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On the Helium fingers in the intracluster medium: In this paper we investigate the convection phenomenon in the intracluster
medium (the weakly-collisional magnetized inhomogeneous plasma permeating
galaxy clusters) where the concentration gradient of the Helium ions is not
ignorable. To this end, we build upon the general machinery employed to study
the salt finger instability found in the oceans. The salt finger instability is
a form of double diffusive convection where the diffusions of two physical
quantities---heat and salt concentrations---occur with different diffusion
rates. The analogous instability in the intracluster medium may result owing to
the magnetic field mediated anisotropic diffusions of the heat and the Helium
ions (in the sea of the Hydrogen ions and the free electrons). These two
diffusions have inherently different diffusion rates. Hence the convection
caused by the onset of this instability is an example of double diffusive
convection in the astrophysical settings. A consequence of this instability is
the formation of the vertical filamentary structures having more concentration
of the Helium ions with respect to the immediate neighbourhoods of the
filaments. We term these structures as Helium fingers in analogy with the salt
fingers found in the case of the salt finger instability. Here we show that the
width of a Helium finger scales as one-fourth power of the radius of the inner
region of the intracluster medium in the supercritical regime. We also
determine the explicit mathematical expression of the criterion for the onset
of the heat-flux-driven buoyancy instability modified by the presence of
inhomogeneously distributed Helium ions. | astro-ph_GA |
The Galactic bar and the large scale velocity gradients in the Galactic
disk: Aims: We investigate whether the cylindrical (galactocentric) radial velocity
gradient of ~ -3 km/s/kpc, directed radially from the Galactic center and
recently observed in the stars of the solar neighborhood with the RAVE survey,
can be explained by the resonant effects of the bar near the solar
neighborhood.
Methods: We compared the results of test particle simulations of the Milky
Way with a potential that includes a rotating bar with observations from the
RAVE survey. To this end we applied the RAVE selection function to the
simulations and convolved these with the characteristic RAVE errors. We
explored different "solar neighborhoods" in the simulations, as well as
different bar models
Results: We find that the bar induces a negative radial velocity gradient at
every height from the Galactic plane, outside the outer Lindblad resonance and
for angles from the long axis of the bar compatible with the current estimates.
The selection function and errors do not wash away the gradient, but often make
it steeper, especially near the Galactic plane, because this is where the RAVE
survey is less radially extended. No gradient in the vertical velocity
ispresent in our simulations, from which we may conclude that this cannot be
induced by the bar. | astro-ph_GA |
Taking apart the dynamical clock. Fat-tailed dynamical kicks shape the
blue-straggler star bimodality: In globular clusters, blue straggler stars are heavier than the average star,
so dynamical friction strongly affects them. The radial distribution of BSS,
normalized to a reference population, appears bimodal in a fraction of Galactic
GCs, with a density peak in the core, a prominent zone of avoidance at
intermediate radii, and again higher density in the outskirts. The zone of
avoidance appears to be located at larger radii the more relaxed the host
cluster, acting as a sort of dynamical clock. We use a new method to compute
the evolution of the BSS radial distribution under dynamical friction and
diffusion. We evolve our BSS in the mean cluster potential under dynamical
friction plus a random fluctuating force, solving the Langevin equation with
the Mannella quasi symplectic scheme. This amounts to a new simulation method
which is much faster and simpler than direct N-body codes but retains their
main feature: diffusion powered by strong, if infrequent, kicks. We compute the
radial distribution of initially unsegregated BSS normalized to a reference
population as a function of time. We trace the evolution of its minimum,
corresponding to the zone of avoidance. We compare the evolution under kicks
extracted from a Gaussian distribution to that obtained using a Holtsmark
distribution. The latter is a fat tailed distribution which correctly models
the effects of close gravitational encounters. We find that the zone of
avoidance moves outwards over time, as expected based on observations, only
when using the Holtsmark distribution. Thus the correct representation of near
encounters is crucial to reproduce the dynamics of the system. We confirm and
extend earlier results that showed how the dynamical clock indicator depends
both on dynamical friction and effective diffusion powered by dynamical
encounters. | astro-ph_GA |
Radio--Far infrared correlation in "blue cloud" galaxies with 0<z<1.2: We study the radio--far infrared (FIR) correlation in "blue cloud" galaxies
chosen from the PRism MUltiobject Survey (PRIMUS) up to redshift ($z$) of 1.2
in the XMM-LSS field. We use rest-frame emission at 1.4 GHz in the radio and
both monochromatic (at 70$\mu$m) and bolometric (between $8-1000~\mu$m)
emission in the FIR. To probe the nature of the correlation up to $z\sim1.2$,
where direct detection of blue star-forming galaxies is impossible with current
technology, we employ the technique of image stacking at 0.325 and 1.4 GHz in
the radio and in six infrared bands, viz. 24, 70, 160, 250, 350 and $500~\mu$m.
For comparison, we also study the correlation for more luminous galaxies that
are directly detected. The stacking analysis allows us to probe the radio--FIR
correlation for galaxies that are up to 2 orders of magnitude fainter than the
ones detected directly. The $k-$correction in the infrared wavebands is
obtained by fitting the observed spectral energy distribution (SED) with a
composite mid-IR power law and a single temperature greybody model. We find
that the radio luminosity at 1.4 GHz ($L_{\rm 1.4GHz}$) is strongly correlated
with monochromatic FIR luminosity at 70 $\mu$m ($L_{\rm 70\mu m}$) having slope
$1.09\pm0.05$ and with bolometric luminosity ($L_{\rm TIR}$) having slope
$1.11\pm0.04$. The quantity $q_{\rm TIR} (=\log_{10}[L_{\rm TIR}/(3.75\times
10^{12} L_{\rm 1.4 GHz})])$ is observed to decrease with redshift as $q_{\rm
TIR} \propto (1+z)^{-0.16\pm0.03}$ probably caused due to the non-linear slope
of the radio--FIR correlation. Within the uncertainties of our measurement and
the limitations of our flux-limited and color-selected sample, we do not find
any evolution of the radio--FIR correlation with redshift. | astro-ph_GA |
Measuring bar pattern speeds from single simulation snapshots: We describe methods to measure simultaneously the orientation angle $\psi$
and pattern speed $\Omega$ from single snapshots of simulated barred galaxies.
Unlike previous attempts, our approach is unbiased, precise, and consistent in
the sense that $\psi=\int\Omega\mathrm{d}t$. It can be extended to obtain the
rate and axis of rotation, i.e. the vector $\boldsymbol{\Omega}$. We provide
computer code implementing our method. | astro-ph_GA |
HI-shielding of ${\rm H_2}$ in UV-irradiated protogalaxies: suppression
of the photodissociation rate: We study the impact of neutral hydrogen absorption on ${\rm H_2}$
photodissociation in protogalactic haloes exposed to soft-UV radiation.
Lyman-series absorption can significantly deplete dissociating photons as line
overlap with the ${\rm H_2}$ Lyman-Werner bands occurs for neutral column
densities exceeding $10^{22}$ ${\rm cm^{-2}}$, but this effect has not been
previously included in studies of protogalactic haloes. We use high-resolution
three-dimensional hydrodynamic simulations to investigate this "HI-shielding"
in three metal-free atomic cooling haloes collapsing at redshift $z \sim
10-20$. We use CLOUDY modeling to update a previous fitting formula for
HI-shielding which is a better model for shielding of non-ground state ${\rm
H_2}$ rovibrational populations and implement the new fit in our simulations.
We find that the inclusion of HI-shielding increases the "critical flux" for
suppression of ${\rm H_2}$ cooling in these haloes by $\sim 60-100$ per cent.
The larger critical flux has implications in particular for the predicted
numbers of candidate haloes in which "direct collapse" could seed massive
($\sim 10^5$ ${\rm M_\odot}$) black holes at $z \sim 15$. | astro-ph_GA |
First Extended Catalogue of Galactic Bubbles InfraRed Fluxes from WISE
and Herschel Surveys: In this paper, we present the first extended catalogue of far-infrared fluxes
of Galactic bubbles. Fluxes were estimated for 1814 bubbles, defined here as
the `golden sample', and were selected from the Milky Way Project First Data
Release (Simpson et al.) The golden sample was comprised of bubbles identified
within the Wide-field Infrared Survey Explorer (WISE) dataset (using 12- and
22-$\mu$m images) and Herschel data (using 70-, 160-, 250-, 350- and 500-$\mu$m
wavelength images). Flux estimation was achieved initially via classical
aperture photometry and then by an alternative image analysis algorithm that
used active contours. The accuracy of the two methods was tested by comparing
the estimated fluxes for a sample of bubbles, made up of 126 H II regions and
43 planetary nebulae, which were identified by Anderson et al. The results of
this paper demonstrate that a good agreement between the two was found. This is
by far the largest and most homogeneous catalogue of infrared fluxes measured
for Galactic bubbles and it is a step towards the fully automated analysis of
astronomical datasets. | astro-ph_GA |
A powerful (and likely young) radio-loud quasar at z=5.3: We present the discovery of PSO J191.05696$+$86.43172 (hereafter PSO
J191$+$86), a new powerful radio-loud quasar (QSO) in the early Universe (z =
5.32). We discovered it by cross-matching the NRAO VLA Sky Survey (NVSS) radio
catalog at 1.4 GHz with the first data release of the Panoramic Survey
Telescope and Rapid Response System (Pan-STARRS PS1) in the optical. With a
NVSS flux density of 74.2 mJy, PSO J191$+$86 is one of the brightest radio QSO
discovered at z$\sim$5. The intensity of its radio emission is also confirmed
by the very high value of radio loudness (R>300). The observed radio spectrum
of PSO J191$+$86 shows a possible turnover around $\sim$1 GHz (i.e., $\sim$6
GHz in the rest frame), making it a Gigahertz-Peaked Spectrum (GPS) source.
However, variability could affect the real shape of the radio spectrum, since
the data in hand have been taken $\sim$25 years apart. By assuming a peak of
the observed radio spectrum between 1 and 2 GHz (i.e. $\sim$ 6 and 13 GHz in
the rest-frame) we found a linear size of the source of $\sim$10-30 pc and a
corresponding kinetic age of 150-460 yr. This would make PSO J191$+$86 a newly
born radio source. However, the large X-ray luminosity (5.3$\times$10$^{45}$
erg s$^{-1}$), the flat X-ray photon index ($\Gamma_X$=1.32) and the
optical-X-ray spectral index ($\tilde{\alpha_{ox}}$=1.329) are typical of
blazars. This could indicate that the non-thermal emission of PSO J191$+$86 is
Doppler boosted. Further radio observations (both on arcsec and parsec scales)
are necessary to better investigate the nature of this powerful radio QSO. | astro-ph_GA |
VII Zw 403: HI Structure in a Blue Compact Dwarf Galaxy: We present optical (UBVJ), ultraviolet (FUV, NUV), and high resolution atomic
hydrogen (HI) observations of the nearby blue compact dwarf (BCD), VII Zw 403.
We find that VII Zw 403 has a relatively high HI mass-to-light ratio for a BCD.
The rotation velocity is nominally 10-15 km/s, but rises to ~20 km/s after
correction for the ~8-10 km/s random motions present in the gas. The velocity
field is complex; including a variation in the position angle of the major axis
going from the NE to the SW parts of the galaxy. Our high resolution HI maps
reveal structure in the central gas, including a large, low-density HI
depression or hole between the southern and northern halves of the galaxy,
coincident with an unresolved x-ray source. Although interactions have been
proposed as the triggering mechanism for the vigorous star formation occurring
in BCDs, VII Zw 403 does not seem to have been tidally triggered by an external
interaction, as we have found no nearby possible perturbers. It also doesn't
appear to fall in the set of galaxies that exhibit a strong central mass
density concentration, as its optical scale length is large in comparison to
similar systems. However, there are some features that are compatible with an
accretion event: optical/HI axis misalignment, a change in position angle of
the kinematic axis, and a complex velocity field. | astro-ph_GA |
Chemical Cartography. I. A Carbonicity Map of the Galactic Halo: We present the first map of carbonicity, [C/Fe], for the halo system of the
Milky Way, based on a sample of over 100,000 main-sequence turnoff stars with
available spectroscopy from the Sloan Digital Sky Survey. This map, which
explores distances up to 15 kpc from the Sun, reveals clear evidence for the
dual nature of the Galactic halo, based on the spatial distribution of stellar
carbonicity. The metallicity distribution functions of stars in the inner- and
outer-halo regions of the carbonicity map reproduce those previously argued to
arise from contributions of the inner- and outer-halo populations, with peaks
at [Fe/H] = -1.5 and -2.2, respectively. From consideration of the absolute
carbon abundances for our sample, A(C), we also confirm that the
carbon-enhanced metal-poor (CEMP) stars in the outer-halo region exhibit a
higher frequency of CEMP-no stars (those with no overabundances of heavy
neutron-capture elements) than of CEMP-s stars (those with strong
overabundances of elements associated with the s-process), whereas the stars in
the inner-halo region exhibit a higher frequency of CEMP-s stars. We argue that
the contrast in the behavior of the CEMP-no and CEMP-s fractions in these
regions arises from differences in the mass distributions of the mini-halos
from which the stars of the inner- and outer-halo populations formed, which
gives rise in turn to the observed dichotomy of the Galactic halo. | astro-ph_GA |
ALMA observations of the archetypal "hot core" that isn't: Orion KL: We present sensitive high angular resolution ($\sim$ 0.1$''$ -- 0.3$''$)
continuum ALMA (The Atacama Large Millimeter/Submillimeter Array) observations
of the archetypal hot core located in Orion-KL. The observations were made in
five different spectral bands (bands 3, 6, 7, 8, and 9) covering a very broad
range of frequencies (149 -- 658 GHz). Apart of the well-know millimeter
emitting objects located in this region (Orion Source I and BN), we report the
first submillimeter detection of three compact continuum sources (ALMA 1-3) in
the vicinities of the Orion-KL hot molecular core. These three continuum
objects have spectral indices between 1.47 to 1.56, and brightness temperatures
between 100 to 200 K at 658 GHz suggesting that we are seeing moderate
optically thick dust emission with possible grain growth. However, as these
objects are not associated with warm molecular gas, and some of them are
farther out from the molecular core, we thus conclude that they cannot heat the
molecular core. This result favours the hypothesis that the hot molecular core
in Orion-KL core is heated externally. | astro-ph_GA |
Comparison of distance measurements to dust clouds using GRB X-ray halos
and 3D dust extinction: X-ray photons from energetic sources such as gamma-ray bursts (GRBs) can be
scattered on dust clouds in the Milky Way, creating a time-evolving halo around
the GRB position. X-ray observations of such halos allow the measurement of
dust clouds distances in the Galaxy on which the scattering occurs. We present
the first systematic comparison of the distances to scattering regions derived
from GRB halos with the 3D dust distribution derived from recently published
optical-to-near infrared extinction maps. GRB halos were observed around 7
sources by the Swift XRT and the XMM-Newton EPIC instruments, namely GRB
031203, GRB 050713A, GRB 050724, GRB 061019, GRB 070129, GRB 160623A and GRB
221009A. We used four 3D extinction maps that exploit photometric data from
different surveys and apply diverse algorithms for the 3D mapping of
extinction, and compared the X-ray halo-derived distances with the local maxima
in the 3D extinction density distribution. We found that in all GRBs we can
find at least one local maximum in the 3D dust extinction map that is in
agreement with the dust distance measured from X-ray rings. For GRBs with
multiple X-ray rings, the dust distance measurements coincide with at least 3
maxima in the extinction map for GRB 160623A, and 5 maxima for GRB 221009A. The
agreement of these independent distance measurements shows that the methods
used to create dust extinction maps may potentially be optimized by the X-ray
halo observations from GRBs. | astro-ph_GA |
The Sixteenth Data Release of the Sloan Digital Sky Surveys: First
Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra: This paper documents the sixteenth data release (DR16) from the Sloan Digital
Sky Surveys; the fourth and penultimate from the fourth phase (SDSS-IV). This
is the first release of data from the southern hemisphere survey of the Apache
Point Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from
APOGEE-2 North are also included. DR16 is also notable as the final data
release for the main cosmological program of the Extended Baryon Oscillation
Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project
are released here. DR16 also includes all the data from the Time Domain
Spectroscopic Survey (TDSS) and new data from the SPectroscopic IDentification
of ERosita Survey (SPIDERS) programs, both of which were co-observed on eBOSS
plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point
Observatory (MaNGA) survey (or the MaNGA Stellar Library "MaStar"). We also
preview future SDSS-V operations (due to start in 2020), and summarize plans
for the final SDSS-IV data release (DR17). | astro-ph_GA |
The influence of magnetic field on the CNM mass fraction and its
alignment with density structures: To contribute to the understanding of the magnetic field's influence on the
segregation of CNM in the solar neighbourhood we analyse MHD simulations which
include the main physical characteristics of the local neutral atomic ISM. The
simulations have a continuous solenoidal Fourier forcing in a periodic box of
100 pc per side and an initial uniform magnetic field ($\vec{B_0}$) with
intensities ranging between $\sim 0.4$ $\mu$G and $\sim 8$ $\mu$G. Our main
results are: i) the CNM mass fraction diminishes with the increase in magnetic
field intensity. ii) There is a preferred alignment between CNM structures and
$\vec{B}$ in all our $B_0$ range but the preference weakens as $B_{0}$
increases. It is worth noticing that this preference is also present in
two-dimensional projections making an extreme angle ($0$ or $\pi / 2$) with
respect to $\vec{B_0}$ and it is only lost for the strongest magnetic field
when the angle of projection is perpendicular to $\vec{B_0}$. iii) The
aforementioned results are prevalent despite the inclusion of self-gravity in
our continuously forced simulations with a mean density similar to the average
value of the solar neighbourhood. iv) Given a fixed $B_0$ and slightly higher
mean densities, up to double, the effects of self-gravity are still not
qualitatively significant. | astro-ph_GA |
Optical Imaging & Spectral Study of FR-I Type Radio Galaxy:CTD 086 (B2
1422+26B): We present optical imaging and spectroscopic studies of the Fanaroff \& Riley
class I (FR I) radio galaxy CTD 086 based on Hubble Space Telescope (HST) and
Sloan Digital Sky Survey (SDSS) observations. We use isophote shape analysis to
show that there is no stellar disk component within CTD 086 and further that
the morphological class of the galaxy is most likely E2. Optical spectroscopy
of this galaxy reveals the presence of narrow emission lines only, and thus it
qualifies to be termed as a narrow-line radio galaxy (type 2 AGN). We also
extract stellar kinematics from the absorption-line spectra of CTD 086 using
Penalized Pixel-Fitting method and derive the black hole mass MBH to be equal
to (8.8\pm2.4)\times10^{7} Msun. | astro-ph_GA |
Direct observations of the atomic-molecular phase transition in the
Milky Way's nuclear wind: Hundreds of high-velocity atomic gas clouds exist above and below the
Galactic Centre, with some containing a molecular component. However, the
origin of these clouds in the Milky Way's wind is unclear. This paper presents
new high-resolution MeerKAT observations of three atomic gas clouds and studies
the relationship between the atomic and molecular phases at $\sim 1$ pc scales.
The clouds' atomic hydrogen column densities, $N_{\mathrm{HI}}$, are less than
a $\mbox{few}\times 10^{20}$ cm$^{-2}$, but the two clouds closest to the
Galactic Centre nonetheless have detectable CO emission. This implies the
presence of H$_{2}$ at levels of $N_{\mathrm{HI}}$ at least a factor of ten
lower than in the typical Galactic interstellar medium. For the cloud closest
to the Galactic Centre, there is little correlation between the
$N_{\mathrm{HI}}$ and the probability that it will harbour detectable CO
emissions. In contrast, for the intermediate cloud, detectable CO is heavily
biased toward the highest values of $N_{\mathrm{HI}}$. The cloud most distant
from the Galactic Centre has no detectable CO at similar $N_{\mathrm{HI}}$
values. Moreover, we find that the two clouds with detectable CO are too
molecule-rich to be in chemical equilibrium, given the depths of their atomic
shielding layers, which suggests a scenario whereby these clouds consist of
pre-existing molecular gas from the disc that the Galactic wind has swept up,
and that is dissociating into atomic hydrogen as it flows away from the Galaxy.
We estimate that entrained molecular material of this type has a $\sim
\mathrm{few}-10$ Myr lifetime before photodissociating. | astro-ph_GA |
Rotation Curves in z~1-2 Star-Forming Disks: Evidence for Cored Dark
Matter Distributions: We report high quality, Halpha or CO rotation curves (RCs) to several Re for
41 large, massive, star-forming disk galaxies (SFGs), across the peak of cosmic
galaxy evolution (z~0.67-2.45), taken with the ESO-VLT, the LBT and IRAM-NOEMA.
Most RC41 SFGs have reflection symmetric RCs plausibly described by equilibrium
dynamics. We fit the major axis position-velocity cuts with beam-convolved,
forward modeling with a bulge, a turbulent rotating disk, and a dark matter
(DM) halo. We include priors for stellar and molecular gas masses, optical
light effective radii and inclinations, and DM masses from abundance matching
scaling relations. Two-thirds or more of the z>1.2 SFGs are baryon dominated
within a few Re of typically 5.5 kpc, and have DM fractions less than maximal
disks (<fDM (Re)>=0.12). At lower redshift (z<1.2) that fraction is less than
one-third. DM fractions correlate inversely with the baryonic angular momentum
parameter, baryonic surface density and bulge mass. Inferred low DM fractions
cannot apply to the entire disk & halo but more plausibly reflect a flattened,
or cored, inner DM density distribution. The typical central 'DM deficit' in
these cores relative to NFW distributions is ~30% of the bulge mass. The
observations are consistent with rapid radial transport of baryons in the first
generation massive gas rich halos forming globally gravitationally unstable
disks, and leading to efficient build-up of massive bulges and central black
holes. A combination of heating due to dynamical friction and AGN feedback may
drive DM out of the initial cusps. | astro-ph_GA |
The Local Cluster Survey II: Disk-Dominated Cluster Galaxies with
Suppressed Star Formation: We investigate the role of dense environments in suppressing star formation
by studying $\rm \log_{10}(M_\star/M_\odot) > 9.7$ star-forming galaxies in
nine clusters from the Local Cluster Survey ($0.0137 < z < 0.0433$) and a large
comparison field sample drawn from the Sloan Digital Sky Survey. We compare the
star-formation rate (SFR) versus stellar mass relation as a function of
environment and morphology. After carefully controlling for mass, we find that
in all environments, the degree of SFR suppression increases with increasing
bulge-to-total (B/T) ratio. In addition, the SFRs of cluster and infall
galaxies at a fixed mass are more suppressed than their field counterparts at
all values of B/T. These results suggest a quenching mechanism that is linked
to bulge growth that operates in all environments and an additional mechanism
that further reduces the SFRs of galaxies in dense environments. We limit the
sample to $B/T < 0.3$ galaxies to control for the trends with morphology and
find that the excess population of cluster galaxies with suppressed SFRs
persists. We model the timescale associated with the decline of SFRs in dense
environments and find that the observed SFRs of the cluster core galaxies are
consistent with a range of models including: a mechanism that acts slowly and
continuously over a long (2-5 Gyr) timescale, and a more rapid ($<1$ Gyr)
quenching event that occurs after a delay period of 1-6 Gyr. Quenching may
therefore start immediately after galaxies enter clusters. | astro-ph_GA |
Shadows around Sgr A* and M87* as a tool to test gravity theories: In the framework of Randall -- Sundrum theory with extra dimension Reissner
-- Nordstr\"om black hole solutions with a tidal charge have been found. The
shadow around the supermassive black hole in M87 was reconstructed in 2019
based on observations with the Event Horizon Telescope (EHT) in April 2017. In
May 2022 the EHT Collaboration presented results of a shadow reconstruction for
our Galactic Center. Earlier, for Reissner -- Nordstr\"om metric we derived
analytical expressions for shadow size as a function of charge and later
generalized these results for a tidal charge case. We discuss opportunities to
evaluate parameters of alternative theories of gravity with shadow size
estimates done by the EHT Collaboration, in particular, a tidal charge could be
estimated from these observations. | astro-ph_GA |
First sample of $\rm N_2H^+$ nitrogen isotopic ratio measurements in
low-mass protostars: Context. The nitrogen isotopic ratio is considered an important diagnostic
tool of the star formation process, and $N_2H^+$ is particularly important
because it is directly linked to molecular nitrogen $N_2$. However, theoretical
models still lack to provide an exhaustive explanation for the observed
$^{14}N/^{15}N$ values.
Aims. Recent theoretical works suggest that the $^{14}N/^{15}N$ behaviour is
dominated by two competing reactions that destroy $ N_2H^+$: dissociative
recombination and reaction with CO. When CO is depleted from the gas phase, if
$N_2H^+$ recombination rate is lower with respect to the $N^{15}NH^+$ one, the
rarer isotopologue is destroyed faster. This implies that the $N_2H^+$ isotopic
ratio in protostars should be lower than the one in prestellar cores, and
consistent with the elemental value of ~440. We aim to test this hypothesis,
producing the first sample of $N_2H^+ / N^{15}NH^+$ measurements in low mass
protostars.
Methods. We observe the $N_2H^+$ and $N^{15}NH^+$ lowest rotational
transition towards six young stellar objects in Perseus and Taurus molecular
clouds. We model the spectra with a custom python code using a constant
$T_{ex}$ approach to fit the observations. We discuss in appendix the validity
of this hypothesis. The derived column densities are used to compute the
nitrogen isotopic ratio.
Results. Our analysis yields an average of $\rm ^{14}N/^{15}N|_{pro} = 420
\pm 15$ in the protostellar sample. This is consistent with the protosolar
value of 440, and significantly lower than the average value previously
obtained in a sample of prestellar objects. Conclusions. Our results are in
agreement with the hypothesis that, when CO is depleted from the gas-phase,
dissociative recombinations with free electrons destroy $N^{15}NH^+$ faster
than $N_2H^+$, leading to high isotopic ratios in prestellar cores, where CO is
frozen on dust grains. | astro-ph_GA |
The origin of low-surface-brightness galaxies in the dwarf regime: Low-surface-brightness galaxies (LSBGs) -- defined as systems that are
fainter than the surface-brightness limits of past wide-area surveys -- form
the overwhelming majority of galaxies in the dwarf regime (M* < 10^9 MSun).
Using NewHorizon, a high-resolution cosmological simulation, we study the
origin of LSBGs and explain why LSBGs at similar stellar mass show the large
observed spread in surface brightness. New Horizon galaxies populate a
well-defined locus in the surface brightness -- stellar mass plane, with a
spread of ~3 mag arcsec^-2, in agreement with deep SDSS Stripe data. Galaxies
with fainter surface brightnesses today are born in regions of higher
dark-matter density. This results in faster gas accretion and more intense star
formation at early epochs. The stronger resultant supernova feedback flattens
gas profiles at a faster rate which, in turn, creates shallower stellar
profiles (i.e. more diffuse systems) more rapidly. As star formation declines
towards late epochs (z<1), the larger tidal perturbations and ram pressure
experienced by these systems (due to their denser local environments)
accelerate the divergence in surface brightness, by increasing their effective
radii and reducing star formation respectively. A small minority of dwarfs
depart from the main locus towards high surface brightnesses, making them
detectable in past wide surveys. These systems have anomalously high
star-formation rates, triggered by recent, fly-by or merger-driven starbursts.
We note that objects considered extreme/anomalous at the depth of current
datasets, e.g. `ultra-diffuse galaxies', actually dominate the predicted dwarf
population and will be routinely visible in future surveys like LSST. | astro-ph_GA |
30 GHz monitoring of broad absorption line (BAL) quasars: Broad absorption line (BAL) quasars have been studied for over thirty years.
Yet it is still unclear why and when we observe broad absorption lines in
quasars. Is this phenomenon caused by geometry or is it connected with the
evolution process? Variability of the BAL quasars, if present, can give us
information about their orientation, namely it can indicate whether they are
oriented more pole-on. Using the Torun 32-metre dish equipped with the One
Centimetre Receiver Array (OCRA) we have started a monitoring campaign of a
sample of compact radio-loud BAL quasars. This 30 GHz variability monitoring
program supplements the high-resolution interferometric observations of these
objects we have carried out with the EVN and VLBA. | astro-ph_GA |
COSMOS2020: Investigating the AGN-obscured accretion phase at $z\sim 1$
via [NeV] selection: We investigated the properties of 94 [NeV]3426AA-selected type 2 AGN in
COSMOS at z=0.6-1.2, performing optical-to-far-infrared spectral energy
distribution fitting. In addition, we analyze the X-ray spectra of the
X-ray-detected sources to obtain reliable values of the AGN obscuration and
intrinsic luminosity.
We found that more than two-thirds of our sample is composed of very obscured
sources, with about 20% of the sources being candidate CT-AGN and half being
AGNs in a strong phase of accretion. With respect to non-active galaxies, we
find a higher fraction of sources within the main sequence and little evidence
for AGNs quenching the SF. The comparison with the prediction from the in situ
co-evolution model suggests that [NeV] is an effective tool for selecting
galaxies in the obscured growth phase of the BH-galaxy co-evolution paradigm.
We find that the "quenching phase" is still to come for most of the sample and
only few galaxies show evidence of quenched SF activity. | astro-ph_GA |
Atomic and Molecular Absorption in Redshifted Radio Sources: We report on a survey for associated HI 21-cm and OH 18-cm absorption with
the Giant Metrewave Radio Telescope at redshifts z = 0.2-0.4. Although the low
redshift selection ensures that our targets are below the critical ultra-violet
luminosity, which is hypothesised to ionise all of the neutral gas in the host
galaxy, we do not obtain any detections in the six sources searched. Analysing
these in context of the previous surveys, in addition to the anti-correlation
with the ultra-violet luminosity (ionising photon rate), we find a correlation
between the strength of the absorption and the blue -- near-infrared colour, as
well as the radio-band turnover frequency. We believe that these are due to the
photo-ionisation of the neutral gas, an obscured sight-line being more
conducive to the presence of cold gas and the compact radio emission being
better intercepted by the absorbing gas, maximising the flux coverage,
respectively. Regarding the photo-ionisation, the compilation of the previous
surveys increases the significance of the critical ionising photon rate, above
which all of the gas in the host galaxy is hypothesised to be ionised, to >5
sigma. This reaffirms that this is an ubiquitous effect, which has profound
implications for the detection of neutral gas in these objects with the Square
Kilometre Array. | astro-ph_GA |
Probing the hot circumgalactic medium of external galaxies in X-ray
absorption II: a luminous spiral galaxy at $z\approx 0.225$: The circumgalactic medium (CGM) is the most massive baryonic component of a
spiral galaxy, shock heated to about $10^6$K for an $\rm L^{\star}$ galaxy. The
CGM of the Milky Way has been well-characterized through X-ray absorption line
spectroscopy. However, the paucity of bright background sources makes it
challenging to probe the CGM of external galaxies. Previously, using broad OVI
absorption as a signpost, we successfully detected the CGM of one galaxy in
X-rays. Here we report on the detection of the OVII $K\alpha$ absorption line
at the redshift of a spiral galaxy at $z\approx0.225$ using 1.2 Ms of Chandra
observations. This is a robust detection, clearly showing the presence of the
hot gas. The mass in the hot phase is at least an order of magnitude larger
than that in the cooler phases detected in the UV. The presence of hot gas
$116h^{-1}$kpc from the center of this galaxy provides credence to the
existence of the extended CGM of the Milky Way. There has been a report of the
detection of OVII absorption from the warm-hot intergalactic medium in this
sightline using stacking analysis on an older dataset. We argue that the
absorption line is from the CGM of the $z\approx0.225$ galaxy instead. | astro-ph_GA |
Galactic nebular lines in the fiber spectra of background QSOs: Reaching
a hundred QSO-galaxy pairs with spectroscopic and photometric measurements: We present photometric and spectroscopic measurements of 53 QSO-galaxy pairs
from the Sloan Digital Sky Survey, where nebular emission lines from a 0<z<0.84
foreground galaxy are detected in the fiber spectra of a background QSO,
bringing the overall sample to 103 QSO-galaxy pairs detected in the SDSS. We
here study the nature of these systems. Detected foreground galaxies appear at
impact parameters between 0.37 kpc and 12.68 kpc. The presence of oxygen and
Balmer emission lines allows us to determine the emission line metallicities
for our sample, which are on average super-solar in value. Star formation rates
for our sample are in the range 0.01-12 M_sol yr^-1. We utilize photometric
redshift fitting techniques to estimate the M_stellar values of our galaxies
(log M_stellar = 7.34 - 11.54), and extrapolate this relationship to those
galaxies with no imaging detections. Where available, we measure the absorption
features present in the QSO spectrum due to the foreground galaxy and the
relationships between their rest equivalent widths. We report an
anti-correlation between impact parameter and E(B-V)_(g-i), as well as a
correlation between galaxy color (u-r) and E(B-V)_(g-i). We find that our
sample is one of late-type, star forming galaxies comparable to field galaxies
in a similar redshift range, providing important clues to better understand
absorption systems. These galaxies represent a sample of typical galaxies in
the local Universe for which abundances, extinction, morphology, and absorption
properties may be measured using background QSOs with great potential for
follow-up observations. | astro-ph_GA |
JADES. The diverse population of infant Black Holes at 4<z<11: merging,
tiny, poor, but mighty: We present 12 new AGN at 4<z<7 in the JADES survey (in addition to the
previously identified AGN in GN-z11 at z=10.6) revealed through the detection
of a Broad Line Region as seen in Halpha. The depth of JADES, together with the
use of three different spectral resolutions, enables us to probe a lower mass
regime relative to previous studies. In a few cases we find evidence for two
broad components of Halpha which suggests that these could be candidate merging
black holes (BHs). The inferred BH masses range between 8 x 10^7 Msun down to 4
x 10^5 Msun, interestingly probing the regime expected for Direct Collapse
Black Holes (DCBHs). The inferred AGN bolometric luminosities (~10^44-10^45
erg/s) imply accretion rates that are < 0.5 times the Eddington rate in most
cases. However, small BHs, with M_BH ~ 10^6 Msun, tend to accrete at Eddington
or super-Eddington rates. These BH at z~4-11 are over-massive relative to their
host galaxies stellar masses when compared to the local M_BH-Mstar relation,
and even approaching M_BH~Mstar, as expected for DCBHs and super-Eddington
scenarios. However, we find that these early BHs tend to be more consistent
with the local relation between M_BH and velocity dispersion, as well as
between M_BH and dynamical mass, suggesting that these are more fundamental and
universal relations. On the BPT excitation-diagnostic diagram these AGN are
located in the region that is that is locally occupied by star-forming
galaxies, implying that they would be missed by the standard classification
techniques if they did not display broad lines. Their location on the diagram
is consistent with what expected for AGN hosted in metal poor galaxies (Z ~
0.1-0.2 Zsun). The fraction of broad line AGN with L_AGN > 10^44 erg/s, among
galaxies in the redshift range 4<z<6, is about 10%, suggesting that the
contribution of AGN and their hosts to the reionization of the Universe is >
10%. | astro-ph_GA |
Compton Thick AGN in the 70 Month Swift-BAT All-Sky Hard X-ray Survey: a
Bayesian approach: The 70-month Swift/BAT catalogue provides a sensitive view of the
extragalactic X-ray sky at hard energies (>10 keV) containing about 800 Active
Galactic Nuclei. We explore its content in heavily obscured, Compton-thick AGN
by combining the BAT (14-195 keV) with the lower energy XRT (0.3-10 keV) data.
We apply a Bayesian methodology using Markov chains to estimate the exact
probability distribution of the column density for each source. We find 53
possible Compton-thick sources (with probability 3 to 100%) translating to a
~7% fraction of the AGN in our sample. We derive the first parametric
luminosity function of Compton-thick AGN. The unabsorbed luminosity function
can be represented by a double power-law with a break at $L_{\star} 2 \times
10^{42}$ $\rm ergs~s^{-1}$ in the 20-40 keV band. | astro-ph_GA |
Differences and similarities of stellar populations in LAEs and LBGs at
$z\sim$ 3.4 - 6.8: The differences between the inherent stellar populations (SPs) of LAEs and
LBGs are a key factor in understanding early galaxy formation and evolution. We
have run a set of SP burst-like models for a sample of 1,558 sources at
$3.4<z<6.8$ from the Survey for High-$z$ Absorption Red and Dead Sources
(SHARDS) over the GOODS-N field. This work focuses on the differences between
the three different observational subfamilies of our sample: LAE-LBGs,
no-Ly$\alpha$ LBGs and pure LAEs. Single and double SP synthetic spectra were
used to model the SEDs, adopting a Bayesian information criterion to analyse
under which situations a second SP is required. We find that the sources are
well modelled using a single SP in $\sim79\%$ of the cases. The best models
suggest that pure LAEs are typically young low mass galaxies
($t\sim26^{+41}_{-25}$ Myr;
$M_{\mathrm{star}}\sim5.6^{+12.0}_{-5.5}\times10^{8}\ M_{\odot}$), undergoing
one of their first bursts of star formation. On the other hand, no-Ly$\alpha$
LBGs require older SPs ($t\sim71\pm12$ Myr), and they are substantially more
massive ($M_{\mathrm{star}}\sim3.5\pm1.1\times10^{9}\ M_{\odot}$). LAE-LBGs
appear as the subgroup that more frequently needs the addition of a second SP,
representing an old and massive galaxy caught in a strong recent star-forming
episode. The relative number of sources found from each subfamily at each $z$
supports an evolutionary scenario from pure LAEs and single SP LAE-LBGs to more
massive LBGs. Stellar Mass Functions are also derived, finding an increase of
$M^{*}$ with cosmic time and a possible steepening of the low mass slope from
$z\sim6$ to $z\sim5$ with no significant change to $z\sim4$. Additionally, we
have derived the SFR-$M_{\mathrm{star}}$ relation, finding a
$\mathrm{SFR}\propto M_{\mathrm{star}}^{\beta}$ behaviour with negligible
evolution from $z\sim4$ to $z\sim6$. | astro-ph_GA |
An astrophysically motivated ranking criterion for low-latency
electromagnetic follow-up of gravitational wave events: We investigate the properties of the host galaxies of compact binary mergers
across cosmic time. To this end, we combine population synthesis simulations
together with galaxy catalogues from the hydrodynamical cosmological simulation
EAGLE to derive the properties of the host galaxies of binary neutron star
(BNS), black hole-neutron star (BHNS) and binary black hole (BBH) mergers.
Within this framework, we derive the host galaxy probability, i.e., the
probability that a galaxy hosts a compact binary coalescence as a function of
its stellar mass, star formation rate, $K_s$ magnitude and $B$ magnitude. This
quantity is particularly important for low-latency searches of gravitational
wave (GW) sources as it provides a way to rank galaxies lying inside the
credible region in the sky of a given GW detection, hence reducing the number
of viable host candidates. Furthermore, even if no electromagnetic counterpart
is detected, the proposed ranking criterion can still be used to classify the
galaxies contained in the error box. Our results show that massive galaxies (or
equivalently galaxies with a high luminosity in $K_s$ band) have a higher
probability of hosting BNS, BHNS, and BBH mergers. We provide the probabilities
in a suitable format to be implemented in future low-latency searches. | astro-ph_GA |
The UV, Lyman-alpha, and dark matter halo properties of high redshift
galaxies: We explore the properties of high-redshift Lyman-alpha emitters (LAE), and
their link with the Lyman-Break galaxy population (LBG), using a semi-analytic
model of galaxy formation that takes into account resonant scattering of Lya
photons in gas outflows. We can reasonably reproduce the abundances of LAEs and
LBGs from redshift 3 to 7, as well as most UV LFs of LAEs. The stronger dust
attenuation for (resonant) Lya photons compared to UV continuum photons in
bright LBGs provides a natural interpretation to the increase of the LAE
fraction in LBG samples, X_LAE, towards fainter magnitudes. The redshift
evolution of X_LAE seems however very sensitive to UV magnitudes limits and EW
cuts. In spite of the apparent good match between the statistical properties
predicted by the model and the observations, we find that the tail of the Lya
equivalent width distribution (EW > 100 A) cannot be explained by our model,
and we need to invoke additional mechanisms. We find that LAEs and LBGs span a
very similar dynamical range, but bright LAEs are about 4 times rarer than LBGs
in massive halos. Moreover, massive halos mainly contain weak LAEs in our
model, which might introduce a bias towards low-mass halos in surveys which
select sources with high EW cuts. Overall, our results are consistent with the
idea that LAEs and LBGs make a very similar galaxy population. Their apparent
differences seem mainly due to EW selections, UV detection limits, and a
decreasing Lya-to-UV escape fraction ratio in high SFR galaxies. | astro-ph_GA |
A multiwavelength study of the star forming region IRAS 18544+0112: This work aims at investigating the molecular and infrared components in the
massive young stellar object (MYSO) candidate IRAS 18544+0112. The purpose is
to determine the nature and the origin of this infrared source. To analyze the
molecular gas towards IRAS 18544+0112, we have carried out observations in a
90" x 90" region around l = 34.69, b = -0.65, using the Atacama Submillimeter
Telescope Experiment (ASTE) in the 12CO J=3-2, 13CO J=3-2, HCO+ J=4-3 and CS
J=7-6 lines with an angular resolution of 22". The infrared emission in the
area has been analyzed using 2MASS and Spitzer public data. From the molecular
analysis, we find self-absorbed 12CO J=3-2 profiles, which are typical in star
forming regions, but we do not find any evidence of outflow activity. Moreover,
we do not detect either HCO+ J=4-3 or CS J=7-6 in the region, which are species
normally enhanced in molecular outflows and high density envelopes. The 12CO
J=3-2 emission profile suggests the presence of expanding gas in the region.
The Spitzer images reveal that the infrared source has a conspicuous extended
emission bright at 8 um with an evident shell-like morphology of ~ 1.5 arcmin
in size (~ 1.4 pc at the proposed distance of 3 kpc) that encircles the 24 um
emission. The non-detection of ionized gas related to IRAS 18544+0112, together
with the fact that it is still embedded in a molecular clump suggest that IRAS
18544+0112, has not reached the UCHII region stage yet. Based on near infrared
photometry we search for YSO candidates in the region and propos that 2MASS
18565878+0116233 is the infrared point source associated with IRAS 18544+0112.
Finally, we suggest that the expansion of a larger nearby HII region,
G034.8-0.7, might be related to the formation of IRAS 18544+0112. | astro-ph_GA |
A thorough view of the nuclear region of NGC 253 - Combined Herschel,
SOFIA and APEX dataset: We present a large set of spectral lines detected in the $40"$ central region
of the starburst galaxy NGC 253. Observations were obtained with the three
instruments SPIRE, PACS and HIFI on board the Herschel Space Observatory,
upGREAT on board of the SOFIA airborne observatory, and the ground based APEX
telescope. Combining the spectral and photometry products of SPIRE and PACS we
model the dust continuum Spectral Energy Distribution (SED) and the most
complete $^{12}$CO Line SED reported so far toward the nuclear region of NGC
253. Properties and excitation of the molecular gas were derived from a
three-component non-LTE radiative transfer model, using the SPIRE $^{13}$CO
lines and ground based observations of the lower-$J$ $^{13}$CO and HCN lines,
to constrain the model parameters. Three dust temperatures were identified from
the continuum emission, and three components are needed to fit the full CO
LSED. Only the third CO component (fitting mostly the HCN and PACS $^{12}$CO
lines) is consistent with a shock/mechanical heating scenario. A hot core
chemistry is also argued as a plausible scenario to explain the high-$J$
$^{12}$CO lines detected with PACS. The effect of enhanced cosmic ray
ionization rates, however, cannot be ruled out, and is expected to play a
significant role in the diffuse and dense gas chemistry. This is supported by
the detection of ionic species like OH$^+$ and H$_2$O$^+$, as well as the
enhanced fluxes of the OH lines with respect to those of H$_2$O lines detected
in both PACS and SPIRE spectrum. | astro-ph_GA |
Mid and Far-Infrared Color-Color Relations within Local Galaxies: We present an extensive archival analysis of a sample of local galaxies,
combining multi-wavelength data from GALEX, Spitzer and Herschel to investigate
"blue-side" mid-infrared (MIR) and "red-side" far-infrared (FIR) color-color
correlations within the observed infrared spectral energy distributions (IR
SEDs). Our sample largely consists of the KINGFISH galaxies, with the important
addition of a select few including NGC5236 (M83) and NGC4449. With data from
the far-ultraviolet FUV (${\sim}0.15$ $\mu$m) through 500 $\mu$m convolved to
common angular resolution, we measure photometry of $kpc$-scale star-forming
regions 36$"\times$36$"$ in size. Star formation rates (SFRs), stellar masses
and metallicity distributions are derived throughout our sample. Focusing on
the $f_{70}/f_{500}$ "FIR" and $f_{8}/f_{24}$ "MIR" flux density ratios
(colors), we find that a sub-sample of galaxies demonstrate a strong IR
color-color correlation within their star-forming regions, while others
demonstrate uncorrelated colors. This division is driven by two main effects:
1) the local strength of star formation (SF) and 2) the metal content of the
interstellar medium (ISM). Galaxies uniformly dominated by high surface
densities of SF (e.g. NGC5236) demonstrate strong IR color-color correlations,
while galaxies that exhibit lower levels of SF and mixed environments (e.g.
NGC5457) demonstrate weaker or no correlation--explained by the increasing
effect of varying ISM heating and metal content on the IR colors, specifically
in the MIR. We find large dispersion in the SFR-$L_{8}$ (8 $\mu$m luminosity)
relation that is traced by the metallicity distributions, consistent with
extant studies, highlighting its problematic use as a SFR indicator across
diverse systems/samples. | astro-ph_GA |
The Case Against Dark Matter and Modified Gravity: Flat Rotation Curves
Are a Rigorous Requirement in Rotating Self-Gravitating Newtonian Gaseous
Disks: By solving analytically the various types of Lane-Emden equations with
rotation, we have discovered two new coupled fundamental properties of
rotating, self-gravitating, gaseous disks in equilibrium: Isothermal disks
must, on average, exhibit strict power-law density profiles in radius $x$ on
their equatorial planes of the form $A x^{k-1}$, where $A$ and $k-1$ are the
integration constants, and "flat" rotation curves precisely such as those
observed in spiral galaxy disks. Polytropic disks must, on average, exhibit
strict density profiles of the form $\left[\ln(A x^k)\right]^n$, where $n$ is
the polytropic index, and "flat" rotation curves described by square roots of
upper incomplete gamma functions. By "on average," we mean that, irrespective
of the chosen boundary conditions, the actual profiles must oscillate around
and remain close to the strict mean profiles of the analytic singular
equilibrium solutions. We call such singular solutions the "intrinsic"
solutions of the differential equations because they are demanded by the
second-order equations themselves with no regard to the Cauchy problem. The
results are directly applicable to gaseous galaxy disks that have long been
known to be isothermal and to protoplanetary disks during the extended
isothermal and adiabatic phases of their evolution. In galactic gas dynamics,
they have the potential to resolve the dark matter--modified gravity
controversy in a sweeping manner, as they render both of these hypotheses
unnecessary. In protoplanetary disk research, they provide observers with
powerful new probing tool, as they predict a clear and simple connection
between the radial density profiles and the rotation curves of self-gravitating
disks in their very early (pre-Class 0 and perhaps the youngest Class Young
Stellar Objects) phases of evolution. | astro-ph_GA |
Radio-Loud and Radio-Quiet BAL Quasars: A Detailed Ultraviolet
Comparison: Studies of radio-loud (RL) broad absorption line (BAL) quasars indicate that
popular orientation-based BAL models fail to account for all observations. Are
these results extendable to radio-quiet (RQ) BAL quasars? Comparisons of RL and
RQ BAL quasars show that many of their properties are quite similar. Here we
extend these analyses to the rest-frame ultraviolet (UV) spectral properties,
using a sample of 73 RL and 473 RQ BAL quasars selected from the Sloan Digital
Sky Survey (SDSS). Each RQ quasar is individually matched to a RL quasar in
both redshift (over the range $1.5 < z < 3.5$) and continuum luminosity. We
compare several continuum, emission line, and absorption line properties, as
well as physical properties derived from these measurements. Most properties in
the samples are statistically identical, though we find slight differences in
the velocity structure of the BALs that cause apparent differences in CIV
emission line properties. Differences in the velocities may indicate an
interaction between the radio jets and the absorbing material. We also find
that UV FeII emission is marginally stronger in RL BAL quasars. All of these
differences are subtle, so in general we conclude that RL and RQ BAL QSOs are
not fundamentally different objects, except in their radio properties. They are
therefore likely to be driven by similar physical phenomena, suggesting that
results from samples of RL BAL quasars can be extended to their RQ
counterparts. | astro-ph_GA |
Lyman-alpha spectroscopy of extreme [OIII] emitting galaxies at
$z\simeq2-3$: Implications for Ly$α$ visibility and LyC leakage at $z>6$: Spectroscopic observations of massive $z>7$ galaxies selected to have
extremely large [OIII]+H$\beta$ equivalent width (EW $\sim1500$ \r{A}) have
recently revealed large Ly$\alpha$ detection rates, in contrast to the weak
emission seen in the general population. Why these systems are uniquely visible
in Ly$\alpha$ at redshifts where the IGM is likely significantly neutral is not
clear. With the goal of better understanding these results, we have begun a
campaign with MMT and Magellan to measure Ly$\alpha$ in galaxies with similar
[OIII]+H$\beta$ EWs at $z\simeq2-3$. At these redshifts, the IGM is highly
ionized, allowing us to clearly disentangle how the Ly$\alpha$ properties
depend on the [OIII]+H$\beta$ EW. Here we present Ly$\alpha$ EWs of $49$
galaxies at $z=2.2-3.7$ with intense [OIII]+H$\beta$ line emission (EW
$=300-3000$ \r{A}). Our results demonstrate that strong Ly$\alpha$ emission (EW
$>20$ \r{A}) becomes more common in galaxies with larger [OIII]+H$\beta$ EW,
reflecting a combination of increasingly efficient ionizing photon production
and enhanced transmission of Ly$\alpha$. Among the galaxies with the most
extreme [OIII]+H$\beta$ emission (EW $\sim1500$ \r{A}), we find that strong
Ly$\alpha$ emission is not ubiquitous, with only $50$ per cent of our
population showing Ly$\alpha$ EW $>20$ \r{A}. Our data suggest that the range
of Ly$\alpha$ strengths is related to the observed ellipticity, with those
systems that appear edge-on or elongated having weaker Ly$\alpha$ emission. We
use these results to interpret the anomalous Ly$\alpha$ properties seen in
$z>7$ galaxies with extreme [OIII]+H$\beta$ emission and discuss implications
for the escape of ionizing radiation from these extreme line emitting galaxies. | astro-ph_GA |
The formation of cosmic fullerenes from arophatic clusters: Fullerenes have recently been identified in space and they may play a
significant role in the gas and dust budget of various astrophysical objects
including planetary nebulae (PNe), reflection nebulae (RNe) and H II regions.
The tenuous nature of the gas in these environments precludes the formation of
fullerene materials following known vaporization or combustion synthesis routes
even on astronomical timescales. We have studied the processing of hydrogenated
amorphous carbon (a-C:H or HAC) nano-particles and their specific derivative
structures, which we name "arophatics", in the circumstellar environments of
young, carbon-rich PNe. We find that UV-irradiation of such particles can
result in the formation of fullerenes, consistent with the known physical
conditions in PNe and with available timescales. | astro-ph_GA |
Stream Members Only: Data-Driven Characterization of Stellar Streams
with Mixture Density Networks: Stellar streams are sensitive probes of the Milky Way's gravitational
potential. The mean track of a stream constrains global properties of the
potential, while its fine-grained surface density constrains galactic
substructure. A precise characterization of streams from potentially noisy data
marks a crucial step in inferring galactic structure, including the dark
matter, across orders of magnitude in mass scales. Here we present a new method
for constructing a smooth probability density model of stellar streams using
all of the available astrometric and photometric data. To characterize a
stream's morphology and kinematics, we utilize mixture density networks to
represent its on-sky track, width, stellar number density, and kinematic
distribution. We model the photometry for each stream as a single-stellar
population, with a distance track that is simultaneously estimated from the
stream's inferred distance modulus (using photometry) and parallax distribution
(using astrometry). We use normalizing flows to characterize the distribution
of background stars. We apply the method to the stream GD-1, and the tidal
tails of Palomar 5. For both streams we obtain a catalog of stellar membership
probabilities that are made publicly available. Importantly, our model is
capable of handling data with incomplete phase-space observations, making our
method applicable to the growing census of Milky Way stellar streams. When
applied to a population of streams, the resulting membership probabilities from
our model form the required input to infer the Milky Way's dark matter
distribution from the scale of the stellar halo down to subhalos. | astro-ph_GA |
Infall of nearby galaxies into the Virgo cluster as traced with HST: We measured the Tip of the Red Giant Branch distances to nine galaxies in the
direction to the Virgo cluster using the Advanced Camera for Surveys on the
Hubble Space Telescope. These distances put seven galaxies: GR 34, UGC 7512,
NGC 4517, IC 3583, NGC 4600, VCC 2037 and KDG 215 in front of the Virgo, and
two galaxies: IC 3023, KDG 177 likely inside the cluster. Distances and radial
velocities of the galaxies situated between us and the Virgo core clearly
exhibit the infall phenomenon toward the cluster. In the case of spherically
symmetric radial infall we estimate the radius of the "zero-velocity surface"
to be (7.2+-0.7) Mpc that yields the total mass of the Virgo cluster to be
(8.0+-2.3) X 10^{14} M_sun in good agreement with its virial mass estimates. We
conclude that the Virgo outskirts does not contain significant amounts of dark
matter beyond its virial radius. | astro-ph_GA |
FSR 1716: A new Milky Way Globular Cluster confirmed using VVV RR Lyrae
stars: We use deep multi-epoch near-IR images of the VISTA Variables in the V\'ia
L\'actea (VVV) Survey to search for RR Lyrae stars towards the Southern
Galactic plane. Here we report the discovery of a group of RR Lyrae stars close
together in VVV tile d025. Inspection of the VVV images and PSF photometry
reveals that most of these stars are likely to belong to a globular cluster,
that matches the position of the previously known star cluster FSR\,1716. The
stellar density map of the field yields a $>100$ sigma detection for this
candidate globular cluster, that is centered at equatorial coordinates
$RA_{J2000}=$16:10:30.0, $DEC_{J2000}=-$53:44:56; and galactic coordinates
$l=$329.77812, $b=-$1.59227. The color-magnitude diagram of this object reveals
a well populated red giant branch, with a prominent red clump at $K_s=13.35 \pm
0.05$, and $J-K_s=1.30 \pm 0.05$. We present the cluster RR Lyrae positions,
magnitudes, colors, periods and amplitudes. The presence of RR Lyrae indicates
an old globular cluster, with age $>10$ Gyr. We classify this object as an
Oosterhoff type I globular cluster, based on the mean period of its RR Lyrae
type ab, $<P>=0.540$ days, and argue that this is a relatively metal-poor
cluster with $[Fe/H] = -1.5 \pm 0.4$ dex. The mean extinction and reddening for
this cluster are $A_{K_s}=0.38 \pm 0.02$, and $E(J-K_s)=0.72 \pm 0.02$ mag,
respectively, as measured from the RR Lyrae colors and the near-IR
color-magnitude diagram. We also measure the cluster distance using the RR
Lyrae type ab stars. The cluster mean distance modulus is $(m-M)_0 = 14.38 \pm
0.03$ mag, implying a distance $D = 7.5 \pm 0.2$ kpc, and a Galactocentric
distance $R_G=4.3$ kpc. | astro-ph_GA |
Physical conditions in high$-$z optically thin C III absorbers: Origin
of cloud sizes and associated correlations: We present detailed photoionization models of well aligned optically thin C
III absorption components at $2.1 < z < 3.4$. Using our models we estimate
density ($n_{\rm \tiny H}$), metallicity ($[C/H]$), total hydrogen column
density and line-of-sight thickness ($L$) in each C III components. We estimate
the systematic errors in these quantities contributed by the allowed range of
the quasar spectral index used in the ultraviolet background radiation
calculations. Our inferred $n_{\rm \tiny H}$ and overdensity ($\Delta$) are
much higher than the measurements available in the literature and favor the
absorption originating from gas associated with circumgalactic medium and
probably not in hydrostatic equilibrium. We also notice $n_{\rm \tiny H}$, $L$
and $[C/H]$ associated with C III components show statistically significant
redshift evolution. To some extent, these redshift evolutions are driven by the
appearance of compact, high $n_{\rm \tiny H}$ and high $[C/H]$ components only
in the low$-z$ end. We find more than 5$\sigma$ level correlation between
$[C/H]$ and $L$, $L$ and neutral hydrogen column density (N (HI)), N (HI) and
$[C/H]$. We show $L$ versus $[C/H]$ correlation can be well reproduced if $L$
is governed by the product of gas cooling time and sound speed as expected in
the case of cloud fragmentation under thermal instabilities. This allows us to
explain other observed correlations by simple photoionization considerations.
Studying the optically thin C III absorbers over a large $z$ range and probably
correlating their $z$ evolution with global star formation rate density
evolution can shed light into the physics of cold clump formation and their
evolution in the circumgalactic medium. | astro-ph_GA |
Nature of shocks revealed by SOFIA OI observations in the Cepheus E
protostellar outflow: Protostellar jets and outflows are key features of the star-formation
process, and primary processes of the feedback of young stars on the
interstellar medium. Understanding the underlying shocks is necessary to
explain how jets and outflows are launched, and to quantify their chemical and
energetic impacts on the surrounding medium. We performed a high-spectral
resolution study of the [OI]$_{\rm 63 \mu m}$ emission in the outflow of the
intermediate-mass Class 0 protostar Cep E-mm. We present observations of the OI
$^3$P$_1 \rightarrow$ $^3$P$_2$, OH between $^2\Pi_{1/2}$ $J = 3/2$ and $J =
1/2$ at 1837.8 GHz, and CO (16-15) lines with SOFIA-GREAT at three positions in
the Cep E outflow: mm (the driving protostar), BI (in the southern lobe), and
BII (the terminal position in the southern lobe). The CO line is detected at
all three positions. The OI line is detected in BI and BII, whereas the OH line
is not detected. In BII, we identify three kinematical components in OI and CO,
already detected in CO: the jet, the HH377 terminal bow-shock, and the outflow
cavity. The OI column density is higher in the outflow cavity than in the jet,
which itself is higher than in the terminal shock. The terminal shock is where
the abundance ratio of OI to CO is the lowest (about 0.2), whereas the jet
component is atomic (ratio $\sim$2.7). In the jet, we compare the OI
observations with shock models that successfully fit the integrated intensity
of 10 CO lines: these models do not fit the OI data. The high intensity of OI
emission points towards the propagation of additional dissociative or
alternative FUV-irradiated shocks, where the illumination comes from the shock
itself. From the sample of low-to-high mass protostellar outflows where similar
observations have been performed, the effects of illumination seem to increase
with the mass of the protostar. | astro-ph_GA |
The SEDIGISM survey: a search for molecular outflows: Context. The formation processes of massive stars are still unclear but a
picture is emerging involving accretion disks and molecular outflows in what
appears to be a scaled-up version of low-mass star formation. A census of
outflow activity towards massive star-forming clumps in various evolutionary
stages has the potential to shed light on massive star formation (MSF).
Aims. We conducted an outflow survey towards ATLASGAL clumps using SEDIGISM
data and aimed to obtain a large sample of clumps exhibiting outflows in
different evolutionary stages.
Methods. We identify the high-velocity wings of the 13CO lines toward
ATLASGAL clumps by (1) extracting the simultaneously observed 13CO and C18O
spectra from SEDIGISM, and (2) subtracting Gaussian fits to the scaled C18O
from the 13CO, line after considering opacity broadening.
Results. We have detected high-velocity gas towards 1192 clumps out of a
total sample of 2052, giving an overall detection rate of 58%. Outflow activity
has been detected in the earliest quiescent clumps (i.e., 70$\mu$m weak), to
the most evolved HII region stages i.e., 8$\mu$m bright with MSF tracers. The
detection rate increases as a function of evolution (quiescent=51%,
protostellar=47%, YSO=57%, UCHII regions=76%).
Conclusion. Our sample is the largest outflow sample identified so far. The
high-detection rate from this large sample is consistent with previous results
and supports that outflows are a ubiquitous feature of MSF. The lower detection
rate in early evolutionary stages may be due to that outflows in the early
stages are weak and difficult to detect. We obtain a statistically significant
sample of outflow clumps for every evolutionary stage, especially for outflow
clumps in the 70$\mu$m dark stage. This suggests that the absence of 70$\mu$m
emission is not a robust indicator of starless/pre-stellar cores. | astro-ph_GA |
Can we believe the strong-line abundances in giant HII regions and
emission-line galaxies?: This review is not a compendium of strong-line methods to derive abundances
in giant HII regions. It is mostly intended for readers who wish to use such
methods but do not have a solid background on the physics of HII regions. It is
also meant to encourage those using abundance results published in the
literature to think more thoroughly about the validity of these results. | astro-ph_GA |
Spectroscopy of the three distant Andromedan satellites Cassiopeia III,
Lacerta I, and Perseus I: We present Keck II/DEIMOS spectroscopy of the three distant dwarf galaxies of
M31 Lacerta I, Cassiopeia III, and Perseus I, recently discovered within the
Pan-STARRS1 3\pi imaging survey. The systemic velocities of the three systems
(v_{r,helio} = -198.4 +/- 1.1 km/s, -371.6 +/- 0.7 km/s, and -326 +/- 3 km/s,
respectively) confirm that they are satellites of M31. In the case of Lacerta I
and Cassiopeia III, the high quality of the data obtained for 126 and 212
member stars, respectively, yields reliable constraints on their global
velocity dispersions (\sigma_{vr} = 10.3 +/- 0.9 km/s and 8.4 +/- 0.6 km/s,
respectively), leading to dynamical-mass estimates for both of ~4x10^7 Msun
within their half-light radius. These translate to V-band mass-to-light ratios
of 15^{+12}_{-9} and 8^{+9}_{-5} in solar units. We also use our spectroscopic
data to determine the average metallicity of the 3 dwarf galaxies ([Fe/H] =
-2.0 +/- 0.1, -1.7 +/- 0.1, and -2.0 +/- 0.2, respectively). All these
properties are typical of dwarf galaxy satellites of Andromeda with their
luminosity and size. | astro-ph_GA |
Models of turbulent dissipation regions in the diffuse interstellar
medium: Supersonic turbulence is a large reservoir of suprathermal energy in the
interstellar medium. Its dissipation, because it is intermittent in space and
time, can deeply modify the chemistry of the gas. We further explore a hybrid
method to compute the chemical and thermal evolution of a magnetized
dissipative structure, under the energetic constraints provided by the observed
properties of turbulence in the cold neutral medium. For the first time, we
model a random line of sight by taking into account the relative duration of
the bursts with respect to the thermal and chemical relaxation timescales of
the gas. The key parameter is the turbulent rate of strain "a" due to the
ambient turbulence. With the gas density, it controls the size of the
dissipative structures, therefore the strength of the burst. For a large range
of rates of strain and densities, the models of turbulent dissipation regions
(TDR) reproduce the CH+ column densities observed in the diffuse medium and
their correlation with highly excited H2. They do so without producing an
excess of CH. As a natural consequence, they reproduce the abundance ratios of
HCO+/OH and HCO+/H2O, and their dynamic range of about one order of magnitude
observed in diffuse gas. Large C2H and CO abundances, also related to those of
HCO+, are another outcome of the TDR models that compare well with observed
values. The abundances and column densities computed for CN, HCN and HNC are
one order of magnitude above PDR model predictions, although still
significantly smaller than observed values. | astro-ph_GA |
Does the galaxy NGC1052-DF2 falsify Milgromian dynamics?: A great challenge in present-day physics is to understand whether the
observed internal dynamics of galaxies is due to dark matter matter or due to a
modification of the law of gravity. Recently, van Dokkum et al. reported that
the ultra-diffuse dwarf galaxy NGC1052-DF2 lacks dark matter, and they claimed
that this would -- paradoxically -- be problematic for modified gravity
theories like Milgromian dynamics (MOND). However, NGC1052-DF2 is not isolated,
so that a valid prediction of its internal dynamics in MOND cannot be made
without properly accounting for the external gravitational fields from
neighbouring galaxies. Including this external field effect following Haghi et
al. shows that NGC1052-DF2 is consistent with MOND. | astro-ph_GA |
A 500 pc filamentary gas wisp in the disk of the Milky Way: Star formation occurs in molecular gas. In previous studies, the structure of
the molecular gas has been studied in terms of molecular clouds, but has been
overlooked beyond the cloud scale. We present an observational study of the
molecular gas at 49.5 degree <l<52.5 degree and -5.0 km/s <v_lsr <17.4 km/s.
The molecular gas is found in the form of a huge (>= 500 pc) filamentary gas
wisp. This has a large physical extent and a velocity dispersion of ~5 km/s.
The eastern part of the filamentary gas wisp is located ~130 pc above the
Galactic disk (which corresponds to 1.5-4 e-folding scale-heights), and the
total mass of the gas wisp is >= 1 X 10^5 M_sun. It is composed of two
molecular clouds and an expanding bubble. The velocity structure of the gas
wisp can be explained as a smooth quiescent component disturbed by the
expansion of a bubble. That the length of the gas wisp exceeds by much the
thickness of the molecular disk of the Milky Way is consistent with the
cloud-formation scenario in which the gas is cold prior to the formation of
molecular clouds. Star formation in the filamentary gas wisp occurs at the edge
of a bubble (G52L nebula), which is consistent with some models of triggered
star formation. | astro-ph_GA |
The potential of tracing the star formation history with HI 21-cm in
intervening absorption systems: Unlike the neutral gas density, which remains largely constant over redshifts
of 0 < z < 5, the star formation density exhibits a strong redshift dependence,
increasing from the present day before peaking at a redshift of z ~ 2.5. Thus,
there is a stark contrast between the star formation rate and the abundance of
raw material available to fuel it. However, using the ratio of the strength of
the HI 21-cm absorption to the total neutral gas column density to quantify the
spin temperature of the gas, it has recently been shown that its reciprocal may
trace the star formation density. This would be expected on the grounds that
the cloud of gas must be sufficiently cool to collapse under its own gravity.
This, however, relies on very limited data and so here we explore the potential
of applying the above method to absorbers for which individual column densities
are not available (primarily MgII absorption systems). By using the mean value
as a proxy to the column density of the gas at a given redshift, we do, again,
find that 1/T (degenerate with the absorber-emitter size ratio) traces the SF
density. If confirmed by higher redshift data, this could offer a powerful tool
for future surveys for cool gas throughout the Universe with the Square
Kilometre Array. | astro-ph_GA |
On planet formation around supermassive black holes and the grain
disruption barriers by radiative torques: It has recently been suggested that planets can form by dust coagulation in
the torus of active galactic nuclei (AGN) with low luminosity of $L_{\rm
bol}\lesssim 10^{42} erg s^{-1}$, constituting a new class of exoplanets
orbiting the supermassive black hole called \textit{blanets}. However, large
dust grains in the AGN torus may be rotationally disrupted by the Radiative
Torque Disruption (RATD) mechanism due to AGN radiation feedback, which would
prevent the blanet formation. To test this scenario, we adopt the simple smooth
and clumpy dust/gas distribution inside the torus region to study the effect of
RATD on the evolution of composite dust grains in the midplane of the torus. We
found that grain growth and then blanet formation are possible in the smooth
torus model. However, in the clumpy torus model, grain growth will be strongly
constrained by RATD, assuming the gas density distribution as adopted in Wada
et al. We also found that icy grain mantles inside clumps are quickly detached
from the grain core by rotational desorption, reducing the sticking coefficient
between icy grains and coagulation efficiency. The grain rotational disruption
and ice desorption occur on timescales much shorter than the growth time up to
a factor of $\sim 10^{4}$, which are the new barriers that grain growth must
overcome to form blanets. Further studies with more realistic AGN models are
required to better constrain the effect of RATD on grain growth and blanet
formation hypothesis around low luminosity AGN. | astro-ph_GA |
Resolved Near-infrared Stellar Photometry from the Magellan Telescope
for 13 Nearby Galaxies: JAGB Method Distances: We present near-infrared JHK photometry for the resolved stellar populations
in 13 nearby galaxies: NGC 6822, IC 1613, NGC 3109, Sextans B, Sextans A, NGC
300, NGC 55, NGC 7793, NGC 247, NGC 5253, Cen A, NGC 1313, and M83, acquired
from the 6.5m Baade-Magellan telescope. We measure distances to each galaxy
using the J-region asymptotic giant branch (JAGB) method, a new standard candle
that leverages the constant luminosities of color-selected, carbon-rich AGB
stars. While only single-epoch, random-phase photometry is necessary to derive
JAGB distances, our photometry is time-averaged over multiple epochs, thereby
decreasing the contribution of the JAGB stars' intrinsic variability to the
measured dispersions in their observed luminosity functions. To cross-validate
these distances, we also measure near-infrared tip of the red giant branch
(TRGB) distances to these galaxies. The residuals obtained from subtracting the
distance moduli from the two methods yield an RMS scatter of $\sigma_{JAGB -
TRGB}= \pm 0.07$ mag. Therefore, all systematics in either the JAGB method and
TRGB method (e.g., crowding, differential reddening, star formation histories)
must be contained within these $\pm0.07$ mag bounds for this sample of galaxies
because the JAGB and TRGB distance indicators are drawn from entirely distinct
stellar populations, and are thus affected by these systematics independently.
Finally, the composite JAGB star luminosity function formed from this diverse
sample of galaxies is well-described by a Gaussian function with a modal value
of $M_J = -6.20 \pm 0.003$ mag (stat), indicating the underlying JAGB star
luminosity function of a well-sampled full star formation history is highly
symmetric and Gaussian, based on over 6,700 JAGB stars in the composite sample. | astro-ph_GA |
The MUSE-Wide survey: A measurement of the Ly$α$ emitting fraction
among $z>3$ galaxies: We present a measurement of the fraction of Lyman $\alpha$ (Ly$\alpha$)
emitters ($X_{\rm{Ly} \alpha}$) amongst HST continuum-selected galaxies at
$3<z<6$ with the Multi-Unit Spectroscopic Explorer (MUSE) on the VLT. Making
use of the first 24 MUSE-Wide pointings in GOODS-South, each having an
integration time of 1 hour, we detect 100 Ly$\alpha$ emitters and find
$X_{\rm{Ly} \alpha}\gtrsim0.5$ for most of the redshift range covered, with 29
per cent of the Ly$\alpha$ sample exhibiting rest equivalent widths (rest-EWs)
$\leq$ 15\AA. Adopting a range of rest-EW cuts (0 - 75\AA), we find no evidence
of a dependence of $X_{\rm{Ly} \alpha}$ on either redshift or UV luminosity. | astro-ph_GA |
Heating Cold Clumps by Jet-inflated Bubbles in Cooling Flow Clusters: We simulate the evolution of dense-cool clumps embedded in the intra-cluster
medium (ICM) of cooling flow clusters of galaxies in response to multiple
jet-activity cycles, and find that the main heating process of the clumps is
mixing with the hot shocked jets' gas, the bubbles, while shocks have a limited
role. We use the PLUTO hydrodynamical code in two dimensions with imposed
axisymmetry, to follow the thermal evolution of the clumps. We find that the
inflation process of hot bubbles, that appear as X-ray deficient cavities in
observations, is accompanied by complicated induced vortices inside and around
the bubbles. The vorticity induces efficient mixing of the hot bubbles' gas
with the ICM and cool clumps, resulting in a substantial increase of the
temperature and entropy of the clumps. For the parameters used by us heating by
shocks barely competes with radiative cooling, even after 25 consecutive shocks
excited during 0.5 Gyr of simulation. Some clumps are shaped to filamentary
structure that can turn to observed optical filaments. We find that not all
clumps are heated. Those that cool to very low temperatures will fall in and
feed the central supermassive black hole (SMBH), hence closing the feedback
cycle in what is termed the cold feedback mechanism. | astro-ph_GA |
SDSS-IV MaNGA: The Nature of an Off-galaxy H$α$ Blob -- A
Multi-wavelength View of Offset Cooling in a Merging Galaxy Group: Galaxies in dense environments, such as groups and clusters, experience
various processes by which galaxies gain and lose gas. Using data from the
SDSS-IV MaNGA survey, we previously reported the discovery of a giant (6 -- 8
kpc in diameter) H$\alpha$ blob, Totoro, about 8 kpc away from a pair of
galaxies (Satsuki and Mei) residing in a galaxy group which is experiencing a
group-group merger. Here, we combine interferometric $^{12}$CO(1--0) molecular
gas data, new wide-field H$\alpha$, $u$-band data, and published X-ray data to
determine the origin of the blob. Several scenarios are discussed to account
for its multi-wavelength properties, including (1) H$\alpha$ gas being stripped
from galaxy Satsuki by ram-pressure; (2) a separated low-surface-brightness
galaxy; (3) gas being ejected or ionized by an active galactic nucleus (AGN);
and (4) a cooling intra-group medium (IGM). Scenarios (1) and (2) are less
favored by the present data. Scenario (3) is also less likely as there is no
evidence for an active ongoing AGN in the host galaxy. We find that the CO
(cold) and H$\alpha$ (warm) gas coexist with X-ray (hot) structures; moreover,
the derived cooling time is within the regime where molecular and H$\alpha$ gas
are expected. The coexistence of gas with different temperatures also agrees
with that of cooling gas in other systems. Our multi-wavelength results
strongly suggest that the CO and H$\alpha$ gas are the product of cooling from
the IGM at its current location, i.e., cooling has occurred, and may be
ongoing, well outside the host-galaxy core. | astro-ph_GA |
Swirls of FIRE: Spatially Resolved Gas Velocity Dispersions and Star
Formation Rates in FIRE-2 Disk Environments: We study the spatially resolved (sub-kpc) gas velocity dispersion
($\sigma$)--star formation rate (SFR) relation in the FIRE-2 (Feedback in
Realistic Environments) cosmological simulations. We specifically focus on
Milky Way mass disk galaxies at late times. In agreement with observations, we
find a relatively flat relationship, with $\sigma \approx 15-30$ km/s in
neutral gas across 3 dex in SFRs. We show that higher dense gas fractions
(ratios of dense gas to neutral gas) and SFRs are correlated at constant
$\sigma$. Similarly, lower gas fractions (ratios of gas to stellar mass) are
correlated with higher $\sigma$ at constant SFR. The limits of the
$\sigma$-$\Sigma_{\rm SFR}$ relation correspond to the onset of strong
outflows. We see evidence of "on-off" cycles of star formation in the
simulations, corresponding to feedback injection timescales of 10-100 Myr,
where SFRs oscillate about equilibrium SFR predictions. Finally, SFRs and
velocity dispersions in the simulations agree well with feedback-regulated and
marginally stable gas disk (Toomre's $Q =1$) model predictions, and the data
effectively rule out models assuming that gas turns into stars at (low)
constant efficiency (i.e., ${\rm 1\%}$ per free-fall time). And although the
simulation data do not entirely exclude gas accretion/gravitationally powered
turbulence as a driver of $\sigma$, it appears to be strongly subdominant to
stellar feedback in the simulated galaxy disks. | astro-ph_GA |
The Environment of z >1 3CR Radio Galaxies and QSOs: From Proto-Clusters
to Clusters of Galaxies?: We study the cluster environment for a sample of 21 radio loud AGN from the
3CR catalog at z>1, 12 radio galaxies and 9 quasars with HST images in the
optical and IR. We use two different approaches to determine cluster
candidates. We identify the early type galaxies (ETGs) in every field by
modeling each of the sources within a 40" radius of the targets with a Sersic
profile. Using a simple passive evolution model, we derive the expected
location of the ETGs on the red sequence (RS) in the color-magnitude diagram
for each of the fields of our sources. For seven targets, the model coincides
with the position of the ETGs. A second approach involves a search for over
densities. We compare the object densities of the sample as a whole and
individually against control fields taken from the GOODS-S region of 3D-HST
survey. With this method we determine the fields of 10 targets to be cluster
candidates. Four cluster candidates are found by both methods. The two methods
disagree in some cases, depending on the specific properties of each field. For
the most distant radio galaxy in the 3CR catalog (3C257 at z = 2.47), we
identify a population of bluer ETGs that lie on the expected location of the RS
model for that redshift. This appears to be the general behavior of ETGs in our
fields and it is possibly a signature of the evolution of such galaxies. Our
results are consistent with half of the z > 1 radio galaxies being located in
dense, rapidly evolving environments. | astro-ph_GA |
MHD Simulation of The Inner Galaxy with Radiative Cooling and Heating: We investigate the role of magnetic field on the gas dynamics in the Galactic
bulge region by three dimensional simulations with radiative cooling and
heating. While high-temperature corona with $T>10^6\ {\rm K}$ is formed in the
halo regions, the temperature near the Galactic plane is $\lesssim 10^4\ {\rm
K}$ following the thermal equilibrium curve determined by the radiative cooling
and heating. Although the thermal energy of the interstellar gas is lost by
radiative cooling, the saturation level of the magnetic field strength does not
significantly depend on the radiative cooling and heating. The magnetic field
strength is amplified to $10\ {\rm \mu G}$ on average, and reaches several
hundred ${\rm \mu G}$ locally. We find the formation of magnetically dominated
regions at mid-latitudes in the case with the radiative cooling and heating,
which is not seen in the case without radiative effect. The vertical thickness
of the mid-latitude regions is $50-150\ {\rm pc}$ at the radial location of
$0.4-0.8 \ {\rm kpc}$ from the Galactic center, which is comparable to the
observed vertical distribution of neutral atomic gas. When we take the average
of different components of energy density integrated over the Galactic bulge
region, the magnetic energy is comparable to the thermal energy. We conclude
that the magnetic field plays a substantial role in controlling the dynamical
and thermal properties of the Galactic bulge region. | astro-ph_GA |
High Resolution Near-Infrared Survey of the Pipe Nebula I: A Deep
Infrared Extinction Map of Barnard 59: We present our analysis of a fully sampled, high resolution dust extinction
map of the Barnard 59 complex in the Pipe Nebula. The map was constructed with
the infrared color excess technique applied to a photometric catalog that
combines data from both ground and space based observations. The map resolves
for the first time the high density center of the main core in the complex,
that is associated with the formation of a small cluster of stars. We found
that the central core in Barnard 59 shows an unexpected lack of significant
substructure consisting of only two significant fragments. Overall, the
material appears to be consistent with being a single, large core with a
density profile that can be well fit by a King model. A series of NH$_3$
pointed observations towards the high column density center of the core appear
to show that the core is still thermally dominated, with sub-sonic non-thermal
motions. The stars in the cluster could be providing feedback to support the
core against collapse, but the relatively narrow radio lines suggest that an
additional source of support, for example a magnetic field, may be required to
stabilize the core. Outside the central core our observations reveal the
structure of peripheral cores and resolve an extended filament into a handful
of significant substructures whose spacing and masses appear to be consistent
with Jeans fragmentation. | astro-ph_GA |
The origin of high velocity stars from Gaia and LAMOST: Based on the second Gaia data (Gaia DR2) and spectroscopy from the LAMOST
Data Release 5, we defined the high-velocity (HiVel) stars sample as those
stars with $v_{\mathrm{gc}} > 0.85 v_{\mathrm{esc}}$, and derived the final
sample of 24 HiVel stars with stellar astrometric parameters and radial
velocities. Most of the HiVel stars are metal-poor and $\alpha$-enhanced. In
order to further explore the origin of these HiVel stars, we traced the
backwards orbits of each HiVel star in the Galactic potential to derive
probability parameters which are used to classify these HiVel stars. Of these,
5 stars are from the tidal debris of disrupted dwarf galaxy and 19 stars are
runaway-star candidates which originate from the stellar disk. | astro-ph_GA |
Time-delay measurement of MgII broad line response for the
highly-accreting quasar HE 0413-4031: Implications for the MgII-based
radius-luminosity relation: We present the monitoring of the AGN continuum and MgII broad line emission
for the quasar HE 0413-4031 ($z=1.38$) based on the six-year monitoring by the
South African Large Telescope (SALT). We managed to estimate a time-delay of
$302.6^{+28.7}_{-33.1}$ days in the rest frame of the source using seven
different methods: interpolated cross-correlation function (ICCF), discrete
correlation function (DCF), $z$-transformed DCF, JAVELIN, two estimators of
data regularity (Von Neumann, Bartels), and $\chi^2$ method. This time-delay is
below the value expected from the standard radius-luminosity relation. However,
based on the monochromatic luminosity of the source and the SED modelling, we
interpret this departure as the shortening of the time-delay due to the higher
accretion rate of the source, with the inferred Eddington ratio of $\sim 0.4$.
The MgII line luminosity of HE 0413-4031 responds to the continuum variability
as $L_{\rm line}\propto L_{\rm cont}^{0.43\pm 0.10}$, which is consistent with
the light-travel distance of the location of MgII emission at $R_{\rm out} \sim
10^{18}\,{\rm cm}$. Using the data of 10 other quasars, we confirm the
radius-luminosity relation for broad MgII line, which was previously determined
for broad H$\beta$ line for lower-redshift sources. In addition, we detect a
general departure of higher-accreting quasars from this relation in analogy to
H$\beta$ sample. After the accretion-rate correction of the light-travel
distance, the MgII-based radius-luminosity relation has a small scatter of only
$0.10$ dex. | astro-ph_GA |
Driven Multifluid MHD Molecular Cloud Turbulence: It is believed that turbulence may have a significant impact on star
formation and the dynamics and evolution of the molecular clouds in which this
occurs. It is also known that non-ideal magnetohydrodynamic effects influence
the nature of this turbulence. We present the results of a numerical study of
4-fluid MHD turbulence in which the dynamics of electrons, ions, charged dust
grains and neutrals and their interactions are followed. The parameters
describing the fluid being simulated are based directly on observations of
molecular clouds. We find that the velocity and magnetic field power spectra
are strongly influenced by multifluid effects on length-scales at least as
large as 0.05 pc. The PDFs of the various species in the system are all found
to be close to log-normal, with charged species having a slightly less
platykurtic (flattened) distribution than the neutrals. We find that the
introduction of multifluid effects does not significantly alter the structure
functions of the centroid velocity increment. | astro-ph_GA |
Plasma dark matter direct detection: Dark matter in spiral galaxies like the Milky Way may take the form of a dark
plasma. Hidden sector dark matter charged under an unbroken $U(1)'$ gauge
interaction provides a simple and well defined particle physics model realising
this possibility. The assumed $U(1)'$ neutrality of the Universe then implies
(at least) two oppositely charged dark matter components with self-interactions
mediated via a massless "dark photon" (the $U(1)'$ gauge boson). In addition to
nuclear recoils such dark matter can give rise to keV electron recoils in
direct detection experiments. In this context, the detailed physical properties
of the dark matter plasma interacting with the Earth is required. This is a
complex system, which is here modelled as a fluid governed by the
magnetohydrodynamic equations. These equations are numerically solved for some
illustrative examples, and implications for direct detection experiments
discussed. In particular, the analysis presented here leaves open the
intriguing possibility that the DAMA annual modulation signal is due primarily
to electron recoils (or even a combination of electron recoils and nuclear
recoils). The importance of diurnal modulation (in addition to annual
modulation) as a means of probing this kind of dark matter is also emphasised. | astro-ph_GA |
A systematic DECam search for RR Lyrae in the outer halo of the Milky
Way: The discovery of very distant stars in the halo of the Milky Way provides
valuable tracers on the Milky Way mass and its formation. Beyond 100 kpc from
the Galactic center, most of the stars are likely to be in faint dwarf galaxies
or tidal debris from recently accreted dwarfs, making the outer reaches of the
Galaxy important for understanding the Milky Way's accretion history. However,
distant stars in the halo are scarce. In that context, RR Lyrae are ideal
probes of the distant halo as they are intrinsically bright and thus can be
seen at large distances, follow well-known period-luminosity relations that
enable precise distance measurements, and are easily identifiable in
time-series data. Therefore, a detailed study of RR Lyrae will help us
understand the accreted outskirts of the Milky Way. In this contribution, we
present the current state of our systematic search for distant RR Lyrae stars
in the halo using the DECam imager at the 4m telescope on Cerro Tololo (Chile).
The total surveyed area consists of more than 110 DECam fields (~ 350 sq. deg)
and includes two recent independent campaigns carried out in 2017 and 2018 with
which we have detected > 650 candidate RR Lyrae stars. Here we describe the
methodology followed to analyze the two latest campaigns. Our catalog contains
a considerable number of candidate RR Lyrae beyond 100 kpc, and reaches out up
to ~ 250 kpc. The number of distant RR Lyrae found is consistent with recent
studies of the outer halo. These stars provide a set of important probes of the
mass of the Milky Way, the nature of the halo, and the accretion history of the
Galactic outskirts. | astro-ph_GA |
From the Outside Looking in: What can Milky Way Analogues Tell us About
the Star Formation Rate of Our Own Galaxy?: The Milky Way has been described as an anaemic spiral, but is its star
formation rate (SFR) unusually low when compared to its peers? To answer this
question, we define a sample of Milky Way Analogues (MWAs) based on stringent
cuts on the best literature estimates of non-transient structural features for
the Milky Way. This selection yields only 176 galaxies from the whole of the
SDSS DR7 spectroscopic sample which have morphological classifications in GZ2,
from which we infer SFRs from two separate indicators. The mean SFRs found are
$\log(\rm{SFR}_{SED}/\rm{M}_{\odot}~\rm{yr}^{-1})=0.53$ with a standard
deviation of 0.23 dex from SED fits, and
$\log(\rm{SFR}_{W4}/\rm{M}_{\odot}~\rm{yr}^{-1})=0.68$ with a standard
deviation of 0.41 dex from a mid-infrared calibration. The most recent estimate
for the Milky Way's star formation rate of
$\log(\rm{SFR}_{MW}/\rm{M}_{\odot}~\rm{yr}^{-1})=0.22$ fits well within
2$\sigma$ of these values, where $\sigma$ is the standard deviation of each of
the SFR indicator distributions. We infer that the Milky Way, while being a
galaxy with a somewhat low SFR, is not unusual when compared to similar
galaxies. | astro-ph_GA |
An Intensity Mapping Detection of Aggregate CO Line Emission at 3 mm: We present a detection of molecular gas emission at $z\sim1-5$ using the
technique of line intensity mapping. We make use of a pair of 3 mm
interferometric data sets, the first from the ALMA Spectroscopic Survey in the
Hubble Ultra Deep Field (ASPECS), and the second from a series of Atacama
Compact Array (ACA) observations conducted between 2016 and 2018, targeting the
COSMOS field. At 100 GHz, we measure non-zero power at 97.8% and 99.9%
confidence in the ACA and ALMA data sets, respectively. In the joint result, we
reject the zero-power hypothesis at 99.99% confidence, finding
$\tilde{I}^{2}_{s}(\nu)=770\pm210\ \mu\textrm{K}^2\ \textrm{Hz}\ \textrm{sr}$.
After accounting for sample variance effects, the estimated spectral shot power
is $\tilde{I}^{2}_{s}(\nu)=1010_{-390}^{+550}\ \mu\textrm{K}^2\ \textrm{Hz}\
\textrm{sr}$. We derive a model for the various line species our measurement is
expected to be sensitive to, and estimate the shot power to be
$120_{-40}^{+80}\ \mu\textrm{K}^2\ h^{-3}\,\textrm{Mpc}^{3}$,
$200^{+120}_{-70}\ \mu\textrm{K}^2\ h^{-3}\,\textrm{Mpc}^{3}$, and
$90^{+70}_{-40}\ \mu\textrm{K}^2\ h^{-3}\,\textrm{Mpc}^{3}$ for CO(2-1) at
$z=1.3$, CO(3-2) at $z=2.5$, and CO(4-3) at $z=3.6$, respectively. Using line
ratios appropriate for high-redshift galaxies, we find these results to be in
good agreement with those from the CO Power Spectrum Survey (COPSS). Adopting
$\alpha_{\rm CO}=3.6\ M_{\odot}\ (\textrm{K}\ \textrm{km}\ \textrm{s}^{-1}\
\textrm{pc}^{2})^{-1}$, we estimate a cosmic molecular gas density of
$\rho_{\textrm{H}_2}(z)\sim 10^{8}\ M_{\odot}\ \textrm{Mpc}^{-3}$ between
$z=1-3$. | astro-ph_GA |
A Search For Supernova Remnants in The Nearby Spiral Galaxy M74 (NGC
628): We have identified nine new SNR candidates in M74 with [S II]/H$\alpha$
$\geq$ 0.4 as the basic criterion. We obtain [S II]/H$\alpha$ ratio in the
range from 0.40 to 0.91 and H$\alpha$ intensities from 2.8 $\times$ $10^{-15}$
erg cm$^{-2}$ s$^{-1}$ to 1.7 $\times$ $10^{-14}$ erg cm$^{-2}$ s$^{-1}$. We
also present spectral follow-up observations of the SNR candidates and can
confirm only three of them (SNR2, SNR3, and SNR5). The lack of confirmation for
the rest might be due to the contamination by the nearby H II emission regions
as well as due to the inaccurate positioning of the long slit on these objects.
In addition, we search the $Chandra$ Observatory archival data for the X-ray
counterparts to the optically identified candidates. We find positional
coincidence with only three SNR candidates, SNR1, SNR2, and SNR8. The spectrum
of SNR2 yields a shock temperature of 10.8 keV with an ionization timescale of
1.6 $\times$ 10$^{10}$ s cm$^{-3}$ indicating a relatively young remnant in an
early Sedov phase which is not supported by our optical wavelength analysis.
Given the high luminosity of 10$^{39}$ erg s$^{-1}$ and the characteristics of
the X-ray spectrum, we favor an Ultra Luminous X-ray Source interpretation for
this source associated with an SNR. We calculate an X-ray flux upper limit of
9.0 $\times$ $10^{-15}$ erg cm$^{-2}$ s$^{-1}$ for the rest of the SNRs
including spectroscopically identified SNR3 and SNR5. | astro-ph_GA |
An HST/COS Observation of Broad Ly$α$ Emission and Associated
Absorption Lines of the BL Lacertae Object H 2356-309: Weak spectral features in BL Lacertae objects (BL Lac) often provide a unique
opportunity to probe the inner region of this rare type of active galactic
nucleus. We present a Hubble Space Telescope/Cosmic Origins Spectrograph
observation of the BL Lac H 2356-309. A weak Ly$\alpha$ emission line was
detected. This is the fourth detection of a weak Ly$\alpha$ emission feature in
the ultraviolet (UV) band in the so-called "high energy peaked BL Lacs", after
Stocke et al. Assuming the line-emitting gas is located in the broad line
region (BLR) and the ionizing source is the off-axis jet emission, we constrain
the Lorentz factor ($\Gamma$) of the relativistic jet to be $\geq 8.1$ with a
maximum viewing angle of 3.6$^\circ$. The derived $\Gamma$ is somewhat larger
than previous measurements of $\Gamma \approx 3 - 5$, implying a covering
factor of $\sim$ 3% of the line-emitting gas. Alternatively, the BLR clouds
could be optically thin, in which case we constrain the BLR warm gas to be
$\sim 10^{-5}\rm\ M_{\odot}$. We also detected two HI and one OVI absorption
lines that are within $|\Delta v| < 150\rm\ km\ s^{-1}$ of the BL Lac object.
The OVI and one of the HI absorbers likely coexist due to their nearly
identical velocities. We discuss several ionization models and find a
photoionization model where the ionizing photon source is the BL Lac object can
fit the observed ion column densities with reasonable physical parameters. This
absorber can either be located in the interstellar medium of the host galaxy,
or in the BLR. | astro-ph_GA |
Element Abundances in a Gas-rich Galaxy at z = 5: Clues to the Early
Chemical Enrichment of Galaxies: Element abundances in high-redshift quasar absorbers offer excellent probes
of the chemical enrichment of distant galaxies, and can constrain models for
population III and early population II stars. Recent observations indicate that
the sub-damped Lyman-alpha (sub-DLA) absorbers are more metal-rich than DLA
absorbers at redshifts 0$<$$z$$<$3. It has also been suggested that the DLA
metallicity drops suddenly at $z$$>$4.7. However, only 3 DLAs at $z$$>$4.5 and
none at $z$$>$3.5 have "dust-free" metallicity measurements of undepleted
elements. We report the first quasar sub-DLA metallicity measurement at
$z$$>$3.5, from detections of undepleted elements in high-resolution data for a
sub-DLA at $z$=5.0. We obtain fairly robust abundances of C, O, Si, and Fe,
using lines outside the Lyman-alpha forest. This absorber is metal-poor, with
O/H]=-2.00$\pm$0.12, which is $\gtrsim$4$\sigma$ below the level expected from
extrapolation of the trend for $z$$<$3.5 sub-DLAs. The C/O ratio is
1.8$^{+0.4}_{-0.3}$ times lower than in the Sun. More strikingly, Si/O is
3.2$^{+0.6}_{-0.5}$ times lower than in the Sun, while Si/Fe is nearly
(1.2$^{+0.4}_{-0.3}$ times) solar. This absorber does not display a clear
alpha/Fe enhancement. Dust depletion may have removed more Si from the gas
phase than is common in the Milky Way interstellar medium, which may be
expected if high-redshift supernovae form more silicate-rich dust. C/O and Si/O
vary substantially between different velocity components, indicating spatial
variations in dust depletion and/or early stellar nucleosynethesis (e.g.,
population III star initial mass function). The higher velocity gas may trace
an outflow enriched by early stars. | astro-ph_GA |
Unravelling the nature of the dual AGN in the galaxy pair system IRAS
05589+2828 and 2MASX J06021107+2828382: We have studied the nuclear region of the previously detected dual AGN system
in the galaxy pair IRAS 05589+2828 and 2MASX J06021107+2828382 through new
optical spectroscopy observations, along with radio and X-ray archival data.
Our multiwavelength data strongly suggest that the Sy1 \iras\,
(z=0.0330$\pm$0.0002) conforms to a dual AGN system with the Sy2 \twomas\,
(z=0.0334$\pm$0.0001) with a projected separation obtained from the radio data
of 20.08\arcsec\, ($\sim$13.3\,kpc). Analysis of the optical spectra reveals a
faint narrow extended emission from H$\alpha$ and [OIII] amidst the two AGN,
supporting evidence for an ongoing merger. \iras\, is a double component narrow
emission line AGN, with complex broad Balmer emission line profiles that
clearly show a strong red-peaklet with a velocity shift of
$\sim$3500\,km\,s$^{-1}$. The black hole mass estimates of \iras\, and
\twomas\, are log\,M$\rm_{BH}$\,=\,8.59\,$\pm$\,0.14 (M$_\odot$) and
log\,M$\rm_{BH}$\,=\,8.21$\pm$0.2 (M$_\odot$), respectively. In the X-ray
bands, \iras\, is compatible with a Type 1 object, showing both spectral and
flux variability. \chandra\, data of 2MASX\,J06021107+2828382 allowed us to
measure a high hardness ratio in this source, providing evidence for a Type 2
AGN. The 22 GHz image obtained with the {\it Karl G. Jansky Very Large Array}
has revealed that both AGN are compact radio objects with spectral indices
-0.26$\pm$0.03 and -0.70$\pm$0.11, confirming for the first time its dual AGN
nature in the radio bands. | astro-ph_GA |
New Maser Emission from Nonmetastable Ammonia in NGC 7538. III.
Detection of the (10,6) Transition and a Velocity Gradient: We present the first astronomical detection of the 14NH3 (J,K) = (10,6) line:
nonthermal emission at several velocities in the Galactic star-forming region
NGC 7538. Using the VLA we have imaged the (10,6) and (9,6) ammonia masers at
several positions within NGC 7538 IRS 1. The individual sources have angular
sizes < 0.1 arcseconds corresponding to brightness temperatures T_B > 1E6 K. We
apply the pumping model of Brown & Cragg, confirming the conjecture that
multiple ortho-ammonia masers can occur with the same value of K. The positions
and velocities of the (10,6) and (9,6) masers are modeled as motion in a
possible disk or torus and are discussed in the context of recent models of the
region. | astro-ph_GA |
Mixing and transport of metals by gravitational instability-driven
turbulence in galactic discs: Metal production in galaxies traces star formation, and is highly
concentrated toward the centers of galactic discs. This suggests that galaxies
should have inhomogeneous metal distributions with strong radial gradients, but
observations of present-day galaxies show only shallow gradients with little
azimuthal variation, implying the existence of a redistribution mechanism. We
study the role of gravitational instability-driven turbulence as a mixing
mechanism by simulating an isolated galactic disc at high resolution, including
metal fields treated as passive scalars. Since any cylindrical field can be
decomposed into a sum of Fourier-Bessel basis functions, we set up initial
metal fields characterized by these functions and study how different modes
mix. We find both shear and turbulence contribute to mixing, but the mixing
strongly depends on the symmetries of the mode. Non-axisymmetric modes have
decay times smaller than the galactic orbital period because shear winds them
up to small spatial scales, where they are erased by turbulence. The decay
timescales for axisymmetric modes are much greater, though for all but the
largest-scale inhomogeneities the mixing timescale is still short enough to
erase chemical inhomogeneities over cosmological times. These different
timescales provide an explanation for why galaxies retain metallicity gradients
while there is almost no variation at a fixed radius. Moreover, the
comparatively long timescales required for mixing axisymmetric modes may
explain the greater diversity of metallicity gradients observed in high
redshift galaxies as compared to local ones: these systems have not yet reached
equilibrium between metal production and diffusion. | astro-ph_GA |
Revisiting the bulge-halo conspiracy I: Dependence on galaxy properties
and halo mass: We carry out a systematic investigation of the total mass density profile of
massive (Mstar>2e11 Msun) early-type galaxies and its dependence on galactic
properties and host halo mass with the aid of a variety of lensing/dynamical
data and large mock galaxy catalogs. The latter are produced via semi-empirical
models that, by design, are based on just a few basic input assumptions.
Galaxies, with measured stellar masses, effective radii and S\'{e}rsic indices,
are assigned, via abundance matching relations, host dark matter halos
characterized by a typical LCDM profile. Our main results are as follows: (i)
In line with observational evidence, our semi-empirical models naturally
predict that the total, mass-weighted density slope at the effective radius
gamma' is not universal, steepening for more compact and/or massive galaxies,
but flattening with increasing host halo mass. (ii) Models characterized by a
Salpeter or variable initial mass function and uncontracted dark matter
profiles are in good agreement with the data, while a Chabrier initial mass
function and/or adiabatic contractions/expansions of the dark matter halos are
highly disfavored. (iii) Currently available data on the mass density profiles
of very massive galaxies (Mstar>1e12 Msun), with Mhalo>3e14 Msun, favor instead
models with a stellar profile flatter than a S\'{e}rsic one in the very inner
regions (r<3-5 kpc), and a cored NFW or Einasto dark matter profile with median
halo concentration a factor of ~2 or <1.3, respectively, higher than those
typically predicted by N-body numerical simulations. | astro-ph_GA |
Precipitation-Regulated Star Formation in Galaxies: Galaxy growth depends critically on the interplay between radiative cooling
of cosmic gas and the resulting energetic feedback that cooling triggers. This
interplay has proven exceedingly difficult to model, even with large
supercomputer simulations, because of its complexity. Nevertheless, real
galaxies are observed to obey simple scaling relations among their primary
observable characteristics. Here we show that a generic emergent property of
the interplay between cooling and feedback can explain the observed scaling
relationships between a galaxy's stellar mass, its total mass, and its chemical
enrichment level, as well as the relationship between the average orbital
velocity of its stars and the mass of its central black hole. These
relationships naturally result from any feedback mechanism that strongly heats
a galaxy's circumgalactic gas in response to precipitation of colder clouds out
of that gas, because feedback then suspends the gas in a marginally
precipitating state. | astro-ph_GA |
The Galaxy's Veil of Excited Hydrogen: Many of the baryons in our Galaxy probably lie outside the well known disk
and bulge components. Despite a wealth of evidence for the presence of some gas
in galactic halos, including absorption line systems in the spectra of quasars,
high velocity neutral hydrogen clouds in our Galaxy halo, line emitting ionised
hydrogen originating from galactic winds in nearby starburst galaxies, and the
X-ray coronas surrounding the most massive galaxies, accounting for the gas in
the halo of any galaxy has been observationally challenging primarily because
of its low density in the expansive halo. The most sensitive measurements come
from detecting absorption by the intervening gas in the spectra of distant
objects such as quasars or distant halo stars, but these have typically been
limited to a few lines of sight to sufficiently bright objects. Massive
spectroscopic surveys of millions of objects provide an alternative approach to
the problem. Here, we present the first evidence for a widely distributed,
neutral, excited hydrogen component of the Galaxy's halo. It is observed as the
slight, (0.779 $\pm$ 0.006)\%, absorption of flux near the rest wavelength of
H$\alpha$ in the combined spectra of hundreds of thousands of galaxy spectra
and is ubiquitous in high latitude lines of sight. This observation provides an
avenue to tracing, both spatially and kinematically, the majority of the gas in
the halo of our Galaxy. | astro-ph_GA |
Discovery of H2O Megamasers in Obscured Active Galactic Nuclei: Recently a new method to discover obscured active galactic nuclei (AGNs) by
utilizing X-ray and Infrared data has been developed. We carried out a survey
of H2O maser emission toward ten obscured AGNs with the Nobeyama 45-m
telescope. We newly detected the maser emission with the signal-noise-ratio
(SNR) of above 4 from two AGNs, NGC 1402 and NGC 7738. We also found a
tentative detection with its SNR > 3 in NGC 5037. The detection rate of 20% is
higher than those of previous surveys (usually several percents). | astro-ph_GA |
The Ionized Gas in Nearby Galaxies as Traced by the [NII] 122 and 205
μm Transitions: The [NII] 122 and 205 \mu m transitions are powerful tracers of the ionized
gas in the interstellar medium. By combining data from 21 galaxies selected
from the Herschel KINGFISH and Beyond the Peak surveys, we have compiled 141
spatially resolved regions with a typical size of ~1 kiloparsec, with
observations of both [NII] far-infrared lines. We measure [NII] 122/205 line
ratios in the ~0.6-6 range, which corresponds to electron gas densities
$n_e$~1-300 cm$^{-3}$, with a median value of $n_e$=30 cm$^{-3}$. Variations in
the electron density within individual galaxies can be as a high as a factor of
~50, frequently with strong radial gradients. We find that $n_e$ increases as a
function of infrared color, dust-weighted mean starlight intensity, and star
formation rate surface density ($\Sigma_{SFR}$). As the intensity of the [NII]
transitions is related to the ionizing photon flux, we investigate their
reliability as tracers of the star formation rate (SFR). We derive relations
between the [NII] emission and SFR in the low-density limit and in the case of
a log-normal distribution of densities. The scatter in the correlation between
[NII] surface brightness and $\Sigma_{SFR}$ can be understood as a property of
the $n_e$ distribution. For regions with $n_e$ close to or higher than the
[NII] line critical densities, the low-density limit [NII]-based SFR
calibration systematically underestimates the SFR since [NII] emission is
collisionally quenched. Finally, we investigate the relation between [NII]
emission, SFR, and $n_e$ by comparing our observations to predictions from the
MAPPINGS-III code. | astro-ph_GA |
Revealing a detailed mass distribution of a high-density core
MC27/L1521F in Taurus with ALMA: We present the results of ALMA observations of dust continuum emission and
molecular rotational lines toward a dense core MC27 (aka L1521F) in Taurus,
which is considered to be at a very early stage of star formation. The detailed
column density distribution on size scales from a few tens AU to ~10,000 AU
scale are revealed by combining the ALMA (12 m array + 7 m array) data with the
published/unpublished single-dish data. The high angular resolution
observations at 0.87 mm with a synthesized beam size of ~0."74 x 0."32 reveal
that a protostellar source, MMS-1, is not spatially resolved and lacks
associated gas emission, while a starless high-density core, MMS-2, has
substructures both in dust and molecular emission. The averaged radial column
density distribution of the inner part of MC27/L1521F (r $\lesssim$ 3000 AU) is
N(H2) ~r$^{-0.4}$, clearly flatter than that of the outer part, ~r$^{-1.0}$.
The complex velocity/spatial structure obtained with previous ALMA observations
is located inside the inner flatter region, which may reflect the dynamical
status of the dense core. | astro-ph_GA |
Constraints on Individual Supermassive Black Hole Binaries from Pulsar
Timing Array Limits on Continuous Gravitational Waves: Pulsar timing arrays (PTAs) are placing increasingly stringent constraints on
the strain amplitude of continuous gravitational waves emitted by supermassive
black hole binaries on subparsec scales. In this paper, we incorporate
independent information about the dynamical masses $M_{bh}$ of supermassive
black holes in specific galaxies at known distances and use this additional
information to further constrain whether or not those galaxies could host a
detectable supermassive black hole binary. We estimate the strain amplitudes
from individual binaries as a function of binary mass ratio for two samples of
nearby galaxies: (1) those with direct dynamical measurements of $M_{bh}$ in
the literature, and (2) the 116 most massive early-type galaxies (and thus
likely hosts of the most massive black holes) within 108 Mpc from the MASSIVE
Survey. Our exploratory analysis shows that the current PTA upper limits on
continuous waves (as a function of angular position in the sky) can already
constrain the mass ratios of hypothetical black hole binaries in many galaxies
in our samples. The constraints are stronger for galaxies with larger $M_{bh}$
and at smaller distances. For the black holes with $M_{bh} \gtrsim 5\times 10^9
M_\odot$ at the centers of NGC 1600, NGC 4889, NGC 4486 (M87) and NGC 4649
(M60), any binary companion in orbit within the PTA frequency bands would have
to have a mass ratio of a few percent or less. | astro-ph_GA |
ALMA Deep Field in SSA22: Survey Design and Source Catalog of a 20
arcmin^2 Survey at 1.1mm: To search for dust-obscured star-formation activity in the early Universe, it
is essential to obtain a deep and wide submillimeter/millimeter map. The advent
of the Atacama Large Millimeter/submillimeter Array (ALMA) has enabled us to
obtain such maps at sufficiently high spatial resolution to be free from source
confusion. We present a new 1.1mm map obtained by ALMA in the SSA22 field.
SSA22 contains a remarkable proto-cluster at z=3.09 and is therefore an ideal
region to investigate the role of large-scale cosmic web on dust-obscured star
formation. The typical 1sigma depth of our map is 73 uJy/beam at a 0.5
resolution; combined with earlier, archived observations, we map an area of 20
arcmin^2 (71 comoving Mpc^2 at z=3.09). Within the combined survey area we have
detected 35 sources at a signal-to-noise ratio (S/N) >5, with flux densities,
S1.1mm=0.43--5.6 mJy, equivalent to star-formation rates of >=100--1000 Msun/yr
at z=3.09, for a Chabrier initial mass function; of these, 17 are new
detections. The cumulative number counts show a factor 3--5x excess compared to
blank fields. The excess suggests enhanced dust-enshrouded star-formation
activity in the proto-cluster on a 10 comoving Mpc scale, indicating
accelerated galaxy evolution in this overdense region. | astro-ph_GA |
Selecting accreted populations: metallicity, elemental abundances, and
ages of the Gaia-Sausage-Enceladus and Sequoia populations: Identifying stars found in the Milky Way as having formed in situ or accreted
can be a complex and uncertain undertaking. We use Gaia kinematics and APOGEE
elemental abundances to select stars belonging to the Gaia-Sausage-Enceladus
(GSE) and Sequoia accretion events. These samples are used to characterize the
GSE and Sequoia population metallicity distribution functions, elemental
abundance patterns, age distributions, and progenitor masses. We find that the
GSE population has a mean [Fe/H] $\sim -1.15$ and a mean age of $10-12$ Gyr.
GSE has a single sequence in [Mg/Fe] vs [Fe/H] consistent with the onset of SN
Ia Fe contributions and uniformly low [Al/Fe] of $\sim -0.25$ dex. The derived
properties of the Sequoia population are strongly dependent on the kinematic
selection. We argue the selection with the least contamination is
$J_{\phi}/J_{\mbox{tot}} < -0.6$ and $(J_z - J_R)/J_{\mbox{tot}} < 0.1$. This
results in a mean [Fe/H] $\sim -1.3$ and a mean age of $12-14$ Gyr. The Sequoia
population has a complex elemental abundance distribution with mainly high
[Mg/Fe] stars. We use the GSE [Al/Fe] vs [Mg/H] abundance distribution to
inform a chemically-based selection of accreted stars, which is used to remove
possible contaminant stars from the GSE and Sequoia samples. | astro-ph_GA |
Temperature structure and kinematics of the IRDC G035.39-00.33: Aims. Infrared dark clouds represent the earliest stages of high-mass star
formation. Detailed observations of their physical conditions on all physical
scales are required to improve our understanding of their role in fueling star
formation.
Methods. We investigate the large-scale structure of the IRDC G035.39-00.33,
probing the dense gas with the classical ammonia thermometer. This allows us to
put reliable constraints on the temperature of the extended, pc-scale dense gas
reservoir and to probe the magnitude of its non-thermal motions. Available
far-infrared observations can be used in tandem with the observed ammonia
emission to estimate the total gas mass contained in G035.39-00.33.
Results. We identify a main velocity component as a prominent filament,
manifested as an ammonia emission intensity ridge spanning more than 6 pc,
consistent with the previous studies on the Northern part of the cloud. A
number of additional line-of-sight components are found, and a large scale,
linear velocity gradient of ~0.2 km s$^{-1}$ pc$^{-1}$ is found along the ridge
of the IRDC. In contrast to the dust temperature map, an ammonia-derived
kinetic temperature map, presented for the entirety of the cloud, reveals local
temperature enhancements towards the massive protostellar cores. We show that
without properly accounting for the line of sight contamination, the dust
temperature is 2-3 K larger than the gas temperature measured with NH$_3$.
Conclusions. While both the large scale kinematics and temperature structure
are consistent with that of starless dark filaments, the kinetic gas
temperature profile on smaller scales is suggestive of tracing the heating
mechanism coincident with the locations of massive protostellar cores. | astro-ph_GA |
A Change of Rotation Profile in the Envelope in the HH 111 Protostellar
System: A Transition to a Disk?: The HH 111 protostellar system consists of two Class I sources (VLA 1 and 2)
with putative disks deeply embedded in a flattened envelope at a distance of
400 pc. Here is a follow-up study of this system in C18O (J=2-1), SO (N_J =
5_6-4_5), and 1.33 mm continuum at ~ 1" (400 AU) resolution, and it may show
for the first time how a rotationally supported disk can be formed inside an
infalling envelope. The 1.33 mm continuum emission is seen arisen from both
sources, likely tracing the dusty putative disks around them. In particular,
the emission around the VLA 1 source is elongated in the equatorial plane with
a radius of ~ 300 AU. The envelope is well seen in C18O, extending to ~ 7000 AU
out from the VLA 1 source, with the innermost part overlapping with the dusty
disk. It has a differential rotation, with the outer part (~ 2000-7000 AU)
better described by a rotation that has constant specific angular momentum and
the inner part (~ 60-2000 AU) by a Keplerian rotation. The envelope seems to
also have some infall motion that is smaller than the rotation motion. Thus,
the material in the outer part of the envelope seems to be slowly spiraling
inward with its angular momentum and the rotation can indeed become Keplerian
in the inner part. A compact SO emission is seen around the VLA 1 source with a
radius of ~ 400 AU and it may trace a shock such as an (inner) accretion shock
around the disk. | astro-ph_GA |
The location of the dust causing internal reddening of active galactic
nuclei: We use the Balmer decrements of the broad-line regions (BLRs) and narrow-line
regions (NLRs) of active galactic nuclei (AGNs) as reddening indicators to
investigate the location of the dust for four samples of AGNs with reliable
estimates of the NLR contribution to the Balmer lines. Intercomparison of the
NLR and BLR Balmer decrements indicates that the reddening of the NLR sets a
lower limit to the reddening of the BLR. Almost no objects have high NLR
reddening but low BLR reddening. The reddening of the BLR is often
substantially greater than the reddening of the NLR. The BLR reddening is
correlated with the equivalent widths of [O III] lines and the intensity of the
[O III] lines relative to broad H\beta. We find these relationships to be
consistent with the predictions of a simple model where the additional dust
reddening the BLR is interior to the NLR. We thus conclude that the dust
causing the additional reddening of the accretion disc and BLR is mostly
located at a smaller radius than the NLR. | astro-ph_GA |
Radio continuum emission and water masers towards CB 54: We present high angular resolution observations of water masers at 1.3 cm and
radio continuum emission at 1.3, 3.6 and 6 cm towards the Bok globule CB 54
using the Very Large Array. At 1.3 cm, with subarsecond angular resolution, we
detect a radio continuum compact source located to the south-west of the
globule and spatially coincident with a mid-infrared embedded object (MIR-b).
The spectral index derived between 6 and 1.3 cm (alpha=0.3+/-0.4) is flat,
consistent with optically thin free-free emission from ionized gas. We propose
the shock-ionization scenario as a viable mechanism to produce the radio
continuum emission observed at cm frequencies. Water masers are detected at two
different positions separated by 2.3'', and coincide spatially with two
mid-infrared sources: MIR-b and MIR-c. The association of these mid-IR sources
with water masers confirms that they are likely protostars undergoing
mass-loss, and they are the best candidate as driving sources of the molecular
outflows in the region. | astro-ph_GA |
The origin of carbon: Low-mass stars and an evolving, initially
top-heavy IMF?: Multi-zone chemical evolution models (CEMs), differing in the nucleosynthesis
prescriptions (yields) and prescriptions of star formation, have been computed
for the Milky Way. All models fit the observed O/H and Fe/H gradients well and
reproduce the main characteristics of the gas distribution, but they are also
designed to do so. For the C/H gradient the results are inconclusive with
regards to yields and star formation. The C/Fe and O/Fe vs. Fe/H, as well as
C/O vs. O/H trends predicted by the models for the solar neighbourhood zone
were compared with stellar abundances from the literature. For O/Fe vs. Fe/H
all models fit the data, but for C/O vs. O/H, only models with increased carbon
yields for zero-metallicity stars or an evolving initial mass function provide
good fits. Furthermore, a steep star formation threshold in the disc can be
ruled out since it predicts a steep fall-off in all abundance gradients beyond
a certain galactocentric distance (~ 13 kpc) and cannot explain the possible
flattening of the C/H and Fe/H gradients in the outer disc seen in
observations. Since in the best-fit models the enrichment scenario is such that
carbon is primarily produced in low-mass stars, it is suggested that in every
environment where the peak of star formation happened a few Gyr back in time,
winds of carbon-stars are responsible for most of the carbon enrichment.
However, a significant contribution by zero-metallicity stars, especially at
very early stages, and by winds of high-mass stars, which are increasing in
strength with metallicity, cannot be ruled out by the CEMs presented here. In
the solar neighbourhood, as much as 80%, or as little as 40% of the carbon may
have been injected to the interstellar medium by low- and intermediate-mass
stars. The stellar origin of carbon remains an open question, although
production in low- and intermediate-mass stars appears to be the simplest
explanation of observed carbon abundance trends. | astro-ph_GA |
Optical photometry and basic parameters of 10 unstudied open clusters: We present BVI CCD photometry of 10 northern open clusters, Berkeley 43,
Berkeley 45, Berkeley 47, NGC 6846, Berkeley 49, Berkeley 51, Berkeley 89,
Berkeley 91, Tombaugh 4 and Berkeley 9, and estimate their fundamental
parameters. Eight of the clusters are located in the first galactic quadrant
and 2 are in the second. This is the first optical photometry for 8 clusters.
All of them are embedded in rich galactic fields and have large reddening
towards them (E(B-V) = 1.0 - 2.3 mag). There is a possibility that some of
these difficult-to-study clusters may be asterisms rather than physical
systems, but assuming they are physical clusters, we find that 8 of them are
located beyond 2 kpc, and 6 clusters (60% of the sample) are located well above
or below the Galactic plane. Seven clusters have ages 500 Myr or less and the
other 3 are 1 Gyr or more in age. This sample of clusters has increased the
optical photometry of clusters in the second half of the first galactic
quadrant, beyond 2 kpc, from 10 to 15. NGC 6846 is found to be one of the most
distant clusters in this region of the Galaxy. | astro-ph_GA |
Doubly substituted isotopologues of HCCCN in TMC-1: Detection of
D13CCCN, DC13CCN, DCC13CN, DCCC15N, H13C13CCN, H13CC13CN, HC13C13CN,
HCC13C15N, and HC13CC15N: We report the first detection in space of a complete sample of nine doubly
substituted isotopologues of HCCCN towards the cyanopolyyne peak of TMC-1 using
observations of the QUIJOTE line survey taken with the Yebes 40 m telescope. We
detected D13CCCN, DC13CCN, DCC13CN, DCCC15N, H13C13CCN, H13CC13CN, HC13C13CN,
HCC13C15N, and HC13CC15N through their J=4-3 and J=5-4 lines in the 7 mm
window. In addition, we present an extensive analysis of the emission of HCCCN
and its singly substituted isotopologues through a large velocity gradient
model of the lines detected at 7 mm and 3 mm using the Yebes 40 m and the IRAM
30 m telescopes, respectively. The derived column densities for all the
isotopologues are consistent in the two spectral bands for an H2 volume density
of 1e4 cm-3 and a kinetic temperature of 10 K. Whereas we observed a 13C
fractionation for HCC13CN and other double isotopologues with a 13C atom
adjacent to the nitrogen atom, we derived similar C/13C abundance ratios for
the three 13C substituted species of DCCCN. This suggests additional chemical
discrimination for deuterated isotopologues of HCCCN. Finally, we present the
spatial distribution of the J=4-3 and J=5-4 lines from the singly substituted
species observed with the Yebes 40 m telescope. The emission peak of the
spatial distribution of DCCCN appears to be displaced by 40'' with respect to
that of HCCCN and the 13C and 15N isotopologues. In addition to a different
formation route for the deuterated species, we could also expect that this
differentiation owing to the deuterium fractionation is more efficient at low
temperatures, and therefore, that deuterated species trace a colder region of
the cloud. | astro-ph_GA |
Mapping the Polarization of the Radio-Loud Ly$α$ Nebula B3
J2330+3927: Lya nebulae, or "Lya blobs", are extended (up to ~100 kpc), bright (L[Lya] >
10^43 erg/s) clouds of Lya emitting gas that tend to lie in overdense regions
at z ~ 2--5. The origin of the Lya emission remains unknown, but recent
theoretical work suggests that measuring the polarization might discriminate
among powering mechanisms. Here we present the first narrowband, imaging
polarimetry of a radio-loud Lya nebula, B3 J2330+3927 at z=3.09, with an
embedded active galactic nucleus (AGN). The AGN lies near the blob's Lya
emission peak and its radio lobes align roughly with the blob's major axis.
With the SPOL polarimeter on the 6.5m MMT telescope, we map the total (Lya +
continuum) polarization in a grid of circular apertures of radius 0.6"
(4.4kpc), detecting a significant (>2sigma) polarization fraction P in nine
apertures and achieving strong upper-limits (as low as 2%) elsewhere. P
increases from <2% at ~5kpc from the blob center to ~17% at ~15-25kpc. The
detections are distributed asymmetrically, roughly along the nebula's major
axis. The polarization angles theta are mostly perpendicular to this axis.
Comparing the Lya flux to that of the continuum, and conservatively assuming
that the continuum is highly polarized (20-100%) and aligned with the total
polarization, we place lower limits on the polarization of the Lya emission
P(Lya) ranging from no significant polarization at ~5 kpc from the blob center
to ~ 3--17% at 10--25kpc. Like the total polarization, the Lya polarization
detections occur more often along the blob's major axis. | astro-ph_GA |
Ionized and molecular gas kinematics in a z=1.4 star-forming galaxy: We present deep observations of a $z=1.4$ massive, star-forming galaxy in
molecular and ionized gas at comparable spatial resolution (CO 3-2, NOEMA;
H$\alpha$, LBT). The kinematic tracers agree well, indicating that both gas
phases are subject to the same gravitational potential and physical processes
affecting the gas dynamics. We combine the one-dimensional velocity and
velocity dispersion profiles in CO and H$\alpha$ to forward-model the galaxy in
a Bayesian framework, combining a thick exponential disk, a bulge, and a dark
matter halo. We determine the dynamical support due to baryons and dark matter,
and find a dark matter fraction within one effective radius of $f_{\rm
DM}(\leq$$R_{e})=0.18^{+0.06}_{-0.04}$. Our result strengthens the evidence for
strong baryon-dominance on galactic scales of massive $z\sim1-3$ star-forming
galaxies recently found based on ionized gas kinematics alone. | astro-ph_GA |
The Next Generation Virgo cluster Survey (NGVS). XXVI. The issues of
photometric age and metallicity estimates for globular clusters: Large samples of globular clusters (GC) with precise multi-wavelength
photometry are becoming increasingly available and can be used to constrain the
formation history of galaxies. We present the results of an analysis of Milky
Way (MW) and Virgo core GCs based on five optical-near-infrared colors and ten
synthetic stellar population models. For the MW GCs, the models tend to agree
on photometric ages and metallicities, with values similar to those obtained
with previous studies. When used with Virgo core GCs, for which photometry is
provided by the Next Generation Virgo cluster Survey (NGVS), the same models
generically return younger ages. This is a consequence of the systematic
differences observed between the locus occupied by Virgo core GCs and models in
panchromatic color space. Only extreme fine-tuning of the adjustable parameters
available to us can make the majority of the best-fit ages old. Although we
cannot exclude that the formation history of the Virgo core may lead to more
conspicuous populations of relatively young GCs than in other environments, we
emphasize that the intrinsic properties of the Virgo GCs are likely to differ
systematically from those assumed in the models. Thus, the large wavelength
coverage and photometric quality of modern GC samples, such as used here, is
not by itself sufficient to better constrain the GC formation histories. Models
matching the environment-dependent characteristics of GCs in multi-dimensional
color space are needed to improve the situation. | astro-ph_GA |
Giant molecular clouds in M 33: are they susceptible to dynamical
friction?: Most of giant molecular clouds (GMCs) in M 33 are connected with spiral-like
gaseous arms (filaments) with the exception of the inner 2 kpc region where the
link between the arms and GMCs disappears (see Tosaki et al. 2011). We check
whether it may be caused by the dynamic friction retarding the clouds. Using
semi-analytical model for this galaxy we calculate the dynamics of GMCs of
different masses situated at different initial galactocentric distances in the
disk plane. We demonstrate that the dynamical friction may really change the
orbits of GMCs in the central 2 kpc-size region. However in this case the
typical lifetimes of GMCs should be close to or greater than $10^8$~yr, which
is larger than the usually accepted values. | astro-ph_GA |
Chemistry of massive young stellar objects with a disk-like structure: Our goal is to take an inventory of complex molecules in three well-known
high-mass protostars for which disks or toroids have been claimed and to study
the similarities and differences with a sample of massive YSOs without evidence
of such flattened disk-like structures. With a disk-like geometry, UV radiation
can escape more readily and potentially affect the ice and gas chemistry on
hot-core scales. A partial submillimeter line survey, targeting CH3OH, H2CO,
C2H5OH, HCOOCH3, CH3OCH3, CH3CN, HNCO, NH2CHO, C2H5CN, CH2CO, HCOOH, CH3CHO,
and CH3CCH, was made toward three massive YSOs with disk-like structures,
IRAS20126+4104, IRAS18089-1732, and G31.41+0.31. Rotation temperatures and
column densities were determined by the rotation diagram method, as well as by
independent spectral modeling. The molecular abundances were compared with
previous observations of massive YSOs without evidence of any disk structure,
targeting the same molecules with the same settings and using the same analysis
method. Consistent with previous studies, different complex organic species
have different characteristic rotation temperatures and can be classified
either as warm (>100 K) or cold (<100 K). The excitation temperatures and
abundance ratios are similar from source to source and no significant
difference can be established between the two source types. Acetone, CH3COCH3,
is detected for the first time in G31.41+0.31 and IRAS18089-1732. Temperatures
and abundances derived from the two analysis methods generally agree within
factors of a few. The lack of chemical differentiation between massive YSOs
with and without observed disks suggest either that the chemical complexity is
already fully established in the ices in the cold prestellar phase or that the
material experiences similar physi- cal conditions and UV exposure through
outflow cavities during the short embedded lifetime. | astro-ph_GA |
Understanding the Structural Scaling Relations of Early-Type Galaxies: We use a large suite of hydrodynamical simulations of binary galaxy mergers
to construct and calibrate a physical prescription for computing the effective
radii and velocity dispersions of spheroids. We implement this prescription
within a semi-analytic model embedded in merger trees extracted from the
Bolshoi Lambda-CDM N-body simulation, accounting for spheroid growth via major
and minor mergers as well as disk instabilities. We find that without disk
instabilities, our model does not predict sufficient numbers of intermediate
mass early-type galaxies in the local universe. Spheroids also form earlier in
models with spheroid growth via disk instabilities. Our model correctly
predicts the normalization, slope, and scatter of the low-redshift size-mass
and Fundamental Plane relations for early type galaxies. It predicts a degree
of curvature in the Faber-Jackson relation that is not seen in local
observations, but this could be alleviated if higher mass spheroids have more
bottom-heavy initial mass functions. The model also correctly predicts the
observed strong evolution of the size-mass relation for spheroids out to higher
redshifts, as well as the slower evolution in the normalization of the
Faber-Jackson relation. We emphasize that these are genuine predictions of the
model since it was tuned to match hydrodynamical simulations and not these
observations. | astro-ph_GA |
Discovery of two new hypervelocity stars from the LAMOST spectroscopic
surveys: We report the discovery of two new unbound hypervelocity stars (HVSs) from
the LAMOST spectroscopic surveys. They are respectively a B2V type star of ~ 7
M$_{\rm \odot}$ with a Galactic rest-frame radial velocity of 502 km/s at a
Galactocentric radius of ~ 21 kpc and a B7V type star of ~ 4 M$_{\rm \odot}$
with a Galactic rest-frame radial velocity of 408 km/s at a Galactocentric
radius of ~ 30 kpc. The origins of the two HVSs are not clear given their
currently poorly measured proper motions. However, the future data releases of
Gaia should provide proper motion measurements accurate enough to solve this
problem. The ongoing LAMOST spectroscopic surveys are expected to yield more
HVSs to form a statistical sample, providing vital constraint on understanding
the nature of HVSs and their ejection mechanisms. | astro-ph_GA |
Why Simple Stellar Population models do not reproduce the colours of
Galactic open clusters: (...) We search for an explanation of the disagreement between the observed
integrated colours of 650 local Galactic clusters and the theoretical colours
of present-day SSP models. We check the hypothesis that the systematic offsets
between observed and theoretical colours, which are $(B$$-$$V)\approx 0.3$ and
$(J$$-$$K_s)\approx 0.8$, are caused by neglecting the discrete nature of the
underlying mass function. Using Monte Carlo simulations, we construct
artificial clusters of coeval stars taken from a mass distribution defined by
an Salpeter initial mass function (IMF) and compare them with corresponding
"continuous-IMF" SSP models. If the discreteness of the IMF is taken into
account, the model fits the observations perfectly and is able to explain
naturally a number of red "outliers" observed in the empirical colour-age
relation. We find that the \textit{systematic} offset between the continuous-
and discrete-IMF colours reaches its maximum of about 0.5 in $(B$$-$$V)$ for a
cluster mass $M_c=10^2 m_\odot$ at ages $\log t\approx 7$, and diminishes
substantially but not completely to about one hundredth of a magnitude at $\log
t >7.9$ at cluster masses $M_c> 10^5 m_\odot$. At younger ages, it is still
present even in massive clusters, and for $M_c \leqslant 10^4 m_\odot$ it is
larger than 0.1 mag in $(B$$-$$V)$. Only for very massive clusters ($M_c>10^6
m_\odot$) with ages $\log t< 7.5$ is the offset small (of the order of 0.04
mag) and smaller than the typical observational error of colours of
extragalactic clusters. | astro-ph_GA |
The Initial Mass Function of the Orion Nebula Cluster across the
H-burning limit: We present a new census of the Orion Nebula Cluster (ONC) over a large field
of view (>30'x30'), significantly increasing the known population of stellar
and substellar cluster members with precisely determined properties. We develop
and exploit a technique to determine stellar effective temperatures from
optical colors, nearly doubling the previously available number of objects with
effective temperature determinations in this benchmark cluster. Our technique
utilizes colors from deep photometry in the I-band and in two medium-band
filters at lambda~753 and 770nm, which accurately measure the depth of a
molecular feature present in the spectra of cool stars. From these colors we
can derive effective temperatures with a precision corresponding to better than
one-half spectral subtype, and importantly this precision is independent of the
extinction to the individual stars. Also, because this technique utilizes only
photometry redward of 750nm, the results are only mildly sensitive to optical
veiling produced by accretion. Completing our census with previously available
data, we place some 1750 sources in the Hertzsprung-Russel diagram and assign
masses and ages down to 0.02 solar masses. At faint luminosities, we detect a
large population of background sources which is easily separated in our
photometry from the bona fide cluster members. The resulting initial mass
function of the cluster has good completeness well into the substellar mass
range, and we find that it declines steeply with decreasing mass. This suggests
a deficiency of newly formed brown dwarfs in the cluster compared to the
Galactic disk population. | astro-ph_GA |
Precision measurement of magnetic field from near to far, from fine to
large scales in ISM: Magnetic fields have important or dominant effects in many areas of
astrophysics, but have been very difficult to quantify. Spectropolarimetry from
Ground State Alignment (GSA) has been suggested as a direct tracer of magnetic
field in interstellar diffuse medium. Owing to the long life of the atoms on
ground states the Larmor precession in an external magnetic field imprints the
direction of the field onto the polarization of absorbing species. This
provides a unique tool for studies of sub-gauss magnetic fields using
polarimetry of UV, optical and radio lines. Many spectral lines with strong
signals from GSA are in the UV band. By discerning magnetic fields in gas with
different dynamical properties, high spectral resolution measurement of
spectral polarization will allow the study of 3D magnetic field distribution
and interstellar turbulence. GSA provides also a unique chance to map 3D
direction of magnetic field on small scales, e.g., disks, where grain alignment
is unreliable. The range of objects suitable for studies is extremely wide and
includes magnetic fields in the interplanetary medium, in the interstellar
medium, and in circumstellar regions as well as diffuse media in extragalactic
objects. | astro-ph_GA |
The Influence of Orbital Eccentricity on Tidal Radii of Star Clusters: We have performed N-body simulations of star clusters orbiting in a
spherically symmetric smooth galactic potential. The model clusters cover a
range of initial half-mass radii and orbital eccentricities in order to test
the historical assumption that the tidal radius of a cluster is imposed at
perigalacticon. The traditional assumption for globular clusters is that since
the internal relaxation time is larger than its orbital period, the cluster is
tidally stripped at perigalacticon. Instead, our simulations show that a
cluster with an eccentric orbit does not need to fully relax in order to
expand. After a perigalactic pass, a cluster re-captures previously unbound
stars, and the tidal shock at perigalacticon has the effect of energizing inner
region stars to larger orbits. Therefore, instead of the limiting radius being
imposed at perigalacticon, it more nearly traces the instantaneous tidal radius
of the cluster at any point in the orbit. We present a numerical correction
factor to theoretical tidal radii calculated at perigalacticon which takes into
consideration both the orbital eccentricity and current orbital phase of the
cluster. | astro-ph_GA |
Photon and neutrino emission from active galactic nuclei: Supermassive black holes in the centers of galaxies are very common. They are
known to rotate, accrete, spin down and eject highly relativistic jets; those
jets pointed at us all seem to show a spectrum with two strong bumps, one in
the TeV photon range, and one in X-rays - ordered by the emission frequency of
the first bump this constitutes the blazar sequence. Here we wish to explain
this sequence as the combined interaction of electrons and protons with the
magnetic field and radiation field at the first strong shockwave pattern in the
relativistic jet. With two key assumptions on particle scattering, this concept
predicts that the two basic maximum peak frequencies scale with the mass of the
central black hole as $M_{BH}^{-1/2}$, have a ratio of $(m_p/m_e)^{3}$, and the
luminosities with the mass itself $M_{BH}$. Due to strong losses of the
leptons, the peak luminosities are generally the same, but with large
variations around equality. This model predicts large fluxes in ultra high
energy cosmic rays, and also large neutrino luminosities. | astro-ph_GA |
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