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SDSS-IV MaNGA: Spatially resolved star-formation histories and the
connection to galaxy physical properties: A key task of observational extragalactic astronomy is to determine where --
within galaxies of diverse masses and morphologies -- stellar mass growth
occurs, how it depends on galaxy properties and what processes regulate star
formation. Using spectroscopic indices derived from the stellar continuum at
$\sim 4000$\AA, we determine the spatially resolved star-formation histories of
980000 spaxels in 2404 galaxies in the SDSS-IV MaNGA IFU survey. We examine the
spatial distribution of star-forming, quiescent, green valley, starburst and
post-starburst spaxels as a function of stellar mass and morphology to see
where and in what types of galaxy star formation is occurring. The spatial
distribution of star-formation is dependent primarily on stellar mass, with a
noticeable change in the distribution at \mstar$>10^{10}$\msun. Galaxies above
this mass have an increasing fraction of regions that are forming stars with
increasing radius, whereas lower mass galaxies have a constant fraction of star
forming regions with radius. Our findings support a picture of inside-out
growth and quenching at high masses. We find that morphology (measured via
concentration) correlates with the fraction of star-forming spaxels, but not
with their radial distribution. We find (post-)starburst regions are more
common outside of the galaxy centre, are preferentially found in asymmetric
galaxies, and have lower gas-phase metallicity than other regions, consistent
with interactions triggering starbursts and driving low metallicity gas into
regions at $<1.5R_e$. | astro-ph_GA |
Revisiting the Mass-Excitation (MEx) diagram using the MaNGA dataset: The diagram comparing the flux ratio of the [OIII] and H$\beta$ emission
lines with the total stellar mass of galaxies (also known as the
mass-excitation diagram, MEx) has been widely used to classify the ionization
mechanism in high redshift galaxies between star formation and active galactic
nuclear ones. This diagram was mainly derived using single-fiber spectroscopy
from the SDSS-DR7 survey. In this study, we revise this diagram using the
central and integrated spectral measurement from the entire Integral Field
Spectroscopic MaNGA sample. Our results suggest that along with the physical
parameters of this diagram, the equivalent width of the H$\alpha$ emission line
is also required to constrain the ionization mechanism of a high-redshifted
galaxy. Furthermore, the location of a galaxy in the excitation-mass diagram
varies depending on the use of central or integrated properties. | astro-ph_GA |
Dynamic Localised Turbulent Diffusion and its Impact on the Galactic
Ecosystem: Modelling the turbulent diffusion of thermal energy, momentum, and metals is
required in all galaxy evolution simulations due to the ubiquity of turbulence
in galactic environments. The most commonly employed diffusion model, the
Smagorinsky model, is known to be over-diffusive due to its strong dependence
on the fluid velocity shear. We present a method for dynamically calculating a
more accurate, locally appropriate, turbulent diffusivity: the dynamic
localised Smagorinsky model. We investigate a set of standard
astrophysically-relevant hydrodynamical tests, and demonstrate that the dynamic
model curbs over-diffusion in non-turbulent shear flows and improves the
density contrast in our driven turbulence experiments. In galactic discs, we
find that the dynamic model maintains the stability of the disc by preventing
excessive angular momentum transport, and increases the metal-mixing timescale
in the interstellar medium. In both our isolated Milky Way-like galaxies and
cosmological simulations, we find that the interstellar and circumgalactic
media are particularly sensitive to the treatment of turbulent diffusion. We
also examined the global gas enrichment fractions in our cosmological
simulations, to gauge the potential effect on the formation sites and
population statistics of Population III stars and supermassive black holes,
since they are theorised to be sensitive to the metallicity of the gas out of
which they form. The dynamic model is, however, not for galaxy evolution
studies only. It can be applied to all astrophysical hydrodynamics simulations,
including those modelling stellar interiors, planetary formation, and star
formation. | astro-ph_GA |
Trans-cis molecular photoswitching in interstellar Space: As many organic molecules, formic acid (HCOOH) has two conformers (trans and
cis). The energy barrier to internal conversion from trans to cis is much
higher than the thermal energy available in molecular clouds. Thus, only the
most stable conformer (trans) is expected to exist in detectable amounts. We
report the first interstellar detection of cis-HCOOH. Its presence in
ultraviolet (UV) irradiated gas exclusively (the Orion Bar photodissociation
region), with a low trans-to-cis abundance ratio of 2.8+-1.0, supports a
photoswitching mechanism: a given conformer absorbs a stellar photon that
radiatively excites the molecule to electronic states above the interconversion
barrier. Subsequent fluorescent decay leaves the molecule in a different
conformer form. This mechanism, which we specifically study with ab initio
quantum calculations, was not considered in Space before but likely induces
structural changes of a variety of interstellar molecules submitted to UV
radiation. | astro-ph_GA |
Extracting galaxy merger timescales I: Tracking haloes with WhereWolf
and spinning orbits with OrbWeaver: Hierarchical models of structure formation predict that dark matter halo
assembly histories are characterised by episodic mergers and interactions with
other haloes. An accurate description of this process will provide insights
into the dynamical evolution of haloes and the galaxies that reside in them.
Using large cosmological N-body simulations, we characterise halo orbits to
study the interactions between substructure haloes and their hosts, and how
different evolutionary histories map to different classes of orbits. We use two
new software tools - WhereWolf, which uses halo group catalogues and merger
trees to ensure that haloes are tracked accurately in dense environments, and
OrbWeaver, which quantifies each halo's orbital parameters. We demonstrate how
WhereWolf improves the accuracy of halo merger trees, and we use OrbWeaver to
quantify orbits of haloes. We assess how well analytical prescriptions for the
merger timescale from the literature compare to measured merger timescales from
our simulations and find that existing prescriptions perform well, provided the
ratio of substructure-to-host mass is not too small. In the limit of small
substructure-to-host mass ratio, we find that the prescriptions can
overestimate the merger timescales substantially, such that haloes are
predicted to survive well beyond the end of the simulation. This work
highlights the need for a revised analytical prescription for the merger
timescale that more accurately accounts for processes such as catastrophic
tidal disruption. | astro-ph_GA |
HST imaging of the brightest z~8-9 galaxies from UltraVISTA: the extreme
bright end of the UV luminosity function: We report on the discovery of three especially bright candidate $z_{phot}
\gtrsim 8$ galaxies. Five sources were targeted for follow-up with HST/WFC3,
selected from a larger sample of 16 bright ($24.8 \lesssim H\lesssim25.5$~mag)
candidate $z\gtrsim 8$ LBGs identified over the 1.6 degrees$^2$ of the
COSMOS/UltraVISTA field. These were identified as Y and J dropouts by
leveraging the deep (Y-to-$K_{S} \sim 25.3-24.8$~mag, $5\sigma$) NIR data from
the UltraVISTA DR3 release, deep ground based optical imaging from the CFHTLS
and Subaru Suprime Cam programs and Spitzer/IRAC mosaics combining observations
from the SMUVS and SPLASH programs. Through the refined spectral energy
distributions, which now also include new HyperSuprime Cam g, r, i, z and Y
band data, we confirm that 3/5 galaxies have robust $z_{phot}\sim8.0-8.7$,
consistent with the initial selection. The remaining 2/5 galaxies have a
nominal $z_{phot}\sim2$. However, if we use the HST data alone, these objects
have increased probability of being at $z\sim9$. Furthermore, we measure mean
UV continuum slopes $\beta=-1.91\pm0.26$ for the three $z\sim8-9$ galaxies,
marginally bluer than similarly luminous $z\sim4-6$ in CANDELS but consistent
with previous measurements of similarly luminous galaxies at $z\sim7$. The
circularized effective radius for our brightest source is $0.9\pm0.2$ kpc,
similar to previous measurements for a bright $z\sim11$ galaxy and bright
$z\sim7$ galaxies. Finally, enlarging our sample to include the six brightest
$z\sim8$ LBGs identified over UltraVISTA (i.e., including three other sources
from Labbe et al. 2017, in prep.) we estimate for the first time the volume
density of galaxies at the extreme bright ($M_{UV}\sim-22$~mag) end of the
$z\sim8$ UV LF. Despite this exceptional result, the still large statistical
uncertainties do not allow us to discriminate between a Schechter and a double
power-law form. | astro-ph_GA |
The chemical evolution of local star forming galaxies: Radial profiles
of ISM metallicity, gas mass, and stellar mass and constraints on galactic
accretion and winds: The radially averaged metallicity distribution of the ISM and the young
stellar population of a sample of 20 disk galaxies is investigated by means of
an analytical chemical evolution model which assumes constant ratios of
galactic wind mass loss and accretion mass gain to star formation rate. Based
on this model the observed metallicities and their gradients can be described
surprisingly well by the radially averaged distribution of the ratio of stellar
mass to ISM gas mass. The comparison between observed and model predicted
metallicity is used to constrain the rate of mass loss through galactic wind
and accretion gain in units of the star formation rate. Three groups of
galaxies are found: galaxies with either mostly winds and only weak accretion,
or mostly accretion and only weak winds, and galaxies where winds are roughly
balanced by accretion. The three groups are distinct in the properties of their
gas disks. Galaxies with approximately equal rates of mass-loss and accretion
gain have low metallicity, atomic hydrogen dominated gas disks with a flat
spatial profile. The other two groups have gas disks dominated by molecular
hydrogen out to 0.5 to 0.7 isophotal radii and show a radial exponential
decline, which is on average steeper for the galaxies with small accretion
rates. The rates of accretion (<1.0 x SFR) and outflow (<2.4 x SFR) are
relatively low. The latter depend on the calibration of the zero point of the
metallicity determination from the use of HII region strong emission lines. | astro-ph_GA |
Study of rotation curves of spiral galaxies with a scalar field dark
matter model: In this work we study rotation curves of spiral galaxies using a model of
dark matter based on a scalar-tensor theory of gravity. We show how to estimate
the scalar field dark matter parameters using a sample of observed rotation
curves. | astro-ph_GA |
Understanding inverse metallicity gradients in galactic discs as a
consequence of inside-out formation: The early stages of a galaxy's evolution leave an imprint on its metallicity
distribution. We discuss the origins and evolution of radial metallicity
gradients in discs of spiral galaxies using an analytical chemical evolution
model. We explain how radial metallicity gradients in stellar populations are
determined by three factors: the radial metallicity profile of the star-forming
ISM, radial changes in the star-formation history (in particular inside-out
formation), and radial mixing of stars. Under reasonable assumptions,
inside-out formation steepens the negative ISM metallicity gradient, but
contributes positively to the stellar metallicity gradient, up to inverting the
metallicity profile to a positive d[Fe/H]/dR. This reconciles steep negative
d[Fe/H]/dR in some high redshift galaxies to generally flatter gradients in
local observations.
We discuss the evidence for inverse radial metallicity gradients (positive
d[X/H]/dR) at high redshifts and the inverse relationship between azimuthal
velocity and the metallicity (positive dV_{\phi}/d[Fe/H]) of stars for the
Milky Way's thick disc. The former can be achieved by high central gas-loss
rates and re-distribution processes, e.g. re-accretion of enriched material in
conjunction with inside-out formation, and near-disc galactic fountaining. For
the Milky Way thick disc, we show that the positive dV_{\phi}/d[Fe/H]
correlation points to comparable timescales for inside-out formation, initial
metal enrichment and SNIa enrichment. We argue that the original ISM
metallicity gradient could be inferred with better data from the
high-metallicity tail of the alpha enhanced population. Including inside-out
formation in our models changes the local vertical metallicity gradient by
about -0.2dex/kpc, in line with local measurements. | astro-ph_GA |
The ACS Nearby Galaxy Survey Treasury: The ACS Nearby Galaxy Survey Treasury (ANGST) is a systematic survey to
establish a legacy of uniform multi-color photometry of resolved stars for a
volume-limited sample of nearby galaxies (D<4 Mpc). The survey volume
encompasses 69 galaxies in diverse environments, including close pairs, small &
large groups, filaments, and truly isolated regions. The galaxies include a
nearly complete range of morphological types spanning a factor of ~10^4 in
luminosity and star formation rate. The survey data consists of images taken
with ACS on HST, supplemented with archival data and new WFPC2 imaging taken
after the failure of ACS. Survey images include wide field tilings covering the
full radial extent of each galaxy, and single deep pointings in uncrowded
regions of the most massive galaxies in the volume. The new wide field imaging
in ANGST reaches median 50% completenesses of m_F475W=28.0 mag, m_F606W=27.3
mag, and m_F814W=27.3 mag, several magnitudes below the tip of the red giant
branch (TRGB). The deep fields reach magnitudes sufficient to fully resolve the
structure in the red clump. The resulting photometric catalogs are publicly
accessible and contain over 34 million photometric measurements of >14 million
stars. In this paper we present the details of the sample selection, imaging,
data reduction, and the resulting photometric catalogs, along with an analysis
of the photometric uncertainties (systematic and random), for both the ACS and
WFPC2 imaging. We also present uniformly derived relative distances measured
from the apparent magnitude of the TRGB. | astro-ph_GA |
Stellar masses, sizes, and radial profiles for 465 nearby early-type
galaxies: an extension to the Spitzer Survey of Stellar Structure in Galaxies
(S$^{4}$G): The Spitzer Survey of Stellar Structure in Galaxies (S$^{4}$G) is a detailed
study of over 2300 nearby galaxies in the near-infrared (NIR), which has been
critical to our understanding of the detailed structures of nearby galaxies.
Because the sample galaxies were selected only using radio-derived velocities,
however, the survey favored late-type disk galaxies over lenticulars and
ellipticals. A follow-up Spitzer survey was conducted to rectify this bias,
adding 465 early-type galaxies (ETGs) to the original sample, to be analyzed in
a manner consistent with the initial survey. We present the data release of
this ETG extension, up to the third data processing pipeline (P3): surface
photometry. We produce curves of growth and radial surface brightness profiles
(with and without inclination corrections) using reduced and masked Spitzer
IRAC 3.6$\mu$m and 4.5$\mu$m images produced through Pipelines 1 and 2,
respectively. From these profiles, we derive the following integrated
quantities: total magnitudes, stellar masses, concentration parameters, and
galaxy size metrics. We showcase NIR scaling relations for ETGs among these
quantities. We examine general trends across the whole S$^{4}$G and ETG
extension among our derived parameters, highlighting differences between ETGs
and late-type galaxies (LTGs). ETGs are, on average, more massive and more
concentrated than LTGs, and also show subtle distinctions among ETG
morphological sub-types. We also derive the following scaling relations and
compare with previous results in visible light: mass--size (both half-light and
isophotal), mass--concentration, mass--surface brightness (central, effective,
and within 1 kpc), and mass--color. We find good agreement with previous works,
though some relations (e.g., mass--central surface brightness) will require
more careful multi-component decompositions to be fully understood. | astro-ph_GA |
The quasar main sequence and its potential for cosmology: The main sequence offers a method for the systematization of quasar spectral
properties. Extreme FeII emitters (or extreme Population A, xA) are believed to
be sources accreting matter at very high rates. They are easily identifiable
along the quasar main sequence, in large spectroscopic surveys over a broad
redshift range. The very high accretion rate makes it possible that massive
black holes hosted in xA quasars radiate at a stable, extreme
luminosity-to-mass ratio. After reviewing the basic interpretation of the main
sequence, we report on the possibility of identifying virial broadening
estimators from low-ionization line widths, and provide evidence of the
conceptual validity of redshift-independent luminosities based on virial
broadening for a known luminosity-to-mass ratio. | astro-ph_GA |
Two sequences of spiral galaxies with different shapes of the
metallicity gradients: We considered two sequences of spiral galaxies with different shapes of the
radial gas-phase oxygen abundance distributions from the galaxies in the MaNGA
survey: (1) Galaxies in which the gradient is well approximated by a single
linear relation across the whole disc, that is, galaxies with an S (slope)
gradients, (2) galaxies in which the metallicity in the inner region of the
disc is at a nearly constant level and the gradient is negative at larger
radii, that is, galaxies with level-slope (LS) gradients. We also selected
galaxies with a nearly uniform oxygen abundance across the whole galaxy, that
is, galaxies with level (L) gradients that can be the final evolutionary stage
of the two galaxy sequences described above. The radial nitrogen abundance
distributions in galaxies with LS oxygen abundance distributions also show
breaks at radii smaller than the O/H distribution breaks. The observed
behaviour of the oxygen and nitrogen abundances with radius in these galaxies
can be explained by the time delay between the nitrogen and oxygen enrichment
together with the variation in the star formation history along the radius.
These galaxies clearly show the effect of the inside-out disc evolution model.
We find that the shape of the radial abundance distribution in a galaxy is not
related to its macroscopic characteristics (rotation velocity, stellar mass,
isophotal radius, and star formation rate). The correlations between the
gradient slopes and macroscopic characteristics of galaxies are weak in the
sense that the scatter of the points in each diagram is large. We also examined
the properties of the Milky Way in the context of the considered galaxy
samples. | astro-ph_GA |
New constraints on the 1.4 GHz source number counts and luminosity
functions in the Lockman Hole field: We present a study of the 1173 sources brighter than $S_{1.4\,\rm GHz}=
120\,\mu$Jy detected over an area of $\simeq 1.4\,\hbox{deg}^{2}$ in the
Lockman Hole field. Exploiting the multi-band information available in this
field for $\sim$79% of the sample, sources have been classified into radio loud
(RL) active galactic nuclei (AGNs), star forming galaxies (SFGs) and radio
quiet (RQ) AGNs, using a variety of diagnostics available in the literature.
Exploiting the observed tight anti-correlations between IRAC band 1 or band 2
and the source redshift we could assign a redshift to 177 sources missing a
spectroscopic measurement or a reliable photometric estimate. A Monte Carlo
approach was used to take into account the spread around the mean relation. The
derived differential number counts and luminosity functions at several
redshifts of each population show a good consistency with models and with
earlier estimates made using data from different surveys and applying different
approaches. Our results confirm that below $\sim300\,\mu$Jy SFGs$+$RQ AGNs
overtake RL AGNs that dominate at brighter flux densities. We also confirm
earlier indications of a similar evolution of RQ AGNs and SFGs. Finally, we
discuss the angular correlation function of our sources and highlight its
sensitivity to the criteria used for the classification. | astro-ph_GA |
The Abundance Inhomogeneity in the Northern Rim of the Cygnus Loop: We observed the northern rim of the Cygnus Loop with the \textit{Suzaku}
observatory in 5 pointings (P21-P25). From the spatially resolved analysis, all
the spectra are well fitted by the single component of the non-equilibrium
ionization plasma model. From the best-fit parameters, we found that the
abundances of the heavy elements are significantly lower than the solar values
except those at the outermost edge in P21 and P22. The origin of the depleted
metal abundances is still unclear while such deficiencies have been reported
from many other rim observations of the Loop. To explain these depletion at the
rim regions, we considered the several possibilities. The effects of the
resonance-line-scattering and the grain condensation lower the values of the
abundances. However, these are not sufficient to account for the abundance
depletion observed.
We found that the abundances at the outermost edge in P21 and P22 are higher
than those at the other regions. From the morphological point of view, it is
reasonable to consider that this abundance inhomogeneity is derived from the
breakout or the thinness of the cavity wall of the Loop. | astro-ph_GA |
Mapping the stellar population and gas excitation of MaNGA galaxies with
MEGACUBES. Results for AGN versus control sample: We present spaxel-by-spaxel stellar population fits for the $\sim$10 thousand
MaNGA datacubes. We provide multiple extension fits files, nominated as
MEGACUBES, with maps of several properties as well as emission-line profiles
that are provided for each spaxel. All the MEGACUBES are available through a
web interface (\url{https://manga.linea.org.br/} or
\url{http://www.if.ufrgs.br/~riffel/software/megacubes/}). We also defined a
final Active Galactic Nuclei (AGN) sample, as well as a control sample matching
the AGN host galaxy properties. We have analysed the stellar populations and
spatially resolved emission-line diagnostic diagrams of these AGNs and compared
them with the control galaxies sample. We find that the relative fractions of
young ($t \leq $56 Myr) and intermediate-age (100 Myr $\leq t \leq$ 2 Gyr) show
predominantly a positive gradient for both AGNs and controls. The relative
fraction of intermediate-age stellar population is higher in AGN hosts when
compared to the control sample, and this difference becomes larger for higher
[O III] luminosity AGNs. We attribute this to the fact that extra gas is
available in these more luminous sources and that it most likely originates
from mass-loss from the intermediate-age stars. The spatially resolved
diagnostic diagrams reveal that the AGN emission is concentrated in the inner
0.5 $R_e$ (effective radius) region of the galaxies, showing that the AGN
classification is aperture dependent and that emission-line ratios have to be
taken together with the H$\alpha$ equivalent width for proper activity
classification. We present a composite ``BPT+WHAN" diagram that produces a more
comprehensive mapping of the gas excitation. | astro-ph_GA |
Chemical evolution in the early phases of massive star formation II:
Deuteration: The chemical evolution in high-mass star-forming regions is still poorly
constrained. Studying the evolution of deuterated molecules allows to
differentiate between subsequent stages of high-mass star formation regions due
to the strong temperature dependence of deuterium isotopic fractionation. We
observed a sample of 59 sources including 19 infrared dark clouds, 20 high-mass
protostellar objects, 11 hot molecular cores and 9 ultra-compact HII regions in
the (3-2) transitions of the four deuterated molecules, DCN, DNC, DCO+ and N2D+
as well as their non-deuterated counterpart. The overall detection fraction of
DCN, DNC and DCO+ is high and exceeds 50% for most of the stages. N2D+ was only
detected in a few infrared dark clouds and high-mass protostellar objects. It
can be related to problems in the bandpass at the frequency of the transition
and to low abundances in the more evolved, warmer stages. We find median D/H
ratios of ~0.02 for DCN, ~0.005 for DNC, ~0.0025 for DCO+ and ~0.02 for N2D+.
While the D/H ratios of DNC, DCO+ and N2D+ decrease with time, DCN/HCN peaks at
the hot molecular core stage. We only found weak correlations of the D/H ratios
for N2D+ with the luminosity of the central source and the FWHM of the line,
and no correlation with the H2 column density. In combination with a previously
observed set of 14 other molecules (Paper I) we fitted the calculated column
densities with an elaborate 1D physico-chemical model with time-dependent
D-chemistry including ortho- and para-H2 states. Good overall fits to the
observed data have been obtained the model. It is one of the first times that
observations and modeling have been combined to derive chemically based
best-fit models for the evolution of high-mass star formation including
deuteration. | astro-ph_GA |
VLT/X-Shooter Survey of BAL Quasars: Large Distance Scale and AGN
Feedback: We conducted a survey of quasar outflows using the VLT/X-shooter
spectrograph. When choosing the 14 BAL and mini-BALs comprising this sample,
the data did not cover the S IV and S IV* troughs, whose ratio can be used to
determine the distance of the outflows from the central source (R). Therefore,
this "Blind Survey" is unbiased towards a particular distance scale. Out of the
eight outflows where R can be measured, six have R > 100 pc (spanning the range
100-4500 pc), one has R > 10 pc, and only one (at R < 60 pc) is compatible with
a much smaller R scale. At least two of the outflows have a kinetic luminosity
greater than 0.5% of their Eddington luminosity, implying that they are able to
provide significant AGN feedback. The outflows span a range of 0 to -10000 km
s$^{-1}$ in velocity; total column density between 10$^{20}$ - 10$^{22.5}$
cm$^{-2}$ ; ionization parameter ($U_H$ ) in the range 0.01 - 1; and electron
number density between 10$^3$ - 10$^{5.5}$ cm$^{-3}$ , with one upper and one
lower limit. The results of this survey can be extrapolated to the majority of
BAL outflows, implying that most of these outflows are situated far away from
the AGN accretion disk; and that a significant portion of them can contribute
to AGN feedback processes. | astro-ph_GA |
The discovery of lensed radio and X-ray sources behind the Frontier
Fields cluster MACS J0717.5+3745 with the JVLA and Chandra: We report on high-resolution JVLA and Chandra observations of the HST
Frontier Cluster MACS J0717.5+3745. MACS J0717.5+3745 offers the largest
contiguous magnified area of any known cluster, making it a promising target to
search for lensed radio and X-ray sources. With the high-resolution 1.0-6.5 GHz
JVLA imaging in A and B configuration, we detect a total of 51 compact radio
sources within the area covered by the HST imaging. Within this sample we find
7 lensed sources with amplification factors larger than $2$. None of these
sources are identified as multiply-lensed. Based on the radio luminosities, the
majority of these sources are likely star forming galaxies with star formation
rates of 10-50 M$_\odot$ yr$^{-1}$ located at $1 \lesssim z \lesssim 2$. Two of
the lensed radio sources are also detected in the Chandra image of the cluster.
These two sources are likely AGN, given their $2-10$ keV X-ray luminosities of
$\sim 10^{43-44}$ erg s$^{-1}$. From the derived radio luminosity function, we
find evidence for an increase in the number density of radio sources at
$0.6<z<2.0$, compared to a $z < 0.3$ sample. Our observations indicate that
deep radio imaging of lensing clusters can be used to study star forming
galaxies, with star formation rates as low as $\sim10$ M$_{\odot}$ yr$^{-1}$,
at the peak of cosmic star formation history. | astro-ph_GA |
Estimation of the size and structure of the broad line region using
Bayesian approach: Understanding the geometry and kinematics of the broad line region (BLR) of
active galactic nuclei (AGN) is important to estimate black hole masses in AGN
and study the accretion process. The technique of reverberation mapping (RM)
has provided estimates of BLR size for more than 100 AGN now, however, the
structure of the BLR has been studied for only a handful number of objects.
Towards this, we investigated the geometry of the BLR for a large sample of 57
AGN using archival RM data. We performed systematic modeling of the continuum
and emission line light curves using a Markov Chain Monte Carlo method based on
Bayesian statistics implemented in PBMAP (Parallel Bayesian code for
reverberation-MAPping data) code to constrain BLR geometrical parameters and
recover velocity integrated transfer function. We found that the recovered
transfer functions have various shapes such as single-peaked, double-peaked and
top-hat suggesting that AGN have very different BLR geometries. Our model lags
are in general consistent with that estimated using the conventional
cross-correlation methods. The BLR sizes obtained from our modeling approach is
related to the luminosity with a slope of 0.583 (+/-) 0.026 and 0.471 (+/-)
0.084 based on H{\beta} and H{\alpha} lines, respectively. We found a
non-linear response of emission line fluxes to the ionizing optical continuum
for 93\% objects. The estimated virial factors for the AGN studied in this work
range from 0.79 to 4.94 having a mean at 1.78 (+/-) 1.77 consistent with the
values found in the literature. | astro-ph_GA |
The Magnetic Field of the Milky Way Galaxy: Cosmic magnetic fields are an integral component of the interstellar medium
(ISM), having influence on scales ranging from star formation to galactic
dynamics. While observations of external galaxies offer a `birds-eye-view' of
magnetic fields within galaxies, it is equally important to explore the
magnetic field of our own Milky Way Galaxy, which offers a more detailed,
albeit more complicated view. Over the past decade there has been a significant
increase in interest in the Galactic magnetic field, fueled largely by
innovations developed through the Canadian Galactic Plane Survey. In this
paper, I review the current state of understanding of the Galactic magnetic
field, and discuss briefly new and future observations that will provide
exciting new insights about the field. | astro-ph_GA |
The Bardeen-Petterson effect in accreting supermassive black-hole
binaries: a systematic approach: Disc-driven migration is a key evolutionary stage of supermassive black-hole
binaries hosted in gas-rich galaxies. Besides promoting the inspiral, viscous
interactions tend to align the spins of the black holes with the orbital
angular momentum of the disc. We present a critical and systematic
investigation of this problem, also known as the Bardeen-Petterson effect. We
design a new iterative scheme to solve the non-linear dynamics of warped
accretion discs under the influence of both relativistic frame dragging and
binary companion. We characterize the impact of the disc "critical obliquity",
which marks regions of the parameter space where stationary solutions do not
exist. We find that black-hole spins reach either complete alignment or a
critical configuration. Reaching the critical obliquity might imply that the
disc breaks as observed in hydrodynamical simulations. Our findings are
important to predict the spin configurations with which supermassive black-hole
binaries enter their gravitational-wave driven regime and become detectable by
LISA. | astro-ph_GA |
Theoretical Models of the Atomic Hydrogen Content in Dark Matter Halos: Atomic hydrogen (H I) gas, mostly residing in dark matter halos after cosmic
reionization, is the fuel for star formation. Its relation with properties of
host halo is the key to understand the cosmic H I distribution. In this work,
we propose a flexible, empirical model of H I-halo relation. In this model,
while the H I mass depends primarily on the mass of host halo, there is also
secondary dependence on other halo properties. We apply our model to the
observation data of the Arecibo Fast Legacy ALFA Survey (ALFALFA), and find it
can successfully fit to the cosmic H I abundance ($\Omega_{\rm HI}$), average H
I-halo mass relation $\langle M_{\rm HI}|M_{\rm h}\rangle$, and the H I
clustering. The bestfit of the ALFALFA data rejects with high confidence level
the model with no secondary halo dependence of H I mass and the model with
secondary dependence on halo spin parameter ($\lambda$), and shows strong
dependence on halo formation time ($a_{1/2}$) and halo concentration ($c_{\rm
vir}$). In attempt to explain these findings from the perspective of
hydrodynamical simulations, the IllustrisTNG simulation confirms the dependence
of H I mass on secondary halo parameters. However, the IllustrisTNG results
show strong dependence on $\lambda$ and weak dependence on $c_{\rm vir}$ and
$a_{1/2}$, and also predict a much larger value of H I clustering on large
scales than observations. This discrepancy between the simulation and
observation calls for improvements in understanding the H I-halo relation from
both theoretical and observational sides. | astro-ph_GA |
The effect of the morphological quenching mechanism on star formation
activity at 0.5 < z < 1.5 in 3D-HST/CANDELS: Several mechanisms for the transformation of blue star-forming to red
quiescent galaxies have been proposed, and the green valley (GV) galaxies amid
them are widely accepted in a transitional phase. Thus, comparing the
morphological and environmental differences of the GV galaxies with early-type
disks (ETDs; bulge dominated and having a disk) and late-type disks (LTDs; disk
dominated) is suitable for distinguishing the corresponding quenching
mechanisms. A large population of massive ($M_* \geqslant 10^{10}M_\odot$) GV
galaxies at $0.5 \leqslant z \leqslant 1.5$ in 3D-HST/CANDELS is selected using
extinction-corrected $(U-V)_{\rm rest}$ color. After eliminating any possible
active galactic nucleus candidates and considering the "mass-matching", we
finally construct two comparable samples of GV galaxies with either 319 ETD or
319 LTD galaxies. Compared to the LTD galaxies, it is found that the ETD
galaxies possess higher concentration index and lower specific star formation
rate, whereas the environments surrounding them are not different. This may
suggest that the morphological quenching may dominate the star formation
activity of massive GV galaxies rather than the environmental quenching. To
quantify the correlation between the galaxy morphology and the star formation
activity, we define a dimensionless morphology quenching efficiency $Q_{\rm
mor}$ and find that $Q_{\rm mor}$ is not sensitive to the stellar mass and
redshift. When the difference between the average star formation rate of ETD
and LTD galaxies is about 0.7 $M_\odot \rm \;yr^{-1}$, the probability of
$Q_{\rm mor}\gtrsim 0.2$ is higher than 90\%, which implies that the degree of
morphological quenching in GV galaxies might be described by $Q_{\rm
mor}\gtrsim 0.2$. | astro-ph_GA |
Standoff Distance of Bow Shocks in Galaxy Clusters as Proxy for Mach
Number: X-ray observations of merging clusters provide many examples of bow shocks
leading merging subclusters. While the Mach number of a shock can be estimated
from the observed density jump using Rankine-Hugoniot condition, it reflects
only the velocity of the shock itself and is generally not equal to the
velocity of the infalling subcluster dark matter halo or to the velocity of the
contact discontinuity separating gaseous atmospheres of the two subclusters.
Here we systematically analyze additional information that can be obtained by
measuring the standoff distance, i.e. the distance between the leading edge of
the shock and the contact discontinuity that drives this shock. The standoff
distance is influenced by a number of additional effects, e.g. (1) the
gravitational pull of the main cluster (causing acceleration/deceleration of
the infalling subcluster), (2) the density and pressure gradients of the
atmosphere in the main cluster, (3) the non-spherical shape of the subcluster,
and (4) projection effects. The first two effects tend to bias the standoff
distance in the same direction, pushing the bow shock closer to (farther away
from) the subcluster during the pre- (post-)merger stages. Particularly, in the
post-merger stage, the shock could be much farther away from the subcluster
than predicted by a model of a body moving at a constant speed in a uniform
medium. This implies that a combination of the standoff distance with
measurements of the Mach number from density/temperature jumps can provide
important information on the merger, e.g. differentiating between the pre- and
post-merger stages. | astro-ph_GA |
A slow lopsided bar in the interacting dwarf galaxy IC 3167: We present surface photometry and stellar kinematics of IC 3167, a dwarf
galaxy hosting a lopsided weak bar and infalling into the Virgo cluster. We
measured the bar radius and strength from broad-band imaging and bar pattern
speed by applying the Tremaine-Weinberg method to stellar-absorption
integral-field spectroscopy. We derived the ratio of the corotation radius to
bar radius (R = 1.7 + 0.5 - 0.3) from stellar kinematics and bar pattern speed.
The probability that the bar is rotating slowly is more than twice as likely as
that the bar is fast. This allows us to infer that the formation of this bar
was triggered by the ongoing interaction rather than to internal processes. | astro-ph_GA |
Amplification of OAM Radiation by Astrophysical Masers: We extend the theory of astrophysical maser propagation through a medium with
a Zeeman-split molecular response to the case of a non-uniform magnetic field,
and allow a component of the electric field of the radiation in the direction
of propagation: a characteristic of radiation with orbital angular momentum. A
classical reduction of the governing equations leads to a set of nine
differential equations for the evolution of intensity-like parameters for each
Fourier component of the radiation. Four of these parameters correspond to the
standard Stokes parameters, whilst the other five represent the $z$-component
of the electric field, and its coupling to the conventional components in the
$x-y$-plane. A restricted analytical solution of the governing equations
demonstrates a non-trivial coupling of the Stokes parameters to those
representing orbital angular momentum: the $z$-component of the electric field
can grow from a background in which only Stokes-$I$ is non-zero. A numerical
solution of the governing equations reveals radiation patterns with a radial
and angular structure for the case of an ideal quadrupole magnetic field
perpendicular to the propagation direction. In this ideal case generation of
radiation orbital angular momentum, like polarization, can approach 100 per
cent. | astro-ph_GA |
Superhydrogenated Polycyclic Aromatic Hydrocarbon Molecules: Vibrational
Spectra in the Infrared: Superhydrogenated polycyclic aromatic hydrocarbons (PAHs) may be present in
H-rich and ultraviolet-poor benign regions. The addition of excess H atoms to
PAHs converts the aromatic bonds into aliphatic bonds, the strongest of which
falls near 3.4 $\mu$m. Therefore, superhydrogenated PAHs are often hypothesized
as a carrier of the 3.4 $\mu$m emission feature which typically accompanies the
stronger 3.3 $\mu$m aromatic C--H stretching feature. To assess this
hypothesis, we use density function theory to compute the IR vibrational
spectra of superhydrogenated PAHs and their ions of various sizes (ranging from
benzene, naphthalene to perylene and coronene) and of various degrees of
hydrogenation (ranging from minimal hydrogenation to heavy hydrogenation). For
each molecule, we derive the intrinsic oscillator strengths of the 3.3 $\mu$m
aromatic C--H stretch ($A_{3.3}$) and the 3.4 $\mu$m aliphatic C--H stretch
($A_{3.4}$). By comparing the computationally-derived mean ratio of $\langle
A_{3.4}/A_{3.3}\rangle\sim1.98$ with the mean ratio of the observed intensities
$\langle I_{3.4}/I_{3.3}\rangle\sim0.12$, we find that the degree of
superhydrogenation --- the fraction of C atoms attached with excess H atoms ---
is only $\sim2.2\%$ for neutral PAHs which predominantly emit the 3.3 and 3.4
$\mu$m features. We also determine for each molecule the intrinsic band
strengths of the 6.2 $\mu$m aromatic C--C stretch ($A_{6.2}$) and the 6.85
$\mu$m aliphatic C--H deformation ($A_{6.85}$). We derive the degree of
superhydrogenation from the mean ratio of the observed intensities $\langle
I_{6.85}/I_{6.2}\rangle\sim0.10$ and $\langle A_{6.85}/A_{6.2}\rangle\sim1.53$
for neutrals and $\langle A_{6.85}/A_{6.2}\rangle\sim1.23$ for cations to be
$\lesssim 3.1\%$ for neutrals and $\lesssim 8.6\%$ for cations. We conclude
that astrophysical PAHs are primarily aromatic and are only marginally
superhydrogenated. | astro-ph_GA |
Obscuration in AGNs: near-infrared luminosity relations and dust colors: We combine two approaches to isolate the AGN luminosity at near-infrared
wavelengths and relate the near-IR pure AGN luminosity to other tracers of the
AGN. Using integral-field spectroscopic data of an archival sample of 51 local
AGNs, we estimate the fraction of non-stellar light by comparing the nuclear
equivalent width of the stellar 2.3 micron CO absorption feature with the
intrinsic value for each galaxy. We compare this fraction to that derived from
a spectral decomposition of the integrated light in the central arc second and
find them to be consistent with each other. Using our estimates of the near-IR
AGN light, we find a strong correlation with presumably isotropic AGN tracers.
We show that a significant offset exists between type 1 and type 2 sources in
the sense that type 1 sources are 7 (10) times brighter in the near-IR at log
L_MIR = 42.5 (log L_X = 42.5). These offsets only becomes clear when treating
infrared type 1 sources as type 1 AGNs.
All AGNs have very red near-to-mid-IR dust colors. This, as well as the range
of observed near-IR temperatures, can be explained with a simple model with
only two free parameters: the obscuration to the hot dust and the ratio between
the warm and hot dust areas. We find obscurations of A_V (hot) = 5 - 15 mag for
infrared type 1 sources and A_V (hot) = 15 - 35 mag for type 2 sources. The
ratio of hot dust to warm dust areas of about 1000 is nicely consistent with
the ratio of radii of the respective regions as found by infrared
interferometry. | astro-ph_GA |
The mm-to-cm SED of spiral galaxies. Synergies between NIKA2 and SRT
instruments: The mm-to-cm range of the Spectral Energy Distribution of spiral galaxies
remains largely unexplored. Its coverage is required to disentangle the
contribution of dust emission, free-free and synchrotron radiation and can
provide constraints on dust models, star-formation rates and ISM properties. We
present the case for a synergy between NIKA2 observations of nearby spirals and
those from planned and current instrumentation at the Sardinia Radio Telescope,
and report on a pilot K-band program to search for Anomalous Microwave
Emission, an elusive emission component which is presumably related to dust. | astro-ph_GA |
Interaction effects on galaxy pairs with GeminiGMOS-III: Stellar
population synthesis: We present an observational study of the impacts of the interactions on the
stellar population in a sample of galaxy pairs. Long-slit spectra in the
wavelength range 3440-7300 {\AA} obtained with the Gemini Multi-Object
Spectrograph (GMOS) at Gemini South for fifteen galaxies in nine close pairs
were used. The spatial distributions of the stellar population contributions
were obtained using the stellar population synthesis code STARLIGHT. Taking
into account the different contributions to the emitted light, we found that
most of the galaxies in our sample are dominated by the young/intermediate
stellar populations. This result differs from the one derived for isolated
galaxies where the old stellar population dominates the disc surface
brightness. We interpreted such different behavior as being due to the effect
of gas inflows along the disk of interacting galaxies on the star formation in
a time scale of the order of about 2Gyr. We also found that, in general, the
secondary galaxy of the pairs has a higher contribution of the young stellar
population than the primary one. We compared the estimated values of the
stellar and nebular extinctions derived from the synthesis method and the
H{\alpha}/H\b{eta} emission-line ratio finding that the nebular extinctions are
systematically higher than stellar ones by about a factor of 2. We did not find
any correlation between nebular and stellar metallicities. We neither found a
correlation between stellar metallicities and ages while a positive correlation
between nebular metallicities and stellar ages was obtained, with the older
regions being the most metal-rich. | astro-ph_GA |
ALMA Observations toward the starburst dwarf galaxy NGC 5253: I.
Molecular cloud properties and scaling relations: We present high-spatial-resolution ($\sim 0\farcs2$, or $\sim$3\,pc) CO(2--1)
observations of the nearest young starburst dwarf galaxy, NGC\,5253, taken with
the Atacama Large Millimeter/submillimeter Array. We have identified 118
molecular clouds with average values of 4.3\,pc in radius and 2.2\,\kms\, in
velocity dispersion, which comprise the molecular cloud complexes observed
previously with $\sim$100\,pc resolution. We derive for the first time in this
galaxy the $I{\rm (CO)}$--$N$(H$_2$) conversion factor, $X$ =
$4.1^{+5.9}_{-2.4}\times10^{20}$\,cm$^{-2}$(K\,\kms)$^{-1}$, based on the
virial method. The line-width and mass-to-size relations of the resolved
molecular clouds present an offset on average toward higher line-widths and
masses with respect to quiescent regions in other nearby spiral galaxies and
our Galaxy. The offset in the scaling relation reaches its maximum in regions
close to the central starburst, where velocity dispersions are $\sim$ 0.5 dex
higher and gas mass surface densities are as high as $\Sigma_{\rm H_2}$ =
10$^3$\,\Msol\,pc $^{-2}$. These central clouds are gravitationally bound
despite the high internal pressure. A spatial comparison with star clusters
found in the literature enables us to identify six clouds that are associated
with young star clusters. Furthermore, the star formation efficiencies (SFEs)
of some of these clouds exceed those found in star-cluster-forming clouds
within our Galaxy. We conclude that once a super star cluster is formed, the
parent molecular clouds are rapidly dispersed by the destructive stellar
feedback, which results in such a high SFE in the central starburst of
NGC\,5253. | astro-ph_GA |
Star formation properties of galaxy cluster A1767: Abell 1767 is a dynamically relaxed, cD cluster of galaxies with a redshift
of 0.0703. Among 250 spectroscopically confirmed member galaxies within a
projected radius of 2.5r_{200}, 243 galaxies (~ 97%) are spectroscopically
covered by the Sloan Digital Sky Survey (SDSS). Based on this homogeneous
spectral sample, the stellar evolutionary synthesis code, STARLIGHT, is applied
to investigate the stellar populations and star formation histories (SFHs) of
cluster galaxies. The star formation properties of galaxies, such as mean
stellar ages, metallicities, stellar masses, and star formation rates (SFRs),
are presented as the functions of local galaxy density. Strong environmental
effect is found in the manner that massive galaxies in the high-density core
region of cluster tend to have higher metallicities, longer mean stellar ages,
and lower specific star formation rates (SSFRs), and their recent star
formation activities have been remarkably suppressed. In addition, the
correlations of the metallicity and SSFR with stellar mass are confirmed. | astro-ph_GA |
Molecular clouds in M51 from high-resolution extinction mapping: Here we present the cloud population extracted from M51, following the
application of our new high-resolution dust extinction technique to the galaxy
(Faustino Vieira et al. 2023). With this technique, we are able to image the
gas content of the entire disc of M51 down to 5 pc (0.14"), which allows us to
perform a statistical characterisation of well-resolved molecular cloud
properties across different large-scale dynamical environments and with
galactocentric distance. We find that cloud growth is promoted in regions in
the galaxy where shear is minimised; i.e. clouds can grow into higher masses
(and surface densities) inside the spiral arms and molecular ring. We do not
detect any enhancement of high-mass star formation towards regions favourable
to cloud growth, indicating that massive and/or dense clouds are not the sole
ingredient for high-mass star formation. We find that in the spiral arms there
is a significant decline of cloud surface densities with increasing
galactocentric radius, whilst in the inter-arm regions they remain relatively
constant. We also find that the surface density distribution for spiral arm
clouds has two distinct behaviours in the inner and outer galaxy, with average
cloud surface densities at larger galactocentric radii becoming similar to
inter-arm clouds. We propose that the tidal interaction between M51 and its
companion (NGC 5195) - which heavily affects the nature of the spiral structure
- might be the main factor behind this. | astro-ph_GA |
Methyl Acetate and its singly deuterated isotopomers in the interstellar
medium: Methyl acetate (CH_3COOCH_3) has been recently observed by IRAM 30 m radio
telescope in Orion though the presence of its deuterated isotopomers is yet to
be confirmed. We therefore study the properties of various forms of methyl
acetate, namely, CH_3COOCH_3, CH_2DCOOCH_3 and CH_3COOCH_2D. Our simulation
reveals that these species could be produced efficiently both in gas as well as
in ice phases. Production of methyl acetate could follow radical-radical
reaction between acetyl (CH_3CO) and methoxy (CH_3O) radicals. To predict
abundances of CH_3COOCH_3 along with its two singly deuterated isotopomers and
its two isomers (ethyl formate and hydroxyacetone), we prepare a gas-grain
chemical network to study chemical evolution of these molecules. Since gas
phase rate coefficients for methyl acetate and its related species were
unknown, either we consider similar rate coefficients for similar types of
reactions (by following existing data bases) or we carry out quantum chemical
calculations to estimate the unknown rate coefficients. For the surface
reactions, we use adsorption energies of reactants from some earlier studies.
Moreover, we perform quantum chemical calculations to obtain spectral
properties of methyl acetate in infrared and sub-millimeter regions. We prepare
two catalog files for the rotational transitions of CH_2DCOOCH_3 and
CH_3COOCH_2D in JPL format, which could be useful for their detection in
regions of interstellar media where CH_3COOCH_3 has already been observed. | astro-ph_GA |
Diversity of Type Ia Supernovae Imprinted in Chemical Abundances: A time delay of Type Ia supernova (SN Ia) explosions hinders the imprint of
their nucleosynthesis on stellar abundances. However, some occasional cases
give birth to stars that avoid enrichment of their chemical compositions by
massive stars and thereby exhibit a SN Ia-like elemental feature including a
very low [Mg/Fe] (~-1). We highlight the elemental feature of Fe-group elements
for two low-Mg/Fe objects detected in nearby galaxies, and propose the presence
of a class of SNe Ia that yield the low abundance ratios of [Cr,Mn,Ni/Fe]. Our
novel models of chemical evolution reveal that our proposed class of SNe Ia
(slow SNe Ia) is associated with ones exploding on a long timescale after their
stellar birth, and gives a significant impact on the chemical enrichment in the
Large Magellanic Cloud (LMC). In the Galaxy, on the other hand, this effect is
unseen due to the overwhelming enrichment by the major class of SNe Ia that
explode promptly (prompt SNe Ia) and eject a large amount of Fe-group elements.
This nicely explains the different [Cr,Mn,Ni/Fe] features between the two
galaxies as well as the puzzling feature seen in the LMC stars exhibiting very
low Ca but normal Mg abundances. Furthermore, the corresponding channel of slow
SN Ia is exemplified by performing detailed nucleosynthesis calculations in the
scheme of SNe Ia resulting from a 0.8+0.6 solar mass white dwarf merger. | astro-ph_GA |
Photometric properties of intermediate redshift Type Ia Supernovae
observed by SDSS-II Supernova Survey: We have analyzed multi-band light curves of 328 intermediate redshift (0.05
<= z < 0.24) type Ia supernovae (SNe Ia) observed by the Sloan Digital Sky
Survey-II Supernova Survey (SDSS-II SN Survey). The multi-band light curves
were parameterized by using the Multi-band Stretch Method, which can simply
parameterize light curve shapes and peak brightness without dust extinction
models. We found that most of the SNe Ia which appeared in red host galaxies (u
- r > 2.5) don't have a broad light curve width and the SNe Ia which appeared
in blue host galaxies (u - r < 2.0) have a variety of light curve widths. The
Kolmogorov-Smirnov test shows that the colour distribution of SNe Ia appeared
in red / blue host galaxies is different (significance level of 99.9%). We also
investigate the extinction law of host galaxy dust. As a result, we find the
value of Rv derived from SNe Ia with medium light curve width is consistent
with the standard Galactic value. On the other hand, the value of Rv derived
from SNe Ia that appeared in red host galaxies becomes significantly smaller.
These results indicate that there may be two types of SNe Ia with different
intrinsic colours, and they are obscured by host galaxy dust with two different
properties. | astro-ph_GA |
Comparing semi-analytic particle tagging and hydrodynamical simulations
of the Milky Way's stellar halo: Particle tagging is an efficient, but approximate, technique for using
cosmological N-body simulations to model the phase-space evolution of the
stellar populations predicted, for example, by a semi-analytic model of galaxy
formation. We test the technique developed by Cooper et al. (which we call
STINGS here) by comparing particle tags with stars in a smooth particle
hydrodynamic (SPH) simulation. We focus on the spherically averaged density
profile of stars accreted from satellite galaxies in a Milky Way (MW)-like
system. The stellar profile in the SPH simulation can be recovered accurately
by tagging dark matter (DM) particles in the same simulation according to a
prescription based on the rank order of particle binding energy. Applying the
same prescription to an N-body version of this simulation produces a density
profile differing from that of the SPH simulation by <10 per cent on average
between 1 and 200 kpc. This confirms that particle tagging can provide a
faithful and robust approximation to a self-consistent hydrodynamical
simulation in this regime (in contradiction to previous claims in the
literature). We find only one systematic effect, likely due to the
collisionless approximation, namely that massive satellites in the SPH
simulation are disrupted somewhat earlier than their collisionless
counterparts. In most cases this makes remarkably little difference to the
spherically averaged distribution of their stellar debris. We conclude that,
for galaxy formation models that do not predict strong baryonic effects on the
present-day DM distribution of MW-like galaxies or their satellites,
differences in stellar halo predictions associated with the treatment of star
formation and feedback are much more important than those associated with the
dynamical limitations of collisionless particle tagging. | astro-ph_GA |
Isolating signatures of major cloud-cloud collisions using
position-velocity diagrams: Collisions between giant molecular clouds are a potential mechanism for
triggering the formation of massive stars, or even super star clusters. The
trouble is identifying this process observationally and distinguishing it from
other mechanisms. We produce synthetic position-velocity diagrams from models
of: cloud-cloud collisions, non-interacting clouds along the line of sight,
clouds with internal radiative feedback and a more complex cloud evolving in a
galactic disc, to try and identify unique signatures of collision. We find that
a broad bridge feature connecting two intensity peaks, spatially correlated but
separated in velocity, is a signature of a high velocity cloud-cloud collision.
We show that the broad bridge feature is resilient to the effects of radiative
feedback, at least to around 2.5Myr after the formation of the first massive
(ionising) star. However for a head on 10km/s collision we find that this will
only be observable from 20-30 per cent of viewing angles. Such broad-bridge
features have been identified towards M20, a very young region of massive star
formation that was concluded to be a site of cloud-cloud collision by Torii et
al (2011), and also towards star formation in the outer Milky Way by Izumi et
al (2014). | astro-ph_GA |
The role of AGN on the structure, kinematics and evolution of ETGs in
the Horizon simulations: Feedback processes play a fundamental role in the regulation of the star
formation (SF) activity in galaxies and, in particular, in the quenching of
early-type galaxies (ETGs) as has been inferred by observational and numerical
studies of Lambda CDM models. At z = 0, ETGs exhibit well-known fundamental
scaling relations, but the connection between them and the physical processes
shaping ETG evolution remains unknown.This work aims at studying the impact of
the energetic feedback due to active galactic nuclei (AGN) on the formation and
evolution of ETGs.We focus on assessing the impact of AGN feedback on the
evolution of the mass-plane and the fundamental plane (FP, defined by using
mass surface density) as well as on morphology, kinematics, and stellar age
across the FP.The Horizon-AGN and Horizon-noAGN cosmological hydrodynamical
simulations were performed with identical initial conditions and including the
same physical processes except for the activation of the AGN feedback in the
former. We select a sample of central ETGs from both simulations using the same
criteria and exhaustively study their SF activity, kinematics, and scaling
relations for z <= 3. We find that Horizon-AGN ETGs identified at z = 0 follow
the observed fundamental scaling relations (mass-plane, FP, mass-size relation)
and qualitatively reproduce kinematic features albeit conserving a rotational
inner component with a mass fraction regulated by the AGN feedback. AGN
feedback seems to be required to reproduce the bimodality in the spin parameter
distribution reported by observational works and the mass-size relation (with
more massive galaxies having older stellar populations (SPs), larger sizes, and
being slower rotators). We study the evolution of the fundamental relations
with redshift, finding .Abridged | astro-ph_GA |
The Hector Survey: integral field spectroscopy of 100,000 galaxies: In March 2013, the Sydney--AAO Multi-object Integral field spectrograph
(SAMI) began a major survey of 3400 galaxies at the AAT, the largest of its
kind to date. At the time of writing, over a third of the targets have been
observed and the scientific impact has been immediate. The Manga galaxy survey
has now started at the SDSS telescope and will target an even larger sample of
nearby galaxies. In Australia, the community is now gearing up to deliver a
major new facility called Hector that will allow integral field spectroscopy of
100 galaxies observed simultaneously. By the close of the decade, it will be
possible to obtain integral field spectroscopy of 100,000 galaxies over 3000
square degrees of sky down to r=17 (median). Many of these objects will have HI
imaging from the new ASKAP radio surveys. We discuss the motivation for such a
survey and the use of new cosmological simulations that are properly matched to
the integral field observations. The Hector survey will open up a new and
unique parameter space for galaxy evolution studies. | astro-ph_GA |
An enduring puzzle: the width variations of the 2175 Angstrom extinction
band: Graphene, a single infinite, planar, sheet of graphite, has the same
dielectric resonances as bulk graphite, but solid state theory indicates that
its features are about half as wide. Based on this theory, the dielectric
functions of mono- and multi-layer graphenes are deduced and compared with
those of terrestrial graphite. The resonance width of an ordered stack of
graphenes is found to increase with the number of layers while the central
frequency stays constant. This is the basis of the polycrystalline model of the
carrier of the 2175 Angstrom interstellar extinction band. In this model, the
carrier dust grains derive from parent hydrocarbon grains. As a grain ages in
the IS medium, the light atoms are expelled, hexagonal carbon rings lump
together into compact planar clusters, which then assemble into stacks of
parallel, equidistant, graphene-like layers. This so-called graphitization is
well known to occur in the earth or under strong heating. As the number of
layers in each stack increases and their relative orientational order improves,
the pi resonance width increases asymptotically towards that of terrestrial
graphite. Because of the initial random structure of the parent grains, many
randomly oriented stacks may coexist in the same grain. Calculations of the
dielectric response of this composite medium show that, for such a grain, the
width of the extinction efficiency peak follows the same trend as the pi
resonance of the average stack, and thus covers the observed range of IS
feature widths, at very nearly constant peak frequency. | astro-ph_GA |
Extreme High-velocity Outflows from High-redshift BOSS Quasars: It is common to assume that all narrow absorption lines (NALs) at extreme
high-velocity shifts form in cosmologically intervening gas or galaxies
unrelated to quasars. However, previous detailed studies of individual quasars
have shown that some NALs at these large velocity shifts do form in high-speed
quasar ejecta. We search for extreme high-velocity NAL outflows (with speeds
$\sim$0.1-0.2c) based on relationships with associated absorption lines (AALs)
and broad absorption-line (BAL) outflows. We find that high-velocity NALs are
strongly correlated with AALs, BALs, and radio loudness, indicating that a
significant fraction of high-velocity systems are either ejected from the
quasars or form in material swept up by the radio jets (and are not unrelated
intervening gas). We also consider line-locked C IV doublets as another
indicator of high-velocity NALs formed in outflows. The fact that line-locked
NALs are highly ionized and correlated with BAL outflows and radio-loud quasars
implies that physical line locking due to radiative forces is both common and
real, which provides indirect evidence that a significant fraction of
high-velocity NALs are intrinsic to quasars. | astro-ph_GA |
Detection of anhydrous hydrochloric acid, HCl, in IRC+10216 with the
Herschel SPIRE and PACS spectrometers: We report on the detection of anhydrous hydrochloric acid (hydrogen chlorine,
HCl) in the carbon-rich star IRC+10216 using the spectroscopic facilities
onboard the Herschel satellite. Lines from J=1-0 up to J=7-6 have been
detected. From the observed intensities, we conclude that HCl is produced in
the innermost layers of the circumstellar envelope with an abundance relative
to H2 of 5x10^-8 and extends until the molecules reach its photodissociation
zone. Upper limits to the column densities of AlH, MgH, CaH, CuH, KH, NaH, FeH,
and other diatomic hydrides have also been obtained. | astro-ph_GA |
Velocity dispersion measurements of dwarf galaxies in the Coma cluster -
implications for the structure of the fundamental plane: We present intermediate-resolution spectroscopic data for a set of dwarf and
giant galaxies in the Coma Cluster, with -20.6 < M_R < -15.7. The photometric
and kinematic properties of the brighter galaxies can be cast in terms of
parameters which present little scatter with respect to a set of scaling
relations known as the Fundamental Plane. To determine the form of these
fundamental scaling relations at lower luminosities, we have measured velocity
dispersions for a sample comprising 69 galaxies on the border of the dwarf and
giant regime. Combining these data with our photometric survey, we find a tight
correlation of luminosity and velocity dispersion, L \propto \sigma^{2.0},
substantially flatter than the Faber-Jackson relation characterising giant
elliptical galaxies. In addition, the variation of mass-to-light ratio with
velocity dispersion is quite weak in our dwarf sample: M/L \propto
\sigma^{0.2}. Our overall results are consistent with theoretical models
invoking large-scale mass removal and subsequent structural readjustment, e.g.,
as a result of galactic winds. | astro-ph_GA |
X-ray Shadowing Experiments Toward Infrared Dark Clouds: We searched for X-ray shadowing toward two infrared dark clouds (IRDCs) using
the MOS detectors on XMM-Newton to learn about the Galactic distribution of
X-ray emitting plasma. IRDCs make ideal X-ray shadowing targets of 3/4 kev
photons due to their high column densities, relatively large angular sizes, and
known kinematic distances. Here we focus on two clouds near 30 deg. Galactic
longitude at distances of 2 and 5 kpc from the Sun. We derive the foreground
and background column densities of molecular and atomic gas in the direction of
the clouds. We find that the 3/4 kev emission must be distributed throughout
the Galactic disk. It is therefore linked to the structure of the cooler
material of the ISM, and to the birth of stars. | astro-ph_GA |
E(B-V), N(H I) and N(H_2): We consider the structure of the N(H I) - E(B-V) relationship when H I is
measured in the 21 cm radio line and \EBV\ is defined by far-IR dust-derived
measures. We derive reddening-dependent corrections to N(H I) based on
interferometric absorption measurements over the past 30 years that follow a
single power-law relationship $\int \tau(H I) dv = 14.07 ~\kms\ $\EBV$^{1.074}$
at 0.02 $\la$ \EBV\ $\la$ 3 mag. Corrections to 21cm line-derived H I column
densities are too small to have had any effect on the ratio N(H I)/\EBV\ $= 8.3
\times 10^{21}\pcc$ mag$^{-1}$ we derived at 0.015 $\la$ \EBV\ $\la$ 0.075 mag
and \absb\ $\ge$ 20\degr; they are also too small to explain the break in the
slope of the N(H I) - \EBV\ relation at \EBV\ $\ga$ 0.1 mag that we
demonstrated around the Galaxy at \absb $\ge 20$\degr. The latter must
therefore be attributed to the onset of \HH-formation and we show that models
of \HH\ formation in a low density diffuse molecular gas can readily explain
the inflected N(H I)- \EBV\ relationship. Below \absb\ = 20\degr\ N(H I)/\EBV\
measured at 0.015 $\la$ \EBV\ $\la$ 0.075 mag increases steadily down to \absb\
= 8\degr\ where sightlines with small \EBV\ no longer occur.
By contrast, the ratio N(H I)/\EBV\ measured over all \EBV\ declines to N(H
I)/\EBV\ $= 5-6 \times 10^{21}\pcc$ mag$^{-1}$ at \absb\ $\la 30$\degr, perhaps
providing an explanation of the difference between our results and the
gas/reddening ratios measured previously using stellar spectra. | astro-ph_GA |
Dissipation of AGN jets in a clumpy interstellar medium: Accreting supermassive black holes (SMBHs) frequently power jets that
interact with the interstellar/circumgalactic medium (ISM/CGM), regulating
star-formation in the galaxy. Highly supersonic jets launched by active
galactic nuclei (AGN) power a cocoon that confines them and shocks the ambient
medium. We build upon the models of narrow conical jets interacting with a
smooth ambient medium, to include the effect of dense clouds that are an
essential ingredient of a multiphase ISM. The key physical ingredient of this
model is that the clouds along the supersonic jet-beam strongly decelerate the
jet-head, but the subsonic cocoon easily moves around the clouds without much
resistance. We propose scalings for important physical quantities -- cocoon
pressure, head & cocoon speed, and jet radius. We obtain, for the first time,
the analytic condition on clumpiness of the ambient medium for the jet to
dissipate within the cocoon and verify it with numerical simulations of conical
jets interacting with a uniform ISM with embedded spherical clouds. A jet is
defined to be dissipated when the cocoon speed exceeds the speed of the
jet-head. We compare our models to more sophisticated numerical simulations,
direct observations of jet-ISM interaction (e.g., quasar J1316+1753), and
discuss implications for the Fermi/eROSITA bubbles. Our work also motivates
effective subgrid models for AGN jet feedback in a clumpy ISM unresolved by the
present generation of cosmological galaxy formation simulations. | astro-ph_GA |
NIR spectroscopic observation of massive galaxies in the protocluster at
z = 3.09: We present the results of near-infrared spectroscopic observations of the
$K$-band selected candidate galaxies in the protocluster at $z=3.09$ in the
SSA22 field. We observed 67 candidates with $K_{\rm AB}<24$ and confirmed
redshifts of the 39 galaxies at $2.0< z_{\rm spec}< 3.4$. Of the 67 candidates,
24 are certainly protocluster members with $3.04\leq z_{\rm spec}\leq 3.12$,
which are massive red galaxies those have been unidentified in previous optical
observations of the SSA22 protocluster. Many distant red galaxies (DRGs;
$J-K_{\rm AB}>1.4$), hyper extremely red objects (HEROs; $J-K_{\rm AB}>2.1$),
{\it Spitzer} MIPS 24 $\mu$m sources, active galactic nuclei (AGNs) as well as
the counterparts of Ly$\alpha$ blobs and the AzTEC/ASTE 1.1-mm sources in the
SSA22 field are also found to be the protocluster members. The mass of the
SSA22 protocluster is estimated to be $\sim2-5\times10^{14}~M_{\odot}$ and this
system is plausibly a progenitor of the most massive clusters of galaxies in
the current Universe. The reddest ($J-K_{\rm AB}\geq 2.4$) protocluster
galaxies are massive galaxies with $M_{\rm star}\sim10^{11}~M_{\odot}$ showing
quiescent star formation activities and plausibly dominated by old stellar
populations. Most of these massive quiescent galaxies host moderately luminous
AGNs detected by X-ray. There are no significant differences in the
[O{\footnotesize III}] $\lambda$5007/H$\beta$ emission line ratios, and
[O{\footnotesize III}] $\lambda$5007 line widths and spatial extents of the
protocluster galaxies from those of massive galaxies at $z\sim2-3$ in the
general field. | astro-ph_GA |
ngVLA: Astrometry and Long Baseline Science: Recent advances in VLBI have led to astrometric accuracy exceeding that of
the Gaia mission goals. This chapter describes some important astrophysical
problems that can be addressed with sub-milliarcsecond imaging and
micro-arcsecond astrometry using the ngVLA with long baselines. | astro-ph_GA |
A $Gaia$ EDR3 search for tidal tails in disintegrating open clusters: We carry out a search for tidal tails in a sample of open clusters with known
relatively elongated morphology. We identify the member stars of these clusters
from the precise astrometric and deep photometric data from $Gaia$ Early Data
Release 3 using the robust membership determination algorithm, ML-MOC. We
identify 46 open clusters having a stellar corona beyond the tidal radius, 20
of which exhibit extended tails aligned with the cluster orbit direction in
galactocentric coordinates. Notably we find NGC 6940 (at a distance of $\sim1$
kpc) is the furthest open cluster exhibiting tidal tails that are $\sim50$ pc
from its center, while also identifying $\sim40$ pc long tidal tails for the
nearby Pleiades. Using the minimum spanning tree length for the most massive
stars relative to all cluster members, we obtain the mass segregation ratio
($\rm\lambda_{MSR}$) profiles as a function of the number of massive stars in
each cluster. From these profiles, we can classify the open clusters into four
classes based on the degree of mass segregation experienced by the clusters. We
find that clusters in the most mass segregated classes are the oldest on
average and have the flattest mass function slope. Of the 46 open clusters
studied in this work, 41 exhibit some degree of mass segregation. Furthermore,
we estimate the initial masses (M$\rm_{i}$) of these open clusters finding that
some of them, having M$\rm_{i}\gtrsim 10^{4} M_{\odot}$, could be the
dissolving remnants of Young Massive Clusters. | astro-ph_GA |
Resolving the shocked gas in HH54 with Herschel: CO line mapping at high
spatial and spectral resolution: The HH54 shock is a Herbig-Haro object, located in the nearby Chamaeleon II
cloud. Observed CO line profiles are due to a complex distribution in density,
temperature, velocity, and geometry. Resolving the HH54 shock wave in the
far-infrared cooling lines of CO constrain the kinematics, morphology, and
physical conditions of the shocked region. We used the PACS and SPIRE
instruments on board the Herschel space observatory to map the full FIR
spectrum in a region covering the HH54 shock wave. Complementary Herschel-HIFI,
APEX, and Spitzer data are used in the analysis as well. The observed features
in the line profiles are reproduced using a 3D radiative transfer model of a
bow-shock, constructed with the Line Modeling Engine code (LIME). The FIR
emission is confined to the HH54 region and a coherent displacement of the
location of the emission maximum of CO with increasing J is observed. The peak
positions of the high-J CO lines are shifted upstream from the lower J CO lines
and coincide with the position of the spectral feature identified previously in
CO(10-9) profiles with HIFI. This indicates a hotter molecular component in the
upstream gas with distinct dynamics. The coherent displacement with increasing
J for CO is consistent with a scenario where IRAS12500-7658 is the exciting
source of the flow, and the 180 K bow-shock is accompanied by a hot (800 K)
molecular component located upstream from the apex of the shock and blueshifted
by -7 km s$^{-1}$. The spatial proximity of this knot to the peaks of the
atomic fine-structure emission lines observed with Spitzer and PACS ([OI]63,
145 $\mu$m) suggests that it may be associated with the dissociative shock as
the jet impacts slower moving gas in the HH54 bow-shock. | astro-ph_GA |
Surface density effects in quenching: cause or effect?: There are very strong observed correlations between the specific
star-formation rates (sSFR) of galaxies and their mean surface mass densities,
{\Sigma}, as well as other aspects of their internal structure. These strong
correlations have often been taken to indicate that the internal structure of a
galaxy must play a major physical role, directly or indirectly, in the control
of star-formation. In this paper we show by means of a very simple toy model
that these correlations can arise naturally without any such physical role once
the observed evolution of the size-mass relation for star-forming galaxies is
taken into account. In particular, the model reproduces the sharp threshold in
{\Sigma} between galaxies that are star-forming and those that are quenched,
and the evolution of this threshold with redshift. Similarly, it produces
iso-quenched-fraction contours in the ${f_Q(m,R_e)}$ plane that are almost
exactly parallel to lines of constant {\Sigma} for centrals and shallower for
satellites. It does so without any dependence on quenching on size or {\Sigma},
and without invoking any differences between centrals and satellites, beyond
the different mass-dependences of their quenching laws. The toy-model also
reproduces several other observations, including the sSFR gradients within
galaxies and the appearance of inside-out build-up of passive galaxies.
Finally, it is shown that curvature in the Main Sequence sSFR-mass relation can
produce curvature in the apparent B/T ratios with mass. Our analysis therefore
suggests that many of the strong correlations that are observed between galaxy
structure and sSFR may well be a consequence of things unrelated to quenching
and should not be taken as evidence of the physical processes that drive
quenching. | astro-ph_GA |
The pride of lions around Messier 105: We undertook a search for new dwarf galaxies in the Leo-I group using the
data from the DECaLS digital sky survey. Five new presumed members of this
group have been found in a wide vicinity of ${\rm M}\,105 ({\rm NGC}\,3379$).
Currently, the group has a population of $83$ galaxies, $33$ of which have
measured radial velocities. More than half of the group members belong to early
types with no signs of ongoing star formation. About a quarter of the galaxies
are outside the group's virial radius, $R_v = 385$~kpc. The presence of
multiple systems with a size of about 15~kpc is evident in the group, but there
are no noticeable global flat or filamentary substructures. The luminosity
function of the group looks to be deficient in galaxies with absolute
magnitudes in the interval $M_B = [-18, -15]$ mag. The ${\rm M}\,105$ group is
characterized by a radial velocity dispersion of $136$~km~s$^{-1}$, orbital
mass estimate $(5.76\pm1.32)\times 10^{12}~M_{\odot}$, and the total
mass-to-K-band-luminosity ratio $(17.8\pm4.1) M_\odot/L_\odot$. The neighboring
group of galaxies around ${\rm M}\,66 ({\rm NGC}\,3627$) has a similar virial
radius, $390$~kpc, velocity dispersion, $135$~km~s$^{-1}$, and total
mass-to-luminosity ratio, $(15.6\pm3.9) M_\odot/L_\odot$. Both groups in the
Leo constellation are approaching the Local Group with a velocity of about
100~km~s$^{-1}$. In the background of the ${\rm M}\,105$ group, we noted a
group of 6 galaxies with an unusually low virial mass-to-luminosity ratio,
$M_T/L_K = (4.1\pm2.2) M_\odot/L_\odot$. | astro-ph_GA |
Dark matter deficient galaxies in the Illustris flat-$Λ$CDM model
structure formation simulation: Surveying dark matter deficient galaxies (those with dark matter mass to
stellar mass ratio $M_{\rm dm}/M_{\rm star}<1$) in the Illustris simulation of
structure formation in the flat-$\Lambda$CDM cosmogony, we find $M_{\rm star}
\approx 2 \times 10^8\, M_\sun$ galaxies that have properties similar to those
ascribed by \citet{vanDokkumetal2018a} to the ultra-diffuse galaxy NGC1052-DF2.
The Illustris simulation also contains more luminous dark matter deficient
galaxies. Illustris galaxy subhalo 476171 is a particularly interesting
outlier, a massive and very compact galaxy with $M_{\rm star} \approx 9 \times
10^{10}\, M_\sun$ and $M_{\rm dm}/M_{\rm star} \approx 0.1$ and a
half-stellar-mass radius of $\approx 2$ kpc. If the Illustris simulation and
the $\Lambda$CDM model are accurate, there are a significant number of dark
matter deficient galaxies, including massive luminous compact ones. It will be
interesting to observationally discover these galaxies, and to also more
clearly understand how they formed, as they are likely to provide new insight
into and constraints on models of structure formation and the nature of dark
matter. | astro-ph_GA |
Simulating MOS science on the ELT: Ly$α$ forest tomography: Mapping of the large-scale structure through cosmic time has numerous
applications in the studies of cosmology and galaxy evolution. At $z > 2$, the
structure can be traced by the neutral intergalactic medium (IGM) by way of
observing the Ly$\alpha$, forest towards densely-sampled lines-of-sight of
bright background sources, such as quasars and star forming galaxies. We
investigate the scientific potential of MOSAIC, a planned multi-object
spectrograph on the European Extremely Large Telescope (ELT), for the 3D
mapping of the IGM at $z \gtrsim 3$. We simulate a survey of $3 \lesssim z
\lesssim 4$ galaxies down to a limiting magnitude of $m_{r}\sim 25.5$ mag in an
area of 1 degree$^2$ in the sky. Galaxies and their spectra (including the
line-of-sight Ly$\alpha$ absorption) are taken from the lightcone extracted
from the Horizon-AGN cosmological hydrodynamical simulation. The quality of the
reconstruction of the original density field is studied for different spectral
resolutions and signal-to-noise ratios of the spectra. We demonstrate that the
minimum $S/N$ (per resolution element) of the faintest galaxies that such
survey has to reach is $S/N = 4$. We show that a survey with such sensitivity
enables a robust extraction of cosmic filaments and the detection of the
theoretically-predicted galaxy stellar mass and star-formation rate gradients
towards filaments. By simulating the realistic performance of MOSAIC we obtain
$S/N(T_{\rm obs}, R, m_{r})$ scaling relations. We estimate that $\lesssim
35~(65)$ nights of observation time are required to carry out the survey with
the instrument's high multiplex mode and with the spectral resolution of
$R=1000~(2000)$. A survey with a MOSAIC-concept instrument on the ELT is found
to enable the mapping of the IGM at $z > 3$ on Mpc scales, and as such will be
complementary to and competitive with other planned IGM tomography surveys.
[abridged] | astro-ph_GA |
The H2O southern Galactic Plane Survey(HOPS): NH3 (1,1) and (2,2)
catalogues: The H2O Southern Galactic Plane Survey (HOPS) has mapped a 100 degree strip
of the Galactic plane (-70deg > l > 30deg, |b| < 0.5deg) using the 22-m Mopra
antenna at 12-mm wavelengths. Observations were conducted in on-the-fly mode
using the Mopra spectrometer (MOPS), targeting water masers, thermal molecular
emission and radio-recombination lines. Foremost among the thermal lines are
the 23 GHz transitions of NH3 J,K = (1,1) and (2,2), which trace the densest
parts of molecular clouds (n > 10^4 cm^{-3}). In this paper we present the NH3
(1,1) and (2,2) data, which have a resolution of 2 arcmin and cover a velocity
range of +/-200 km/s. The median sensitivity of the NH3 data-cubes is sigma_Tmb
= 0.20 +/1 0.06 K. For the (1,1) transition this sensitivity equates to a 3.2
kpc distance limit for detecting a 20 K, 400 Msun cloud at the 5-sigma level.
Similar clouds of mass 5,000 Msun would be detected as far as the Galactic
centre, while 30,000 Msun clouds would be seen across the Galaxy. We have
developed an automatic emission finding procedure based on the ATNF DUCHAMP
software and have used it to create a new catalogue of 669 dense molecular
clouds. The catalogue is 100 percent complete at the 5-sigma detection limit
(Tmb = 1.0 K). A preliminary analysis of the ensemble cloud properties suggest
that the near kinematic distances are favoured. The cloud positions are
consistent with current models of the Galaxy containing a long bar. Combined
with other Galactic plane surveys this new molecular-line dataset constitutes a
key tool for examining Galactic structure and evolution. Data-cubes, spectra
and catalogues are available to the community via the HOPS website. | astro-ph_GA |
Understanding the X-ray spectral curvature of Mkn 421 using broadband
AstroSat observations: We present a time-resolved X-ray spectral study of the high energy peaked
blazar Mkn 421 using simultaneous broadband observations from the LAXPC and SXT
instruments on-board AstroSat. The ~ 400 ksec long observation taken during 3-8
January, 2017 was divided into segments of 10 ksecs. Each segment was fitted
using synchrotron emission from particles whose energy distribution was
represented by a log-parabola model. We also considered particle energy
distribution models where (i) the radiative cooling leads to a maximum energy
({\xi} max model), (ii) the system has energy dependent diffusion (EDD) and
(iii) has energy dependent acceleration (EDA). We found that all these models
describe the spectra, although the EDD and EDA models were marginally better.
Time resolved spectral analysis allowed for studying the correlation between
the spectral parameters for different models. In the simplest and direct
approach, the observed correlations are not compatible with the predictions of
the {\xi} max model. While the EDD and EDA models do predict the correlations,
the values of the inferred physical parameters are not compatible with the
model assumptions. Thus, we show that spectrally degenerate models, can be
distinguished based on spectral parameter correlations (especially those
between the model normalization and spectral shape ones) making time-resolved
spectroscopy a powerful tool to probe the nature of these systems. | astro-ph_GA |
The physical properties of z>2 Lyman limit systems: new constraints for
feedback and accretion models: We study the physical properties of a homogeneous sample of 157
optically-thick absorption line systems at redshifts ~1.8-4.4, selected from a
high-dispersion spectroscopic survey of Lyman limit systems (LLSs). By means of
multiple ionisation models and Bayesian techniques, we derive the posterior
probability distribution functions for the density, metallicity, temperature,
and dust content of the absorbing gas. We find that z>2 LLSs are highly ionised
with ionisation parameters between -3<log U<-2, depending on the HI column
density. LLSs are characterised by low temperatures (T<5x10^4 K) and reside in
dust-poor environments. Between z~2.5-3.5, ~80% of the LLSs have physical
densities between n(H)~10^-3.5-10^-2 cm^-3 for the assumed UV background, but
we caution that a degeneracy between the ionisation parameter and the intensity
of the radiation field prevents robust inference on the density and sizes of
LLSs. Conversely, metallicity estimates are less sensitive to the assumptions
behind ionisation corrections. LLSs at z>2 are characterised by a broad
unimodal distribution over >4 orders of magnitude, with a peak at log
Z/Zsun~-2. LLSs are metal poor, significantly less enriched than DLAs, with
~70% of the metallicity PDF below log Z/Zsun<-1.5. The median metallicity of
super LLSs with log N(HI)>19 rapidly evolves with redshift, with a ten-fold
increase between z~2.1-3.6 (~1.5 Gyr). Based on this sample, we find that LLSs
at z=2.5-3.5 account for ~15% of all the metals produced by UV-selected
galaxies. The implications for theories of cold gas accretion and metal
ejection from galaxies are also discussed. | astro-ph_GA |
Extended narrow-line region in Seyfert galaxies: We present our recent results about the extended narrow-line region (ENLR) of
two nearby Seyfert 2 galaxies (IC 5063 and NGC 7212) obtained by modelling the
observed line profiles and spectra with composite models
(photoionization+shocks) in the different regions surrounding the AGN. Then, we
compare the Seyfert 2 ENLRs with the very extended one recently discovered in
the narrow-line Seyfert 1 (NLS1) galaxy Mrk 783. We have found several
evidences of interaction between the ISM of the galaxies and their radio jets,
such as a) the contribution of shocks in ionizing the high velocity gas, b) the
complex kinematics showed by the profile of the emission lines, c) the high
fragmentation of matter, etc. The results suggest that the ENLR of IC 5063 have
a hollow bi-conical shape, with one edge aligned to the galaxy disk, which may
cause some kind of dependence on velocity of the ionization parameter.
Regarding the Mrk 783 properties, it is found that the extension of the optical
emission is almost twice the size of the radio one and it seems due to the AGN
activity, although there is contamination by star formation around 12 arcsec
from the nucleus. Diagnostic diagrams excluded the contribution of star
formation in IC 5063 and NGC 7212, while the shock contribution was used to
explain the spectra emitted by their high velocity gas. | astro-ph_GA |
SDSS J0159 as an outlier in the Mbh-sigma space: further clues to
support a central tidal disruption event?: In this Letter, properties of black hole (BH) mass are well checked for the
interesting object SDSS J0159, a changing-look AGN and also a host galaxy of a
tidal disruption event (TDE). Through spectral absorption features, the stellar
velocity dispersion of SDSS J0159 can be well measured as $\sigma\sim81~{\rm
km/s}$, leading to SDSS J0159 being an apparent outlier in the \msig space,
because of the BH mass estimated through the \msig relation about two
magnitudes lower than the reported virial BH mass of about $10^8~{\rm
M_\odot}$. After considerations of contributions of stellar debris from the
central TDE to broad line emission clouds, the over-estimated virial BH mass
could be well explained in SDSS J0159. Therefore, over-estimated virial BH
masses through broad line properties in the \msig space could be treated as
interesting clues to support central TDEs. | astro-ph_GA |
Herschel SPIRE and PACS observations of the red supergiant VY CMa:
analysis of the molecular line spectra: We present an analysis of the far-infrared and submillimetre molecular
emission line spectrum of the luminous M-supergiant VY CMa, observed with the
SPIRE and PACS spectrometers aboard the Herschel Space Observatory. Over 260
emission lines were detected in the 190-650-micron SPIRE FTS spectra, with
one-third of the observed lines being attributable to H2O. Other detected
species include CO, 13CO, H2^18O, SiO, HCN, SO, SO2, CS, H2S, and NH3. Our
model fits to the observed 12CO and 13CO line intensities yield a 12C/13C ratio
of 5.6+-1.8, consistent with measurements of this ratio for other M
supergiants, but significantly lower than previously estimated for VY CMa from
observations of lower-J lines. The spectral line energy distribution for twenty
SiO rotational lines shows two temperature components: a hot component at 1000
K, which we attribute to the stellar atmosphere and inner wind, plus a cooler
~200 K component, which we attribute to an origin in the outer circumstellar
envelope. We fit the line fluxes of 12CO, 13CO, H2O and SiO, using the SMMOL
non-LTE line transfer code, with a mass-loss rate of 1.85x10^-4 Msun yr^-1
between 9 R* and 350 R*. To fit the observed line fluxes of 12CO, 13CO, H2O and
SiO with SMMOL non-LTE line radiative transfer code, along with a mass-loss
rate of 1.85x10^-4 Msun yr^-1.
To fit the high rotational lines of CO and H2O, the model required a rather
flat temperature distribution inside the dust condensation radius, attributed
to the high H2O opacity. Beyond the dust condensation radius the gas
temperature is fitted best by an r^-0.5 radial dependence, consistent with the
coolant lines becoming optically thin. Our H2O emission line fits are
consistent with an ortho:para ratio of 3 in the outflow. | astro-ph_GA |
The First VLBI Detection of a Spiral DRAGN Core: The existence of spiral DRAGNs challenges standard galaxy formation theories.
We present the first observation of 0313$-$192, the archetypal spiral DRAGN, at
VLBI resolutions. Spiral DRAGNs are Double Radio Sources Associated with
Galactic Nuclei (DRAGNs) that are hosted by spiral galaxies. 0313$-$192 is an
edge-on spiral galaxy that appears to host a 360 kpc double-lobed radio source.
The core of this galaxy is clearly detected at L, S, and X-bands using the
VLBA, signifying an ongoing active nucleus in the galaxy. This rules out the
possibility that the spiral DRAGN is merely a chance alignment. The radio core
has L$_{1.4\,GHz} \sim 3.0 \times 10^{23}$W Hz$^{-1}$. Radio components are
detected to the South-West of the core, but there are no detections of a
counterjet. Assuming a symmetric, relativistic jet, we estimate an upper limit
to the inclination angle of $\theta \lesssim 72$ degrees. The VLBI-detected
radio jet components are extremely well-aligned with the larger-scale radio
source suggesting little to no jet disruption or interaction with the ISM of
the host galaxy. | astro-ph_GA |
The mass-metallicity relation of local active galaxies: We systematically measure the gas-phase metallicities and the
mass-metallicity relation of a large sample of local active galaxies for the
first time. Observed emission-line fluxes from the Sloan Digital Sky Survey
(SDSS) are compared to a four-dimensional grid of photoionization models using
the Bayesian parameter estimation code NebulaBayes. For the first time we take
into account arbitrary mixing between HII region and narrow-line region (NLR)
emission, and the models are also varied with metallicity, ionization parameter
in the NLR, and the gas pressure. The active galactic nucleus (AGN) oxygen
abundance is found to increase by $\Delta {\rm O/H} \sim 0.1$ dex as a function
of host galaxy stellar mass over the range $10.1 < \log M_* / M_\odot < 11.3$.
We also measure the metallicity and ionization parameter of 231000 star-forming
galaxies for comparison with the sample of 7670 Seyfert 2 galaxies. A
systematic offset in oxygen abundance of 0.09 dex is observed between the
mass-metallicity relations of the star-forming and active galaxies. We
investigate potential causes of the offset, including sample selection and the
treatment in the models of diffuse ionized gas, pressure, and ionization
parameter. We cannot identify the major cause(s), but suspect contributions due
to deficiencies in modeling the ionizing spectra and the treatment of dust
physics. Optical diagnostic diagrams are presented with the star-forming and
Seyfert data colored by the inferred oxygen abundance, ionization parameter and
gas pressure, clearly illustrating the trends in these quantities. | astro-ph_GA |
On the possible common origin of M16 and M17: It has been suggested that the well-studied giant HII regions M16 and M17 may
have had a common origin, being an example of large-scale triggered star
formation. While some features of the distribution of the interstellar medium
in the region support this interpretation, no definitive detection of an
earlier population of massive stars responsible for the triggering has been
made thus far. We have carried out observations looking for red supergiants in
the area covered by a giant shell seen in HI and CO centered on galactic
coordinates $l \sim 14^\circ 5$, $b\sim +1^\circ$ that peaks near the same
radial velocity as the bulk of the emission from both giant HII regions, which
are located along the shell. Red supergiants have ages in the range expected
for the parent association whose most massive members could have triggered the
formation of the shell and of the giant HII regions along its rim. Out of a
sample of 37 bright red stars, we identify four red supergiants that confirm
the existence of massive stars in the age range between $\sim 10$ and $\sim
30$~Myr in the area. At least three of them have Gaia DR2 parallaxes consistent
with them being at the same distance as M16 and M17. The evidence of past
massive star formation within the area of the gaseous shell lends support to
the idea that it was formed by the combined action of stellar winds and
ionizing radiation of the precursors of the current red supergiants. These
could be the remnants of a richer population, whose most massive members have
exploded already as core-collapse supernovae. The expansion of the shell
against the surrounding medium, perhaps combined with the overrun of
preexisting clouds, is thus a plausible trigger of the formation of a second
generation of stars currently responsible for the ionization of M16 and M17. | astro-ph_GA |
A Number of Nearby Moving Groups may be Fragments of Dissolving Open
Clusters: We propose that fourteen co-moving groups of stars uncovered by Kounkel &
Covey (2019) may be related to known nearby moving groups and bridge those and
nearby open clusters with similar ages and space velocities. This indicates
that known nearby moving groups may be spatially much more extended than
previously though, and some of them might be parts of tidal tails around the
cores of known open clusters, reminiscent of those recently found around the
Hyades and a handful of other nearby clusters. For example, we find that both
the nearby Carina and Columba associations may be linked to Theia 208 from
Kounkel & Covey (2019) and together form parts of a large tidal tail around the
Platais 8 open cluster. The AB Doradus moving group and Theia 301 may form a
trailing tidal tail behind the Pleiades open cluster, with hints of a possible
leading tidal tail in Theia 369. We similarly find that IC 2391 and its tidal
tails identified by Meingast et al. (2021) may be extended by the nearby Argus
association and are possibly further extended by Theia 115. The nearby Octans
and Octans-Near associations, as well as Theia 94 and 95, may form a large
tidal tail leading the poorly studied Platais 5 open cluster candidate. While a
preliminary analysis of Gaia color-magnitude sequences hint that these
structures are plausibly related, more observational evidence is still required
to corroborate their consistent ages and space velocities. These observations
may change our current understanding of nearby moving groups and the different
pathways through which they can form. While some moving groups may have formed
loosely in extended star-formation events with rich spatial structure, others
may in fact correspond to the tidal tails of nearby open clusters. | astro-ph_GA |
The Behavior of Selected Diffuse Interstellar Bands with Molecular
Fraction in Diffuse Atomic and Molecular Clouds: We study the behavior of eight diffuse interstellar bands (DIBs) in different
interstellar environments, as characterized by the fraction of hydrogen in
molecular form [$f$(H$_2$)], with comparisons to the corresponding behavior of
various known atomic and molecular species. The equivalent widths of the five
"normal" DIBs ($\lambda\lambda$5780.5, 5797.1, 6196.0, 6283.8, and 6613.6),
normalized to $E(B-V)$, show a "Lambda-shaped" behavior: they increase at low
$f$(H$_2$), peak at $f$(H$_2$) ~ 0.3, and then decrease. The similarly
normalized column densities of Ca, Ca$^+$, Ti$^+$, and CH$^+$ also decline for
$f$(H$_2$) > 0.3. In contrast, the normalized column densities of Na, K, CH,
CN, and CO increase monotonically with $f$(H$_2$), and the trends exhibited by
the three C$_2$ DIBs ($\lambda\lambda$4726.8, 4963.9, and 4984.8) lie between
those two general behaviors. These trends with $f$(H$_2$) are accompanied by
cosmic scatter, the dispersion at any given $f$(H$_2$) being significantly
larger than the individual errors of measurement. The Lambda-shaped trends
suggest the balance between creation and destruction of the DIB carriers
differs dramatically between diffuse atomic and diffuse molecular clouds;
additional processes besides ionization and shielding are needed to explain
those observed trends. Except for several special cases, the highest
$W$(5780)/$W$(5797) ratios, characterizing the so-called "sigma-zeta effect",
occur only at $f$(H$_2$) < 0.2. We propose a sequence of DIBs based on trends
in their pair-wise strength ratios with increasing $f$(H$_2$). In order of
increasing environmental density, we find the $\lambda$6283.8 and
$\lambda$5780.5 DIBs, the $\lambda$6196.0 DIB, the $\lambda$6613.6 DIB, the
$\lambda$5797.1 DIB, and the C$_2$ DIBs. | astro-ph_GA |
Photon-Dominated Region Modeling of the [C I],[C II], and CO Line
Emission from a Boundary in the Taurus Molecular Cloud: We present [Ci] and [Cii] observations of a linear edge region in the Taurus
molecular cloud, and model this region as a cylindrically symmetric PDR exposed
to a low-intensity UV radiation field. The sharp, long profile of the linear
edge makes it an ideal case to test PDR models and determine cloud parameters.
We compare observations of the [C i], 3P1 -> 3P0 (492 GHz), [C i] 3P2 -> 3P1
(809 GHz), and [Cii] 2P3/2 -> 2P1/2 (1900 GHz) transitions, as well as the
lowest rotational transitions of 12CO and 13CO, with line intensities produced
by the RATRAN radiative transfer code from the results of the Meudon PDR code.
We constrain the density structure of the cloud by fitting a cylindrical
density function to visual extinction data. We study the effects of variation
of the FUV field, 12C/13C isotopic abundance ratio, sulfur depletion, cosmic
ray ionization rate, and inclination of the filament relative to the sky-plane
on the chemical network of the PDR model and resulting line emission. We also
consider the role of suprathermal chemistry and density inhomogeneities. We
find good agreement between the model and observations, and that the integrated
line intensities can be explained by a PDR model with an external FUV field of
0.05 G0, a low ratio of 12C to 13C ~ 43, a highly depleted sulfur abundance (by
a factor of at least 50), a cosmic ray ionization rate (3 - 6) x 10-17 s^-1,
and without significant effects from inclination, clumping or suprathermal
chemistry. | astro-ph_GA |
Constraining nuclear star cluster formation using MUSE-AO observations
of the early-type galaxy FCC47: Nuclear star clusters (NSCs) are found in at least 70% of all galaxies, but
their formation path is still unclear. In the most common scenarios, NSCs form
in-situ from the galaxy's central gas reservoir, through merging of globular
clusters (GCs), or through a combination of the two. As the scenarios pose
different expectations for angular momentum and stellar population properties
of the NSC in comparison to the host galaxy and the GC system, it is necessary
to characterise the stellar light, NSC and GCs simultaneously. The large NSC
(r$_\rm{eff} = 66$ pc) and rich GC system of the early-type Fornax cluster
galaxy FCC47 (NGC1336) render this galaxy an ideal laboratory to constrain NSC
formation. Using MUSE science verification data assisted by adaptive optics, we
obtained maps for the stellar kinematics and for stellar-population properties
of FCC47. We extracted the spectra of the central NSC and determined
line-of-sight velocities of 24 GCs and metallicities of five. FCC47 shows two
decoupled components (KDCs): a rotating disk and the NSC. Our orbit-based
dynamical Schwarzschild model revealed that the NSC is a distinct kinematic
feature and it constitutes the peak of metallicity and old ages in the galaxy.
The main body consists of two counter-rotating populations and is dominated by
a more metal-poor population. The GC system is bimodal with a dominant
metal-poor population and the total GC system mass is $\sim 17\%$ of the NSC
mass ($\sim$ 7 $\times$ $10^8 M_\odot$). The rotation, high metallicity and
high mass of the NSC cannot be uniquely explained by GC-inspiral and most
likely requires additional, but quickly quenched, in-situ formation. The
presence of two KDCs most probably are evidence of a major merger that has
altered the structure of FCC47 significantly, indicating the important role of
galaxy mergers in forming the complex kinematics in the galaxy-NSC system. | astro-ph_GA |
A 95 GHz Methanol Emission Survey Toward Eight Small Supernova Remnants: We report on a 95 GHz ($8_0-7_1$ A$^{+}$) methanol (CH$_3$OH) emission survey
with the Purple Mountain Observatory Delingha 13.7 m telescope. Eight supernova
remnants (SNRs) with angular size $\lesssim$ 10' were observed, but emission
was only detected in three SNRs near the Galactic center (Sgr A East, G
0.1-0.1, and G 359.92-0.09). CH$_3$OH emission mainly surrounds the SNRs and
can be decomposed into nine spatial peaks with velocity range of eight peaks
being (-30, 70) km s$^{-1}$, and the other (70, 120) km s$^{-1}$. They are
probably excited by interaction with these SNRs and adjacent molecular gas in
the central molecular zone (CMZ), although star formation may play an important
role in exciting CH$_3$OH emission in some regions of CMZ. We infer that tidal
action is unlikely to be an excitation source for CH$_3$OH emission. | astro-ph_GA |
A sharp rise in the detection rate of broad absorption line variations
in a quasar SDSS J141955.26+522741.1: We present an analysis of the variability of broad absorption lines (BALs) in
a quasar SDSS J141955.26+522741.1 at $z=2.145$ with 72 observations from the
Sloan Digital Sky Survey Data Release 16 (SDSS DR16). The strong correlation
between the equivalent widths of BAL and the continuum luminosity, reveals that
the variation of BAL trough is dominated by the photoionization. The
photoionization model predicts that when the time interval $\Delta T$ between
two observations is longer than the recombination timescale $t_{\rm rec}$, the
BAL variations can be detected. This can be characterized as a "sharp rise" in
the detection rate of BAL variation at $\Delta T=t_{\rm rec}$. For the first
time, we detect such a "sharp rise" signature in the detection rate of BAL
variations. As a result, we propose that the $t_{\rm rec}$ can be obtained from
the "sharp rise" of the detection rate of BAL variation. It is worth mentioning
that the BAL variations are detected at the time-intervals less than the
$t_{\rm rec}$ for half an order of magnitude in two individual troughs. This
result indicates that there may be multiple components with different $t_{\rm
rec}$ but the same velocity in an individual trough. | astro-ph_GA |
Chemical abundances in Seyfert galaxies -- V. The discovery of shocked
emission outside the AGN ionization axis: We present maps for the electron temperature in the inner kpc of three
luminous Seyfert galaxies: Mrk 79, Mrk 348, and Mrk 607 obtained from Gemini
GMOS-IFU observations at spatial resolutions of 110-280 pc. We study the
distributions of electron temperature in active galaxies and find temperatures
varying in the range from 8000 to >30000 K. Shocks due to gas outflows play an
important role in the observed temperature distributions of Mrk 79 and Mrk 348,
while standard photoionization models reproduce the derived temperature values
for Mrk 607. In Mrk 79 and Mrk 348, we find direct evidence for
shock-ionization with overall orientation orthogonal to the ionization axis,
where shocks can be easily observed as the AGN radiation field is shielded by
the nuclear dusty torus. This also indicates that even when the ionization
cones are narrow, the shocks can be much wider-angle. | astro-ph_GA |
Mapping kiloparsec-scale structures in the extended HI disc of the
galaxy UGC 00439 by HI 21-cm absorption: We study the properties of HI gas in the outer regions (~2r_25) of a spiral
galaxy, UGC 00439 (z = 0.01769), using HI 21-cm absorption towards different
components of an extended background radio source, J0041$-$0043 (z = 1.679).
The radio source exhibits a compact core coincident with the optical quasar and
two lobes separated by ~7 kpc, all at an impact parameter ~25 kpc. The HI 21-cm
absorption detected towards the southern lobe is found to extend over ~2 kpc^2.
The absorbing gas shows sub-kpc-scale structures with the line-of-sight
velocities dominated by turbulent motions. Much larger optical depth variations
over 4-7 kpc-scale are revealed by the non-detection of HI 21-cm absorption
towards the radio core and the northern lobe, and the detection of NaI and CaII
absorption towards the quasar. This could reflect a patchy distribution of cold
gas in the extended HI disc. We also detect HI 21-cm emission from UGC 00439
and two other galaxies within ~150 kpc to it, that probably form an interacting
group. However, no HI 21-cm emission from the absorbing gas is detected.
Assuming a linear extent of ~4 kpc, as required to cover both the core and the
southern lobe, we constrain the spin temperature <~300 K for the absorbing gas.
The kinematics of the gas and the lack of signatures of any ongoing in situ
star formation are consistent with the absorbing gas being at the kinematical
minor axis and corotating with the galaxy. Deeper HI 21-cm observations would
help to map in greater detail both the large- and small-scale structures in the
HI gas associated with UGC 00439. | astro-ph_GA |
IMF radial gradients in most massive early-type galaxies: Using new long-slit spectroscopy obtained with X-Shooter at ESO-VLT, we
study, for the first time, radial gradients of optical and Near-Infrared
IMF-sensitive features in a representative sample of galaxies at the very
high-mass end of the galaxy population. The sample consists of seven early-type
galaxies (ETGs) at $z\sim0.05$, with central velocity dispersion in the range
$300<\sigma<350$km/s. Using state-of-art stellar population synthesis models,
we fit a number of spectral indices, from different chemical species (including
TiO's and Na indices), to constrain the IMF slope (i.e. the fraction of
low-mass stars), as a function of galactocentric distance, over a radial range
out to $\sim4$kpc. ETGs in our sample show a significant correlation of IMF
slope and surface mass density. The bottom-heavy population (i.e. an excess of
low-mass stars in the IMF) is confined to central galaxy regions with surface
mass density above $\sim 10^{10} M_\odot kpc^{-2}$, or, alternatively, within a
characteristic radius of $\sim2$~kpc. Radial distance, in physical units, and
surface mass density, are the best correlators to IMF variations, with respect
to other dynamical (e.g. velocity dispersion) and stellar population (e.g.
metallicity) properties. Our results for the most massive galaxies suggest that
there is no single parameter} that fully explains variations in the stellar
IMF, but IMF radial profiles at z$\sim$0 rather result from the complex
formation and mass accretion history of galaxy inner and outer regions. | astro-ph_GA |
The density variance -- Mach number relation in supersonic, isothermal
turbulence: We examine the relation between the density variance and the mean-square Mach
number in supersonic, isothermal turbulence, assumed in several recent analytic
models of the star formation process. From a series of calculations of
supersonic, hydrodynamic turbulence driven using purely solenoidal Fourier
modes, we find that the `standard' relationship between the variance in the log
of density and the Mach number squared, i.e., sigma^2_(ln rho/rhobar)=ln (1+b^2
M^2), with b = 1/3 is a good fit to the numerical results in the supersonic
regime up to at least Mach 20, similar to previous determinations at lower Mach
numbers. While direct measurements of the variance in linear density are found
to be severely underestimated by finite resolution effects, it is possible to
infer the linear density variance via the assumption of log-normality in the
Probability Distribution Function. The inferred relationship with Mach number,
consistent with sigma_(rho/rhobar) ~ b M with b=1/3, is, however, significantly
shallower than observational determinations of the relationship in the Taurus
Molecular Cloud and IC5146 (both consistent with b~ 0.5), implying that
additional physics such as gravity is important in these clouds and/or that
turbulent driving in the ISM contains a significant compressive component.
Magnetic fields are not found to change this picture significantly, in general
reducing the measured variances and thus worsening the discrepancy with
observations. | astro-ph_GA |
A Robust Measure of Dark Matter Halo Ellipticities: In simulations of the standard cosmological model (LCDM), dark matter halos
are aspherical. However, so far the asphericity of an individual galaxy's halo
has never been robustly established. We use the Jeans equations to define a
quantity which robustly characterizes a deviation from rotational symmetry.
This quantity is essentially the gravitational torque and it roughly provides
the ellipticity projected along the line of sight. We show that the Thirty
Meter Telescope (TMT), with a single epoch of observations combined with those
of the Gaia space telescope, can distinguish the LCDM value of the torque from
zero for each Sculptor-like dwarf galaxy with a confidence between 0 and 5
sigma, depending on the orientation of each halo. With two epochs of
observations, TMT will achieve a 5 sigma discovery of torque and so asphericity
for most such galaxies, and so will provide a new and powerful test of the LCDM
model. | astro-ph_GA |
A binning-free method reveals a continuous relationship between
galaxies' AGN power and offset from main sequence: Studies investigating the relationship between AGN power and the star
formation rates (SFRs) of their host galaxies often rely on averaging
techniques -- such as stacking -- to incorporate information from
non-detections. However, averages, and especially means, can be strongly
affected by outliers and can therefore give a misleading indication of the
"typical" case. Recently, a number of studies have taken a step further by
binning their sample in terms of AGN power (approximated by the 2-10keV
luminosity of the AGN), and investigating how the SFR distribution differs
between these bins. These bin thresholds are often weakly motivated, and
binning implicitly assumes that sources within the same bin have similar (or
even identical) properties. In this paper, we investigate whether the
distribution of host SFRs -- relative to the locus of the star-forming main
sequence (i.e., $R_{\rm MS}$) -- changes continuously as a function of AGN
power. We achieve this by using a hierarchical Bayesian model that completely
removes the need to bin in AGN power. In doing so, we find strong evidence that
the $R_{\rm MS}$ distribution changes with 2-10keV X-ray luminosity. The
results suggest that higher X_ray luminosity AGNs have a tighter physical
connection to the star-forming process than lower X-ray luminosity AGNs, at
least within the $0.8 < z < 1.2$ redshift range considered here. | astro-ph_GA |
Schwarzschild dynamical model of the Fornax dwarf spheroidal galaxy: We present a full dynamical model of the Fornax dwarf spheroidal galaxy
obtained with the spherically symmetric Schwarzschild orbit superposition
method applied to the largest kinematic data set presently available. We
modelled the total mass content of the dwarf with the mass-to-light ratio
$\Upsilon$ varying with radius and found that Fornax is with high probability
embedded in a massive and extended dark matter halo. We estimated the total
mass contained within 1$\,$kpc to be $M(<1\,$kpc$)=1.25^{+0.06}_{-0.13} \times
10^8\,$M$_{\odot}$. The data are consistent with the constant mass-to-light
ratio, i.e. the mass-follows-light model, only at 3$\sigma$ level, but still
require a high value of $\Upsilon \approx 11.2\,$M$_{\odot}/$L$_{\odot}$. Our
results are in general agreement with previous estimates of the dynamical mass
profile of Fornax. As the Schwarzschild method does not require any assumptions
on the orbital anisotropy of the stars, we obtained a profile of the anisotropy
parameter $\beta$ as an output of our modelling. The derived anisotropy is
close to zero in the centre of the galaxy and decreases with radius, but
remains consistent with isotropic orbits at all radii at 1$\sigma$ confidence
level. | astro-ph_GA |
Symplectic coarse graining approach to the dynamics of spherical
self-gravitating systems: We investigate the evolution of the phase-space distribution function around
slightly perturbed stationary states and the process of violent relaxation in
the context of the dissipationless collapse of an isolated spherical
self-gravitating system. By means of the recently introduced symplectic coarse
graining technique, we obtain an effective evolution equation that allows us to
compute the scaling of the frequencies around a stationary state, as well as
the damping times of Fourier modes of the distribution function, with the
magnitude of the Fourier $k-$vectors themselves. We compare our analytical
results with $N$-body simulations. | astro-ph_GA |
Common origin for Hercules-Aquila and Virgo Clouds in Gaia DR2: We use a sample of ~350 RR Lyrae stars with radial velocities and Gaia DR2
proper motions to study orbital properties of the Hercules-Aquila Cloud (HAC)
and Virgo Over-density (VOD). We demonstrate that both structures are dominated
by stars on highly eccentric orbits, with peri-centres around ~1 kpc and
apo-centres between 15 and 25 kpc from the Galactic centre. Given that the
stars in the HAC and the VOD occupy very similar regions in the space spanned
by integrals of motion, we conclude that these diffuse debris clouds are part
of the same accretion event. More precisely, these inner halo sub-structures
likely represent two complementary not-fully-mixed portions of an ancient
massive merger, also known as the "sausage" event. | astro-ph_GA |
Studying the late evolution of a radio-loud AGN in a galaxy group with
LOFAR: Feedback by radio-loud active galactic nuclei (AGN) in galaxy groups is not
fully understood. Open questions include the duty cycle of the AGN, the spatial
extent of the radio lobes, the effect they have on the intragroup medium, and
the fate of the cosmic rays. We present the discovery of a 650 kpc-radio galaxy
embedded in steep diffuse emission at $z = 0.18793 \pm 5 \times 10^{-5}$
located at the center of the galaxy group MaxBCG J199.31832+51.72503 using an
observation from the LOFAR Two-meter Sky Survey (LoTSS) at the central
frequency of 144 MHz. Subsequently, we performed a GMRT observation at the
central frequency of 607 MHz to study the spectral properties of the source.
The observations reveal a radio galaxy with a total radio power $P_{\rm tot,
1.4} \sim 2.1 \times 10^{24}$ W Hz$^{-1}$, exhibiting two asymmetrical jets and
lobes. The derived spectral index map shows a steepening toward the inner
regions and a steep-spectrum core region. We model the integrated radio
spectrum, providing two possible interpretations: the radio source is evolved
but still active or it is just at the end of its active phase. Finally, in the
same field of view we have discovered Mpc-sized emission surrounding a close
pair of AGN located at a redshift $z = 0.0587 \pm 2 \times 10^{-4}$ (SDSS
J131544.56+521213.2 and SDSS J131543.99+521055.7) which could be a radio
remnant source. | astro-ph_GA |
Circum-galactic medium in the halo of quasars: The properties of circum-galactic gas in the halo of quasar host galaxies are
investigated analyzing Mg II 2800 and C IV 1540 absorption-line systems along
the line of sight close to quasars. We used optical spectroscopy of closely
aligned pairs of quasars (projected distance $\leq$ 200 kpc, but at very
different redshift) obtained at the VLT and Gran Telescopio Canarias to
investigate the distribution of the absorbing gas for a sample of quasars at
z$\sim$1. Absorption systems of EW $\geq$ 0.3 $\rm{\AA}$ associated with the
foreground quasars are revealed up to 200 kpc from the centre of the host
galaxy, showing that the structure of the absorbing gas is patchy with a
covering fraction quickly decreasing beyond 100 kpc. In this contribution we
use optical and near-IR images obtained at VLT to investigate the relations
between the properties of the circum-galactic medium of the host galaxies and
of the large scale galaxy environments of the foreground quasars. | astro-ph_GA |
The dimensionality of stellar chemical space using spectra from the
Apache Point Observatory Galactic Evolution Experiment: Chemical tagging of stars based on their similar compositions can offer new
insights about the star formation and dynamical history of the Milky Way. We
investigate the feasibility of identifying groups of stars in chemical space by
forgoing the use of model derived abundances in favour of direct analysis of
spectra. This facilitates the propagation of measurement uncertainties and does
not presuppose knowledge of which elements are important for distinguishing
stars in chemical space. We use ~16,000 red-giant and red-clump H-band spectra
from the Apache Point Observatory Galactic Evolution Experiment and perform
polynomial fits to remove trends not due to abundance-ratio variations. Using
expectation maximized principal component analysis, we find principal
components with high signal in the wavelength regions most important for
distinguishing between stars. Different subsamples of red-giant and red-clump
stars are all consistent with needing about 10 principal components to
accurately model the spectra above the level of the measurement uncertainties.
The dimensionality of stellar chemical space that can be investigated in the
H-band is therefore $\lesssim 10$. For APOGEE observations with typical
signal-to-noise ratios of 100, the number of chemical space cells within which
stars cannot be distinguished is approximately $10^{10\pm2} \times (5\pm
2)^{n-10}$ with $n$ the number of principal components. This high
dimensionality and the fine-grained sampling of chemical space are a promising
first step towards chemical tagging based on spectra alone. | astro-ph_GA |
The Astrochemical Impact of Cosmic Rays in Protoclusters I: Molecular
Cloud Chemistry: We present astrochemical photo-dissociation region models in which cosmic ray
attenuation has been fully coupled to the chemical evolution of the gas. We
model the astrochemical impact of cosmic rays, including those accelerated by
protostellar accretion shocks, on molecular clouds hosting protoclusters. Our
models with embedded protostars reproduce observed ionization rates. We study
the imprint of cosmic ray attenuation on ions for models with different surface
cosmic ray spectra and different star formation efficiencies. We find that
abundances, particularly ions, are sensitive to the treatment of cosmic rays.
We show the column densities of ions are under predicted by the `classic'
treatment of cosmic rays by an order of magnitude. We also test two common
chemistry approximations used to infer ionization rates. We conclude that the
approximation based on the H$_3^+$ abundance under predicts the ionization rate
except in regions where the cosmic rays dominate the chemistry. Our models
suggest the chemistry in dense gas will be significantly impacted by the
increased ionization rates, leading to a reduction in molecules such as NH$_3$
and causing H$_2$-rich gas to become [C II] bright. | astro-ph_GA |
Angular momentum evolution of bulge stars in disc galaxies in NIHAO: We study the origin of bulge stars and their angular momentum (AM) evolution
in 10 spiral galaxies with baryonic masses above $10^{10}$M$_\odot$ in the
NIHAO galaxy formation simulations. The simulated galaxies are in good
agreement with observations of the relation between specific AM and mass of the
baryonic component and the stellar bulge-to-total ratio ($B/T$). We divide the
star particles at $z=0$ into disc and bulge components using a hybrid
photometric/kinematic decomposition method that identifies all central mass
above an exponential disc profile as the `bulge'. By tracking the bulge star
particles back in time, we find that on average 95\% of the bulge stars formed
{\it in situ}, 3\% formed {\it ex situ} in satellites of the same halo, and
only 2\% formed {\it ex situ} in external galaxies. The evolution of the AM
distribution of the bulge stars paints an interesting picture: the higher the
final $B/T$ ratio, the more the specific AM remains preserved during the bulge
formation. In all cases, bulge stars migrate significantly towards the central
region, reducing their average galactocentric radius by roughly a factor 2,
independently of the final $B/T$ value. However, in the higher $B/T$
($\gtrsim0.2$) objects, the velocity of the bulge stars increases and the AM of
the bulge is almost conserved, whereas at lower $B/T$ values, the velocity of
the bulge stars decreases and the AM of bulge reduces. The correlation between
the evolution of the AM and $B/T$ suggests that bulge and disc formation are
closely linked and cannot be treated as independent processes. | astro-ph_GA |
Herschel-PACS spectroscopy of the intermediate mass protostar NGC7129
FIRS 2: Aims: We present preliminary results of the first Herschel spectroscopic
observations of NGC7129 FIRS2, an intermediate mass star-forming region. We
attempt to interpret the observations in the framework of an in-falling
spherical envelope. Methods: The PACS instrument was used in line spectroscopy
mode (R=1000-5000) with 15 spectral bands between 63 and 185 microns. This
provided good detections of 26 spectral lines seen in emission, including lines
of H2O, CO, OH, O I, and C II. Results: Most of the detected lines,
particularly those of H2O and CO, are substantially stronger than predicted by
the spherical envelope models, typically by several orders of magnitude. In
this paper we focus on what can be learned from the detected CO emission lines.
Conclusions: It is unlikely that the much stronger than expected line emission
arises in the (spherical) envelope of the YSO. The region hot enough to produce
such high excitation lines within such an envelope is too small to produce the
amount of emission observed. Virtually all of this high excitation emission
must arise in structures such as as along the walls of the outflow cavity with
the emission produced by a combination of UV photon heating and/or
non-dissociative shocks. | astro-ph_GA |
Star Cluster Classification using Deep Transfer Learning with PHANGS-HST: Currently available star cluster catalogues from HST imaging of nearby
galaxies heavily rely on visual inspection and classification of candidate
clusters. The time-consuming nature of this process has limited the production
of reliable catalogues and thus also post-observation analysis. To address this
problem, deep transfer learning has recently been used to create neural network
models which accurately classify star cluster morphologies at production scale
for nearby spiral galaxies (D < 20 Mpc). Here, we use HST UV-optical imaging of
over 20,000 sources in 23 galaxies from the Physics at High Angular Resolution
in Nearby GalaxieS (PHANGS) survey to train and evaluate two new sets of
models: i) distance-dependent models, based on cluster candidates binned by
galaxy distance (9-12 Mpc, 14-18 Mpc, 18-24 Mpc), and ii) distance-independent
models, based on the combined sample of candidates from all galaxies. We find
that the overall accuracy of both sets of models is comparable to previous
automated star cluster classification studies (~60-80 per cent) and show
improvement by a factor of two in classifying asymmetric and multi-peaked
clusters from PHANGS-HST. Somewhat surprisingly, while we observe a weak
negative correlation between model accuracy and galactic distance, we find that
training separate models for the three distance bins does not significantly
improve classification accuracy. We also evaluate model accuracy as a function
of cluster properties such as brightness, colour, and SED-fit age. Based on the
success of these experiments, our models will provide classifications for the
full set of PHANGS-HST candidate clusters (N ~ 200,000) for public release. | astro-ph_GA |
Chemodynamical evolution of the Milky Way disk II: Variations with
Galactic radius and height above the disk plane: [Abridge] In the first paper of this series (paper I) we presented a new
approach for studying the chemo-odynamical evolution in disk galaxies, focusing
on the Milky Way. Here we extend these results to different distances from the
Galactic center, looking for variations of observables that can be related to
on-going and future spectroscopic surveys. By separating the effects of
kinematic heating and radial migration, we show that migration is much more
important, even for the oldest and hottest stellar population. The
distributions of stellar birth guiding radii and final guiding radii
(signifying contamination from migration and heating, respectively) widen with
increasing distance from the Galactic center. As a result, the slope in the
age-metallicity relation flattens significantly at Galactic radii larger than
solar. The radial metallicity and [Mg/Fe] gradients in our model show
significant variations with height above the plane due to changes in the
mixture of stellar ages. An inversion in the radial metallicity gradient is
found from negative to weakly positive (at r<10 kpc), and from positive to
negative for the [Mg/Fe] gradient, with increasing distance from the disk
plane. We relate this to the combined effect of (i) the predominance of young
stars close to the disk plane and old stars away from it, (ii) the more
concentrated older stellar component, and (iii) the flaring of mono-age disk
populations. We also investigate the effect of recycled gas flows on the mean
[Fe/H] and find that in the region 4<r<12 kpc the introduced errors are less
than 0.05-0.1 dex, related to the fact that inward and outward flows mostly
cancel in that radial range. We show that radial migration cannot compete with
the inside-out formation of the disk, exposed by the more centrally
concentrated older disk populations, and consistent with recent observations. | astro-ph_GA |
The SKA view of the Neutral Interstellar Medium in Galaxies: Two major questions in galaxy evolution are how star-formation on small
scales leads to global scaling laws and how galaxies acquire sufficient gas to
sustain their star formation rates. HI observations with high angular
resolution and with sensitivity to very low column densities are some of the
important observational ingredients that are currently still missing. Answers
to these questions are necessary for a correct interpretation of observations
of galaxy evolution in the high-redshift universe and will provide crucial
input for the sub-grid physics in hydrodynamical simulations of galaxy
evolutions. In this chapter we discuss the progress that will be made with the
SKA using targeted observations of nearby individual disk and dwarf galaxies. | astro-ph_GA |
The Bizarre Chemical Inventory of NGC 2419, An Extreme Outer Halo
Globular Cluster: We present new Keck/HIRES observations of six red giants in the globular
cluster NGC 2419. Although the cluster is among the most distant and most
luminous in the Milky Way, it was considered chemically ordinary until very
recently. Our previous work showed that the near-infrared Ca II triplet line
strength varied more than expected for a chemically homogeneous cluster, and
that at least one star had unusual abundances of Mg and K. Here, we confirm
that NGC 2419 harbors a population of stars, comprising about one third of its
mass, that is depleted in Mg by a factor of 8 and enhanced in K by a factor of
6 with respect to the Mg-normal population. Although the majority, Mg-normal
population appears to have a chemical abundance pattern indistinguishable from
ordinary, inner halo globular clusters, the Mg-poor population exhibits
dispersions of several elements. The abundances of K and Sc are strongly
anti-correlated with Mg, and some other elements (Si and Ca among others) are
weakly anti-correlated with Mg. These abundance patterns suggest that the
different populations of NGC 2419 sample the ejecta of diverse supernovae in
addition to AGB ejecta. However, the abundances of Fe-peak elements except Sc
show no star-to-star variation. We find no nucleosynthetic source that
satisfactorily explains all of the abundance variations in this cluster.
Because NGC 2419 appears like no other globular cluster, we reiterate our
previous suggestion that it is not a globular cluster at all, but rather the
core of an accreted dwarf galaxy. | astro-ph_GA |
Young stellar clusters in the Rosette molecular cloud. Arguments against
triggered star formation: The Rosette complex is a well studied region of the galactic plane which
presents the apparent characteristics of a triggered star forming region. This
is however still debated as no strong evidence corroborates this statement. We
focus on characterizing the young stellar population in the Rosette complex to
improve our understanding of the processes that regulate the star formation in
this region. We propose an original method that relies on the joint analysis of
the star color and density in the near-infrared. It leads to mapping the
molecular cloud spatial distribution and detecting the embedded clusters with
their characterization in terms of member number and age estimation. We have
identified 13 clusters, 2 of which are new discoveries, and we estimate that
the total number of young stellar objects in the Rosette ranges between 4000
and 8000 members. We find that the age distribution of the young clusters is
not consistent with a general triggered scenario for the star formation in this
molecular cloud. This study proves that the Rosette complex evolution is not
governed by the influence of its OB star population. It suggests that the
simple morphological appearance of an active region is not sufficient to
conclude much about the triggering role in the star formation process. Our
method of constraining the cluster properties using UKIDSS and WISE data has
proven efficient, and studies of other regions of the galactic plane would
definitely benefit from this approach. | astro-ph_GA |
Dwarf galaxy archaeology from chemical abundances and star formation
histories: We model the stellar abundances and ages of two disrupted dwarf galaxies in
the Milky Way stellar halo: Gaia-Sausage Enceladus (GSE) and Wukong/LMS-1.
Using a statistically robust likelihood function, we fit one-zone models of
galactic chemical evolution with exponential infall histories to both systems,
deriving e-folding timescales of $\tau_\text{in} = 1.01 \pm 0.13$ Gyr for GSE
and $\tau_\text{in} = 3.08^{+3.19}_{-1.16}$ Gyr for Wukong/LMS-1. GSE formed
stars for $\tau_\text{tot} = 5.40^{+0.32}_{-0.31}$ Gyr, sustaining star
formation for $\sim$$1.5 - 2$ Gyr after its first infall into the Milky Way
$\sim$10 Gyr ago. Our fit suggests that star formation lasted for
$\tau_\text{tot} = 3.36^{+0.55}_{-0.47}$ Gyr in Wukong/LMS-1, though our sample
does not contain any age measurements. The differences in evolutionary
parameters between the two are qualitatively consistent with trends with
stellar mass $M_\star$ predicted by simulations and semi-analytic models of
galaxy formation. Our fitting method is based only on poisson sampling from an
evolutionary track and requires no binning of the data. We demonstrate its
accuracy by testing against mock data, showing that it accurately recovers the
input model across a broad range of sample sizes ($20 \leq N \leq 2000$) and
measurement uncertainties ($0.01 \leq \sigma_\text{[$\alpha$/Fe]},
\sigma_\text{[Fe/H]} \leq 0.5$; $0.02 \leq \sigma_{\log_{10}(\text{age})} \leq
1$). Our inferred values of the outflow mass-loading factor reasonably match
$\eta \propto M_\star^{-1/3}$ as predicted by galactic wind models. Due to the
generic nature of our derivation, this likelihood function should be applicable
to one-zone models of any parametrization and easily extensible to other
astrophysical models which predict tracks in some observed space. | astro-ph_GA |
Comparison of the Orbital Properties of the Milky Way Globular Clusters
from the Data of the Gaia DR2 and EDR3 Catalogs: We provide new values of the orbital parameters of 152 globular clusters,
which are calculated using the new mean proper motions obtained from the Gaia
EDR3 catalog data. The orbits were integrated 5 Gyr back in an axisymmetric
three-component potential with a spherical bulge, disk component, and spherical
dark halo in the Navarro-Frenk-White form, which we refined using the rotation
curve of objects with large galactocentric distances up to 200 kpc. The
obtained orbital parameters were compared with the orbital parameters of the
same globular clusters calculated earlier in the same gravitational potential
using proper motions from the Gaia DR2 catalog data. The objects whose orbits
underwent significant changes were identified. | astro-ph_GA |
The Evolution Of The Faint End Of The UV Luminosity Function During The
Peak Epoch Of Star Formation (1<z<3): [Abridged] We present a robust measurement of the rest-frame UV luminosity
function (LF) and its evolution during the peak epoch of cosmic star formation
at 1<z<3. We use our deep near ultraviolet imaging from WFC3/UVIS on the Hubble
Space Telescope (HST) and existing ACS/WFC and WFC3/IR imaging of three lensing
galaxy clusters, Abell 2744 and MACSJ0717 from the Hubble Frontier Field survey
and Abell 1689. We use photometric redshifts to identify 780 ultra-faint
galaxies with $M_{UV}$<-12.5 AB mag at 1<z<3. From these samples, we identified
5 new, faint, multiply imaged systems in A1689. We compute the rest-frame UV LF
and find the best-fit faint-end slopes of $\alpha=-1.56\pm0.04$,
$\alpha=-1.72\pm0.04$ and $\alpha=-1.94\pm0.06$ at 1.0<z<1.6, 1.6<z<2.2 and
2.2<z<3.0, respectively. Our results demonstrate that the UV LF becomes steeper
from z\sim1.3 to z\sim2.6 with no sign of a turnover down to $M_{UV}=-14$ AB
mag. We further derive the UV LFs using the Lyman break "dropout" selection and
confirm the robustness of our conclusions against different selection
methodologies. Because the sample sizes are so large, and extend to such faint
luminosities, the statistical uncertainties are quite small, and systematic
uncertainties (due to the assumed size distribution, for example), likely
dominate. If we restrict our analysis to galaxies and volumes above > 50%
completeness in order to minimize these systematics, we still find that the
faint-end slope is steep and getting steeper with redshift, though with
slightly shallower (less negative) values ($\alpha=-1.55\pm0.06$,
$-1.69\pm0.07$ and $-1.79\pm0.08$ for $z\sim1.3$, 1.9 and 2.6, respectively).
Finally, we conclude that the faint star-forming galaxies with UV magnitudes of
$-18.5<M_{UV}<-12.5$ covered in this study, produce the majority (55%-60%) of
the unobscured UV luminosity density at 1<z<3. | astro-ph_GA |
Formation of galactic bulges from the cold gas filaments in
high-redshift dark matter halos: Formation process(es) of galactic bulges are not yet clarified although
several mechanisms have been proposed. In a previous study, we suggested one
possibility that galactic bulges have been formed from the cold gas inflowing
through surrounding hot halo gas in massive dark matter halos at high
redshifts. It was shown that this scenario leads to the bulge-to-total stellar
mass ratio increasing with the galaxy mass, in agreement with the well-known
observed trend. We here indicate that it also reproduces recent observational
results that the mean stellar age of the bulge increases with the galaxy mass
while the age gradient across the bulge decreases. We infer that this formation
path applies mainly to high-mass galaxies and the bulges in lower-mass galaxies
have different origins such as secular formation from the disc material. | astro-ph_GA |
Two distinct halo populations in the solar neighborhood. III. Evidence
from stellar ages and orbital parameters: In Papers I and II of this series, the existence of two distinct halo
populations of stars have been found in the solar neighborhood. Precise
relative ages and orbital parameters are determined for 67 halo and 16
thick-disk stars having metallicities in the range -1.4 < [Fe/H] < -0.4 to
better understand the context of the two halo populations in the formation and
evolution of the Galaxy. Ages are derived by comparing the positions of stars
in the logT_{eff}-log(g) diagram with isochrones from the Y^2 models
interpolated to the exact [Fe/H] and [alpha/Fe] values of each star. Possible
systematic errors in T_{eff} and log(g) are considered and corrected. With
space velocities from Paper I as initial conditions, orbital integrations have
been carried out using a detailed, observationally constrained Milky Way model
including a bar and spiral arms. The `high-alpha' halo stars have ages 2-3 Gyr
larger than the `low-alpha' ones. The orbital parameters show very distinct
differences between the `high-alpha' and `low-alpha' halo stars. The
`low-alpha' ones have r_{max}'s to 30-40 kpc, z_{max}'s to approx. 18 kpc, and
e_{max}'s clumped at values greater than 0.85, while the `high-alpha' ones,
r_{max}'s to about 16 kpc, z_{max}'s to 6-8 kpc, and e_{max} more or less
uniformly distributed over 0.4-1.0. A dual in situ-plus-accretion formation
scenario best explains the existence and characteristics of these two halo
populations, but one remaining defect is that this model is not consistent
regarding the r_{max}'s obtained for the in situ `high-alpha' component; the
predicted values are too small. It appears that omega Cen may have contributed
in a significant way to the existence of the `low-alpha' component; recent
models, including dynamical friction and tidal stripping, have produced orbital
parameters as great as those of the `low-alpha' component. | astro-ph_GA |
Analyzing temporal variations of AGN emission line profiles in the
context of (dusty) cloud structure formation in the broad line region: The formation processes and the exact appearance of the dust torus and broad
line region (BLR) of active galactic nuclei (AGN) are under debate. Theoretical
studies show a possible connection between the dust torus and BLR through a
common origin in the accretion disk. However observationally the dust torus and
BLR are typically studied separately. NGC~4151 is possibly one of the best
suited Seyfert~1 galaxies for simultaneous examinations because of its high
number of both photometric and spectroscopic observations in the past. Here we
compare changes of the dust radius to shape variations of broad emission lines
(BEL). While the radius of the dust torus decreased by almost a factor of two
from 2004 to 2006 shape variations can be seen in the red wing of BELs of
NGC~4151. These simultaneous changes are discussed in a dust and BEL formation
scheme. We also use the BEL shape variations to assess possible cloud
distributions, especially in azimuthal direction, which could be responsible
for the observed variations. Our findings can best be explained in the
framework of a dust inflated accretion disk. The changes in the BELs suggest
that this dusty cloud formation does not happen continuously, and over the
whole accretion disk, but on the contrary in spatially confined areas over
rather short amount of times. We derive limits to the azimuthal extension of
the observed localized BEL flux enhancement event. | astro-ph_GA |
Fast rotating and low-turbulence discs at $z\simeq 4.5$: Dynamical
evidence of their evolution into local early-type galaxies: Massive starburst galaxies in the early Universe are estimated to have
depletion times of $\sim 100$ Myr and thus be able to convert their gas very
quickly into stars, possibly leading to a rapid quenching of their star
formation. For these reasons, they are considered progenitors of massive
early-type galaxies (ETGs). In this paper, we study two high-$z$ starbursts,
AzTEC/C159 ($z\simeq 4.57$) and J1000+0234 ($z\simeq 4.54$), observed with ALMA
in the [CII] 158-$\mu$m emission line. These observations reveal two massive
and regularly rotating gaseous discs. A 3D modelling of these discs returns
rotation velocities of about $500$ km/s and gas velocity dispersions as low as
$\approx 20$ km/s, leading to very high ratios between regular and random
motion ($V/\sigma {\lower.7ex\hbox{$\;\stackrel{\textstyle>}{\sim}\;$}} 20$),
at least in AzTEC/C159. The mass decompositions of the rotation curves show
that both galaxies are highly baryon-dominated with gas masses of $\approx
10^{11}M_{\odot}$, which, for J1000+0234, is significantly higher than previous
estimates. We show that these high-$z$ galaxies overlap with $z=0$ massive ETGs
in the ETG analogue of the stellar-mass Tully-Fisher relation once their gas is
converted into stars. This provides dynamical evidence of the connection
between massive high-$z$ starbursts and ETGs, although the transformation
mechanism from fast rotating to nearly pressure-supported systems remains
unclear. | astro-ph_GA |
HST/WFC3 Observations of Low-Mass Globular Clusters AM 4 and Palomar 13:
Physical Properties and Implications for Mass Loss: We investigate the loss of low-mass stars in two of the faintest globular
clusters known, AM 4 and Palomar 13 (Pal 13), using HST/WFC3 F606W and F814W
photometry. To determine the physical properties of each cluster --- age, mass,
metallicity, extinction, present day mass function (MF) --- we use the maximum
likelihood color-magnitude diagram (CMD) fitting program MATCH and the
Dartmouth, Padova and BaSTI stellar evolution models. For AM 4, the Dartmouth
models provide the best match to the CMD and yield an age of >13 Gyr,
metallicity log Z/Z_solar = -1.68 +/- 0.08, a distance modulus (m-M)_V = 17.47
+/- 0.03 and reddening A_V = 0.19 +/- 0.02. For Pal 13 the Dartmouth models
give an age of 13.4 +/- 0.5 Gyr, log Z/Z_solar = -1.55 +/- 0.06, (m-M)_V =
17.17 +/- 0.02 and A_V = 0.43 +/- 0.01. We find that the systematic
uncertainties due to choice in assumed stellar model greatly exceed the random
uncertainties, highlighting the importance of using multiple stellar models
when analyzing stellar populations. Assuming a single-sloped power law MF, we
find that AM 4 and Pal 13 have spectral indices alpha = +0.68 +/- 0.34 and
alpha = -1.67 +/- 0.25 (where a Salpeter MF has alpha = +1.35), respectively.
Comparing our derived slopes with literature measurements of cluster integrated
magnitude (M_V) and MF slope indicates that AM 4 is an outlier. Its MF slope is
substantially steeper than clusters of comparable luminosity, while Pal 13 has
a MF in line with the general trend. We discuss both primordial and dynamical
origins for the unusual MF slope of AM 4 and tentatively favor the dynamical
scenario. However, MF slopes of more low luminosity clusters are needed to
verify this hypothesis. | astro-ph_GA |
A sensitive search for predicted methanol maser transitions with the
Australia Telescope Compact Array: We have used the Australia Telescope Compact Array (ATCA) to search for a
number of centimetre wavelength methanol transitions which are predicted to
show weak maser emission towards star formation regions. Sensitive, high
spatial and spectral resolution observations towards four high-mass star
formation regions which show emission in a large number of class II methanol
maser transitions did not result in any detections. From these observations we
are able to place an upper limit of <~1300K on the brightness temperature of
any emission from the $3_1$A$^+$-$3_1$A$^-$, $17_{-2}$-$18_{-3}$E ($v_t=1$),
$12_4$-$13_3$A$^-$, $12_4$-$13_3$A$^+$ and $4_1$A$^+$-$4_1$A$^-$ transitions of
methanol in these sources on angular scales of 2 arcseconds. This upper limit
is consistent with current models for class II methanol masers in high-mass
star formation regions and better constraints than those provided here will
likely require observations with next-generation radio telescopes. | astro-ph_GA |
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