galaxy in each group with CIGALE. The mass, age and specific star
formation rates (sSFR) of the galaxies range from $0.15 <$ age/Gyr $< 11$; $6
<$ log (M$_{\star}$/M$_{\odot}$) $< 11.26$, and $-14.67 <$ log (sSFR/yr
$^{-1}$) $< -8$. The groups are well defined in their properties with galaxies
having clear emission lines also having lower mass, are younger and have higher
sSFR than those with elliptical like patterns. The characteristic values of
galaxies showing clear emission lines are in agreement with the literature for
starburst galaxies in COSMOS and GOODS-N fields at low redshift. The
star-forming main sequence, sSFR vs. stellar mass and UVJ diagram show clearly
that different groups fall into different regions with some overlap among
groups. Our main result is that the joint of low-resolution (R $\sim$ 50)
photometric spectra provided by the PAU survey together with the unsupervised
classification provides an excellent way to classify galaxies. Moreover, it
helps to find and extend the analysis of extreme ELGs to lower masses and lower
SFRs in the local Universe. | astro-ph_GA |
Stellar Populations With Optical Spectra: Deep Learning vs. Popular
Spectrum Fitting Codes: We compare the performance of several popular spectrum fitting codes
(Firefly, starlight, pyPipe3D and pPXF), and a deep-learning convolutional
neural network (StarNet), in recovering known stellar population properties
(mean stellar age, stellar metallicity, stellar mass-to-light ratio M*/L_r and
the internal E(B-V)) of simulated galaxy spectra in optical wavelengths. Our
mock spectra are constructed from star-formation histories from the
IllustrisTNG100-1 simulation. These spectra mimic the Sloan Digital Sky Survey
(SDSS) through a novel method of including the noise, sky residuals and
emission lines taken directly from SDSS. We find that StarNet vastly
outperforms all conventional codes in both speed and recovery of stellar
population properties (error scatter < 0.08 dex, average biases < 0.02 dex for
all tested quantities), but it requires an appropriate training set. Of the
non-machine-learning codes, pPXF was a factor of 3-4 times faster than the
other codes, and was the best in recovering stellar population properties
(error scatter of < 0.11 dex, average biases < 0.08 dex). However, the errors
and biases are strongly dependent on both true and predicted values of stellar
age and metallicity, and signal-to-noise ratio. The biases of all codes can
approach 0.15 dex in stellar ages, metallicities and log M*/L_r , but remain <
0.05 for E(B-V). Using unrealistic Gaussian noise in the construction of mock
spectra will underestimate the errors in the metallicities by a factor of two
or more, and mocks without emission lines will underestimate the errors in
stellar age and M*/L_r by a factor of two. | astro-ph_GA |
Testing broad line region models with Reverberation Mapping: New reverberation mapping (RM) measurements, combined with accurate
luminosities and line ratios, provide strong constraints on the location of the
line emitting gas in the broad line region (BLR) of active galactic nuclei
(AGN). In this paper I present new calculations of radiation pressure and
magnetic pressure confined clouds and apply them to a ``generic AGN'' and to
NGC 5548. The new calculations are in good agreement with the observed lags of
all broad emission lines, and with the luminosities of La, Civ 1549, Ovi 1035
and Heii 1640. They are also in reasonable agreement with the luminosities of
Mgii 2798 and the 1990A blend of Ciii] and Siiii] lines for high metallicity
gas. They explain the changes in time-lag following an increase in continuum
luminosity and their dependencies on the inner and outer boundaries of the BLR.
They also predict very strong Balmer and Paschen continua with important
implications to continuum RM experiments. However, the calculated Balmer and
Paschen line luminosities are too weak, by factors of 2-5. This ``Balmer line
crisis'' was noted in several earlier works and is now confirmed and
constrained by RM measurements that were not available in the past. It seems
that present photoionization codes that use the escape probability formalism,
fail to correctly compute the Balmer line luminosities in high density, large
optical depth gas. | astro-ph_GA |
First HETDEX Spectroscopic Determinations of Ly$α$ and UV
Luminosity Functions at $z=2-3$: Bridging a Gap Between Faint AGN and Bright
Galaxies: We present Ly$\alpha$ and ultraviolet-continuum (UV) luminosity functions
(LFs) of galaxies and active galactic nuclei (AGN) at $z=2.0-3.5$ determined by
the un-targetted optical spectroscopic survey of the Hobby-Eberly Telescope
Dark Energy Experiment (HETDEX). We combine deep Subaru imaging with HETDEX
spectra resulting in $11.4$ deg$^2$ of fiber-spectra sky coverage, obtaining
$18320$ galaxies spectroscopically identified with Ly$\alpha$ emission, $2126$
of which host type 1 AGN showing broad (FWHM$~>1000$ km s$^{-1}$) Ly$\alpha$
emission lines. We derive the Ly$\alpha$ (UV) LF over 2 orders of magnitude
covering bright galaxies and AGN in $\log
L_\mathrm{Ly\alpha}/\mathrm{[erg~s^{-1}]}=43.3-45.5$ ($-27<M_\mathrm{UV}<-20$)
by the $1/V_\mathrm{max}$ estimator. Our results reveal the bright-end hump of
the Ly$\alpha$ LF is composed of type 1 AGN. In conjunction with previous
spectroscopic results at the faint end, we measure a slope of the best-fit
Schechter function to be $\alpha_\mathrm{Sch}=-1.70^{+0.13}_{-0.14}$, which
indicates $\alpha_\mathrm{Sch}$ steepens from $z=2-3$ towards high redshift.
Our UV LF agrees well with previous AGN UV LFs, and extends to faint-AGN and
bright-galaxy regimes. The number fraction of Ly$\alpha$-emitting objects
($X_\mathrm{LAE}$) increases from $M_\mathrm{UV}^*\sim-21$ to bright magnitude
due to the contribution of type 1 AGN, while previous studies claim that
$X_\mathrm{Ly\alpha}$ decreases from faint magnitude to $M_\mathrm{UV}^*$,
suggesting a valley in the $X_\mathrm{Ly\alpha}-$magnitude relation at
$M_\mathrm{UV}^*$. Comparing our UV LF of type 1 AGN at $z=2-3$ with those at
$z=0$, we find that the number density of faint ($M_\mathrm{UV}>-21$) type 1
AGN increases from $z\sim2$ to $z\sim0$ as opposed to the evolution of bright
($M_\mathrm{UV}<-21$) type 1 AGN, suggesting the AGN downsizing in the
rest-frame UV luminosity. | astro-ph_GA |
Stratified Distribution of Organic Molecules at the Planet-Formation
Scale in the HH 212 Disk Atmosphere: Formamide (NH2CHO) is considered an important prebiotic molecule because of
its potential to form peptide bonds. It was recently detected in the atmosphere
of the HH 212 protostellar disk on the Solar-System scale where planets will
form. Here we have mapped it and its potential parent molecules HNCO and H2CO,
along with other molecules CH3OH and CH3CHO, in the disk atmosphere, studying
its formation mechanism. Interestingly, we find a stratified distribution of
these molecules, with the outer emission radius increasing from ~ 24 au for
NH2CHO and HNCO, to 36 au for CH3CHO, to 40 au for CH3OH, and then to 48 au for
H2CO. More importantly, we find that the increasing order of the outer emission
radius of NH2CHO, CH3OH, and H2CO is consistent with the decreasing order of
their binding energies, supporting that they are thermally desorbed from the
ice mantle on dust grains. We also find that HNCO, which has much lower binding
energy than NH2CHO, has almost the same spatial distribution, kinematics, and
temperature as NH2CHO, and is thus more likely a daughter species of desorbed
NH2CHO. On the other hand, we find that H2CO has a more extended spatial
distribution with different kinematics from NH2CHO, thus questioning whether it
can be the gas-phase parent molecule of NH2CHO. | astro-ph_GA |
On the Virialization of Disk Winds: Implications for the Black Hole Mass
Estimates in AGN: Estimating the mass of a supermassive black hole (SMBH) in an active galactic
nucleus (AGN) usually relies on the assumption that the broad line region (BLR)
is virialized. However, this assumption seems invalid in BLR models that
consists of an accretion disk and its wind. The disk is likely Keplerian and
therefore virialized. However, the wind material must, beyond a certain point,
be dominated by an outward force that is stronger than gravity. Here, we
analyze hydrodynamic simulations of four different disk winds: an isothermal
wind, a thermal wind from an X-ray heated disk, and two line-driven winds, one
with and the other without X-ray heating and cooling. For each model, we check
whether gravity governs the flow properties, by computing and analyzing the
volume-integrated quantities that appear in the virial theorem: internal,
kinetic, and gravitational energies, We find that in the first two models, the
winds are non-virialized whereas the two line-driven disk winds are virialized
up to a relatively large distance. The line-driven winds are virialized because
they accelerate slowly so that the rotational velocity is dominant and the wind
base is very dense. For the two virialized winds, the so-called projected
virial factor scales with inclination angle as $1/ \sin^2{i}$. Finally, we
demonstrate that an outflow from a Keplerian disk becomes unvirialized more
slowly when it conserves the gas specific angular momentum -- as in the models
considered here, than when it conserves the angular velocity -- as in the
so-called magneto-centrifugal winds. | astro-ph_GA |
The ALPINE-ALMA [CII] Survey: Multi-Wavelength Ancillary Data and Basic
Physical Measurements: We present the ancillary data and basic physical measurements for the
galaxies in the ALMA Large Program to Investigate C+ at Early Times (ALPINE)
survey - the first large multi-wavelength survey which aims at characterizing
the gas and dust properties of 118 main-sequence galaxies at redshifts 4.4 < z
< 5.9 via the measurement of [CII]-emission at 158 micro-meter (64% at
>3.5$\sigma$) and the surrounding far-infrared (FIR) continuum in conjunction
with a wealth of optical and near-infrared data. We outline in detail the
spectroscopic data and selection of the galaxies as well as the ground- and
space-based imaging products. In addition, we provide several basic
measurements including stellar masses, star formation rates (SFR), rest-frame
ultra-violet (UV) luminosities, UV continuum slopes ($\beta$), and absorption
line redshifts, as well as H-alpha emission derived from Spitzer colors. We
find that the ALPINE sample is representative of the 4 < z < 6 galaxy
population selected by photometric methods and only slightly biased towards
bluer colors ($\Delta\beta$ ~ 0.2). Using [CII] as tracer of the systemic
redshift (confirmed for one galaxy at z=4.5 out of 118 for which we obtained
optical [OII]$\lambda$3727A emission), we confirm red shifted Ly-alpha emission
and blue shifted absorption lines similar to findings at lower redshifts. By
stacking the rest-frame UV spectra in the [CII] rest-frame we find that the
absorption lines in galaxies with high specific SFR are more blue shifted,
which could be indicative of stronger winds and outflows. | astro-ph_GA |
A Deep Chandra ACIS Survey of M83: We have obtained a series of deep X-ray images of the nearby galaxy M83 using
Chandra, with a total exposure of 729 ks. Combining the new data with earlier
archival observations totaling 61 ks, we find 378 point sources within the D25
contour of the galaxy. We find 80 more sources, mostly background AGN, outside
of the D25 contour. Of the X-ray sources, 47 have been detected in a new radio
survey of M83 obtained using the Australia Telescope Compact Array. Of the
X-ray sources, at least 87 seem likely to be supernova remnants (SNRs), based
on a combination of their properties in X-rays and at other wavelengths. We
attempt to classify the point source population of M83 through a combination of
spectral and temporal analysis. As part of this effort, we carry out an initial
spectral analysis of the 29 brightest X-ray sources. The soft X-ray sources in
the disk, many of which are SNRs, are associated with the spiral arms, while
the harder X-ray sources, mostly X-ray binaries (XRBs), do not appear to be.
After eliminating AGN, foreground stars and identified SNRs from the sample, we
construct the cumulative luminosity function (CLF) of XRBs brighter than 8
10$^{35}$ ergs/s. Despite M83's relatively high star formation rate, the CLF
indicates that most of the XRBs in the disk are low mass XRBs. | astro-ph_GA |
Fundamental plane of elliptical galaxies in $f(R)$ gravity: the role of
luminosity: The global properties of elliptical galaxies are connected through the
so-called fundamental plane of ellipticals, which is an empirical relation
between their parameters: effective radius, central velocity dispersion and
mean surface brightness within the effective radius. We investigated the
relation between the parameters of the fundamental plane equation and the
parameters of modified gravity potential $f(R)$. With that aim, we compared
theoretical predictions for circular velocity in $f(R)$ gravity with the
corresponding values from a large sample of observed elliptical galaxies.
Besides, we consistently reproduced the values of coefficients of the
fundamental plane equation as deduced from observations, showing that the
photometric quantities like mean surface brightness are related to
gravitational parameters. We show that this type of modified gravity,
especially its power-law version - $R^n$, is able to reproduce the stellar
dynamics in elliptical galaxies. Also, it is shown that $R^n$ gravity fits the
observations very well, without need for a dark matter. | astro-ph_GA |
Photodissociation Region Diagnostics Across Galactic Environments: We present three-dimensional astrochemical simulations and synthetic
observations of magnetised, turbulent, self-gravitating molecular clouds. We
explore various galactic interstellar medium environments, including cosmic-ray
ionization rates in the range of $\zeta_{\rm CR}=10^{-17}$-$10^{-14}\,{\rm
s}^{-1}$, far-UV intensities in the range of $G_0=1$-$10^3$ and metallicities
in the range of $Z=0.1$-$2\,{\rm Z}_{\odot}$. The simulations also probe a
range of densities and levels of turbulence, including cases where the gas has
undergone recent compression due to cloud-cloud collisions. We examine: i) the
column densities of carbon species across the cycle of CII, CI and CO, along
with OI, in relation to the HI-to-H$_2$ transition; ii) the velocity-integrated
emission of [CII]~$158\mu$m, [$^{13}$CII]~$158\mu$m, [CI]~$609\mu$m and
$370\mu$m, [OI]~$63\mu$m and $146\mu$m, and of the first ten $^{12}$CO
rotational transitions; iii) the corresponding Spectral Line Energy
Distributions; iv) the usage of [CII] and [OI]~$63\mu$m to describe the
dynamical state of the clouds; v) the behavior of the most commonly used ratios
between transitions of CO and [CI]; and vi) the conversion factors for using CO
and CI as H$_2$-gas tracers. We find that enhanced cosmic-ray energy densities
enhance all aforementioned line intensities. At low metallicities, the emission
of [CII] is well connected with the H$_2$ column, making it a promising new
H$_2$ tracer in metal-poor environments. The conversion factors of $X_{\rm CO}$
and $X_{\rm CI}$ depend on metallicity and the cosmic-ray ionization rate, but
not on FUV intensity. In the era of ALMA, SOFIA and the forthcoming CCAT-prime
telescope, our results can be used to understand better the behaviour of
systems in a wide range of galactic and extragalactic environments. | astro-ph_GA |
The fate of the pre-main sequence-rich clusters Collinder197 and vdB92:
dissolution?: We investigate the nature and possible evolution of the young Galactic star
clusters Collinder 197 (Cr 197) and vdB 92. The colour-magnitude diagrams
(CMDs) are basically characterised by a poorly-populated MS and a dominant
fraction ($\ga75%$) of PMS stars, and the combined MS and PMS CMD morphology in
both clusters consistently constrains the age to within $5\pm4$ Myr, with a
$\sim10$ Myr spread in the star formation process. The MS$ + $PMS stellar
masses are $\approx660^{+102}_{-59} \ms$ (Cr 197) and $\approx750^{+101}_{-51}
\ms$ (vdB 92). Cr 197 and vdB 92 appear to be abnormally large, when compared
to clusters within the same age range. They have irregular stellar radial
density distributions (RDPs) with a marked excess in the innermost region, a
feature that, at less than 10 Myr, is more likely related to the star formation
and/or molecular cloud fragmentation than to age-dependent dynamical effects.
The velocity dispersion of both clusters, derived from proper motions, is in
the range $\sim15 - 22 \kms$. Both clusters appear to be in a super-virial
state, with velocity dispersions higher than those expected of
nearly-virialised clusters of similar mass and size. A possible interpretation
is that Cr 197 and vdB 92 deviate critically from dynamical equilibrium, and
may dissolve into the field. We also conclude that early cluster dissolution
leaves detectable imprints on RDPs of clusters as massive as several $10^2
\ms$. Cr 197 and vdB 92 may be the link between embedded clusters and young
stellar associations. | astro-ph_GA |
PROBES-I: A Compendium of Deep Rotation Curves and Matched multiband
Photometry: We present the Photometry and Rotation Curve Observations from Extragalactic
Surveys (PROBES) compendium of extended rotation curves for 3163 late-type
spirals, with matching homogeneous multiband photometry for 1677 of them.
PROBES rotation curves originally extracted from Halpha long-slit spectra and
aperture synthesis HI (21cm) velocity maps typically extend out to a median
2R_e (or 1R_{23.5, r}). Our uniform photometry takes advantage of GALEX,
DESI-LIS, and WISE images and the software AutoProf to yield multiband
azimuthally averaged surface brightness profiles that achieve depths greater
than 25 mag/arcsec^2 (FUV, NUV), 27 mag/arcsec^2 (g, r), and 26 mag/arcsec^2
(z, W1, W2). With its library of spatially resolved profiles and an extensive
table of structural parameters, the versatile PROBES data set will benefit
studies of galaxy structure and formation. | astro-ph_GA |
Spiral Structure in Scale-free, Thin Discs: Rigid Rotation: In this paper we suggest the existence in the central regions of spiral
galaxies of collisionless, scale-free, rigidly rotating, self-gravitating discs
with spiral symmetry. Such discs must be truncated at a finite radius, and they
must be stabilized and rendered self-similar by a suitable halo. The halo and
the rotating disc share the self-similar class and must form together to arrive
at the suggested state. We make comparisons with the well-known rigidly
rotating, Kalnajs discs; one of which is axi-symmetric and finite while the
other is infinite and decomposed into spiral modes. We find the
self-consistent, self-similar, distribution functions in one and two dimensions
in a rigidly rotating, collisionless system. In the case of two dimensions we
deduce the self-consistency condition for discrete spiral arms.
We give an estimate of the disturbance created in the halo by the presence of
the disc, and argue that the halo itself should be close to self-similarity. A
very weak cusp in the halo may be necessary. The necessary spatial coincidence
of the halo results in a kind of disc-halo `conspiracy'. Finally the disc
equations are formulated in `spiral' coordinates, and the passage to an
approximately discrete `line spiral' is given as an example. Although in two
dimensions the collisionless particles enter and leave the arms in non-linear
epicycles, they move approximately parallel to the arms in the line spiral
limit. The spiral pattern is however in rigid rotation. Aperiodic spiral arms
are suggested wherein discontinuities may be coarse-grained to appear as
collisionless shocks. | astro-ph_GA |
Lagrangian statistics of a shock-driven turbulent dynamo in decaying
turbulence: Small-scale fluctuating magnetic fields of order $n$G are observed in
supernova shocks and galaxy clusters, where its amplification is likely caused
by the Biermann battery mechanism. However, these fields cannot be amplified
further without the turbulent dynamo, which generates magnetic energy through
the stretch-twist-fold (STF) mechanism. Thus, we present here novel
three-dimensional magnetohydrodynamic (MHD) simulations of a laser-driven shock
propagating into a stratified, multiphase medium, to investigate the post-shock
turbulent magnetic field amplification via the turbulent dynamo. The
configuration used here is currently being tested in the shock tunnel at the
National Ignition Facility (NIF). In order to probe the statistical properties
of the post-shock turbulent region, we use $384 \times 512 \times 384$ tracers
to track its evolution through the Lagrangian framework, thus providing a
high-fidelity analysis of the shocked medium. Our simulations indicate that the
growth of the magnetic field, which accompanies the near-Saffman kinetic energy
decay ($E_{\textrm{kin}} \propto t^{-1.15})$ without turbulence driving,
exhibits slightly different characteristics as compared to periodic box
simulations. Seemingly no distinct phases exist in its evolution, because the
shock passage and time to observe the magnetic field amplification during the
turbulence decay are very short ($\sim\!0.3$ of a turbulent turnover time).
Yet, the growth rate is still consistent with those expected for compressive
(curl-free) turbulence driving in subsonic, compressible turbulence.
Phenomenological understanding of the dynamics of the magnetic and velocity
fields are also elucidated via Lagrangian frequency spectra, which are
consistent with the expected inertial range scalings in the Eulerian-Lagrangian
bridge. | astro-ph_GA |
On the Dispersal of Young Stellar Hierarchies: Hierarchical structure in young star fields has been demonstrated in a
variety of ways, including two point correlation functions (TPCFs) that are
power laws for spatial scales up to at least several hundred parsecs. As the
stars age, this power law decreases in slope until it becomes nearly flat at
~100 Myr, at which point the hierarchical structure has disappeared. The fact
that the TPCF remains nearly a power law during this time implies that the
dispersal mechanism is somewhat independent of scale. This rules out dispersal
by random stellar motions at either the local gas turbulent speed or a constant
speed, because in both cases the hierarchy would disappear at small scales
first, causing the TPCF to bend over. Destruction by shear has the right
property as the shear rate in a galaxy is independent of scale for kpc-size
regions, but shear converts the hierarchy into an azimuthal stream which still
has a power-law TPCF. What does explain the observation is the overlapping of
several independent hierarchies from successive generations of star formation
in the same region. If stellar age is determined from magnitude intervals on
the main sequence of a color-magnitude diagram, or if clusters ages are grouped
together logarithmically into bins, then multiple generations will overlap more
and more as the grouped populations age, and this overlap will lower the
spatial correlations between group members. Models of these processes
illustrate their relative roles in removing the appearance of young stellar
hierarchies. | astro-ph_GA |
Robust statistical tools for identifying multiple stellar populations in
globular clusters in the presence of measurement errors. A case study: NGC
2808: The finding of multiple stellar populations (MP), defined by patterns in the
stellar element abundances, is nowadays considered a distinctive feature of
globular clusters. However, while data availability and quality improved in
last decades, this is not always true for the techniques adopted to their
analysis, rising problems of objectivity of the claims and reproducibility.
Using NGC 2808 as test case we show the use of well established statistical
clustering methods. We focus the analysis to the RGB phase, where two data sets
are available from recent literature for low- and high-resolution spectroscopy.
We adopt both hierarchical clustering and partition methods. We explicitly
address the usually neglected problem of measurement errors. The results of the
clustering algorithms were subjected to silhouette width analysis to compare
the performance of the split into different number of MP. For both data sets
the results are at odd with those reported in the literature. Two MP are
detected for both data sets, while the literature reports five and four MP from
high- and low-resolution spectroscopy respectively. The silhouette analysis
suggests that the population sub-structure is reliable for high-resolution
spectroscopy data, while the actual existence of MP is questionable for the
low-resolution spectroscopy data. The discrepancy with literature claims is
explainable due to the difference of methods adopted to MP characterisation. By
means of Monte Carlo simulations and multimodality statistical tests we show
that the often adopted study of the histogram of the differences in some key
elements is prone to multiple false positive findings. The adoption of
statistically grounded methods, which adopt all the available information to
subset the data and explicitly address the problem of data uncertainty, is of
paramount importance to present more robust and reproducible researches. | astro-ph_GA |
ALMA sub-/millimeter sources among $Spitzer$ SMUVS galaxies at $z>2$ in
the COSMOS field: Sub-millimeter observations reveal the star-formation activity obscured by
dust in the young Universe. It still remains unclear how galaxies detected at
sub-millimeter wavelengths are related to ultraviolet/optical-selected galaxies
in terms of their observed quantities, physical properties, and evolutionary
stages. Deep near- and mid-infrared observational data are crucial to
characterize the stellar properties of galaxies detected with sub-millimeter
emission. In this study, we make use of a galaxy catalog from the $Spitzer$
Matching Survey of the UltraVISTA ultra-deep Stripes. By cross-matching with a
sub-millimeter source catalog constructed with the archival data of the Atacama
Large Millimeter/submillimeter Array (ALMA), we search for galaxies at $z>$ 2
with a sub-millimeter detection in our galaxy catalog. We find that the
ALMA-detected galaxies at $z>$ 2 are systematically massive and have redder
$K_s$-[4.5] colors than the non-detected galaxies. The redder colors are
consistent with the larger dust reddening values of the ALMA-detected galaxies
obtained from SED fitting. We also find that the ALMA-detected galaxies tend to
have brighter 4.5 $\mu$m magnitudes. This may suggest that they tend to have
smaller mass-to-light ratios, and thus, to be younger than star-forming
galaxies fainter at sub-millimeter wavelengths with similar stellar masses. We
identify starburst galaxies with high specific star-formation rates among both
ALMA-detected and non-detected SMUVS sources. Irrespective of their brightness
at sub-millimeter wavelengths, these populations have similar dust reddening
values, which may suggest a variety of dust SED shapes among the starburst
galaxies at $z>2$. | astro-ph_GA |
Simulated Galaxy Interactions as Probes of Merger Spectral Energy
Distributions: We present the first systematic comparison of ultraviolet-millimeter spectral
energy distributions (SEDs) of observed and simulated interacting galaxies. Our
sample is drawn from the Spitzer Interacting Galaxy Survey, and probes a range
of galaxy interaction parameters. We use 31 galaxies in 14 systems which have
been observed with Herschel, Spitzer, GALEX, and 2MASS. We create a suite of
GADGET-3 hydrodynamic simulations of isolated and interacting galaxies with
stellar masses comparable to those in our sample of interacting galaxies.
Photometry for the simulated systems is then calculated with the SUNRISE
radiative transfer code for comparison with the observed systems. For most of
the observed systems, one or more of the simulated SEDs match reasonably well.
The best matches recover the infrared luminosity and the star formation rate of
the observed systems, and the more massive systems preferentially match SEDs
from simulations of more massive galaxies. The most morphologically distorted
systems in our sample are best matched to simulated SEDs close to coalescence,
while less evolved systems match well with SEDs over a wide range of
interaction stages, suggesting that an SED alone is insufficient to identify
interaction stage except during the most active phases in strongly interacting
systems. This result is supported by our finding that the SEDs calculated for
simulated systems vary little over the interaction sequence. | astro-ph_GA |
EVN observations of 6.7 GHz methanol maser polarization in massive
star-forming regions. V. Completion of the flux-limited sample: Although the role of magnetic fields in launching molecular outflows in
massive YSOs has been convincingly demonstrated by theoretical arguments,
observationally, the alignment of the magnetic field lines with the molecular
outflows is still under debate. We aim to complete the measurements of the
direction of the magnetic fields at mas resolution around a sample of massive
star-forming regions (MSFRs) to determine whether the magnetic field and
outflows are aligned. In 2012, we started a large VLBI campaign with the EVN to
measure the magnetic field orientation and strength toward a sample of 31 MSFRs
(the flux-limited sample) by analyzing the polarized emission of 6.7GHz CH3OH
masers. In the previous papers of the series, we have presented 80% of the
sample. Here, we report the linearly and circularly polarized emission of
6.7GHz CH3OH masers toward the last five MSFRs of the flux-limited sample. The
sources are G30.70-0.07, G30.76-0.05, G31.28+0.06, G32.03+0.06, and
G69.52-0.97. We detected a total of 209 masers, 15% of which show linearly
polarized emission (0.07%-16.7%), and 2% of which show circularly polarized
emission (0.2%-4.2%). Zeeman splitting was measured toward G30.70-0.07,
G32.03+0.06, and G69.52-0.97. The statistical analysis of the entire
flux-limited sample shows that the observations are consistent with a bimodal
distribution in the difference between the 3D magnetic field direction and the
outflow axis, with half the magnetic field directions being perpendicular and
the other half being parallel to the outflow. In addition, we determined that
typical values of the linear and circular polarization fractions for 6.7 GHz
CH3OH masers are Pl=1.0%-2.5% and Pv=0.5%-0.75%, respectively. We found that a
typical Zeeman splitting is in the range between 0.5 m/s and 2.0 m/s. This
would correspond to 9 mG<$|B_{||}|$<40 mG if F=3->4 is the most favored
hyperfine transition. | astro-ph_GA |
A rogues gallery of Andromeda's dwarf galaxies II. Precise Distances to
17 Faint Satellites: We present new horizontal branch (HB) distance measurements to 17 of the
faintest known M31 satellites ($-6 \lesssim M_{V} \lesssim -13$) based on deep
Hubble Space Telescope (HST) imaging. The color-magnitude diagrams extend
$\sim$1-2 magnitudes below the HB, which provides for well-defined HBs, even
for faint galaxies in which the tip of the red giant branch (TRGB) is sparsely
populated. We determine distances across the sample to an average precision of
4% ($\sim 30$~kpc at $800$~kpc). We find that the majority of these galaxies
are in good agreement, though slightly farther (0.1-0.2 mag) when compared to
recent ground-based TRGB distances. Two galaxies (And~IX and And~XVII) have
discrepant HST and ground-based distances by $\sim 0.3$ mag ($\sim 150$~kpc),
which may be due to contamination from Milky Way foreground stars and/or M31
halo stars in sparsely populated TRGB regions. We use the new distances to
update the luminosities and structural parameters for these 17 M31 satellites.
The new distances do not substantially change the spatial configuration of the
M31 satellite system. We comment on future prospects for precise and accurate
HB distances for faint galaxies in the Local Group and beyond. | astro-ph_GA |
Analysing surveys of our Galaxy I: basic astrometric data: We consider what is the best way to extract science from large surveys of the
Milky Way galaxy. The diversity of data gathered in these surveys, together
with our position within the Galaxy, imply that science must be extracted by
fitting dynamical models to the data in the space of the observables. Models
based on orbital tori promise to be superior for this task than traditional
types of models, such as N-body models and Schwarzschild models. A formalism
that allows such models to be fitted to data is developed and tested on
pseudodata of varying richness. | astro-ph_GA |
Age bimodality in the central region of pseudobulges in S0 galaxies: We present evidence for bimodal stellar age distribution of pseudobulges of
S0 galaxies as probed by the $D_n(4000)$ index. We do not observe any
bimodality in age distribution for pseudobulges in spiral galaxies. Our sample
is flux limited and contains 2067 S0 and 2630 spiral galaxies drawn from the
Sloan Digital Sky Survey. We identify pseudobulges in S0 and spiral galaxies,
based on the position of the bulge on the Kormendy diagram and their central
velocity dispersion. Dividing the pseudobulges of S0 galaxies into those
containing old and young stellar populations, we study the connection between
global star formation and pseudobulge age on the $u-r$ color-mass diagram. We
find that most old pseudobulges are hosted by passive galaxies while majority
of young bulges are hosted by galaxies which are star forming. Dividing our
sample of S0 galaxies into early-type S0s and S0/a galaxies, we find that old
pseudobulges are mainly hosted by early-type S0 galaxies while most of the
pseudobulges in S0/a galaxies are young. We speculate that morphology plays a
strong role in quenching of star formation in the disc of these S0 galaxies,
which stops the growth of pseudobulges, giving rise to old pseudobulges and the
observed age bimodality. | astro-ph_GA |
Chemical abundances of giant stars in the Crater stellar system: We obtained spectra for two giants of Crater (Crater J113613-105227 and
Crater J113615-105244) using X-Shooter at the VLT. The spectra have been
analysed with the MyGIsFoS code using a grid of synthetic spectra computed from
one dimensional, Local Thermodynamic Equilibrium (LTE) model atmospheres.
Effective temperature and surface gravity have been derived from photometry
measured from images obtained by the Dark Energy Survey. The radial velocities
are 144.3+-4.0 km/s for Crater J113613-105227 and and 134.1+-4.0 km/s for
Crater J113615-105244. The metallicities are [Fe/H]=-1.73 and [Fe/H]=-1.67,
respectively. Beside the iron abundance we could determine abundances for nine
elements: Na, Mg, Ca, Ti, V, Cr, Mn, Ni and Ba. For Na and Ba we took into
account deviations from LTE, since the corrections are significant. The
abundance ratios are similar in the two stars and resemble those of Galactic
stars of the same metallicity. On the deep photometric images we could detect
several stars that lie to the blue of the turn-off. conclusions heading
(optional), leave it empty if necessary The radial velocities imply that both
stars are members of the Crater stellar system. The difference in velocity
between the two taken at face value, implies a velocity dispersion > 3.7 km/s
at 95% confidence level. Our spectroscopic metallicities are in excellent
agreement with that determined by previous investigations using photometry. Our
deep photometry and the spectroscopic metallicity imply an age of 7 Gyr for the
main population of the system. The stars to the blue of the turn-off can be
interpreted as a younger population, of the same metallicity and an age of 2.2
Gyr. Finally, spatial and kinematical parameters support the idea that this
system is associated to the galaxies Leo~IV and Leo~V. All the observations
favour the interpretation of Crater as a dwarf galaxy. (Abridged). | astro-ph_GA |
Long period variable stars in NGC 147 and NGC 185. I. Their star
formation histories: NGC 147 and NGC 185 are two of the most massive satellites of the Andromeda
galaxy (M 31). Close together in the sky, of similar mass and morphological
type dE, they possess different amounts of interstellar gas and tidal
distortion. The question therefore is, how do their histories compare? Here we
present the first reconstruction of the star formation histories of NGC 147 and
NGC 185 using long-period variable stars. These represent the final phase of
evolution of low- and intermediate-mass stars at the asymptotic giant branch,
when their luminosity is related to their birth mass. Combining near-infrared
photometry with stellar evolution models, we construct the mass function and
hence the star formation history. For NGC 185 we found that the main epoch of
star formation occurred 8.3 Gyr ago, followed by a much lower, but relatively
constant star formation rate. In the case of NGC 147, the star formation rate
peaked only 7 Gyr ago, staying intense until ~ 3 Gyr ago, but no star formation
has occurred for at least 300 Myr. Despite their similar masses, NGC 147 has
evolved more slowly than NGC 185 initially, but more dramatically in more
recent times. This is corroborated by the strong tidal distortions of NGC 147
and the presence of gas in the centre of NGC 185. | astro-ph_GA |
Redshift and stellar mass dependence of intrinsic shapes of
disc-dominated galaxies from COSMOS observations below $z = 1.0$: The high abundance of disc galaxies without a large central bulge challenges
predictions of current hydrodynamic simulations of galaxy formation. We aim to
shed light on the formation of these objects by studying the redshift and mass
dependence of their intrinsic 3D shape distributions in the COSMOS galaxy
survey below redshift $z=1.0$. This distribution is inferred from the observed
distribution of 2D shapes, using a reconstruction method which we test using
hydrodynamic simulations. Our tests reveal a moderate bias for the inferred
average disc circularity and relative thickness, but a large bias on the
dispersion of these quantities. Applying the reconstruction method on COSMOS
data, we find variations of the average disc circularity and relative thickness
with redshift of around $\sim1\%$ and $\sim10\%$ respectively, which is
comparable to the error estimates on these quantities. The average relative
disc thickness shows a significant mass dependence which can be accounted for
by the scaling of disc radius with galaxy mass. We conclude that our data
provides no evidence for a strong dependence of the average circularity and
absolute thickness of disc-dominated galaxies on redshift and mass that is
significant with respect to the statistical uncertainties in our analysis.
These findings are expected in the absence of disruptive merging or feedback
events that would affect galaxy shapes. They hence support a scenario where
present-day discs form early ($z>1.0$) and subsequently undergo a tranquil
evolution in isolation. However, more data and a better understanding of
systematics are needed to reaffirm our results. | astro-ph_GA |
Molecular cloud determination in the Northern Galactic Plane: The Exeter FCRAO CO Galactic Plane Survey consists of 12CO and 13CO (J=1-0)
observations over the galactic plane covering 55 degrees <= l <= 102 degrees,
|b| >= 1 degree and 141 degrees <= l <= 195 degrees, -3.5 degrees <= b <= 5.5
degrees with a spatial resolution of ~45" and a spectral resolution of
~0.15km/s. We will present the methodology of a threshold-based cloud and clump
determination method which retains hierarchical information, then discuss
associating sources with clouds in the catalogue. Once complete, this catalogue
of clouds and clumps will encompass the majority of the Northern Galactic
Plane, providing knowledge of the molecular structure of the galaxy and the
starting point for studies of the variation in star formation efficiency. In
addition, it will allow us to identify clouds that have no or little star
formation taking place inside them, which are often overlooked in the study of
the conditions required for star formation to take place. | astro-ph_GA |
Extremely Low Molecular Gas Content in the Vicinity of a Red Nugget
Galaxy at $z=1.91$: We present Atacama Large Millimeter/submillimeter Array (ALMA) Band 5
observations of a galaxy at $z=1.91$, GDS24569, in search of molecular gas in
its vicinity via the [C I] $^3$P$_1$-$^3$P$_0$ line. GDS24569 is a massive
($\log M_*/M_\odot=11$) passively evolving galaxy, and characterized by compact
morphology with an effective radius of $\sim0.5$ kpc. We apply two blind
detection algorithms to the spectral data cubes, and find no promising
detection in or around GDS24569 out to projected distance of $\sim320$ kpc,
while a narrow tentative line ($4.1 \sigma$) is identified at $+1200$ km/s by
one of the algorithms. From the non-detection of [C I], we place a $3\sigma$
upper limit on molecular hydrogen mass, $\sim 7.1 \times 10^9 M_\odot$, which
converts to an extremely low gas-to-stellar mass fraction, $< 5 \%$. We conduct
a spectral energy distribution modeling by including optical-to-far-infrared
data, and find a considerably high ($\sim0.1\%$) dust-to-stellar mass ratio,
$\sim10$-$100\times$ higher than those of local early-type galaxies. In
combination with a previous result of an insufficient number of surrounding
satellite galaxies, it is suggested that GDS24569 is unlikely to experience
significant size evolution via satellite mergers. We discuss possible physical
mechanisms that quenched GDS24569. | astro-ph_GA |
Dust Reverberation Mapping of Z229-15: We report results of the dust reverberation mapping (DRM) on the Seyfert 1
galaxy Z229-15 at z = 0.0273. Quasi-simultaneous photometric observations for a
total of 48 epochs were acquired during the period 2017 July to 2018 December
in B, V, J, H and Ks bands. The calculated spectral index ({\alpha}) between B
and V bands for each epoch was used to correct for the accretion disk (AD)
component present in the infrared light curves. The observed {\alpha} ranges
between -0.99 and 1.03. Using cross correlation function analysis we found
significant time delays between the optical V and the AD corrected J, H and Ks
light curves. The lags in the rest frame of the source are 12.52 (+10.00/-9.55)
days (between V and J), 15.63 (+5.05/-5.11) days (between V and H) and 20.36
(+5.82/-5.68) days (between V and Ks). Given the large error bars, these lags
are consistent with each other. However, considering the lag between V and Ks
bands to represent the inner edge of the dust torus, the torus in Z229-15 lies
at a distance of 0.017 pc from the central ionizing continuum. This is smaller
than that expected from the radius luminosity (R-L) relationship known from
DRM. Using a constant {\alpha} = 0.1 to account for the AD component, as is
normally done in DRM, the deduced radius (0.025 pc) lies close to the expected
R-L relation. However, usage of constant {\alpha} in DRM is disfavoured as the
{\alpha} of the ionizing continuum changes with the flux of the source. | astro-ph_GA |
The formation and evolution of Andromeda IX: Local Group (LG), the nearest and most complete galactic environment,
provides valuable information on the formation and evolution of the Universe.
Studying galaxies of different sizes, morphologies, and ages can provide this
information. For this purpose, we chose the And\,IX dSph galaxy, which is one
of the observational targets of the Isaac Newton Telescope (INT) survey. A
total of 50 long-period variables (LPVs) were found in And\,IX in two filters,
Sloan $i'$ and Harris $V$ at a half-light radius of 2.5 arcmin. The And\,IX's
star formation history (SFH) was constructed with a maximum star formation rate
(SFR) of about $0.00082\pm0.00031$ M$_\odot$ yr$^{-1}$, using LPVs as a tracer.
The total mass return rate of LPVs was calculated based on the spectral energy
distribution (SED) of about $2.4\times10^{-4}$ M$_\odot$ yr$^{-1}$. The
distance modulus of $24.56_{-0.15}^{+0.05}$ mag was estimated based on the tip
of the red giant branch (TRGB). | astro-ph_GA |
The Si+SO$_2$ collision and an extended network of neutral-neutral
reactions between silicon and sulphur bearing species: The Si+SO$_2$ reaction is investigated to verify its impact on the abundances
of molecules with astrochemical interest, such as SiS, SiO, SO and others.
According to our results Si($^3$P) and SO$_2$ react barrierlessly yielding only
the monoxides SO and SiO as products. No favourable pathway has been found
leading to other products, and this reaction should not contribute to SiS
abundance. Furthermore, it is predicted that SiS is stable in collisions with
O$_2$, and that S($^3$P)+SiO$_2$ and O($^3$P)+OSiS will also produce SO+SiO.
Using these results and gathering further experimental and computational data
from the literature, we provide an extended network of neutral-neutral
reactions involving Si- and S-bearing molecules. The effects of these reactions
were examined in a protostellar shock model, using the Nautilus gas-grain code.
This consisted in simulating the physicochemical conditions of a shocked gas
evolving from $i.$ primeval cold core, $ii.$ the shock region itself, $iii.$
and finally the gas bulk conditions after the passage of the shock. Emphasising
on the cloud ages and including systematically these chemical reactions, we
found that [SiS/H$_2$] can be of the order of $\sim$ 10$^{-8}$ in shocks that
evolves from clouds of $t=1\times 10^6$ yr, whose values are mostly affected by
the SiS+O $\longrightarrow$SiO+S reaction. Perspectives on further models along
with observations are discussed in the context of sources harbouring molecular
outflows. | astro-ph_GA |
The SSA22 HI Tomography Survey (SSA22-HIT). I. Data Set and Compiled
Redshift Catalog: We conducted a deep spectroscopic survey, named SSA22-HIT, in the SSA22 field
with the DEep Imaging MultiObject Spectrograph (DEIMOS) on the Keck telescope,
designed to tomographically map high-z HI gas through analysis of Lya
absorption in background galaxies' spectra. In total, 198 galaxies were
spectroscopically confirmed at 2.5 < z < 6 with a few low-z exceptions in the
26 x 15 arcmin^2 area, of which 148 were newly determined in this study. Our
redshift measurements were merged with previously confirmed redshifts available
in the 34 x 27 arcmin^2 area of the SSA22 field. This compiled catalog
containing 730 galaxies of various types at z > 2 is useful for various
applications, and it is made publicly available. Our SSA22-HIT survey has
increased by approximately twice the number of spectroscopic redshifts of
sources at z > 3.2 in the observed field. From a comparison with publicly
available redshift catalogs, we show that our compiled redshift catalog in the
SSA22 field is comparable to those among major extragalactic survey fields in
terms of a combination of wide area and high surface number density of objects
at z > 2. About 40 % of the spectroscopically confirmed objects in SSA22-HIT
show reasonable quality of spectra in the wavelengths shorter than Lya when a
sufficient amount of smoothing is adopted. Our data set enables us to make the
HI tomographic map at z > 3, which we present in a parallel study. | astro-ph_GA |
A Census of Protostellar Outflows in Nearby Molecular Clouds: We adopt the deep learning method CASI-3D (Convolutional Approach to
Structure Identification-3D) to systemically identify protostellar outflows in
12CO and 13CO observations of the nearby molecular clouds, Ophiuchus, Taurus,
Perseus and Orion. The total outflow masses are 267 Msun, 795 Msun, 1305 Msun
and 6332 Msun for Ophiuchus, Taurus, Perseus and Orion, respectively. We show
the outflow mass in each cloud is linearly proportional to the total number of
young stellar objects. The estimated total 3D deprojected outflow energies are
9e45 ergs, 6e46 ergs, 1.2e47 ergs and 6e47 ergs for Ophiuchus, Taurus, Perseus
and Orion, respectively. The energy associated with outflows is sufficient to
offset turbulent dissipation at the current epoch for all four clouds. All
clouds also exhibit a break point in the spatial power spectrum of the outflow
prediction map, which likely corresponds to the typical outflow mass and energy
injection scale. | astro-ph_GA |
ALMA-IMF. V. Prestellar and protostellar core populations in the W43
cloud complex: The origin of the stellar initial mass function (IMF) and its relation with
the core mass function (CMF) are actively debated issues with important
implications in astrophysics. Recent observations in the W43 molecular complex
of top-heavy CMFs, with an excess of high-mass cores compared to the canonical
mass distribution, raise questions about our understanding of the star
formation processes and their evolution in space and time. We aim to compare
populations of protostellar and prestellar cores in three regions imaged in the
ALMA-IMF Large Program. We created an homogeneous core catalogue in W43,
combining a new core extraction in W43-MM1 with the catalogue of W43-MM2&MM3
presented in a previous work. Our detailed search for protostellar outflows
enabled us to identify between 23 and 30 protostellar cores out of 127 cores in
W43-MM1 and between 42 and 51 protostellar cores out of 205 cores in
W43-MM2&MM3. Cores with neither outflows nor hot core emission are classified
as prestellar candidates. We found a similar fraction of cores which are
protostellar in the two regions, about 35%. This fraction strongly varies in
mass, from 15-20% at low mass, between 0.8 and 3$M_{\odot} $ up to about 80%
above 16$M_{\odot}$. Protostellar cores are found to be, on average, more
massive and smaller in size than prestellar cores. Our analysis also revealed
that the high-mass slope of the prestellar CMF in W43,
$\alpha=-1.46_{-0.19}^{+0.12}$, is consistent with the Salpeter slope, and thus
the top-heavy form measured for the global CMF, $\alpha=-0.96$, is due to the
protostellar core population. Our results could be explained by clump-fed
models in which cores grow in mass, especially during the protostellar phase,
through inflow from their environment. The difference between the slopes of the
prestellar and protostellar CMFs moreover implies that high-mass cores grow
more in mass than low-mass cores. | astro-ph_GA |
The Evolution of Magellanic-like Galaxy Pairs and The Production of
Magellanic Stream Analogues in Simulations with Tides, Ram Pressure, and
Stellar Feedback: We present a series of chemodynamical simulations of Magellanic-like systems
consisting of two interacting, equal-mass dwarf galaxies orbiting a massive
host galaxy, including feedback and star formation, tides, and ram pressure. We
study the star formation and chemical enrichment history of the dwarfs, and the
production of a Magellanic Stream analogue. The dwarfs interact with each other
through tidal forces, distorting their morphologies and triggering star
formation. A stream is naturally produced as outflows, induced by feedback and
interactions, are stretched by tidal forces. Counter to some recent
simulations, we find that the leading arm persists even in the presence of ram
pressure from the host galaxy. Interactions between the dwarfs and the host
galaxies produce multiple kinematic components in the stream, as observed. A
combination of ongoing star-formation and entrained low-metallicity gas causes
the stream to have a complex chemical structure, with an average metallicity
that is generally lower than that of the dwarfs. | astro-ph_GA |
Surface Brightness Evolution of Galaxies in the CANDELS GOODS Fields up
to $z \sim 6$: High-z Galaxies are Unique or Remain Undetected: We investigate the rest-frame Ultraviolet (UV, $\lambda\sim2000$\AA) surface
brightness (SB) evolution of galaxies up to $z\sim6$ using a variety of deep
Hubble Space Telescope imaging. UV SB is a measure of the density of emission
from mostly young stars and correlates with an unknown combination of star
formation rate, initial mass function, cold gas mass density, dust attenuation,
and the size evolution of galaxies. In addition to physical effects, the SB is,
unlike magnitude, a more direct way in which a galaxy's detectability is
determined. We find a very strong evolution in the intrinsic SB distribution
which declines as $(1+z)^{3}$, decreasing by 4-5 mag arcsec$^{-2}$ between
$z=6$ to $z=1$. This change is much larger than expected in terms of the
evolution in UV luminosity, sizes or dust extinction and we demonstrate that
this evolution is 'unnatural' and due to selection biases. We also find no
strong correlation between mass and UV SB. Thus, deep HST imaging is unable to
discover all of the most massive galaxies in the distant universe. Through
simulations we show that only $\sim15$\% of galaxies that we can detect at
$z=2$ would be detected at high-$z$. We furthermore explore possible origins of
high SB galaxies at high-$z$ by investigating the relationship between
intrinsic SB and star formation rates. We conclude that ultra-high SB galaxies
are produced by very gas rich dense galaxies which are in a unique phase of
evolution, possibly produced by mergers. Analogues of such galaxies do not
exist in the relatively nearby universe. | astro-ph_GA |
Stellar Mass Black Holes in Young Galaxies: We explore the potential cumulative energy production of stellar mass black
holes in early galaxies. Stellar mass black holes may accrete substantially
from the higher density interstellar media of primordial galaxies, and their
energy release would be distributed more uniformly over the galaxy, perhaps
providing a different mode of energy feedback into young galaxies than central
supermassive black holes. We construct a model for the production and growth of
stellar mass black holes over the first few gigayears of a young galaxy. With
the simplifying assumption of a constant density of the ISM, n ~ 10^4 - 10^5
per cubic centimeter, we estimate the number of accreting stellar mass black
holes to be ~ 10^6 and the potential energy production to be as high as 10^61
ergs over several billion years. For densities less than 10^5 per cubic
centimeter, stellar mass black holes are unlikely to reach their Eddington
limit luminosities. The framework we present could be incorporated in numerical
simulations to compute the feedback from stellar-mass black holes with
inhomogeneous, evolving interstellar media. | astro-ph_GA |
What determines the formation and characteristics of protoplanetary
discs?: Planets form in protoplanetary discs. Their masses, distribution, and orbits
sensitively depend on the structure of the protoplanetary discs. However, what
sets the initial structure of the discs in terms of mass, radius and accretion
rate is still unknown. We perform non-ideal MHD numerical simulations using the
adaptive mesh refinement code Ramses, of a collapsing, one solar mass,
molecular core to study the disc formation and early, up to 100 kyr, evolution,
paying great attention to the impact of numerical resolution and accretion
scheme. We found that while the mass of the central object is almost
independent of the numerical parameters such as the resolution and the
accretion scheme onto the sink particle, the disc mass, and to a lower extent
its size, heavily depend on the accretion scheme, which we found, is itself
resolution dependent. This implies that the accretion onto the star and through
the disc are largely decoupled. For a relatively large domain of initial
conditions (except at low magnetisation), we found that the properties of the
disc do not change too significantly. In particular both the level of initial
rotation and turbulence do not influence the disc properties provide the core
is sufficiently magnetized. After a short relaxation phase, the disc settles in
a stationary state. It then slowly grows in size but not in mass. The disc
itself is weakly magnetized but its immediate surrounding is on the contrary
highly magnetized. Our results show that the disc properties directly depend on
the inner boundary condition, i.e. the accretion scheme onto the central
object, suggesting that the disc mass is eventually controlled by the small
scale accretion process, possibly the star-disc interaction. Because of
ambipolar diffusion and its significant resistivity, the disc diversity remains
limited and except for low magnetisation, their properties are (abridged). | astro-ph_GA |
New Optical Reddening Maps of the Large and Small Magellanic Clouds: We present new reddening maps of the SMC and LMC based on the data of the
third phase of the Optical Gravitational Lensing Experiment (OGLE III). We have
used two different methods to derive optical reddening maps. We adopt a
theoretical mean unreddened colour for the red clump in the SMC and LMC,
respectively. We subdivide the photometric data for both Clouds into subfields
and calculate the difference between the observed red clump position and the
theoretical value for each field, which provides us with the reddening value in
(V-I). Furthermore reddening values are obtained for 13490 LMC RR Lyrae ab and
1529 SMC RR Lyrae ab stars covering the whole OGLE III region of the MCs. The
observed colours (V-I) of the RR Lyrae stars are compared with the colour from
the absolute magnitudes. The absolute magnitude of each RR Lyrae star is
computed using its period and metallicity derived from Fourier decomposition of
its lightcurve. In general we find a low and uniform reddening distribution in
both Magellanic Clouds. The red clump method indicates a mean reddening of the
LMC of E(V-I) = 0.09 +/- 0.07 mag, while for the SMC E(V-I) = 0.04 +/- 0.06 mag
is obtained. With RR Lyrae stars a median value of E(V-I) = 0.11 +/- 0.06 mag
for the LMC and E(V-I) = 0.07 +/- 0.06 mag for the SMC is found. The LMC shows
very low reddening in the bar region, whereas the reddening in the star-forming
leading edge and 30 Doradus is considerably higher. In the SMC three pronounced
regions with higher reddening are visible. Two are located along the bar, while
the highest reddening is found in the star-forming wing of the SMC. In general
the regions with higher reddening are in good spatial agreement with infrared
reddening maps as well as with reddening estimations of other studies. The
position-dependent reddening values from the red clump method are available via
the Virtual Observatory interface. | astro-ph_GA |
Constraining the physical properties of the first lensed $z\sim10-16$
galaxy candidates with JWST: The first deep-field observations of the JWST have immediately yielded a
surprisingly large number of very high redshift candidates, pushing the
frontier of observability well beyond $z\gtrsim10$. We here present a detailed
SED-fitting analysis of the 15 gravitationally lensed $z\sim10-16$ galaxy
candidates detected behind the galaxy cluster SMACS J0723.3-7327 in Atek et al.
(2022) using the BEAGLE tool. Our analysis makes use of dynamical
considerations to place limits on the ages of these galaxies and of all three
published SL models of the cluster to account for lensing systematics. We find
these galaxies to have relatively low stellar masses
$M_{\star}\sim10^7-10^8\,\mathrm{M}_{\odot}$ and young ages
$t_{\mathrm{age}}\sim10-100$\,Myr. Due to their very blue UV-slopes, down to
$\beta\sim-3$, all of the galaxies in our sample have extremely low dust
attenuations $A_V\lesssim0.02$. Placing the measured parameters into relation,
we find a very shallow $M_{\star}-M_{\mathrm{UV}}$-slope and high sSFRs above
the main sequence of star-formation with no significant redshift-evolution in
either relation. This is in agreement with the bright UV luminosities measured
for these objects and indicates that we are naturally selecting galaxies that
are currently undergoing a star-bursting episode at the time they are observed.
Finally, we discuss the robustness of our high-redshift galaxy sample regarding
low-redshift interlopers and conclude that low-redshift solutions can safely be
ruled out for roughly half of the sample, including the highest-redshift
galaxies at $z\sim12-16$. These objects represent compelling targets for
spectroscopic follow-up observations with JWST and ALMA. | astro-ph_GA |
Spectroscopic investigation of a reionized galaxy overdensity at z=7: We present deep spectroscopic follow-up observations of the Bremer Deep Field
(BDF) where the two $z\sim$7 bright Ly$\alpha$ emitters (LAE) BDF521 and
BDF3299 were previously discovered by Vanzella et al. (2011) and where a factor
of $\sim$3-4 overdensity of faint LBGs has been found by Castellano et al.
(2016). We confirm a new bright Ly$\alpha$ emitter, BDF2195, at the same
redshift of BDF521, $z=7.008$, and at only $\sim$90 kpc physical distance from
it, confirming that the BDF area is likely an overdense, reionized region. A
quantitative assessment of the Ly$\alpha$ fraction shows that the number of
detected bright emitters is much higher than the average found at z$\sim$7,
suggesting a high Ly$\alpha$ transmission through the inter-galactic medium
(IGM). However, the line visibility from fainter galaxies is at odds with this
finding, since no Ly$\alpha$ emission is found in any of the observed
candidates with $M_{UV}>$-20.25. This discrepancy can be understood either if
some mechanism prevents Ly$\alpha$ emission from fainter galaxies within the
ionized bubbles from reaching the observer, or if faint galaxies are located
outside the reionized area and bright LAEs are solely responsible for the
creation of their own HII regions. A thorough assessment of the nature of the
BDF region and of its sources of re-ionizing radiation will be made possible by
JWST spectroscopic capabilities. | astro-ph_GA |
The Stellar-to-Halo Mass Ratios of Passive and Star-Forming Galaxies at
z~2-3 from the SMUVS survey: In this work, we use measurements of galaxy stellar mass and two-point
angular correlation functions to constrain the stellar-to-halo mass ratios
(SHMRs) of passive and \np\ galaxies at $z\sim2-3$, as identified in the
\emph{Spitzer} Matching Survey of the UltraVISTA ultra-deep Stripes (SMUVS). We
adopt a sophisticated halo modeling approach to statistically divide our two
populations into central and satellite galaxies. For central galaxies, we find
that the normalization of the SHMR is greater for our passive population.
Through the modeling of $\Lambda$ cold dark matter halo mass accretion
histories, we show that this can only arise if the conversion of baryons into
stars was more efficient at higher redshifts and additionally that passive
galaxies can be plausibly explained as residing in halos with the highest
formation redshifts (i.e., those with the lowest accretion rates) at a given
halo mass. At a fixed stellar mass, satellite galaxies occupy host halos with a
greater mass than central galaxies, and we find further that the fraction of
passive galaxies that are satellites is higher than for the combined
population. This, and our derived satellite quenching timescales, combined with
earlier estimates from the literature, support dynamical/environmental
mechanisms as the dominant process for satellite quenching at $z\lesssim3$. | astro-ph_GA |
Modelling the CO streamers in the explosive ejection of Orion BN/KL
region: We present reactive gasdynamic, axisymmetric simulations of dense, high
velocity clumps for modelling the CO streamers observed in Orion BN/KL. We have
considered 15 chemical species, a cooling function for atomic and molecular
gas, and heating through cosmic rays. Our numerical simulations explore
different ejection velocities, interstellar medium density configurations, and
CO content. Using the CO density and temperature, we have calculated the CO
($J=2\to1$) emissivity, and have built CO maps and spatially resolved line
profiles, allowing us to see the CO emitting regions of the streamers and to
obtain position velocity diagrams to compare with observations. We find that in
order to reproduce the images and line profiles of the BN/KL CO streamers and
H$_2$ fingers, we need to have clumps that first travel within a dense cloud
core, and then emerge into a lower-density environment. | astro-ph_GA |
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