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Solving the puzzle of discrepant quasar variability on monthly
time-scales implied by SDSS and CRTS data sets: We present an improved photometric error analysis for the 7,100 CRTS
(Catalina Real-Time Transient Survey) optical light curves for quasars from the
SDSS (Sloan Digital Sky Survey) Stripe 82 catalogue. The SDSS imaging survey
has provided a time-resolved photometric data set which greatly improved our
understanding of the quasar optical continuum variability: Data for monthly and
longer time-scales are consistent with a damped random walk (DRW). Recently,
newer data obtained by CRTS provided puzzling evidence for enhanced
variability, compared to SDSS results, on monthly time-scales. Quantitatively,
SDSS results predict about 0.06 mag root-mean-square (rms) variability for
monthly time-scales, while CRTS data show about a factor of 2 larger rms, for
spectroscopically confirmed SDSS quasars. Our analysis has successfully
resolved this discrepancy as due to slightly underestimated photometric
uncertainties from the CRTS image processing pipelines. As a result, the
correction for observational noise is too small and the implied quasar
variability is too large. The CRTS photometric error correction factors,
derived from detailed analysis of non-variable SDSS standard stars that were
re-observed by CRTS, are about 20-30%, and result in reconciling quasar
variability behaviour implied by the CRTS data with earlier SDSS results. An
additional analysis based on independent light curve data for the same objects
obtained by the Palomar Transient Factory provides further support for this
conclusion. In summary, the quasar variability constraints on weekly and
monthly time-scales from SDSS, CRTS and PTF surveys are mutually compatible, as
well as consistent with DRW model. | astro-ph_GA |
Understanding Galaxy Mergers & AGN Feedback with UVIT: Simulations expect an enhanced star-formation and active galactic nuclei
(AGN) activity during galaxy mergers, which can lead to formation of
binary/dual AGN. AGN feedback can enhance or suppress star-formation. We have
carried out a pilot study of a sample of 10 dual nuclei galaxies with
AstroSat's Ultraviolet Imaging Telescope (UVIT). Here, we present the initial
results for two sample galaxies (Mrk 739, ESO 509) and deep multi-wavelength
data of another galaxy (Mrk 212). UVIT observations have revealed signatures of
positive AGN feedback in Mrk 739 and Mrk 212, and negative feedback in ESO 509.
Deeper UVIT observations have recently been approved; these will provide better
constraints on star-formation as well as AGN feedback in these systems. | astro-ph_GA |
Investigating 16 Open Clusters in the Kepler/K2-Gaia DR3 field. I.
Membership, Binary, and Rotation: Using data from the Gaia Data Release 3 (Gaia DR3) and Kepler/K2, we present
a catalog of 16 open clusters with ages ranging from 4 to 4000 Myr, which
provides detailed information on membership, binary systems, and rotation. We
assess the memberships in 5D phase space, and estimate the basic parameters of
each cluster. Among the 20,160 members, there are 4,381 stars identified as
binary candidates and 49 stars as blue straggler stars. The fraction of
binaries vary in each cluster, and the range between 9% to 44%. We obtain the
rotation periods of 5,467 members, of which 4,304 are determined in this work.
To establish a benchmark for the rotation-age-color relation, we construct
color-period diagrams. We find that the rotational features of binaries are
similar to that of single stars, while features for binaries are more scattered
in the rotation period. Moreover, the morphology of the color-period
relationship is already established for Upper Scorpius at the age of 19 Myr,
and some stars of varying spectral types (i.e. FG-, K-, and M-type) show
different spin-down rates after the age of ~110 Myr. By incorporating the
effects of stalled spin-down into our analysis, we develop an empirical
rotation-age-color relation, which is valid with ages between 700 - 4000 Myr
and colors corresponding to a range of 0.5 < (G_BP-G_RP)0 < 2.5 mag. | astro-ph_GA |
Searching for shocks in high-mass starless clump candidates: In order to search for shocks in the very early stage of star formation, we
performed single-point surveys of SiO J=1-0, 2-1 and 3-2 lines and the H$_2$CO
$2_{12}-1_{11}$ line toward a sample of 100 high-mass starless clump candidates
(SCCs) by using the Korean VLBI Network (KVN) 21-m radio telescopes. The
detection rates of the SiO J=1-0, 2-1, 3-2 lines and the H$_2$CO line are
$31.0\%$, $31.0\%$, $19.5\%$ and $93.0\%$, respectively. Shocks seem to be
common in this stage of massive star formation. The widths of the observed SiO
lines (full width at zero power (FWZP)) range from 3.4 to 55.1 km s$^{-1}$. A
significant fraction ($\sim29\%$) of the detected SiO spectra have broad line
widths (FWZP $>20~km~s^{-1}$), which are very likely associated with fast
shocks driven by protostellar outflows. This result suggests that about one
third of the SiO-detected SCCs are not really starless but protostellar. On the
other hand, about 40$\%$ of the detected SiO spectra show narrow line widths
(FWZP<10 $km~s^{-1}$) probably associated with low-velocity shocks which are
not necessarily protostellar in origin. The estimated SiO column densities are
mostly $0.31-4.32\times10^{12}~cm^{-2}$. Comparing the SiO column densities
derived from SiO J=1-0 and 2-1 lines, we suggest that the SiO molecules in the
SCCs may be in the non-LTE condition. The SiO abundances to H$_2$ are usually
$0.20-10.92\times10^{-10}$. | astro-ph_GA |
Properties of the Circumgalactic Medium in Cosmic Ray-Dominated Galaxy
Halos: We investigate the impact of cosmic rays (CRs) on the circumgalactic medium
(CGM) in FIRE-2 simulations, for ultra-faint dwarf through Milky Way (MW)-mass
halos hosting star-forming (SF) galaxies. Our CR treatment includes injection
by supernovae, anisotropic streaming and diffusion along magnetic field lines,
collisional and streaming losses, with constant parallel diffusivity
$\kappa\sim3\times10^{29}\,\mathrm{cm^2\ s^{-1}}$ chosen to match $\gamma$-ray
observations. With this, CRs become more important at larger halo masses and
lower redshifts, and dominate the pressure in the CGM in MW-mass halos at
$z\lesssim 1-2$. The gas in these "CR-dominated" halos differs significantly
from runs without CRs: the gas is primarily cool (a few $\sim10^{4}\,$K), and
the cool phase is volume-filling and has a thermal pressure below that needed
for virial or local thermal pressure balance. Ionization of the "low" and "mid"
ions in this diffuse cool gas is dominated by photo-ionization, with O VI
columns $\gtrsim 10^{14.5}\,\mathrm{cm^{-2}}$ at distances $\gtrsim
150\,\mathrm{kpc}$. CR and thermal gas pressure are locally anti-correlated,
maintaining total pressure balance, and the CGM gas density profile is
determined by the balance of CR pressure gradients and gravity. Neglecting CRs,
the same halos are primarily warm/hot ($T\gtrsim 10^{5}\,$K) with thermal
pressure balancing gravity, collisional ionization dominates, O VI columns are
lower and Ne VIII higher, and the cool phase is confined to dense filaments in
local thermal pressure equilibrium with the hot phase. | astro-ph_GA |
Preliminary results on SiO v=3 J=1-0 maser emission from AGB stars: We present the results of SiO maser observations at 43GHz toward two AGB
stars using the VLBA. Our preliminary results on the relative positions of the
different J=1-0 SiO masers (v=1,2 and 3) indicate that the current ideas on SiO
maser pumping could be wrong at some fundamental level. A deep revision of the
SiO pumping models could be necessary. | astro-ph_GA |
Lyman-$α$ emission from a WISE-selected optically faint powerful
radio galaxy M151304.72-252439.7 at $z$ = 3.132: We report the detection of a large ($\sim90$ kpc) and luminous
$\mathrm{Ly\alpha}$ nebula [$L\mathrm{_{Ly\alpha}}$ = $(6.80\pm0.08)\times
10^{44}$] $\rm{\,erg\,s^{-1}}$ around an optically faint (r$>23$ mag) radio
galaxy M1513-2524 at $z\mathrm{_{em}}$=3.132. The double-lobed radio emission
has an extent of 184 kpc, but the radio core, i.e., emission associated with
the active galactic nucleus (AGN) itself, is barely detected. This object was
found as part of our survey to identify high-$z$ quasars based on Wide-field
Infrared Survey Explorer (WISE) colors. The optical spectrum has revealed
$\mathrm{Ly\alpha}$, NV, CIV and HeII emission lines with a very weak
continuum. Based on long-slit spectroscopy and narrow band imaging centered on
the $\mathrm{Ly\alpha}$ emission, we identify two spatial components: a
"compact component" with high velocity dispersion ($\sim
1500$$\rm{\,km\,s^{-1}}$) seen in all three lines, and an "extended component",
having low velocity dispersion (i.e., 700-1000$\rm{\,km\,s^{-1}}$). The
emission line ratios are consistent with the compact component being in
photoionization equilibrium with an AGN. We also detect spatially extended
associated $\mathrm{Ly\alpha}$ absorption, which is blue-shifted within
250-400$\rm{\,km\,s^{-1}}$ of the $\mathrm{Ly\alpha}$ peak. The probability of
$\mathrm{Ly\alpha}$ absorption detection in such large radio sources is found
to be low ($\sim$10%) in the literature. M1513-2524 belongs to the top few
percent of the population in terms of $\mathrm{Ly\alpha}$ and radio
luminosities. Deep integral field spectroscopy is essential for probing this
interesting source and its surroundings in more detail. | astro-ph_GA |
A Characteristic Mass Scale in the Mass-Metallicity Relation of Galaxies: We study the shape of the gas-phase mass-metallicity relation (MZR) of a
combined sample of present-day dwarf and high-mass star-forming galaxies using
IZI, a Bayesian formalism for measuring chemical abundances presented in Blanc
et al. 2015. We observe a characteristic stellar mass scale at $M_* \simeq
10^{9.5}$M$_{\odot}$, above which the ISM undergoes a sharp increase in its
level of chemical enrichment. In the $10^{6}-10^{9.5}$M$_{\odot}$ range the MZR
follows a shallow power-law ($Z\propto M^{\alpha}_*$) with slope
$\alpha=0.14\pm0.08$. At approaching $M_* \simeq 10^{9.5}$M$_{\odot}$ the MZR
steepens significantly, showing a slope of $\alpha=0.37\pm0.08$ in the
$10^{9.5}-10^{10.5}$M$_{\odot}$ range, and a flattening towards a constant
metallicity at higher stellar masses. This behavior is qualitatively different
from results in the literature that show a single power-law MZR towards the low
mass end. We thoroughly explore systematic uncertainties in our measurement,
and show that the shape of the MZR is not induced by sample selection, aperture
effects, a changing N/O abundance, the adopted methodology used to construct
the MZR, secondary dependencies on star formation activity, nor diffuse ionized
gas (DIG) contamination, but rather on differences in the method used to
measure abundances. High resolution hydrodynamical simulations can
qualitatively reproduce our result, and suggest a transition in the ability of
galaxies to retain their metals for stellar masses above this threshold. The
MZR characteristic mass scale also coincides with a transition in the scale
height and clumpiness of cold gas disks, and a typical gas fraction below which
the efficiency of star formation feedback for driving outflows is expected to
decrease sharply. | astro-ph_GA |
The creation and persistence of a misaligned gas disc in a simulated
early-type galaxy: Massive early-type galaxies commonly have gas discs which are kinematically
misaligned with the stellar component. These discs feel a torque from the stars
and the angular momentum vectors are expected to align quickly. We present
results on the evolution of a misaligned gas disc in a cosmological simulation
of a massive early-type galaxy from the Feedback In Realistic Environments
project. This galaxy experiences a merger which, together with a strong
galactic wind, removes most of the original gas disc. The galaxy subsequently
reforms a gas disc through accretion of cold gas, but it is initially 120
degrees misaligned with the stellar rotation axis. This misalignment persists
for about 2 Gyr before the gas-star misalignment angle drops below 20 degrees.
The time it takes for the gaseous and stellar components to align is much
longer than previously thought, because the gas disc is accreting a significant
amount of mass for about 1.5 Gyr after the merger, during which the angular
momentum change induced by accreted gas dominates over that induced by stellar
torques. Once the gas accretion rate has decreased sufficiently, the gas disc
decouples from the surrounding halo gas and realigns with the stellar component
in about 6 dynamical times. During the late evolution of the misaligned gas
disc, the centre aligns faster than the outskirts, resulting in a warped disc.
We discuss the observational consequences of the long survival of our
misaligned gas disc and how our results can be used to calibrate merger rate
estimates from observed gas misalignments. | astro-ph_GA |
Milky Way's Thick and Thin disk: Is there distinct thick disk?: This article is based on our discussion session on Milky Way models at the
592 WE-Heraeus Seminar, Reconstructing the Milky Way's History: Spectroscopic
Surveys, Asteroseismology and Chemodynamical models. The discussion focused on
the following question: "Are there distinct thick and thin disks?". The answer
to this question depends on the definition one adopts for thin and thick disks.
The participants of this discussion converged to the idea that there are at
least two different types of disks in the Milky Way. However, there are still
important open questions on how to best define these two types of disks
(chemically, kinematically, geometrically or by age?). The question of what is
the origin of the distinct disks remains open. The future Galactic surveys
which are highlighted in this conference should help us answering these
questions. The almost one-hour debate involving researchers in the field
representing different modelling approaches (Galactic models such as TRILEGAL,
Besancon and Galaxia, chemical evolution models, extended distribution
functions method, chemodynamics in the cosmological context, and
self-consistent cosmological simulations) illustrated how important is to have
all these parallel approaches. All approaches have their advantages and
shortcomings (also discussed), and different approaches are useful to address
specific points that might help us answering the more general question above. | astro-ph_GA |
Galaxy to cloud scales: Simulations from the scales of isolated galaxies to clouds have been
instrumental in informing us about molecular cloud formation and evolution.
Simulations are able to investigate the roles of gravity, feedback, turbulence,
heating and cooling, and magnetic fields on the physics of the interstellar
medium, and star formation. Compared to simulations of individual clouds,
galactic and sub-galactic scale simulations can include larger galactic scale
processes such as spiral arms, bars, and larger supernovae bubbles, which may
influence star formation. Simulations show cloud properties and lifetimes in
broad agreement with observations. Gravity and spiral arms are required to
produce more massive GMCs, whilst stellar feedback, likely photoionisation,
leads to relatively short cloud lifetimes. On larger scales, supernovae may be
more dominant in driving the structure and dynamics, but photoionisation may
still have a role. In terms of the dynamics, feedback is probably the main
driver of velocity dispersions, but large scale processes such as gravity and
spiral arms may also be significant. Magnetic fields are generally found to
decrease star formation on galaxy or cloud scales, and simulations are ongoing
to study whether clouds are sub or supercritical on different scales in galaxy
scale simulations. Simulations on subgalactic scales, or zoom in simulations,
allow better resolution of feedback processes, filamentary structure within
clouds, and the study of stellar clusters. | astro-ph_GA |
A population of galaxy-scale jets discovered using LOFAR: The effects of feedback from high luminosity radio-loud AGN have been
extensively discussed in the literature, but feedback from low-luminosity
radio-loud AGN is less well understood. The advent of high sensitivity, high
angular resolution, large field of view telescopes such as LOFAR is now
allowing wide-area studies of such faint sources for the first time. Using the
first data release of the LOFAR Two Metre Sky Survey (LoTSS) we report on our
discovery of a population of 195 radio galaxies with 150 MHz luminosities
between $3\times10^{22}$ and $1.5\times10^{25}\text{ W Hz}^{-1}$ and total
radio emission no larger than 80 kpc. These objects, which we term galaxy-scale
jets (GSJ), are small enough to be directly influencing the evolution of the
host on galaxy scales. We report upon the typical host properties of our
sample, finding that 9 per cent are hosted by spirals with the remainder being
hosted by elliptical galaxies. Two of the spiral-hosted GSJ are highly unusual
with low radio luminosities and FRII-like morphology. The host properties of
our GSJ show that they are ordinary AGN observed at a stage in their life
shortly after the radio emission has expanded beyond the central regions of the
host. Based on our estimates, we find that about half of our GSJ have internal
radio lobe energy within an order of magnitude of the ISM energy so that, even
ignoring any possible shocks, GSJ are energetically capable of affecting the
evolution of the host. The current sample of GSJ will grow in size with future
releases of LoTSS and can also form the basis for further studies of feedback
from low-luminosity radio sources. | astro-ph_GA |
The VVV Open Cluster Project. Near-infrared sequences of NGC6067,
NGC6259, NGC4815, Pismis18, Trumpler23, and Trumpler20: Open clusters are central elements of our understanding of the Galactic disk
evolution, as an accurate determination of their parameters leads to an
unbiased picture of our Galaxy's structure. Extending the analysis towards
fainter magnitudes in cluster sequences has a significant impact on the derived
fundamental parameters, such as extinction and total mass. We perform a
homogeneous analysis of six open stellar clusters in the Galactic disk using
kinematic and photometric information from the Gaia DR2 and VVV surveys:
NGC6067, NGC6259, NGC4815, Pismis18, Trumpler23, and Trumpler20. We implement
two coarse-to-fine characterization methods: first, we employ Gaussian mixture
models to tag fields around each open cluster in the proper motion space, and
then we apply an unsupervised machine learning method to make the membership
assignment to each cluster. For the studied clusters, with ages in the
$\sim$120-1900 Myr range, we report an increase of $\sim$45 % new member
candidates on average in our sample. The data-driven selection approach of
cluster members makes our catalog a valuable resource for testing stellar
evolutionary models and for assessing the cluster low-to-intermediate mass
populations. This study is the first of a series intended to homogeneously
reveal open cluster near-infrared sequences. | astro-ph_GA |
Massive Galaxies Impede Massive Outflows: A set of 66 3D hydrodynamical simulations explores how galactic stellar mass
affects three-phase, starburst-driven outflows. Simulated velocities are
compared to two basic analytic models: with (Johnson \& Axford 1971) and
without (Chevalier \& Clegg 1985) a gravitational potential. For stellar mass
$<10^{10}$ solar masses, simulated velocities match those of both analytical
models and are unaffected by the potential; above they reduce significantly as
expected from the analytic model with gravity. Gravity also affects total
outflow mass and each of the three phases differently. Outflow mass in the hot,
warm, and cold phases each scale with stellar mass as $\log M_*=$ -0.25, -0.97,
and -1.70, respectively. Thus, the commonly used Chevalier \& Clegg analytic
model should be modified to include gravity when applied to higher mass
galaxies. In particular, using M82 as the canonical galaxy to interpret
hydrodynamical simulations of starburst-driven outflows from higher mass
galaxies will underestimate the retarding effect of gravity. Using the analytic
model of Johnson \& Axford with realistic thermalization efficiency and mass
loading I find that only galaxy masses that are less than $\sim10^{11.5}$ solar
masses can outflow. | astro-ph_GA |
Structural parameters and possible association of the Ultra-Faint Dwarfs
Pegasus III and Pisces II from deep Hubble Space Telescope photometry: We present deep Hubble Space Telescope (HST) photometry of the ultra-faint
dwarf (UFD) galaxies Pegasus III (Peg III) and Pisces II (Psc II), two of the
most distant satellites in the halo of the Milky Way (MW). We measure the
structure of both galaxies, derive mass-to-light ratios with newly determined
absolute magnitudes, and compare our findings to expectations from UFD-mass
simulations. For Peg III, we find an elliptical half-light radius of
$a_h=1.88^{+0.42}_{-0.33}$ arcminutes ($118^{+31}_{-30}$ pc) and
$M_V{=}{-4.17}^{+0.19}_{-0.22}$; for Psc II, we measure
$a_h{=}1.31^{+0.10}_{-0.09}$ arcminutes ($69\pm8$ pc) and
$M_V{=}{-4.28}^{+0.19}_{-0.16}$. We do not find any morphological features that
indicate a significant interaction between the two has occurred, despite their
close separation of only $\sim$40 kpc. Using proper motions (PMs) from Gaia
early Data Release 3, we investigate the possibility of any past association by
integrating orbits for the two UFDs in a MW-only and a combined MW and Large
Magellanic Cloud (LMC) potential. We find that including the gravitational
influence of the LMC is crucial, even for these outer-halo satellites, and that
a possible orbital history exists where Peg III and Psc II experienced a close
($\sim$10-20 kpc) passage about each other just over $\sim$1 Gyr ago, followed
by a collective passage around the LMC ($\sim$30-60 kpc) just under $\sim$1 Gyr
ago. Considering the large uncertainties on the PMs and the restrictive priors
imposed to derive them, improved PM measurements for Peg III and Psc II will be
necessary to clarify their relationship. This would add to the rare findings of
confirmed pairs of satellites within the Local Group. | astro-ph_GA |
Selection bias in dynamically-measured supermassive black hole samples:
Scaling relations and correlations between residuals in semi-analytic galaxy
formation models: Recent work has confirmed that the masses of supermassive black holes,
estimated from scaling relations with global properties such as the stellar
masses of their host galaxies, may be biased high. Much of this may be caused
by the requirement that the gravitational sphere of influence of the black hole
must be resolved for the black-hole mass to be reliably estimated. We revisit
this issue by using a comprehensive galaxy evolution semi-analytic model, which
self-consistently evolves supermassive black holes from high-redshift seeds via
gas accretion and mergers, and also includes AGN feedback. Once tuned to
reproduce the (mean) correlation of black-hole mass with velocity dispersion,
the model is unable to also account for the correlation with stellar mass. This
behaviour is independent of the model's parameters, thus suggesting an internal
inconsistency in the data. The predicted distributions, especially at the
low-mass end, are also much broader than observed. However, if selection
effects are included, the model's predictions tend to align with the
observations. We also demonstrate that the correlations between the residuals
of the local scaling relations are more effective than the scaling relations
themselves at constraining AGN feedback models. In fact, we find that our
semi-analytic model, while in apparent broad agreement with the scaling
relations when accounting for selection biases, yields very weak correlations
between their residuals at fixed stellar mass, in stark contrast with
observations. This problem persists when changing the AGN feedback strength,
and is also present in the $z\sim 0$ outputs of the hydrodynamic cosmological
simulation Horizon-AGN, which includes state-of-the-art treatments of AGN
feedback. This suggests that current AGN feedback models may be too weak or are
simply not capturing the effect of the black hole on the stellar velocity
dispersion. | astro-ph_GA |
Tracing the Local Volume galaxy halo-to-stellar mass ratio with
satellite kinematics: Rapid advance has been made recently in accurate distance measurements for
nearby ($D < 11$ Mpc) galaxies based on the magnitude of the tip of red giant
branch stars resolved with the Hubble Space Telescope. We use observational
properties of galaxies presented in the last version of Updated Nearby Galaxy
Catalog to derive a halo mass of luminous galaxies via orbital motion of their
companions. Our sample contains 298 assumed satellites with known radial
velocities around 25 Milky Way-like massive galaxies and 65 assumed satellites
around 47 fainter dominant galaxies. The average total mass-to-$K$-band
luminosity ratio is $31\pm6 M_\odot/L_\odot$ for the luminous galaxies,
increasing up to $\sim200 M_\odot/L_\odot$ toward dwarfs. The bulge-dominated
luminous galaxies are characterized with $\langle{}M_T/L_K\rangle = 73\pm15
M_\odot/L_\odot$, while the disc-dominated spirals have
$\langle{}M_T/L_K\rangle = 17.4\pm2.8 M_\odot/L_\odot$. We draw attention to a
particular subsample of luminous spiral galaxies with signs of declining
rotation curve, which have a radial velocity dispersion of satellites less than
55 km/s and a poor dark matter halo with $\langle{}M_T/L_K\rangle = 5.5\pm1.1
M_\odot/L_\odot$. We note that a fraction of quenched (dSph, dE) companions
around Milky Way-like galaxies decreases with their linear projected separation
as $0.75 \exp(-R_p/350\,\mathrm{kpc})$. | astro-ph_GA |
A law of motion for spherical shells in special relativity: Self-similar solutions to the problem of a special relativistic law of motion
for thin shells of matter are calculated. These solutions represent the special
relativistic generalization of momentum conservation for the thin layer
approximation in classical physics. The analytical and numerical results are
applied to Supernova Remnant 1987 A. | astro-ph_GA |
A z=2.5 protocluster associated with the radio galaxy MRC 2104-242: star
formation and differing mass functions in dense environments: We present results from a narrow-band survey of the field around the high
redshift radio galaxy MRC 2104-242. We have selected Halpha emitters in a
7sq.arcmin field and compared the measured number density with that of a field
sample at similar redshift. We find that MRC 2104-242 lies in an overdensity of
galaxies that is 8.0 +/- 0.8 times the average density of a blank field,
suggesting it resides in a large-scale structure that may eventually collapse
to form a massive cluster. We find that there is more dust obscured star
formation in the protocluster galaxies than in similarly selected control field
galaxies and there is tentative evidence of a higher fraction of starbursting
galaxies in the denser environment. However, on average we do not find a
difference between the star formation rate (SFR)-mass relations of the
protocluster and field galaxies and so conclude that the SFR of these galaxies
at z~2.5 is governed predominantly by galaxy mass and not the host environment.
We also find that the stellar mass distribution of the protocluster galaxies is
skewed towards higher masses and there is a significant lack of galaxies at M <
10^10Msun within our small field of view. Based on the level of overdensity we
expect to find ~22 star forming galaxies below 10^10Msun in the protocluster
and do not detect any. This lack of low mass galaxies affects the level of
overdensity which we detect. If we only consider high mass (M > 10^10.5Msun)
galaxies, the density of the protocluster field increases to ~55 times the
control field density. | astro-ph_GA |
Lessons from Comparisons between the Nuclear Region of the Milky Way &
Those in Nearby Spirals: The Milky Way appears is a typical barred spiral, and comparisons can be made
between its nuclear region and those of structurally similar nearby spirals.
Maffei 2, M83, IC 342 and NGC 253 are nearby systems whose nuclear region
properties contrast with those of the Milky Way. Stellar masses derived from
NIR photometery, molecular gas masses and star formation rates allow us to
assess the evolutionary states of this set of nuclear regions. These data
suggest similarities between nuclear regions in terms of their stellar content
while highlighting significant differences in current star formation rates. In
particular current star formation rates appear to cover a larger range than
expected based on the molecular gas masses. This behavior is consistent with
nuclear region star formation experiencing episodic variations. Under this
hypothesis the Milky Way's nuclear region currently may be in a low star
formation rate phase. | astro-ph_GA |
Radio Jet Feedback and Star Formation in Heavily Obscured Quasars at
Redshifts ~0.3-3, I: ALMA Observations: We present ALMA 870 micron (345 GHz) data for 49 high redshift (0.47<z<2.85),
luminous (11.7 < log L(bol) (Lsun) < 14.2) radio-powerful AGN, obtained to
constrain cool dust emission from starbursts concurrent with highly obscured
radiative-mode black hole (BH) accretion in massive galaxies which possess a
small radio jet. The sample was selected from WISE with extremely steep (red)
mid-infrared (MIR) colors and with compact radio emission from NVSS/FIRST.
Twenty-six sources are detected at 870 microns, and we find that the sample has
large mid- to far-infrared luminosity ratios consistent with a dominant and
highly obscured quasar. The rest-frame 3 GHz radio powers are 24.7 < log P3.0
GHz (W/Hz) < 27.3, and all sources are radio-intermediate or radio-loud. BH
mass estimates are 7.7 < log M(BH) (Msun) < 10.2. The rest frame 1-5 um SEDs
are very similar to the "Hot DOGs" (Hot Dust Obscured Galaxies), and steeper
(redder) than almost any other known extragalactic sources. ISM masses
estimated for the ALMA detected sources are 9.9 < log M(ISM) (Msun) < 11.75
assuming a dust temperature of 30K. The cool dust emission is consistent with
star formation rates (SFRs) reaching several thousand Msun/yr, depending on the
assumed dust temperature, however we cannot rule out the alternative that the
AGN powers all the emission in some cases. Our best constrained source has
radiative transfer solutions with ~ equal contributions from an obscured AGN
and a young (10-15 Myr) compact starburst. | astro-ph_GA |
On the distribution of the Cold Neutral Medium in galaxy discs: The Cold Neutral Medium (CNM) is an important part of the galactic gas cycle
and a precondition for the formation of molecular and star forming gas, yet its
distribution is still not fully understood. In this work we present extremely
high resolution simulations of spiral galaxies with time-dependent chemistry
such that we can track the formation of the CNM, its distribution within the
galaxy, and its correlation with star formation. We find no strong radial
dependence between the CNM fraction and total HI due to the decreasing
interstellar radiation field counterbalancing the decreasing gas column density
at larger galactic radii.However, the CNM fraction does increase in spiral arms
where the CNM distribution is clumpy, rather than continuous, overlapping more
closely with H2. The CNM doesn't extend out radially as far as HI, and the
vertical scale height is smaller in the outer galaxy compared to HI with no
flaring. The CNM column density scales with total midplane pressure and
disappears from the gas phase below values of PT/kB =1000 K/cm3. We find that
the star formation rate density follows a similar scaling law with CNM column
density to the total gas Kennicutt-Schmidt law. In the outer galaxy we produce
realistic vertical velocity dispersions in the HI purely from galactic dynamics
but our models do not predict CNM at the extremely large radii observed in HI
absorption studies of the Milky Way. We suggest that extended spiral arms might
produce isolated clumps of CNM at these radii. | astro-ph_GA |
On estimating angular momenta of infalling protostellar cores from
observations: We use numerical simulations of molecular cloud formation in the colliding
flow scenario to investigate the reliability of observational estimates of the
angular momenta of early-state, low-mass protostellar cores. We show that, with
suitable corrections for projection factors, molecular line observations of
velocity gradients in NH$_3$ can be used to provide reasonable estimates of
core angular momenta within a factor of two to three, with a few large
underestimates due to unfavorable viewing angles. Our results differ from
previous investigations which suggested that observations might overestimate
true angular momenta by as much as an order of magnitude; the difference is
probably due to the much smoother velocity field on small scales in our
simulations, which result from allowing turbulence to decay and gravitational
infall to dominate. The results emphasize the importance of understanding the
nature of 'turbulent' velocities, with implications for the formation of
protostellar disks during core collapse. | astro-ph_GA |
Narrow double-peaked emission lines of SDSS J131642.90+175332.5:
signature of a single or a binary AGN in a merger, jet-cloud interaction, or
unusual narrow-line region geometry: We present an analysis of the active galaxy SDSS J131642.90+175332.5, which
is remarkable because all of its narrow emission lines are double-peaked, and
because it additionally shows an extra broad component (FHWM ~ 1400 km/s) in
most of its forbidden lines, peaking in between the two narrow systems. The
peaks of the two narrow systems are separated by 400--500 km/s in velocity
space. The spectral characteristics of double-peaked [O III] emission have
previously been interpreted as a signature of dual or binary active galactic
nuclei (AGNs), among other models. In the context of the binary scenario, SDSS
J131642.90+175332.5 is a particularly good candidate because not just one line
but all of its emission lines are double-peaked. However, we also discuss a
number of other scenarios which can potentially account for double-peaked
narrow emission lines, including projection effects, a two-sided outflow,
jet-cloud interactions, special narrow-line region (NLR) geometries (disks,
bars, or inner spirals), and a galaxy merger with only one AGN illuminating two
NLRs. We argue that the similarity of the emission-line ratios in both systems,
and the presence of the very unusual broad component at intermediate velocity,
makes a close pair of unrelated AGNs unlikely, and rather argues for processes
in a single galaxy or merger. We describe future observations which can
distinguish between these remaining possibilities. | astro-ph_GA |
Dynamics of Starbursting Dwarf Galaxies. III. A HI study of 18 nearby
objects: We investigate the dynamics of starbursting dwarf galaxies, using both new
and archival HI observations. We consider 18 nearby galaxies that have been
resolved into single stars by HST observations, providing their star formation
history and total stellar mass. We find that 9 objects have a
regularly-rotating HI disk, 7 have a kinematically disturbed HI disk, and 2
show unsettled HI distributions. Two galaxies (NGC 5253 and UGC 6456) show a
velocity gradient along the minor axis of the HI disk, that we interpret as
strong radial motions. For galaxies with a regularly rotating disk we derive
rotation curves, while for galaxies with a kinematically disturbed disk we
estimate the rotation velocities in their outer parts. We derive baryonic
fractions within about 3 optical scale lengths and find that, on average,
baryons constitute at least 30$\%$ of the total mass. Despite the star
formation having injected $\sim$10$^{56}$ ergs in the ISM in the last $\sim$500
Myr, these starbursting dwarfs have both baryonic and gas fractions similar to
those of typical dwarf irregulars, suggesting that they did not eject a large
amount of gas out of their potential wells. | astro-ph_GA |
Mapping the Interstellar Reddening and Extinction towards Baade's Window
Using Minimum Light Colors of ab-type RR Lyrae Stars. Revelations from the
De-reddened Color-Magnitude Diagrams: We have obtained repeated images of 6 fields towards the Galactic bulge in 5
passbands (u, g, r, i, z) with the DECam imager on the Blanco 4m telescope at
CTIO. From over 1.6 billion individual photometric measurements in the field
centered on Baade's window, we have detected 4877 putative variable stars. 474
of these have been confirmed as fundamental mode RR Lyrae stars, whose colors
at minimum light yield line-of-sight reddening determinations as well as a
reddening law towards the Galactic Bulge which differs significantly from the
standard R_V = 3.1 formulation. Assuming that the stellar mix is invariant over
the 3 square-degree field, we are able to derive a line-of-sight reddening map
with sub-arcminute resolution, enabling us to obtain de-reddened and extinction
corrected color-magnitude diagrams (CMD's) of this bulge field using up to 2.5
million well-measured stars. The corrected CMD's show unprecedented detail and
expose sparsely populated sequences: e.g., delineation of the very wide red
giant branch, structure within the red giant clump, the full extent of the
horizontal branch, and a surprising bright feature which is likely due to stars
with ages younger than 1 Gyr. We use the RR Lyrae stars to trace the spatial
structure of the ancient stars, and find an exponential decline in density with
Galactocentric distance. We discuss ways in which our data products can be used
to explore the age and metallicity properties of the bulge, and how our larger
list of all variables is useful for learning to interpret future LSST alerts. | astro-ph_GA |
PAH Spectroscopy from 1-5 $μ$m: The PAH model predicts many weak emission features in the 1-5 $\mu$m region
that can resolve significant questions that it has faced since its inception in
the mid-80s. These features contain fundamental information about the PAH
population that is inaccessible via the much stronger PAH bands in the 5-20
$\mu$m region. Apart from the 3.3 $\mu$m band and plateau, PAH spectroscopy
across most of the 1-5 $\mu$m region has been unexplored due to its low
intrinsic intensity. ISO and Akari covered some of this wavelength range, but
lacked the combined sensitivity and resolution to measure the predicted bands
with sufficient fidelity. The spectroscopic capabilities of the NIRSpec
instrument on board JWST will make it possible to measure and fully
characterize many of the PAH features expected in this region. These include
the fundamental, overtone and combination C-D and C$\equiv$N stretching bands
of deuterated PAHs, cyano-PAHs (PAH-C$\equiv$ N), and the overtones and
combinations of the strong PAH bands that dominate the 5-20 $\mu$m region.
These bands will reveal the amount of D tied up in PAHs, the PAH D/H ratio, the
D distribution between PAH aliphatic and aromatic subcomponents, and delineate
key stages in PAH formation and evolution on an object-by-object basis and
within extended objects. If cyano-PAHs are present, these bands will also
reveal the amount of cyano groups tied up in PAHs, determine the N/C ratio
within that PAH subset, and distinguish between the bands near 4.5 $\mu$m that
arise from CD versus C$\equiv$N. | astro-ph_GA |
Heavy Element Absorption Systems at $5.0<z<6.8$: Metal-Poor Neutral Gas
and a Diminishing Signature of Highly Ionized Circumgalactic Matter: Ratios of different ions of the same element encode ionization information
independently from relative abundances in quasar absorption line systems,
crucial for understanding the multiphase nature and origin of absorbing gas,
particularly at $z>6$ where H I cannot be observed. Observational
considerations have limited such studies to a small number of sightlines, with
most surveys at $z>6$ focused upon the statistical properties of individual
ions such as Mg II or C IV. Here we compare high- and low-ionization absorption
within 69 intervening systems at $z>5$, including 16 systems at $z>6$, from
Magellan/FIRE spectra of 47 quasars together with a Keck/HIRES spectrum of the
`ultraluminous' $z=6.3$ quasar SDSSJ010013.02+280225.8. The highest redshift
absorbers increasingly exhibit low-ionization species alone, consistent with
previous single-ion surveys that show the frequency of Mg II is unchanging with
redshift while C IV absorption drops markedly toward $z=6$. We detect no C IV
or Si IV in half of all metal-line absorbers at $z>5.7$, with stacks not
revealing any slightly weaker C IV just below our detection threshold, and most
of the other half have $N_\mathrm{CII}>N_\mathrm{CIV}$. In contrast, only 20\%
of absorbers at 5.0--5.7 lack high-ionization gas, and a search of 25 HIRES
sightlines at $z\sim3$ yielded zero such examples. We infer these
low-ionization high-redshift absorption systems may be analogous to metal-poor
Damped Lyman-$\alpha$ systems ($\sim1\%$ of the absorber population at
$z\sim3$), based on incidence rates and absolute and relative column densities.
Simple photoionization models suggest that circumgalactic matter at redshift
six has systematically lower chemical abundances and experiences a softer
ionizing background relative to redshift three. | astro-ph_GA |
Chemical Diversity in the Ultra-faint Dwarf Galaxy Tucana II: We present the first detailed chemical abundance study of the ultra-faint
dwarf galaxy Tucana II based on high-resolution Magellan/MIKE spectra of four
red giant stars. The metallicity of these stars ranges from [Fe/H] = -3.2 to
-2.6, and all stars are low in neutron-capture abundances ([Sr/Fe] and [Ba/Fe]
< -1). However, a number of anomalous chemical signatures are present. Three
stars are carbon-enhanced, including the most metal-rich star. This star
([Fe/H]=-2.6) shows [Na,$\alpha$,Sc/Fe] < 0, suggesting an extended star
formation history with contributions from AGB stars and Type Ia supernovae. The
other carbon-enhanced stars have [Fe/H] < -3 and may be consistent with
enrichment by faint supernovae, if such supernovae can produce neutron-capture
elements. A fourth star with [Fe/H] = -3 is carbon-normal, and exhibits
distinct light element abundance ratios from the carbon-enhanced stars. The
carbon-normal star implies that at least two distinct nucleosynthesis sources,
both possibly associated with Population III stars, contributed to the early
chemical enrichment of this galaxy. Despite its very low luminosity, Tucana II
shows a diversity of chemical signatures that preclude it from being a simple
"one-shot" first galaxy, but still provide a window to star and galaxy
formation in the early universe. | astro-ph_GA |
Water emission from the high-mass star-forming region IRAS 17233-3606.
High water abundances at high velocities: We investigate the physical and chemical processes at work during the
formation of a massive protostar based on the observation of water in an
outflow from a very young object previously detected in H2 and SiO in the IRAS
17233-3606 region. We estimated the abundance of water to understand its
chemistry, and to constrain the mass of the emitting outflow. We present new
observations of shocked water obtained with the HIFI receiver onboard Herschel.
We detected water at high velocities in a range similar to SiO. We
self-consistently fitted these observations along with previous SiO data
through a state-of-the-art, one-dimensional, stationary C-shock model. We found
that a single model can explain the SiO and H2O emission in the red and blue
wings of the spectra. Remarkably, one common area, similar to that found for H2
emission, fits both the SiO and H2O emission regions. This shock model
subsequently allowed us to assess the shocked water column density,
N(H2O)=1.2x10^{18} cm^{-2}, mass, M(H2O)=12.5 M_earth, and its maximum
fractional abundance with respect to the total density, x(H2O)=1.4x10^{-4}. The
corresponding water abundance in fractional column density units ranges between
2.5x10^{-5} and 1.2x10^{-5}, in agreement with recent results obtained in
outflows from low- and high-mass young stellar objects. | astro-ph_GA |
TREX: Kinematic Characterisation of a High-Dispersion Intermediate-Age
Stellar Component in M33: The dwarf galaxy Triangulum (M33) presents an interesting testbed for
studying stellar halo formation: it is sufficiently massive so as to have
likely accreted smaller satellites, but also lies within the regime where
feedback and other "in-situ" formation mechanisms are expected to play a role.
In this work, we analyse the line-of-sight kinematics of stars across M33 from
the TREX survey with a view to understanding the origin of its halo. We split
our sample into two broad populations of varying age, comprising 2032 "old" red
giant branch (RGB) stars, and 671 "intermediate-age" asymptotic giant branch
(AGB) and carbon stars. We find decisive evidence for two distinct kinematic
components in both old and intermediate-age populations: a low-dispersion (~22
km/s) disk-like component co-rotating with M33's HI gas, and a significantly
higher-dispersion component (~50-60 km/s) which does not rotate in the same
plane as the gas and is thus interpreted as M33's stellar halo. While
kinematically similar, the fraction of stars associated with the halo component
differs significantly between the two populations: this is consistently ~10%
for the intermediate age population, but decreases from ~34% to ~10% as a
function of radius for the old population. We additionally find evidence that
the intermediate-age halo population is systematically offset from the systemic
velocity of M33 by ~25 km/s, with a preferred central LOS velocity of ~-155
km/s. This is the first detection and characterisation of an intermediate-age
halo in M33, and suggests in-situ formation mechanisms, as well as potentially
tidal interactions, have helped shaped it. | astro-ph_GA |
Self-similarity in the chemical evolution of galaxies and the delay time
distribution of SNe Ia: Recent improvements in the age dating of stellar populations and single stars
allow us to study the ages and abundance of stars and galaxies with
unprecedented accuracy. We here compare the relation between age and
\alpha-element abundances for stars in the solar neighborhood to that of local,
early-type galaxies. We find both relations to be very similar. Both fall into
two regimes with a flat slope for ages younger than ~9 Gyr and a steeper slope
for ages older than that value. This quantitative similarity seems surprising,
given the different types of galaxies and scales involved. For the sample of
early-type galaxies we also show that the data are inconsistent with literature
delay time distributions of either single or double Gaussian shape. The data
are consistent with a power law delay time distribution. We thus confirm that
the delay time distribution inferred for the Milky Way from chemical evolution
arguments also must apply to massive early-type galaxies. We also offer a
tentative explanation for the seeming universality of the age-[\alpha/Fe]
relation as the manifestation of averaging of different stellar populations
with varying chemical evolution histories. | astro-ph_GA |
Line shapes in narrow-line Seyfert 1 galaxies: a tracer of physical
properties?: Line profiles can provide fundamental information on the physics of active
galactic nuclei (AGN). In the case of narrow-line Seyfert 1 galaxies (NLS1s)
this is of particular importance since past studies revealed how their
permitted line profiles are well reproduced by a Lorentzian function instead of
a Gaussian. This has been explained with different properties of the broad-line
region (BLR), which may present a more pronounced turbulent motions in NLS1s
with respect to other AGN. We investigated the line profiles in a recent large
NLS1 sample classified using SDSS, and we divided the sources into two
subsamples according to their line shapes, Gaussian or Lorentzian. The line
profiles clearly separate all the properties of NLS1s. Black hole mass,
Eddington ratio, [O III], and Fe II strength are all very different in the
Lorentzian and Gaussian samples. We interpret this in terms of evolution within
the class of NLS1s. The Lorentzian sources may be the youngest objects, while
Gaussian profiles may be typically associated to more evolved objects. Further
detailed spectroscopic studies are needed to fully confirm our hypothesis. | astro-ph_GA |
Inferring the star formation histories of the most massive and passive
early-type galaxies at z<0.3: Massive galaxies are key probes to understand how the baryonic matter evolves
within the dark matter halos. We use the "archaeological" approach to infer the
stellar population properties and star formation histories of the most massive
(M > 10^10.75 Msun) and passive early-type galaxies (ETGs) at 0 < z < 0.3,
based on stacked, high signal to noise ratio (SNR), Sloan Digital Sky Survey
spectra. We exploit the information present in the full-spectrum by means of
the STARLIGHT public code to retrieve the ETGs evolutionary properties, such as
age, metallicity and star formation history. We find that the stellar
metallicities are slightly supersolar (Z ~ 0.027 +/- 0.002) and do not depend
on redshift. Dust extinction is very low, with a mean of Av ~ 0.08 +/- 0.03
mag. The ETGs show an anti-hierarchical evolution (downsizing) where more
massive galaxies are older. The SFHs can be approximated by a parametric
function of the form SFR(t) \propto \tau^-(c+1) t^(c) exp(-t/\tau), with
typical short e-folding times of \tau ~ 0.6 - 0.8 Gyr (and a dispersion of +/-
0.1 Gyr) and c ~ 0.1 (and a dispersion of +/- 0.05). The inferred SFHs are also
used to place constraints on the properties and evolution of the ETG
progenitors. In particular, the ETGs of our samples should have formed most
stars through a phase of vigorous star formation (SFRs > 350-400 Msun yr^-1) at
z ~ 4 - 5, and are quiescent by z ~ 1.5 -2. Our results represent an attempt to
demonstrate quantitatively the evolutionary link between the most massive ETGs
at z < 0.3 and the properties of suitable progenitors at high redshifts, also
showing that the full-spectrum fitting is a powerful approach to reconstruct
the star formation histories of massive quiescent galaxies. | astro-ph_GA |
A Search For Supernova Remnants in The Nearby Spiral Galaxy M74 (NGC
628): We have identified nine new SNR candidates in M74 with [S II]/H$\alpha$
$\geq$ 0.4 as the basic criterion. We obtain [S II]/H$\alpha$ ratio in the
range from 0.40 to 0.91 and H$\alpha$ intensities from 2.8 $\times$ $10^{-15}$
erg cm$^{-2}$ s$^{-1}$ to 1.7 $\times$ $10^{-14}$ erg cm$^{-2}$ s$^{-1}$. We
also present spectral follow-up observations of the SNR candidates and can
confirm only three of them (SNR2, SNR3, and SNR5). The lack of confirmation for
the rest might be due to the contamination by the nearby H II emission regions
as well as due to the inaccurate positioning of the long slit on these objects.
In addition, we search the $Chandra$ Observatory archival data for the X-ray
counterparts to the optically identified candidates. We find positional
coincidence with only three SNR candidates, SNR1, SNR2, and SNR8. The spectrum
of SNR2 yields a shock temperature of 10.8 keV with an ionization timescale of
1.6 $\times$ 10$^{10}$ s cm$^{-3}$ indicating a relatively young remnant in an
early Sedov phase which is not supported by our optical wavelength analysis.
Given the high luminosity of 10$^{39}$ erg s$^{-1}$ and the characteristics of
the X-ray spectrum, we favor an Ultra Luminous X-ray Source interpretation for
this source associated with an SNR. We calculate an X-ray flux upper limit of
9.0 $\times$ $10^{-15}$ erg cm$^{-2}$ s$^{-1}$ for the rest of the SNRs
including spectroscopically identified SNR3 and SNR5. | astro-ph_GA |
Abundance gradients in spiral disks: is the gradient inversion at high
redshift real?: We compute the abundance gradients along the disk of the Milky Way by means
of the two-infall model: in particular, the gradients of oxygen and iron and
their temporal evolution. First, we explore the effects of several physical
processes which influence the formation and evolution of abundance gradients.
They are: i) the inside-out formation of the disk, ii) a threshold in the gas
density for star formation, iii) a variable star formation efficiency along the
disk, iv) radial flows and their speed, and v) different total surface mass
density (gas plus stars) distributions for the halo. We are able to reproduce
at best the present day gradients of oxygen and iron if we assume an inside-out
formation, no threshold gas density, a constant efficiency of star formation
along the disk and radial gas flows. It is particularly important the choice of
the velocity pattern for radial flows and the combination of this velocity
pattern with the surface mass density distribution in the halo. Having selected
the best model, we then explore the evolution of abundance gradients in time
and find that the gradients in general steepen in time and that at redshift z~3
there is a gradient inversion in the inner regions of the disk, in the sense
that at early epochs the oxygen abundance decreases toward the Galactic center.
This effect, which has been observed, is naturally produced by our models if an
inside-out formation of the disk and and a constant star formation efficiency
are assumed. The inversion is due to the fact that in the inside-out formation
a strong infall of primordial gas, contrasting chemical enrichment, is present
in the innermost disk regions at early times. The gradient inversion remains
also in the presence of radial flows, either with constant or variable speed in
time, and this is a new result. | astro-ph_GA |
Impact of turbulence intensity and fragmentation velocity on dust
particle size evolution and non-ideal magnetohydrodynamics effects: We investigate the influence of dust particle size evolution on non-ideal
magnetohydrodynamic effects during the collapsing phase of star-forming cores,
taking both the turbulence intensity in the collapsing cloud core and the
fragmentation velocity of dust particles as parameters. When the turbulence
intensity is small, the dust particles do not grow significantly, and the
non-ideal MHD effects work efficiently in high-density regions. The dust
particles rapidly grow in a strongly turbulent environment, while the
efficiency of non-ideal MHD effects in such an environment depends on the
fragmentation velocity of the dust particles. When the fragmentation velocity
is small, turbulence promotes coagulation growth and collisional fragmentation
of dust particles, producing small dust particles. In this case, the adsorption
of charged particles on the dust particle surfaces becomes efficient and the
abundance of charged particles decreases, making non-ideal MHD effects
effective at high densities. On the other hand, when the fragmentation velocity
is high, dust particles are less likely to fragment, even if the turbulence is
strong. In this case, the production of small dust particles become inefficient
and non-ideal MHD effects become less effective. We also investigate the effect
of the dust composition on the star and disk formation processes. We constrain
the turbulence intensity of a collapsing core and the fragmentation velocity of
dust for circumstellar disk formation due to the dissipation of the magnetic
field. | astro-ph_GA |
Stellar Dynamics and Stellar Phenomena Near A Massive Black Hole: Most galactic nuclei harbor a massive black hole (MBH), whose birth and
evolution are closely linked to those of its host galaxy. The unique conditions
near the MBH: high velocity and density in the steep potential of a massive
singular relativistic object, lead to unusual modes of stellar birth,
evolution, dynamics and death. A complex network of dynamical mechanisms,
operating on multiple timescales, deflect stars to orbits that intercept the
MBH. Such close encounters lead to energetic interactions with observable
signatures and consequences for the evolution of the MBH and its stellar
environment. Galactic nuclei are astrophysical laboratories that test and
challenge our understanding of MBH formation, strong gravity, stellar dynamics,
and stellar physics. I review from a theoretical perspective the wide range of
stellar phenomena that occur near MBHs, focusing on the role of stellar
dynamics near an isolated MBH in a relaxed stellar cusp. | astro-ph_GA |
The angular momentum of disc galaxies at z=1: We investigate the relation between stellar mass and specific stellar angular
momentum, or `Fall relation', for a sample of 17 isolated, regularly rotating
disc galaxies at z=1. All galaxies have a) rotation curves determined from
Halpha emission-line data; b) HST imaging in optical and infrared filters; c)
robust determinations of their stellar masses. We use HST images in f814w and
f160w filters, roughly corresponding to rest-frames B and I bands, to extract
surface brightness profiles for our systems. We robustly bracket the specific
angular momentum by assuming that rotation curves beyond the outermost Halpha
rotation point stay either flat or follow a Keplerian fall-off. By comparing
our measurements with those determined for disc galaxies in the local Universe,
we find no evolution in the Fall relation in the redshift range 0<z<1,
regardless of the band used and despite the uncertainties in the stellar
rotation curves at large radii. This result holds unless stellar masses at z=1
are systematically underestimated by more than 50%. Our findings are compatible
with expectations based on a LCDM cosmological framework and support a scenario
where both the stellar Tully-Fisher and mass-size relations for spirals do not
evolve significantly in this redshift range. | astro-ph_GA |
Evaluating the Magnetorotational Instability's Dependence on Numerical
Algorithms and Resolution: We have studied saturated, MRI-driven turbulence using three-dimensional,
isothermal simulations with resolutions that extend from 64 to 192 zones in
each direction. The simulations were performed with several higher order
Godunov algorithms. A variety of reconstruction strategies as well as a variety
of Riemann solvers are tried. We show that the details of the isothermal
MRI-driven turbulence depend principally on the Riemann solver and secondarily
on the reconstruction strategy. Furthermore, we find that the effective
viscosity parameter parameter tends to show progressively smaller decrements
with increasing resolution when the best reconstruction strategy (WENO) and the
best Riemann solver (linearized)are used. We attribute this result to the more
sophisticated dissipation mechanisms that are used in higher-order Godunov
schemes. Spectral analysis and transfer functions have been used to quantify
the dissipative processes in these higher-order Godunov schemes. | astro-ph_GA |
Neutral island statistics during reionization from 21-cm tomography: We present the prospects of extracting information about the Epoch of
Reionization by identifying the remaining neutral regions, referred to as
islands, in tomographic observations of the redshifted 21-cm signal. Using
simulated data sets we show that at late times the 21-cm power spectrum is
fairly insensitive to the details of the reionization process but that the
properties of the neutral islands can distinguish between different
reionization scenarios. We compare the properties of these islands with those
of ionized bubbles. At equivalent volume filling fractions, neutral islands
tend to be fewer in number but larger compared to the ionized bubbles. In
addition, the evolution of the size distribution of neutral islands is found to
be slower than that of the ionized bubbles and also their percolation behaviour
differs substantially. Even though the neutral islands are relatively rare,
they will be easier to identify in observations with the low-frequency
component of the Square Kilometre Array (SKA-Low) due to their larger size and
the lower noise levels at lower redshifts. The size distribution of neutral
islands at the late stages of reionization is found to depend on the source
properties, such as the ionizing efficiency of the sources and their minimum
mass. We find the longest line of sight through a neutral region to be more
than 100 comoving Mpc until very late stages (90-95 per cent reionized), which
may have relevance for the long absorption trough at $z=5.6-5.8$ in the
spectrum of quasar ULAS J0148+0600. | astro-ph_GA |
Surface chemistry in the interstellar medium - I - H2 formation by
Langmuir-Hinshelwood and Eley-Rideal mechanisms: H2 formation remains a major issue for the understanding of interstellar
physics. We investigate H2 formation in the interstellar medium at the light of
the most recent experimental and theoretical data. We implemented detailed H2
formation mechanisms on grains surface in the Meudon PDR code : i)
Langmuir-Hinshelwood mechanism taking into account the contribution of the
different sizes of dust grains in the diffusion processes and ii) the
Eley-Rideal mechanism. We show that, thanks to these processes, H2 can be
formed even in regions where dust temperature is larger than 25 K. We also show
that formation by Eley-Rideal mechanism can be a significant source of heating
of the gas. We derive line intensities for various astrophysical conditions.
Such an approach results in an enhanced H2 formation rate compared to the
standard formation determined by observations in absorption in the UV. We
derive some H2 line intensities for isobaric and isochoric models. | astro-ph_GA |
Constraining UV Continuum Slopes of Active Galactic Nuclei With CLOUDY
Models of Broad Line Region EUV Emission Lines: Understanding the composition and structure of the broad-line region (BLR) of
active galactic nuclei (AGN) is important for answering many outstanding
questions in supermassive black hole evolution, galaxy evolution, and
ionization of the intergalactic medium. We used single-epoch UV spectra from
the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope to measure
EUV emission-line fluxes from four individual AGN with $0.49 \le z \le 0.64$,
two AGN with $0.32 \le z \le 0.40$, and a composite of 159 AGN. With the Cloudy
photoionization code, we calculated emission-line fluxes from BLR clouds with a
range of density, hydrogen ionizing flux and incident continuum spectral
indices. The photoionization grids were fit to the observations using
single-component and locally optimally emitting cloud (LOC) models. The LOC
models provide good fits to the measured fluxes, while the single-component
models do not. The UV spectral indices preferred by our LOC models are
consistent with those measured from COS spectra. EUV emission lines such as N
IV \lambda 765, O II \lambda 833, and O III \lambda 834 originate primarily
from gas with electron temperatures between 37000 K and 55000 K. This gas is
found in BLR clouds with high hydrogen densities (n_H \ge 10^12 cm^-3) and
hydrogen ionizing photon fluxes (\Phi_H \ge 10^22 cm^-2 s^-1). | astro-ph_GA |
The JCMT Gould Belt Survey: First results from SCUBA-2 observations of
the Cepheus Flare Region: We present observations of the Cepheus Flare obtained as part of the James
Clerk Maxwell Telescope (JCMT) Gould Belt Legacy Survey (GBLS) with the SCUBA-2
instrument. We produce a catalogue of sources found by SCUBA-2, and separate
these into starless cores and protostars. We determine masses and densities for
each of our sources, using source temperatures determined by the Herschel Gould
Belt Survey. We compare the properties of starless cores in four different
molecular clouds: L1147/58, L1172/74, L1251 and L1228. We find that the core
mass functions for each region typically show shallower-than-Salpeter
behaviour. We find that L1147/58 and L1228 have a high ratio of starless cores
to Class II protostars, while L1251 and L1174 have a low ratio, consistent with
the latter regions being more active sites of current star formation, while the
former are forming stars less actively. We determine that, if modelled as
thermally-supported Bonnor-Ebert spheres, most of our cores have stable
configurations accessible to them. We estimate the external pressures on our
cores using archival $^{13}$CO velocity dispersion measurements and find that
our cores are typically pressure-confined, rather than gravitationally bound.
We perform a virial analysis on our cores, and find that they typically cannot
be supported against collapse by internal thermal energy alone, due primarily
to the measured external pressures. This suggests that the dominant mode of
internal support in starless cores in the Cepheus Flare is either non-thermal
motions or internal magnetic fields. | astro-ph_GA |
EMPRESS. XI. SDSS and JWST Search for Local and z~4-5 Extremely
Metal-Poor Galaxies (EMPGs): Clustering and Chemical Properties of Local
EMPGs: We search for local extremely metal-poor galaxies (EMPGs), selecting
photometric candidates by broadband color excess and machine-learning
techniques with the SDSS photometric data. After removing stellar contaminants
by shallow spectroscopy with Seimei and Nayuta telescopes, we confirm that
three candidates are EMPGs with 0.05--0.1 $Z_\odot$ by deep Magellan/MagE
spectroscopy for faint {\sc[Oiii]}$\lambda$4363 lines. Using a statistical
sample consisting of 105 spectroscopically-confirmed EMPGs taken from our study
and the literature, we calculate cross-correlation function (CCF) of the EMPGs
and all SDSS galaxies to quantify environments of EMPGs. Comparing another CCF
of all SDSS galaxies and comparison SDSS galaxies in the same stellar mass
range ($10^{7.0}-10^{8.4} M_\odot$), we find no significant ($>1\sigma$)
difference between these two CCFs. We also compare mass-metallicity relations
(MZRs) of the EMPGs and those of galaxies at $z\sim$ 0--4 with a steady
chemical evolution model and find that the EMPG MZR is comparable with the
model prediction on average. These clustering and chemical properties of EMPGs
are explained by a scenario of stochastic metal-poor gas accretion on
metal-rich galaxies showing metal-poor star formation. Extending the broadband
color-excess technique to a high-$z$ EMPG search, we select 17 candidates of
$z\sim$ 4--5 EMPGs with the deep ($\simeq30$ mag) near-infrared JWST/NIRCam
images obtained by ERO and ERS programs. We find galaxy candidates with
negligible {\sc[Oiii]}$\lambda\lambda$4959,5007 emission weaker than the local
EMPGs and known high-$z$ galaxies, suggesting that some of these candidates may
fall in 0--0.01 $Z_\odot$, which potentially break the lowest metallicity limit
known to date. | astro-ph_GA |
Fullerenes in circumstellar and interstellar environments: In recent years, the fullerene species C60 (and to a lesser extent also C70)
has been reported in the mid-IR spectra of various astronomical objects. Cosmic
fullerenes form in the circumstellar material of evolved stars, and survive in
the interstellar medium (ISM). It is not entirely clear how they form or what
their excitation mechanism is. | astro-ph_GA |
Reconciling the emission mechanism discrepancy in Mira's tail, and its
evolution in an interface with shear: GALEX observations of the Mira AB binary system revealed a surrounding
structure that has been successfully hydrodynamically interpreted as a bow
shock and tail of ram-pressure-stripped material. Even the narrow tail,
initially difficult to model, has been understood as the effect of the passage
of Mira from a warm neutral medium into a hot, low-density medium, postulated
to be the Local Bubble. However, no model to date has explained the observed
kink and associated general curvature of the tail. We test the hypothesis that
before entering the Local Bubble, Mira was travelling through a shear flow with
approximately 1/3 Mira's own velocity at an angle of ~30degrees to Mira's
proper motion. The hypothesis reproduces the kinked nature of Mira's tail and
predicts recompression and reheating of the tail material to the same or
greater levels of density and temperature predicted in the shock. This provides
a heat source for the FUV emission, allowing for an extended lifetime of the
FUV emission in line with other estimates of the age of the tail. The
uniqueness of Mira's situation implies that the chances of observing other FUV
tails behind AGB stars is highly unlikely. | astro-ph_GA |
BiPoS1 -- a computer programme for the dynamical processing of the
initial binary star population: The first version of the Binary Population Synthesizer (BiPoS1) is made
publicly available. It allows to efficiently calculate binary distribution
functions after the dynamical processing of a realistic population of binary
stars during the first few Myr in the hosting embedded star cluster. Instead of
time-consuming N-body simulations, BiPoS1 uses a stellar dynamical operator
which determines the fraction of surviving binaries depending on the binding
energy of the binaries. The stellar dynamical operator depends on the initial
star cluster density as well as the time until the residual gas of the star
cluster is expelled. BiPoS1 has also a galactic-field mode, in order to
synthesize the stellar population of a whole galaxy. At the time of gas
expulsion, the dynamical processing of the binary population is assumed to
efficiently end due to the subsequent expansion of the star cluster. While
BiPoS1 $has been used previously unpublished, here we demonstrate its use in
the modelling of the binary populations in the Orion Nebula Cluster, in OB
associations and as an input for simulations of globular clusters. | astro-ph_GA |
A universal, turbulence-regulated star formation law: from Milky Way
clouds to high-redshift disk and starburst galaxies: Whilst the star formation rate (SFR) of molecular clouds and galaxies is key
in understanding galaxy evolution, the physical processes which determine the
SFR remain unclear. This uncertainty about the underlying physics has resulted
in various different star formation laws, all having substantial intrinsic
scatter. Extending upon previous works that define the column density of star
formation (Sigma_SFR) by the gas column density (Sigma_gas), we develop a new
universal star formation (SF) law based on the multi-freefall prescription of
gas. This new SF law relies predominantly on the probability density function
(PDF) and on the sonic Mach number of the turbulence in the star-forming
clouds. By doing so we derive a relation where the star formation rate (SFR)
correlates with the molecular gas mass per multi-freefall time, whereas
previous models had used the average, single-freefall time. We define a new
quantity called maximum (multi-freefall) gas consumption rate (MGCR) and show
that the actual SFR is only about 0.4% of this maximum possible SFR, confirming
the observed low efficiency of star formation. We show that placing
observations in this new framework (Sigma_SFR vs. MGCR) yields a significantly
improved correlation with 3-4 times reduced scatter compared to previous SF
laws and a goodness-of-fit parameter R^2=0.97. By inverting our new
relationship, we provide sonic Mach number predictions for kpc-scale
observations of Local Group galaxies as well as unresolved observations of
local and high-redshift disk and starburst galaxies that do not have
independent, reliable estimates for the turbulent cloud Mach number. | astro-ph_GA |
The THESAN project: Lyman-alpha emitter luminosity function calibration: The observability of Lyman-alpha emitting galaxies (LAEs) during the Epoch of
Reionization can provide a sensitive probe of the evolving neutral hydrogen gas
distribution, thus setting valuable constraints to distinguish different
reionization models. In this study, we utilize the new THESAN suite of
large-volume (95.5 cMpc) cosmological radiation-hydrodynamic simulations to
directly model the Ly$\alpha$ emission from individual galaxies and the
subsequent transmission through the intergalactic medium. THESAN combines the
AREPO-RT radiation-hydrodynamic solver with the IllustrisTNG galaxy formation
model and includes high- and medium-resolution simulations designed to
investigate the impacts of halo-mass-dependent escape fractions, alternative
dark matter models, and numerical convergence. We find important differences in
the Ly$\alpha$ transmission based on reionization history, bubble morphology,
frequency offset from line centre, and galaxy brightness. For a given global
neutral fraction, Ly$\alpha$ transmission reduces when low mass haloes dominate
reionization over high mass haloes. Furthermore, the variation across
sightlines for a single galaxy is greater than the variation across all
galaxies. This collectively affects the visibility of LAEs, directly impacting
observed Ly$\alpha$ luminosity functions (LFs). We employ Gaussian Process
Regression using SWIFTEmulator to rapidly constrain an empirical model for dust
escape fractions and emergent spectral line profiles to match observed LFs. We
find that dust strongly impacts the Ly$\alpha$ transmission and covering
fractions of $M_{UV} < -19$ galaxies in $M_{vir} > 10^{11} {\rm M}_{\odot}$
haloes, such that the dominant mode of removing Ly$\alpha$ photons in non-LAEs
changes from low IGM transmission to high dust absorption around $z \sim 7$. | astro-ph_GA |
Morphological evolution in situ: Disk-dominated cluster red sequences at
z ~ 1.25: We have carried out a joint photometric and structural analysis of red
sequence galaxies in four clusters at a mean redshift of z ~ 1.25 using optical
and near-IR HST imaging reaching to at least 3 magnitudes fainter than $M^*$.
As expected, the photometry and overall galaxy sizes imply purely passive
evolution of stellar populations in red sequence cluster galaxies. However, the
morphologies of red sequence cluster galaxies at these redshifts show
significant differences to those of local counterparts. Apart from the most
massive galaxies, the high redshift red sequence galaxies are significantly
diskier than their low redshift analogues. These galaxies also show significant
colour gradients, again not present in their low redshift equivalents, most
straightforwardly explained by radial age gradients. A clear implication of
these findings is that red sequence cluster galaxies originally arrive on the
sequence as disk-dominated galaxies whose disks subsequently fade or evolve
secularly to end up as high S\'ersic index early-type galaxies (classical S0s
or possibly ellipticals) at lower redshift. The apparent lack of growth seen in
a comparison of high and low redshift red sequence galaxies implies that any
evolution is internal and is unlikely to involve significant mergers. While
significant star formation may have ended at high redshift, the cluster red
sequence population continues to evolve (morphologically) for several Gyrs
thereafter. | astro-ph_GA |
Seeking the growth of the first black hole seeds with JWST: In this paper we provide predictions for the BH population that would be
observable with planned JWST surveys at $5 \le z \le 15$. We base our study on
the recently developed Cosmic Archaeology Tool (CAT), which allows us to model
BH seeds formation and growth, while being consistent with the general
population of AGNs and galaxies observed at $4 \le z \le 7$. We find that JWST
planned surveys will provide a complementary view on active BHs at $z > 5$,
with JADES-Medium/-Deep being capable of detecting the numerous BHs that
populate the faint-end of the distribution, COSMOS-Web sampling a large enough
area to detect the rarest brightest systems, and CEERS/PRIMER bridging the gap
between these two regimes. The relatively small field of view of the above
surveys preferentially selects BHs with masses $6 \leq {\rm Log} (M_{\rm
BH}/M_\odot) < 8$ at $7 \le z < 10$, residing in relatively metal poor (${\rm
Log} (Z/Z_\odot) \ge -2$) and massive ($8\leq {\rm Log} (M_*/M_\odot) < 10$)
galaxies. At $z \ge 10$, only JADES-Deep will have the sensitivity to detect
growing BHs with masses $4 \leq {\rm Log} (M_{\rm BH}/M_\odot) < 6$, hosted by
more metal poor ($-3 \leq {\rm Log} (Z/Z_\odot) < -2$) and less massive ($6
\leq {\rm Log} (M_*/M_\odot) < 8$) galaxies. In our model, the latter
population corresponds to heavy BH seeds formed by the direct collapse of
super-massive stars in their earliest phases of mass growth. Detecting these
systems would provide invaluable insights on the nature and early growth of the
first BH seeds. | astro-ph_GA |
Mapping the Galactic Halo VIII: Quantifying substructure: We have measured the amount of kinematic substructure in the Galactic halo
using the final data set from the Spaghetti project, a pencil-beam high
latitude sky survey. Our sample contains 101 photometrically selected and
spectroscopically confirmed giants with accurate distance, radial velocity and
metallicity information. We have developed a new clustering estimator: the
"4distance" measure, which when applied to our data set leads to the
identification of 1 group and 7 pairs of clumped stars. The group, with 6
members, can confidently be matched to tidal debris of the Sagittarius dwarf
galaxy. Two pairs match the properties of known Virgo structures. Using models
of the disruption of Sagittarius in Galactic potentials with different degrees
of dark halo flattening, we show that this favors a spherical or prolate halo
shape, as demonstrated by Newberg et al. (2007) using SDSS data. One additional
pair can be linked to older Sagittarius debris. We find that 20% of the stars
in the Spaghetti data set are in substructures. From comparison with random
data sets we derive a very conservative lower limit of 10% to the amount of
substructure in the halo. However, comparison to numerical simulations shows
that our results are also consistent with a halo entirely built up from
disrupted satellites, provided the dominating features are relatively broad due
to early merging or relatively heavy progenitor satellites. | astro-ph_GA |
Radio Jet Feedback and Star Formation in Heavily Obscured Quasars at
Redshifts ~0.3-3, I: ALMA Observations: We present ALMA 870 micron (345 GHz) data for 49 high redshift (0.47<z<2.85),
luminous (11.7 < log L(bol) (Lsun) < 14.2) radio-powerful AGN, obtained to
constrain cool dust emission from starbursts concurrent with highly obscured
radiative-mode black hole (BH) accretion in massive galaxies which possess a
small radio jet. The sample was selected from WISE with extremely steep (red)
mid-infrared (MIR) colors and with compact radio emission from NVSS/FIRST.
Twenty-six sources are detected at 870 microns, and we find that the sample has
large mid- to far-infrared luminosity ratios consistent with a dominant and
highly obscured quasar. The rest-frame 3 GHz radio powers are 24.7 < log P3.0
GHz (W/Hz) < 27.3, and all sources are radio-intermediate or radio-loud. BH
mass estimates are 7.7 < log M(BH) (Msun) < 10.2. The rest frame 1-5 um SEDs
are very similar to the "Hot DOGs" (Hot Dust Obscured Galaxies), and steeper
(redder) than almost any other known extragalactic sources. ISM masses
estimated for the ALMA detected sources are 9.9 < log M(ISM) (Msun) < 11.75
assuming a dust temperature of 30K. The cool dust emission is consistent with
star formation rates (SFRs) reaching several thousand Msun/yr, depending on the
assumed dust temperature, however we cannot rule out the alternative that the
AGN powers all the emission in some cases. Our best constrained source has
radiative transfer solutions with ~ equal contributions from an obscured AGN
and a young (10-15 Myr) compact starburst. | astro-ph_GA |
Evolution of dust extinction curves in galaxy simulation: To understand the evolution of extinction curve, we calculate the dust
evolution in a galaxy using smoothed particle hydrodynamics simulations
incorporating stellar dust production, dust destruction in supernova shocks,
grain growth by accretion and coagulation, and grain disruption by shattering.
The dust species are separated into carbonaceous dust and silicate. The
evolution of grain size distribution is considered by dividing grain population
into large and small gains, which allows us to estimate extinction curves. We
examine the dependence of extinction curves on the position, gas density, and
metallicity in the galaxy, and find that extinction curves are flat at $t
\lesssim 0.3$ Gyr because stellar dust production dominates the total dust
abundance. The 2175 \AA\ bump and far-ultraviolet (FUV) rise become prominent
after dust growth by accretion. At $t \gtrsim 3$ Gyr, shattering works
efficiently in the outer disc and low density regions, so extinction curves
show a very strong 2175 \AA\ bump and steep FUV rise. The extinction curves at
$t\gtrsim 3$ Gyr are consistent with the Milky Way extinction curve, which
implies that we successfully included the necessary dust processes in the
model. The outer disc component caused by stellar feedback has an extinction
curves with a weaker 2175 \AA\ bump and flatter FUV slope. The strong
contribution of carbonaceous dust tends to underproduce the FUV rise in the
Small Magellanic Cloud extinction curve, which supports selective loss of small
carbonaceous dust in the galaxy. The snapshot at young ages also explain the
extinction curves in high-redshift quasars. | astro-ph_GA |
30 Years of Star Formation at UKIRT: It's safe to say that UKIRT's contribution to star formation at
near-infrared, mid-infrared, and even sub-millimetre wavelengths has been
considerable. From the early days of single-detector photometers, through the
development of 2-D arrays and complex multi-mode imager-spectrometers, to the
present-day large-format imager WFCAM, UKIRT has offered the international
community access to some of the world's most innovating, competitive, and
versatile instrumentation possible. Suffice to say, UKIRT users have made the
most of these instruments! In this article I try to give a taste of the variety
of star formation research that has come to pass at UKIRT (with apologies to
those whose important work I fail to mention). | astro-ph_GA |
The cosmic abundance of cold gas in the local Universe: We determine the cosmic abundance of molecular hydrogen (H2) in the local
universe from the xCOLD GASS survey. To constrain the H2 mass function at low
masses and correct for the effect of the lower stellar mass limit of 10^9 Msun
in the xCOLD GASS survey, we use an empirical approach based on an observed
scaling relation between star formation rate and gas mass. We also constrain
the HI and HI+H2 mass functions using the xGASS survey, and compare it to the
HI mass function from the ALFALFA survey. We find the cosmic abundance of
molecular gas in the local Universe to be Omega_H2=(5.34+/-0.47)x10^-5 h^-1.
Molecular gas accounts for 19.6 +/- 3.9% of the total abundance of cold gas,
Omega_HI+H2=(4.66+/-0.70)x10^-4 h^-1. Galaxies with stellar masses in excess of
10^9 Msun account for 89% of the molecular gas in the local Universe, while in
comparison such galaxies only contain 73% of the cold atomic gas as traced by
the HI 21cm line. The xCOLD GASS CO, molecular gas and cold gas mass functions
and Omega_H2 measurements provide constraints for models of galaxy evolution
and help to anchor blind ALMA and NOEMA surveys attempting to determine the
abundance of molecular gas at high redshifts. | astro-ph_GA |
Black hole mass measurement using ALMA observations of [CI] and CO
emissions in the Seyfert 1 galaxy NGC7469: We present a supermassive black hole (SMBH) mass measurement in the Seyfert 1
galaxy NGC7469 using Atacama Large Millimeter/submillimeter Array (ALMA)
observations of the atomic-${\rm [CI]}$(1-0) and molecular-$^{12}$CO(1-0)
emission lines at the spatial resolution of $\approx0.3$" (or $\approx$ 100
pc). These emissions reveal that NGC7469 hosts a circumnuclear gas disc (CND)
with a ring-like structure and a two-arm/bi-symmetric spiral pattern within it,
surrounded by a starbursting ring. The CND has a relatively low
$\sigma/V\approx0.35$ ($r\sim0.5$") and $\sim0.19$ ($r>0.5"$), suggesting that
the gas is dynamically settled and suitable for dynamically deriving the mass
of its central source. As is expected from X-ray dominated region (XDR) effects
that dramatically increase an atomic carbon abundance by dissociating CO
molecules, we suggest that the atomic [CI](1-0) emission is a better probe of
SMBH masses than CO emission in AGNs. Our dynamical model using the ${\rm
[CI]}$(1-0) kinematics yields a $M_{\rm
BH}=1.78^{+2.69}_{-1.10}\times10^7$M$_\odot$ and $M/L_{\rm
F547M}=2.25^{+0.40}_{-0.43}$ (M$_\odot$/L$_\odot$). The model using the CO(1-0)
kinematics also gives a consistent $M_{\rm BH}$ with a larger uncertainty, up
to an order of magnitude, i.e.\ $M_{\rm
BH}=1.60^{+11.52}_{-1.45}\times10^7$M$_\odot$. This newly dynamical $M_{\rm
BH}$ is $\approx$ 2 times higher than the mass determined from the
reverberation mapped (RM) method using emissions arising in the unresolved
broad-line region (BLR). Given this new $M_{\rm BH}$, we are able to constrain
the specific RM dimensionless scaling factor of $f=7.2^{+4.2}_{-3.4}$ for the
AGN BLR in NGC7469. The gas within the unresolved BLR thus has a Keplerian
virial velocity component and the inclination of
$i\approx11.0^\circ$$_{-2.5}^{+2.2}$, confirming its face-on orientation in a
Seyfert 1 AGN by assuming a geometrically thin BLR model. | astro-ph_GA |
Chemical abundances of distant extremely metal-poor unevolved stars: Aims: The purpose of our study is to determine the chemical composition of a
sample of 16 candidate Extremely Metal-Poor (EMP) dwarf stars, extracted from
the Sloan Digital Sky Survey (SDSS). There are two main purposes: in the first
place to verify the reliability of the metallicity estimates derived from the
SDSS spectra; in the second place to see if the abundance trends found for the
brighter nearer stars studied previously also hold for this sample of fainter,
more distant stars. Methods: We used the UVES at the VLT to obtain
high-resolution spectra of the programme stars. The abundances were determined
by an automatic analysis with the MyGIsFOS code, with the exception of lithium,
for which the abundances were determined from the measured equivalent widths of
the Li I resonance doublet. Results: All candidates are confirmed to be EMP
stars, with [Fe/H]<= -3.0. The chemical composition of the sample of stars is
similar to that of brighter and nearer samples. We measured the lithium
abundance for 12 stars and provide stringent upper limits for three other
stars, for a fourth star the upper limit is not significant, owing to the low
signal-to noise ratio of the spectrum. The "meltdown" of the Spite plateau is
confirmed, but some of the lowest metallicity stars of the sample lie on the
plateau. Conclusions: The concordance of the metallicities derived from
high-resolution spectra and those estimated from the SDSS spectra suggests that
the latter may be used to study the metallicity distribution of the halo. The
abundance pattern suggests that the halo was well mixed for all probed
metallicities and distances. The fact that at the lowest metallicities we find
stars on the Spite plateau suggests that the meltdown depends on at least
another parameter, besides metallicity. (abridged) | astro-ph_GA |
Ionised gas structure of 100 kpc in an over-dense region of the galaxy
group COSMOS-Gr30 at z ~ 0.7: We report the discovery of a 10^4 kpc^2 gaseous structure detected in [OII]
in an over-dense region of the COSMOS-Gr30 galaxy group at z~0.725 thanks to
deep MUSE Guaranteed Time Observations. We estimate the total amount of diffuse
ionised gas to be of the order of (~5+-3)x10^10 Msun and explore its physical
properties to understand its origin and the source(s) of the ionisation. The
MUSE data allow the identification of a dozen of group members embedded in this
structure from emission and absorption lines. We extracted spectra from small
apertures defined for both the diffuse ionised gas and the galaxies. We
investigated the kinematics and ionisation properties of the various galaxies
and extended gas regions thanks to line diagnostics (R23, O32 and
[OIII]/H\beta) available within the MUSE wavelength range. We compared these
diagnostics to photo-ionisation models and shock models. The structure is
divided in two kinematically distinct sub-structures. The most extended
sub-structure of ionised gas is likely rotating around a massive galaxy and
displays filamentary patterns linking some galaxies. The second sub-structure
links another massive galaxy hosting an Active Galactic Nucleus to a low mass
galaxy but also extends orthogonally to the AGN host disk over ~35 kpc. This
extent is likely ionised by the AGN itself. The location of small diffuse
regions in the R23 vs. O32 diagram is compatible with photo-ionisation.
However, the location of three of these regions in this diagram (low O32, high
R23) can also be explained by shocks, which is supported by their large
velocity dispersions. One edge-on galaxy shares the same properties and may be
a source of shocks. Whatever the hypothesis, the extended gas seems to be non
primordial. We favour a scenario where the gas has been extracted from galaxies
by tidal forces and AGN triggered by interactions between at least the two
sub-structures. | astro-ph_GA |
Discovery of inverse-Compton X-ray emission and estimate of the
volume-averaged magnetic field in a galaxy group: Observed in a significant fraction of clusters and groups of galaxies,
diffuse radio synchrotron emission reveals the presence of relativistic
electrons and magnetic fields permeating large-scale systems of galaxies.
Although these non-thermal electrons are expected to upscatter cosmic microwave
background photons up to hard X-ray energies, such inverse-Compton (IC) X-ray
emission has so far not been unambiguously detected on cluster/group scales.
Using deep, new proprietary XMM-Newton observations ($\sim$200 ks of clean
exposure), we report a 4.6$\sigma$ detection of extended IC X-ray emission in
MRC 0116+111, an extraordinary group of galaxies at $z = 0.131$. Assuming a
spectral slope derived from low-frequency radio data, the detection remains
robust to systematic uncertainties. Together with low-frequency radio data from
GMRT, this detection provides an estimate for the volume-averaged magnetic
field of $(1.9 \pm 0.3)$ $\mu$G within the central part of the group. This
value can serve as an anchor for studies of magnetic fields in the largest
gravitationally bound systems in the Universe. | astro-ph_GA |
The PAU Survey: Close galaxy pairs identification and analysis: Galaxy pairs constitute the initial building blocks of galaxy evolution,
which is driven through merger events and interactions. Thus, the analysis of
these systems can be valuable in understanding galaxy evolution and studying
structure formation. In this work, we present a new publicly available
catalogue of close galaxy pairs identified using photometric redshifts provided
by the Physics of the Accelerating Universe Survey (PAUS). To efficiently
detect them we take advantage of the high-precision photo$-z$ ($\sigma_{68} <
0.02$) and apply an identification algorithm previously tested using simulated
data. This algorithm considers the projected distance between the galaxies
($r_p < 50$ kpc), the projected velocity difference ($\Delta V < 3500$ km/s)
and an isolation criterion to obtain the pair sample. We applied this technique
to the total sample of galaxies provided by PAUS and to a subset with
high-quality redshift estimates. Finally, the most relevant result we achieved
was determining the mean mass for several subsets of galaxy pairs selected
according to their total luminosity, colour and redshift, using galaxy-galaxy
lensing estimates. For pairs selected from the total sample of PAUS with a mean
$r-$band luminosity $10^{10.6} h^{-2} L_\odot$, we obtain a mean mass of
$M_{200} = 10^{12.2} h^{-1} M_\odot$, compatible with the mass-luminosity ratio
derived for elliptical galaxies. We also study the mass-to-light ratio $M/L$ as
a function of the luminosity $L$ and find a lower $M/L$ (or steeper slope with
$L$) for pairs than the one extrapolated from the measurements in groups and
galaxy clusters. | astro-ph_GA |
Update on HI data collection from GBT, Parkes and Arecibo telescopes for
the Cosmic Flows project: Cosmic Flows is an international multi-element project with the goal to map
motions of galaxies in the Local Universe. Kinematic information from
observations in the radio HI line and photometry at optical or near-infrared
bands are acquired to derive the large majority of distances that are obtained
through the luminosity-linewidth or Tully-Fisher relation. This paper gathers
additional observational radio data, frequently unpublished, retrieved from the
archives of Green Bank, Parkes and Arecibo telescopes. Extracted HI profiles
are consistently processed to produce linewidth measurements. Our current
"All-Digital HI Catalog" contains a total of 20,343 HI spectra for 17,738
galaxies with 14,802 galaxies with accurate linewidth measurement useful for
Tully-Fisher galaxy distances. This addition of 4,117 new measurements
represents an augmentation of 34\% compared to our last release. | astro-ph_GA |
Constraints on the temperature inhomogeneity in quasar accretion discs
from the ultraviolet-optical spectral variability: The physical mechanisms of the quasar ultraviolet (UV)-optical variability
are not well understood despite the long history of observations. Recently,
Dexter & Agol presented a model of quasar UV-optical variability, which assumes
large local temperature fluctuations in the quasar accretion discs. This
inhomogeneous accretion disc model is claimed to describe not only the
single-band variability amplitude, but also microlensing size constraints and
the quasar composite spectral shape. In this work, we examine the validity of
the inhomogeneous accretion disc model in the light of quasar UV-optical
spectral variability by using five-band multi-epoch light curves for nearly 9
000 quasars in the Sloan Digital Sky Survey (SDSS) Stripe 82 region. By
comparing the values of the intrinsic scatter $\sigma_{\text{int}}$ of the
two-band magnitude-magnitude plots for the SDSS quasar light curves and for the
simulated light curves, we show that Dexter & Agol's inhomogeneous accretion
disc model cannot explain the tight inter-band correlation often observed in
the SDSS quasar light curves. This result leads us to conclude that the local
temperature fluctuations in the accretion discs are not the main driver of the
several years' UV-optical variability of quasars, and consequently, that the
assumption that the quasar accretion discs have large localized temperature
fluctuations is not preferred from the viewpoint of the UV-optical spectral
variability. | astro-ph_GA |
Molecular hydrogen in absorption at high redshifts. Science cases for
CUBES: Absorption lines from molecular hydrogen ($\rm H_2$) in the spectra of
background sources are a powerful probe of the physical conditions in
intervening cold neutral medium. At high redshift, $z>2$, $\rm H_2$ lines are
conveniently shifted in the optical domain, allowing the use of ground-based
telescopes to perform high-resolution spectroscopy, which is essential for a
proper analysis of the cold gas. We describe recent observational progress,
based on the development of efficient pre-selection techniques in
low-resolution spectroscopic surveys such as the Sloan Digital Sky Survey
(SDSS). The next generation of spectrographs with high blue-throughput, such as
CUBES, will certainly significantly boost the efficiency and outcome of
follow-up observations. In this paper, we discuss high priority science cases
for CUBES, building on recent $\rm H_2$ observations at high-z: probing the
physical conditions in the cold phase of regular galaxies and outflowing gas
from active galactic nucleus. | astro-ph_GA |
Mapping Spatial Variations of HI Turbulent Properties in the Small and
Large Magellanic Cloud: We developed methods for mapping spatial variations of the spatial power
spectrum (SPS) and structure function (SF) slopes, with a goal of connecting
neutral hydrogen (HI) statistical properties with the turbulent drivers. The
new methods were applied on the HI observations of the Small and Large
Magellanic Clouds (SMC and LMC). In the case of the SMC, we find highly uniform
turbulent properties of HI, with no evidence for local enhancements of
turbulence due to stellar feedback. Such properties could be caused by a
significant turbulent driving on large-scales. Alternatively, a significant
line-of-sight depth of the SMC could be masking out localized regions with a
steeper SPS slope caused by stellar feedback. In contrast to the SMC, the LMC
HI shows a large diversity in terms of its turbulent properties. Across most of
the LMC, the small-scale SPS slope is steeper than the large-scale slope due to
the presence of the HI disk. On small spatial scales, we find several areas of
localized steepening of the SPS slope around major HII regions, with the 30
Doradus region being the most prominent. This is in agreement with predictions
from numerical simulations which suggest steepening of the SPS slope due to
stellar feedback eroding and destroying interstellar clouds. We also find
localized steepening of the large-scale SPS slope in the outskirts of the LMC.
This is likely caused by the flaring of the HI disk, or alternatively
ram-pressure stripping of the LMC disk due to the interactions with the
surrounding halo gas. | astro-ph_GA |
New Insights into the Evolution of Massive Stars and Their Effects on
Our Understanding of Early Galaxies: The observable characteristics and subsequent evolution of young stellar
populations is dominated by their massive stars. As our understanding of those
massive stars and the factors affecting their evolution improves, so our
interpretation of distant, unresolved stellar systems can also advance. As
observations increasingly probe the distant Universe, and the rare low
metallicity starbursts nearby, so the opportunity arises for these two fields
to complement one another, and lead to an improved conception of both stars and
galaxies. Here we review the current state of the art in modelling of massive
star dominated stellar populations, and discuss their applications and
implications for interpreting the distant Universe. Our principle findings
include:
- Binary evolutionary pathways must be included to understand the stellar
populations in early galaxies.
- Observations constraining the extreme ultraviolet spectrum of early
galaxies are showing that current models are incomplete. The best current guess
is that some form of accretion onto compact remnants is required.
- The evolution and fates of very massive stars, of the order of 100Msun and
above, may be key to fully understand aspects of early galaxies. | astro-ph_GA |
The physics and modes of star cluster formation: simulations: We review progress in numerical simulations of star cluster formation. These
simulations involve the bottom-up assembly of clusters through hierarchical
mergers, which produces a fractal stellar distribution at young (~0.5 Myr)
ages. The resulting clusters are predicted to be mildly aspherical and highly
mass-segregated, except in the immediate aftermath of mergers. The upper
initial mass function within individual clusters is generally somewhat flatter
than for the aggregate population. Recent work has begun to clarify the factors
that control the mean stellar mass in a star-forming cloud and also the
efficiency of star formation. The former is sensitive to the thermal properties
of the gas while the latter depends both on the magnetic field and the initial
degree of gravitational boundedness of the natal cloud. Unmagnetized clouds
that are initially bound undergo rapid collapse, which is difficult to reverse
by ionization feedback or stellar winds. | astro-ph_GA |
Herschel/HIFI search for H2-17O and H2-18O in IRC+10216: constraints on
models for the origin of water vapor: We report the results of a sensitive search for the minor isotopologues of
water, H2-17O and H2-18O, toward the carbon-rich AGB star IRC+10216 (a.k.a. CW
Leonis) using the HIFI instrument on the Herschel Space Observatory. This
search was motivated by the fact that any detection of isotopic enhancement in
the H2-17O and H2-18O abundances would have strongly implicated CO
photodissociation as the source of the atomic oxygen needed to produce water in
a carbon-rich circumstellar envelope. Our observations place an upper limit of
1/470 on the H2-17O/H2-16O abundance ratio. Given the isotopic 17O/16O ratio of
1/840 inferred previously for the photosphere of IRC+10216, this result places
an upper limit of a factor 1.8 on the extent of any isotope-selective
enhancement of H2-17O in the circumstellar material, and provides an important
constraint on any model that invokes CO photodissociation as the source of O
for H2O production. In the context of the clumpy photodissociation model
proposed previously for the origin of water in IRC+10216, our limit implies
that 12C-16O (not 13C-16O or SiO) must be the dominant source of 16O for H2O
production, and that the effects of self-shielding can only have reduced the
12C-16O photodissociation rate by at most a factor ~ 2. | astro-ph_GA |
Young Galaxy Candidates in the Hubble Frontier Fields - III.
MACSJ0717.5+3745: In this paper we present the results of our search for and study of $z
\gtrsim 6$ galaxy candidates behind the third Frontier Fields (FF) cluster,
MACSJ0717.5+3745, and its parallel field, combining data from Hubble and
Spitzer. We select 39 candidates using the Lyman Break technique, for which the
clear non-detection in optical make the extreme mid-$z$ interlopers hypothesis
unlikely. We also take benefit from $z \gtrsim 6$ samples selected using
previous Frontier Fields datasets of Abell 2744 and MACS0416 to improve the
constraints on the properties of very high-redshift objects. We compute the
redshift and the physical properties, such emission lines properties, star
formation rate, reddening, and stellar mass for all Frontier Fields objects
from their spectral energy distribution using templates including nebular
emission lines. We study the relationship between several physical properties
and confirm the trend already observed in previous surveys for evolution of
star formation rate with galaxy mass, and between the size and the UV
luminosity of our candidates. The analysis of the evolution of the UV
Luminosity Function with redshift seems more compatible with an evolution of
density. Moreover, no robust $z\ge$8.5 object is selected behind the cluster
field, and few $z$$\sim$9 candidates have been selected in the two previous
datasets from this legacy survey, suggesting a strong evolution in the number
density of galaxies between $z$$\sim$8 and 9. Thanks to the use of the lensing
cluster, we study the evolution of the star formation rate density produced by
galaxies with L$>$0.03L$^{\star}$, and confirm the strong decrease observed
between $z$$\sim$8 and 9. | astro-ph_GA |
ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): A Hot Corino
Survey toward Protostellar Cores in the Orion Cloud: The presence of complex organic molecules (COMs) in the interstellar medium
(ISM) is of great interest since it may link to the origin and prevalence of
life in the universe. Aiming to investigate the occurrence of COMs and their
possible origins, we conducted a chemical census toward a sample of
protostellar cores as part of the ALMA Survey of Orion Planck Galactic Cold
Clumps (ALMASOP) project. We report the detection of 11 hot corino sources,
which exhibit compact emissions from warm and abundant COMs, among 56 Class 0/I
protostellar cores. All the hot corino sources discovered are likely Class 0
and their sizes of the warm region ($>$ 100 K) are comparable to 100 au. The
luminosity of the hot corino sources exhibits positive correlations with the
total number of methanol and the extent of its emissions. Such correlations are
consistent with the thermal desorption picture for the presence of hot corino
and suggest that the lower luminosity (Class 0) sources likely have a smaller
region with COMs emissions. With the same sample selection method and detection
criteria being applied, the detection rates of the warm methanol in the Orion
cloud (15/37) and the Perseus cloud (28/50) are statistically similar when the
cloud distances and the limited sample size are considered. Observing the same
set of COM transitions will bring a more informative comparison between the
cloud properties. | astro-ph_GA |
The HI Gas Disk Thickness of the Ultra-diffuse Galaxy AGC 242019: Ultra-diffuse galaxies (UDGs) are as faint as dwarf galaxies but whose sizes
are similar to those of spiral galaxies. A variety of formation mechanisms have
been proposed, some of which could result in different disk thicknesses. In
this study, we measure the radial profile of the HI scale height (h_g) and
flaring angle (h_g/R) of AGC 242019 through the joint Poisson-Boltzmann
equation based on its well spatially-resolved HI gas maps. The mean HI scale
height of AGC 242019 is <h_g> \approx 537.15 \pm 89.4 pc, and the mean flaring
angle is <h_g/R> \approx 0.19 \pm 0.03. As a comparison, we also derive the
disk thickness for a sample of 14 dwarf irregulars. It is found that the HI
disk of AGC 242019 has comparable thickness to dwarfs. This suggests that AGC
242019 is unlikely to experience much stronger stellar feedback than dwarf
galaxies, which otherwise leads to a thicker disk for this galaxy. | astro-ph_GA |
The Spitzer Space Telescope Survey of the Orion A and B Molecular Clouds
II: the Spatial Distribution and Demographics of Dusty Young Stellar Objects: We analyze the spatial distribution of dusty young stellar objects (YSOs)
identified in the Spitzer Survey of the Orion Molecular clouds, augmenting
these data with Chandra X-ray observations to correct for incompleteness in
dense clustered regions. We also devise a scheme to correct for spatially
varying incompleteness when X-ray data are not available. The local surface
densities of the YSOs range from 1 pc$^{-2}$ to over 10,000 pc$^{-2}$, with
protostars tending to be in higher density regions. This range of densities is
similar to other surveyed molecular clouds with clusters, but broader than
clouds without clusters. By identifying clusters and groups as continuous
regions with surface densities $\ge10$ pc$^{-2}$, we find that 59% of the YSOs
are in the largest cluster, the Orion Nebular Cluster (ONC), while 13% of the
YSOs are found in a distributed population. A lower fraction of protostars in
the distributed population is evidence that it is somewhat older than the
groups and clusters. An examination of the structural properties of the
clusters and groups show that the peak surface densities of the clusters
increase approximately linearly with the number of members. Furthermore, all
clusters with more than 70 members exhibit asymmetric and/or highly elongated
structures. The ONC becomes azimuthally symmetric in the inner 0.1 pc,
suggesting that the cluster is only $\sim 2$ Myr in age. We find the star
formation efficiency (SFE) of the Orion B cloud is unusually low, and that the
SFEs of individual groups and clusters are an order of magnitude higher than
those of the clouds. Finally, we discuss the relationship between the young low
mass stars in the Orion clouds and the Orion OB 1 association, and we determine
upper limits to the fraction of disks that may be affected by UV radiation from
OB stars or by dynamical interactions in dense, clustered regions. | astro-ph_GA |
Dust temperature uncertainties hamper the inference of dust and
molecular gas masses from the dust continuum emission of quiescent
high-redshift galaxies: Single flux density measurements at observed-frame sub-millimeter and
millimeter wavelengths are commonly used to probe dust and gas masses in
galaxies. In this Letter, we explore the robustness of this method to infer
dust mass, focusing on quiescent galaxies, using a series of controlled
experiments on four massive haloes from the Feedback in Realistic Environments
(FIRE) project. Our starting point is four star-forming, central galaxies at
seven redshifts between z=1.5 and z=4.5. We generate modified quiescent
galaxies that have been quenched for 100Myr, 500Myr, or 1Gyr prior to each of
the studied redshifts by re-assigning stellar ages. We derive spectral energy
distributions for each fiducial and modified galaxy using radiative transfer.
We demonstrate that the dust mass inferred is highly dependent on the assumed
dust temperature, T_dust, which is often unconstrained observationally.
Motivated by recent work on quiescent galaxies that assumed T_dust~25K, we show
that the ratio between dust mass and 1.3mm flux density can be higher than
inferred by up to an order of magnitude, due to the considerably lower dust
temperatures seen in non star-forming galaxies. This can lead to an
underestimation of dust mass (and, when sub-mm flux density is used as a proxy
for molecular gas content, gas mass). This underestimation is most severe at
higher redshifts, where the observed-frame 1.3mm flux density probes rest-frame
wavelengths far from the Rayleigh-Jeans regime, and hence depends
super-linearly on dust temperature. We fit relations between ratios of
rest-frame far-infrared flux densities and mass-weighted dust temperature that
can be used to constrain dust temperatures from observations and hence derive
more reliable dust and molecular gas masses. | astro-ph_GA |
Galactic fountains and the rotation of disc-galaxy coronae: In galaxies like the Milky Way, cold (~ 10^4 K) gas ejected from the disc by
stellar activity (the so-called galactic-fountain gas) is expected to interact
with the virial-temperature (~ 10^6 K) gas of the corona. The associated
transfer of momentum between cold and hot gas has important consequences for
the dynamics of both gas phases. We quantify the effects of such an interaction
using hydrodynamical simulations of cold clouds travelling through a hot medium
at different relative velocities. Our main finding is that there is a velocity
threshold between clouds and corona, of about 75 km/s, below which the hot gas
ceases to absorb momentum from the cold clouds. It follows that in a disc
galaxy like the Milky Way a static corona would be rapidly accelerated: the
corona is expected to rotate and to lag, in the inner regions, by ~ 80-120 km/s
with respect to the cold disc. We also show how the existence of this velocity
threshold can explain the observed kinematics of the cold extra-planar gas. | astro-ph_GA |
Evolution of dust grain size distribution and grain porosity in galaxies: The radiative properties of interstellar dust are affected not only by the
grain size distribution but also by the grain porosity. We develop a model for
the evolution of size-dependent grain porosity and grain size distribution over
the entire history of galaxy evolution. We include stellar dust production,
supernova dust destruction, shattering, coagulation, and accretion. Coagulation
is {assumed to be} the source of grain porosity. We use a one-zone model with a
constant dense gas fraction ($\eta_\mathrm{dense}$), which regulates the
balance between shattering and coagulation. We find that porosity develops
after small grains are sufficiently created by the interplay between shattering
and accretion (at age $t\sim 1$ Gyr for star formation time-scale
$\tau_\mathrm{SF}=5$ Gyr) and are coagulated. The filling factor drops down to
0.3 at grain radii $\sim 0.03~\mu$m for $\eta_\mathrm{dense}=0.5$. The grains
are more porous for smaller $\eta_\mathrm{dense}$ because small grains, from
which porous coagulated grains form, are more abundant. We also calculate the
extinction curves based on the above results. The porosity steepens the
extinction curve significantly for silicate, but not much for amorphous carbon.
The porosity also increases the collisional cross-sections and produces
slightly more large grains through the enhanced coagulation; however, the
extinction curve does not necessarily become flatter because of the steepening
effect by porosity. We also discuss the implication of our results for the
Milky Way extinction curve. | astro-ph_GA |
The Galactic Center Lobe Filled with Thermal Plasma: An observational result of a radio continuum and H92$\alpha$ radio
recombination line of the Galactic Center Lobe (GCL), using the Yamaguchi 32 m
radio telescope, is reported. The obtained spatial intensity distribution of
the radio recombination line shows two distinctive ridge-like structures
extending from the galactic plane vertically to the north at the eastern and
western sides of the galactic center, which are connected to each other at a
latitude of $1.2^{\circ}$ to form a loop-like structure as a whole. This
suggests that most of the radio continuum emission of the GCL is free-free
emission, and that the GCL is filled with thermal plasma. The east ridge of the
GCL observed with the radio recombination line separates 30 pc from the radio
arc, which has been considered as a part of the GCL, but coincides with a ridge
of the radio continuum at a galactic longitude of $0^{\circ}$. The radial
velocity of the radio recombination line is found to be between $-4$ and $+10$
km s$^{-1}$ across the GCL. This velocity is much smaller than the one expected
from the galactic rotation, and hence indicates that the GCL exists apart from
the galactic center. These characteristics of the GCL suggest that the
long-standing hypothesis that the GCL was created by an explosive activity in
the galactic center is unlikely, but favor that the GCL is a giant HII region. | astro-ph_GA |
VVV Survey Microlensing: the Galactic Longitude Dependence: We completed the search for microlensing events in the zero latitude area of
the Galactic bulge using the VVV Survey near-IR data obtained between 2010 and
2015. We have now a total sample of N = 630 events Using the near-IR
Color-Magnitude Diagram we selected the Red Clump sources to analyze the
longitude dependence of microlensing across the central region of the Galactic
plane. The events show a homogeneous distribution, smoothly increasing in
numbers towards the Galactic centre, as predicted by different models. We find
a slight asymmetry, with a larger number of events toward negative longitudes
than positive longitudes. This asymmetry is seen both in the complete sample
and the subsample of red clump giant sources, and it is possibly related with
the inclination of the bar along the line of sight. The timescale distribution
is fairly symmetric with a peak in 17.4 $\pm$ 1.0 days for the complete sample
(N = 630 events), and 20.7 $\pm$ 1.0 days for the Red Clump stars (N = 291
events), in agreement with previous results. | astro-ph_GA |
Is there a maximum mass for black holes in galactic nuclei?: The largest observed supermassive black holes (SMBHs) have a mass of M_BH ~
10^{10} M_sun, nearly independent of redshift, from the local (z~0) to the
early (z>6) Universe. We suggest that the growth of SMBHs above a few 10^{10}
M_sun is prevented by small-scale accretion physics, independent of the
properties of their host galaxies or of cosmology. Growing more massive BHs
requires a gas supply rate from galactic scales onto a nuclear region as high
as >10^3 M_sun/yr. At such a high accretion rate, most of the gas converts to
stars at large radii (~10-100 pc), well before reaching the BH. We adopt a
simple model (Thompson et al. 2005) for a star-forming accretion disk, and find
that the accretion rate in the sub-pc nuclear region is reduced to the smaller
value of at most a few M_sun/yr. This prevents SMBHs from growing above
~10^{11} M_sun in the age of the Universe. Furthermore, once a SMBH reaches a
sufficiently high mass, this rate falls below the critical value at which the
accretion flow becomes advection dominated. Once this transition occurs, BH
feeding can be suppressed by strong outflows and jets from hot gas near the BH.
We find that the maximum SMBH mass, given by this transition, is between
M_{BH,max} ~ (1-6) * 10^{10} M_sun, depending primarily on the efficiency of
angular momentum transfer inside the galactic disk, and not on other properties
of the host galaxy. | astro-ph_GA |
A refined search for high-velocity gas in the Cygnus Loop supernova
remnant: We present the results of a sensitive search for high-velocity gas in
interstellar absorption lines associated with the Cygnus Loop supernova remnant
(SNR). We examine high-resolution, high signal-to-noise ratio optical spectra
of six stars in the Cygnus Loop region with distances greater than ~700 pc. All
stars show low-velocity Na I and Ca II absorption. However, only one star, HD
198301, exhibits high-velocity Ca II absorption components, at velocities of
+62, +82, and +96 km/s. The distance to this star of ~870 pc helps to constrain
the distance to the receding edge of the Cygnus Loop's expanding shock front.
One of our targets, HD 335334, was previously thought to exhibit high positive
and high negative velocity interstellar Na I and Ca II absorption. This was one
factor leading Fesen et al. to derive a distance to the Cygnus Loop of 725 pc.
However, we find that HD 335334 is in fact a double-line spectroscopic binary
and shows no evidence of high-velocity interstellar absorption. As such, the
distance to HD 335334 cannot be used to constrain the distance to the Cygnus
Loop. Our detection of Ca II absorption approaching 100 km/s toward HD 198301
is the first conclusive detection of high-velocity absorption from a low
ionization species associated with the Cygnus Loop SNR. A large jump in the Na
I column density toward BD+31 4218, a star located beyond the northwestern
boundary of the Cygnus Loop, helps to constrain the distance to a large
molecular cloud complex with which the Cygnus Loop is evidently interacting. | astro-ph_GA |
Ly-alpha Radiative Transfer: A Stokes Vector Approach to Ly-alpha
Polarization: Ly-alpha emitting galaxies and giant Ly-alpha blobs (LABs) have been
extensively observed to study the formation history of galaxies. However, the
origin of their extended Ly-alpha emission, especially of LABs, remains
controversial. Polarization signals from some LABs have been discovered, and
this is commonly interpreted as strong evidence supporting that the extended
Ly-alpha emission originates from the resonance scattering. The Monte Carlo
Ly-alpha radiative transfer code LaRT is updated to investigate the
polarization of Ly-alpha using the Stokes vector formalism. We apply LaRT to a
few models to explore the fundamental polarization properties of Ly-alpha.
Interestingly, individual Ly-alpha photon packets are found to be almost
completely polarized by a sufficient number of scatterings (N_scatt > 10^4-10^5
in a static medium) or Doppler shifts induced by gas motion, even starting from
unpolarized light. It is also found that the polarization pattern can exhibit a
non-monotonically increasing pattern in some cases, besides the commonly-known
trend that the polarization monotonically increases with radius. The
polarization properties are primarily determined by the degree of polarization
of individual photon packets and the anisotropy of the Ly-alpha radiation
field, which are eventually controlled by the medium's optical depth and
velocity field. If once Ly-alpha photon packets achieve ~100% polarization, the
radial profile of polarization appears to correlate with the surface brightness
profile. A steep surface brightness profile tends to yield a rapid increase of
the linear polarization near the Ly-alpha source location. In contrast, a
shallow surface brightness profile gives rise to a slowly increasing
polarization pattern. | astro-ph_GA |
No Evidence for [O III] Variability in Mrk 142: Using archival data from the 2008 Lick AGN Monitoring Project, Zhang & Feng
(2016) claimed to find evidence for flux variations in the narrow [O III]
emission of the Seyfert 1 galaxy Mrk 142 over a two-month time span. If
correct, this would imply a surprisingly compact size for the narrow-line
region. We show that the claimed [O III] variations are merely the result of
random errors in the overall flux calibration of the spectra. The data do not
provide any support for the hypothesis that the [O III] flux was variable
during the 2008 monitoring period. | astro-ph_GA |
New Limits on an Intermediate Mass Black Hole in Omega Centauri: I.
Hubble Space Telescope Photometry and Proper Motions: We analyze data from the Hubble Space Telescope's Advanced Camera for Surveys
of the globular cluster Omega Cen. We construct a photometric and proper-motion
catalog using the GO-9442, GO-10252, and GO-10775 data sets. The 2.5- to 4-year
baseline between observations yields a catalog of some 10^5 proper motions,
with 53,382 high-quality measurements in a central field. We determine the
cluster center to ~1-arcsecond accuracy using two different star-count methods,
and a completely independent method using 2MASS images. We also determine the
kinematical center of the proper motions, which agrees with the star-count
center to within its uncertainty. The proper-motion dispersion of the cluster
increases gradually inwards, but there is no variation in kinematics with
position within the central ~15 arcsec: there is no dispersion cusp and no
stars with unusually high velocities. We measure for the first time in any
globular cluster the variation in proper-motion dispersion with mass along the
main sequence, and find the cluster not yet to be in equipartition. Our
proper-motion results do not confirm the arguments put forward by Noyola,
Gebhardt & Bergmann to suspect an intermediate-mass black hole (IMBH) in Omega
Cen. In Paper II we present new dynamical models for the high-quality data
presented here, with the aim of putting quantitative contraints on the mass of
any possible IMBH. | astro-ph_GA |
SAMI-HI: The HI view of the H$α$ Tully-Fisher relation and data
release: We present SAMI-HI, a survey of the atomic hydrogen content of 296 galaxies
with integral field spectroscopy available from the SAMI Galaxy Survey. The
sample spans nearly 4 dex in stellar mass ($M_\star = 10^{7.4}-10^{11.1}~ \rm
M_\odot$), redshift $z<0.06$, and includes new Arecibo observations of 153
galaxies, for which we release catalogues and HI spectra. We use these data to
compare the rotational velocities obtained from optical and radio observations
and to show how systematic differences affect the slope and scatter of the
stellar-mass and baryonic Tully-Fisher relations. Specifically, we show that
H$\alpha$ rotational velocities measured in the inner parts of galaxies (1.3
effective radii in this work) systematically underestimate HI global
measurements, with HI/H$\alpha$ velocity ratios that increase at low stellar
masses, where rotation curves are typically still rising and H$\alpha$
measurements do not reach their plateau. As a result, the H$\alpha$ stellar
mass Tully-Fisher relation is steeper (when $M_\star$ is the independent
variable) and has larger scatter than its HI counterpart. Interestingly, we
confirm the presence of a small fraction of low-mass outliers of the H$\alpha$
relation that are not present when HI velocity widths are used and are not
explained by "aperture effects". These appear to be highly disturbed systems
for which H$\alpha$ widths do not provide a reliable estimate of the rotational
velocity. Our analysis reaffirms the importance of taking into account
differences in velocity definitions as well as tracers used when interpreting
offsets from the Tully-Fisher relation, at both low and high redshifts and when
comparing with simulations. | astro-ph_GA |
Another Look at the EBS: A Stellar Debris Stream and a Possible
Progenitor: Using the Sloan Digital Sky Survey Data Release 7, we reexamine the Eastern
Banded Structure (EBS), a stellar debris stream first discovered in Data
Release 5 and more recently detected in velocity space by Schlaufman et al. The
visible portion of the stream is 18 degrees long, lying roughly in the Galactic
Anticenter direction and extending from Hydra to Cancer. At an estimated
distance of 9.7 kpc, the stream is approximately 170 pc across on the sky. The
curvature of the stream implies a fairly eccentric box orbit that passes close
to both the Galactic center and to the sun, making it dynamically distinct from
the nearby Monoceros, Anticenter, and GD-1 streams. Within the stream is a
relatively strong, 2 degree-wide concentration of stars with a very similar
color-magnitude distribution that we designate Hydra I. Given its prominence
within the stream and its unusual morphology, we suggest that Hydra I is the
last vestige of the EBS's progenitor, possibly already unbound or in the final
throes of tidal dissolution. Though both Hydra I and the EBS have a relatively
high velocity dispersion, given the comparatively narrow width of the stream
and the high frequency of encounters with the bulge and massive constituents of
the disk that such an eccentric orbit would entail, we suggest that the
progenitor was likely a globular cluster, and that both it and the stream have
undergone significant heating over time. | astro-ph_GA |
Toward an Empirical Theory of Pulsar Emission. IX. On the Peculiar
Properties and Geometric Regularity of Lyne & Manchester's "Partial Cone"
Pulsars: Lyne & Manchester (1988) identified a group of some 50 pulsars they called
"partial cones" which they found difficult to classify and interpret. They were
notable for their asymmetric average profiles and asymmetric polarization
position-angle (PPA) traverses, wherein the steepest gradient (SG) point fell
toward one edge of the total intensity profile. Over the last two decades, this
population of pulsars has raised cautions regarding the core/cone model of the
radio pulsar-emission beam which implies a high degree of order, symmetry and
geometric regularity. In this paper we reinvestigate this population "partial
cone" pulsars on the basis of new single pulse polarimetric observations of 39
of them, observed with the Giant Meterwave Radio Telescope in India and the
Arecibo Observatory in Puerto Rico. These highly sensitive observations help us
to establish that most of these "partial cones" exhibit a core/cone structure
just as did the "normal" pulsars studied in the earlier papers of this series.
In short, we find that many of these "partial cones" are partial in the sense
that the emission above different areas of their polar caps can be (highly)
asymmetric. However, when studied closely we find that their emission
geometries are overall identical to core/double cone structure encountered
earlier-that is, with specific conal dimensions scaling as the polar cap size. | astro-ph_GA |
Predicting Images for the Dynamics Of stellar Clusters (π-DOC): a
deep learning framework to predict mass, distance and age of globular
clusters: Dynamical mass estimates of simple systems such globular clusters (GCs) still
suffer from up to a factor of 2 uncertainty. This is primarily due to the
oversimplifications of standard dynamical models that often neglect the effects
of the long-term evolution of GCs. Here, we introduce a new approach to measure
the dynamical properties of GCs, based on the combination of a deep-learning
framework and the large amount of data from direct $N$-body simulations. Our
algorithm, $\texttt{$\pi$-DOC}$ ($\textit{Predicting Images for the Dynamics Of
stellar Clusters}$) is composed of two convolutional networks, trained to learn
the non-trivial transformation between an observed GC luminosity map and its
associated mass distribution, age, and distance. The training set is made of
V-band luminosity and mass maps constructed as mock observations from $N$-body
simulations. The tests on $\texttt{$\pi$-DOC}$ demonstrate that we can predict
the mass distribution with a mean error per pixel of 27%, and the age and
distance with an accuracy of 1.5 Gyr and 6 kpc, respectively. In turn, we
recover the shape of the mass-to-light profile and its global value with a mean
error of 12%, which implies that we efficiently trace mass segregation. A
preliminary comparison with observations indicates that our algorithm is able
to predict the dynamical properties of GCs within the limits of the training
set. These encouraging results demonstrate that our deep-learning framework and
its forward modelling approach can offer a rapid and adaptable tool competitive
with standard dynamical models. | astro-ph_GA |
First [NII]122$μ$m line detection in a QSO-SMG pair BRI 1202-0725 at
$z=4.69$: We report the first detection obtained with ALMA of the [N II] 122$\mu$m line
emission from a galaxy group BRI 1202-0725 at $z=4.69$ consisting of a QSO and
a submilimeter-bright galaxy (SMG). Combining with a detection of [N II]
205$\mu$m line in both galaxies, we constrain the electron densities of the
ionized gas based on the line ratio of [NII]122/205. The derived electron
densities are $26^{+12}_{-11}$ and $134^{+50}_{-39}$ cm$^{-3}$ for the SMG and
the QSO, respectively. The electron density of the SMG is similar to that of
the Galactic Plane and to the average of the local spirals. Higher electron
densities by up to a factor of three could, however, be possible for systematic
uncertainties of the line flux estimates. The electron density of the QSO is
comparable to high-$z$ star-forming galaxies at $z=1.5-2.3$, obtained using
rest-frame optical lines and with the lower limits suggested from stacking
analysis on lensed starbursts at $z=1-3.6$ using the same tracer of [NII]. Our
results suggest a large scatter of electron densities in global scale at fixed
star formation rates for extreme starbursts. The success of the [N II]
122$\mu$m and 205$\mu$m detections at $z=4.69$ demonstrates the power of future
systematic surveys of extreme starbursts at $z>4$ for probing the ISM
conditions and the effects on surrounding environments. | astro-ph_GA |
The role of the Galactic bar in the chemical evolution of the Milky Way: In the absence of an interaction, central bars might be the most effective
mechanism for radial motions of gas in barred spiral galaxies, which represent
two-thirds of disc galaxies. The dynamical effects induced by bars in the first
few kpc of discs might play an important role in the disc profiles in this
region. In this work, a chemical evolution model with radial gas flows is
proposed in order to mimic the effects of the Milky Way bar in the bulge and
inner disc. The model is an update of a chemical evolution model with the
inclusion of radial gas flows in the disc and bulge. The exchange of gas
between the cylindrical concentric regions that form the Galaxy is modelled
considering the flows of gas from and to the adjacent cylindrical regions. The
most recent data for the bulge metallicity distribution are reproduced by means
of a single and longer bulge collapse time-scale (2 Gyr) than other chemical
evolution models predict. The model is able to reproduce the peak in the
present star formation rate at 4 kpc and the formation of the molecular gas
ring. The model with a bar predicts a flattening of the oxygen radial gradient
of the disc. Additionally, models with radial gas flows predict a higher star
formation rate during the formation of the bulge. This is in agreement with the
most recent observations of the star formation rate at the centre of massive
barred spiral galaxies. | astro-ph_GA |
The impact of stripped Nuclei on the Super-Massive Black Hole number
density in the local Universe: The recent discovery of super-massive black holes (SMBHs) in the centers of
high-mass ultra compact dwarf galaxies (UCDs) suggests that at least some UCDs
are the stripped nuclear star clusters of lower mass galaxies. Tracing these
former nuclei of stripped galaxies provides a unique way to track the assembly
history of a galaxy or galaxy cluster. In this paper we present a new method to
estimate how many UCDs host an SMBH in their center and thus are stripped
galaxy nuclei. We revisit the dynamical mass measurements that suggest many
UCDs have more mass than expected from stellar population estimates, which
recent observations have shown is due to the presence of an SMBH. We revise the
stellar population mass estimates using a new empirical relation between the
mass-to-light ratio (M/L) and metallicity, and use this to predict which UCDs
are most likely to host an SMBH. This enables us to calculate the fraction of
UCDs that host SMBHs across their entire luminosity range for the first time.
We then apply the SMBH occupation fraction to the observed luminosity function
of UCDs and estimate that in the Fornax and Virgo cluster alone there should be
$69^{+32}_{-25}$ stripped nuclei with SMBHs. This analysis shows that stripped
nuclei with SMBHs are almost as common in clusters as present-day galaxy
nuclei. We estimate the local SMBH number density in stripped nuclei to
$3-8\times10^{-3}Mpc^{-3}$, which represents a significant fraction (10-40\%)
of the SMBH density in the local Universe. These SMBHs hidden in stripped
nuclei will increase expected event rates for tidal disruption events and
SMBH-SMBH and SMBH-BH mergers. The existence of numerous stripped nuclei with
SMBHs are a direct consequence of hierarchical galaxy formation, but until now
their impact on the SMBH density had not been quantified. | astro-ph_GA |
Gas accretion onto the disc of a simulated Milky Way-mass galaxy: In the standard paradigm of galaxy formation and evolution, the baryonic
component of galaxies forms from the collapse and condensation of gas within
dark matter haloes, and later grows from continuous accretion of gaseous mass,
both in diffuse form and in mergers with other systems. After a first period of
rapid and violent halo growth, the gas settles into a rotationally-supported
structure, eventually giving rise to the formation of a stellar disc. Stars
evolve and return chemically-processed gas and energy to the interstellar
medium, mainly through Type II supernova explosions. In the disc region, the
cosmological accretion of gas combines with the outflows resulting from
supernovae, affecting the hydrodynamical and structural properties of the disc
and producing gas flows in the vertical and radial directions. In this work, we
use a simulation of the Auriga Project, a suite of magneto-hydrodynamical,
zoom-in cosmological simulations of Milky Way-like galaxies, to study the
temporal and radial dependencies of gas accretion onto the disc. We also
investigate the disc evolution, focusing on the inside-out disc formation
scenario, which is one of the fundamental hypotheses of chemical evolution
models of the Galaxy. | astro-ph_GA |
Hierarchical Bayesian inference of the Initial Mass Function in
Composite Stellar Populations: The initial mass function (IMF) is a key ingredient in many studies of galaxy
formation and evolution. Although the IMF is often assumed to be universal,
there is continuing evidence that it is not universal. Spectroscopic studies
that derive the IMF of the unresolved stellar populations of a galaxy often
assume that this spectrum can be described by a single stellar population
(SSP). To alleviate these limitations, in this paper we have developed a unique
hierarchical Bayesian framework for modelling composite stellar populations
(CSPs). Within this framework we use a parameterized IMF prior to regulate a
direct inference of the IMF. We use this new framework to determine the number
of SSPs that is required to fit a set of realistic CSP mock spectra. The CSP
mock spectra that we use are based on semi-analytic models and have an IMF that
varies as a function of stellar velocity dispersion of the galaxy. Our results
suggest that using a single SSP biases the determination of the IMF slope to a
higher value than the true slope, although the trend with stellar velocity
dispersion is overall recovered. If we include more SSPs in the fit, the
Bayesian evidence increases significantly and the inferred IMF slopes of our
mock spectra converge, within the errors, to their true values. Most of the
bias is already removed by using two SSPs instead of one. We show that we can
reconstruct the variable IMF of our mock spectra for signal-to-noise ratios
exceeding $\sim$75. | astro-ph_GA |
Reproducing sub-millimetre galaxy number counts with cosmological
hydrodynamic simulations: Matching the number counts of high-$z$ sub-millimetre-selected galaxies
(SMGs) has been a long standing problem for galaxy formation models. In this
paper, we use 3D dust radiative transfer to model the sub-mm emission from
galaxies in the SIMBA cosmological hydrodynamic simulations, and compare
predictions to the latest single-dish observational constraints on the
abundance of 850$\mathrm{\mu m}$-selected sources. We find good agreement with
the shape of the integrated 850$\mathrm{\mu m}$ luminosity function, and the
normalisation is within 0.25 dex at $> 3 \; \mathrm{mJy}$, unprecedented for a
fully cosmological hydrodynamic simulation, along with good agreement in the
redshift distribution of bright SMGs. The agreement is driven primarily by
SIMBA's good match to infrared measures of the star formation rate (SFR)
function between $z = 2-4$ at high SFRs. Also important is the self-consistent
on-the-fly dust model in SIMBA, which predicts, on average, higher dust masses
(by up to a factor of 2.5) compared to using a fixed dust-to-metals ratio of
0.3. We construct a lightcone to investigate the effect of far-field blending,
and find that 52% of sources are blends of multiple components, which makes a
small contribution to the normalisation of the bright-end of the number counts.
We provide new fits to the 850$\mathrm{\mu m}$ luminosity as a function of SFR
and dust mass. Our results demonstrate that exotic solutions to the discrepancy
between sub-mm counts in simulations and observations, such as a top-heavy IMF,
are unnecessary, and that sub-millimetre-bright phases are a natural
consequence of massive galaxy evolution. | astro-ph_GA |
A High Resolution Study of the Atomic Hydrogen in CO-Rich Early-Type
Galaxies: We present an analysis of new and archival VLA HI observations of a sample of
eleven early-type galaxies rich in CO, with detailed comparisons of CO and HI
distributions and kinematics. The early-type sample consists of both lenticular
and elliptical galaxies in a variety of environments. A range of morphologies
and environments were selected in order to give a broader understanding of the
origins, distribution, and fate of the cold gas in early-type galaxies. Six of
the eleven galaxies in the sample are detected in both HI and CO. The H$_{2}$
to HI mass ratios for this sample range from 0.2-120. The HI morphologies of
the sample are consistent with that of recent HI surveys of early-type galaxies
which also find a mix of HI morphologies and masses, low HI peak surface
densities, and a lack of HI in early-type galaxies which reside in high density
environments. The HI-detected galaxies have a wide range of HI masses
(1.4$\times10^{6}$ to 1.1$\times10^{10}$ M$_{\odot}$). There does not appear to
be any correlation between the HI mass and morphology (E versus S0). When HI is
detected, it is centrally peaked - there are no central kpc-scale central HI
depressions like those observed for early-type spiral galaxies at similar
spatial resolutions and scales. A kinematic comparison between the HI and CO
indicates that both cold gas components share the same origin. The primary goal
of this and a series of future papers is to better understand the relationship
between the atomic and molecular gas in early-type galaxies, and to compare the
observed relationships with those of spiral galaxies where this relationship
has been studied in depth. | astro-ph_GA |
Herschel Spectroscopy of the Taffy Galaxies (UGC 12914/12915 = VV 254):
Enhanced [C II] emission in the collisionally-formed bridge: Using the PACS and SPIRE spectrometers on-board Herschel, we obtained
observations of the Taffy galaxies (UGC 12914/12915) and bridge. The Taffy
system is believed to be the result of a face-on collision between two gas-rich
galaxies, in which the stellar disks passed through each other, but the gas was
dispersed into a massive H I and molecular bridge between them. Emission is
detected and mapped in both galaxies and the bridge in the [C II]157.7 $\mu$m
and [O I]63.2 $\mu$m fine-structure lines. Additionally, SPIRE FTS spectroscopy
detects the [C I] $^3$P$_2$$\rightarrow$$^3$P$_1$(809.3 GHz) and [C I]
$^3$P$_1$$\rightarrow$$3$P$_0$(492.2 GHz) neutral carbon lines, and weakly
detects high-J CO transitions in the bridge. These results indicate that the
bridge is composed of a warm multi-phase medium consistent with shock and
turbulent heating. Despite low star formation rates in the bridge, the [C II]
emission appears to be enhanced, reaching [C II]/FIR ratios of 3.3% in parts of
the bridge. Both the [C II] and [O I] lines show broad intrinsic
multi-component profiles, similar to those seen in previous CO 1-0 and H I
observations. The [C II] emission shares similar line profiles with both the
double-peaked H I profiles and shares a high-velocity component with
single-peaked CO profiles in the bridge, suggesting that the [C II] emission
originates in both the neutral and molecular phases. We show that it is
feasible that a combination of turbulently heated H$_2$ and high column-density
H I, resulting from the galaxy collision, is responsible for the enhanced [C
II] emission. | astro-ph_GA |
No evidence for large-scale outflows in the extended ionised halo of
ULIRG Mrk273: We present deep new GTC/OSIRIS narrow-band images and optical WHT/ISIS
long-slit spectroscopy of the merging system Mrk273 that show a spectacular
extended halo of warm ionised gas out to a radius of $\sim45$ kpc from the
system nucleus. Outside of the immediate nuclear regions (r > 6 kpc), there is
no evidence for kinematic disturbance in the ionised gas: in the extended
regions covered by our spectroscopic slits the emission lines are relatively
narrow (FWHM $\lesssim$ 350 km$\rm s^{-1}$) and velocity shifts small
(|$\Delta$V| $\lesssim{} $250 km$\rm s^{-1}$). This is despite the presence of
powerful near-nuclear outflows (FWHM > 1000 km$\rm s^{-1}$; |$\Delta$V| > 400
km$\rm s^{-1}$; r < 6 kpc). Diagnostic ratio plots are fully consistent with
Seyfert 2 photo-ionisation to the NE of the nuclear region, however to the SW
the plots are more consistent with low-velocity radiative shock models. The
kinematics of the ionised gas, combined with the fact that the main structures
are aligned with low-surface-brightness tidal continuum features, are
consistent with the idea that the ionised halo represents tidal debris left
over from a possible triple-merger event, rather than a reservoir of outflowing
gas. | astro-ph_GA |
Differences in Halo-Scale Environments between Type 1 and Type 2 AGNs at
Low Redshift: Using low-redshift (z<0.09) samples of AGNs, normal galaxies and groups of
galaxies selected from the Sloan Digital Sky Survey (SDSS), we study the
environments of type 1 and type 2 AGNs both on small and large scales.
Comparisons are made for galaxy samples matched in redshift, $r$-band
luminosity, [OIII] luminosity, and also the position in groups (central or
satellite). We find that type 2 AGNs and normal galaxies reside in similar
environments. Type 1 and type 2 AGNs have similar clustering properties on
large scales ($\gtrsim1$Mpc), but at scales smaller than 100 kpc, type 2s have
significant more neighbors than type 1s ($3.09\pm0.69$ times more for central
AGNs at $\lesssim30$kpc). These results suggest that type 1 and type 2 AGNs are
hosted by halos of similar masses, as is also seen directly from the mass
distributions of their host groups ($\sim10^{12}h^{-1} M_{\odot}$ for centrals
and $\sim10^{13}h^{-1} M_{\odot}$ for satellites). Type~2s have significantly
more satellites around them, and the distribution of their satellites is also
more centrally concentrated. The host galaxies of both types of AGNs have
similar optical properties, but their infrared colors are significantly
different. Our results suggest that the simple unified model based solely on
torus orientation is not sufficient, but that galaxy interactions in dark
matter halos must have played an important role in the formation of the dust
structure that obscures AGNs. | astro-ph_GA |
HI absorption spectra for Supernova Remnants in the VGPS survey: The set of supernova remnants (SNR) from Green's SNR catalog which are found
in the VLA Galactic Plane Survey (VGPS) are the objects considered in this
study. For these SNR, we extract and analyse HI absorption spectra in a uniform
way and construct a catalogue of absorption spectra and distance
determinations. | astro-ph_GA |
Outflows, Accretion, and Clustered Protostellar Cores around a Forming O
Star: We present a Submillimeter Array study in the 1.3 mm waveband of the NGC 7538
IRS 1--3 massive star-forming region. The brightest core in the mm continuum
map, MM1, harbors the IRS 1 young O star. The core has a gas temperature of
about 245 K and shows spatially unresolved emission in complex organic
molecules, all typical of a hot molecular core. Toward MM1, redshifted
absorption is seen in molecular lines with different energies above the ground
state. This absorption probes inward motion of the dense gas toward the central
young O star, and the estimated mass accretion rate reaches 10^{-3} Msun/yr.
Multiple outflows are seen in the CO and 13CO maps. The gas mass of 50 Msun and
mass outflow rate of 2.5 by 10^{-3} Msun/yr measured in CO line wings are
dominated by the MM1 outflow, which is most likely driven by a fast wide-angle
wind. Apart from MM1, we discover eight new dusty cores, MM2--9, within a
projected distance of 0.35 pc from MM1. These cores show no counterpart in
infrared or radio continuum emission, while seven of them appear to be forming
intermediate- to high-mass stars. This manifests a deeply embedded star-forming
component of the parent cloud of IRS 1--3. Apparently we are observing a
Trapezium system in formation, and the system is presumably surrounded by a
cluster of lower mass stars. | astro-ph_GA |
Stochastic 2-D Models of Galaxy Disk Evolution. The Galaxy M33: We have developed a fast numerical 2-D model of galaxy disk evolution
(resolved along the galaxy radius and azimuth) by adopting a scheme of
parameterized stochastic self-propagating star formation. We explore the
parameter space of the model and demonstrate its capability to reproduce 1-D
radial profiles of the galaxy M33: gas surface density, surface brightness in
the i and GALEX FUV passbands, and metallicity. | astro-ph_GA |
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