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Herschel survey of brown dwarf disks in Rho Ophiuchi: Recent observations of the Rho Ophiuchi cluster with the Herschel Space
Observatory allow us to probe the spectral energy distribution (SED) of the
brown dwarf population in the far-IR, where the disk emission peaks. We
performed aperture photometry at 70, 100, and 160 micron, and constructed SEDs
for all previously known brown dwarfs detected. These were complemented with
ancillary photometry at shorter wavelengths. We compared the observed SEDs to a
grid of synthetic disks produced with the radiative transfer code MCFOST, and
used the relative figure of merit estimated from the Bayesian inference of each
disk parameter to analyse the structural properties. We detected 12 Class II
brown dwarfs with Herschel, which corresponds to one-third of all currently
known brown dwarf members of Rho Ophiuchi. We do not detect any of the known
Class III brown dwarfs. Comparison to models reveals that the disks are best
described by an inner radius between 0.01 and 0.07 AU, and a flared disk
geometry with a flaring index between 1.05 and 1.2. Furthermore, we can exclude
values of the disk scale-height lower than 10 AU (measured at a fiducial radius
of 100 AU). We combined the Herschel data with recent ALMA observations of the
brown dwarf GY92 204 (ISO-Oph 102), and by comparing its SED to the same grid
of disk models, we derived an inner disk radius of 0.035 AU, a scale height of
15 AU with a flaring index of beta~1.15, an exponent for dust settling of -1.5,
and a disk mass of 0.001 MSun. This corresponds to a disk-to-central object
mass ratio of ~1%. The structural parameters constrained by the extended SED
coverage (inner radius and flaring index) show a narrow distribution for the 11
young brown dwarfs detected in Rho Ophiuchi, suggesting that these objects
share the same disk evolution and, perhaps, formation. | astro-ph_GA |
Fuzzy dark matter dynamics in tidally perturbed dwarf spheroidal galaxy
satellites: Fuzzy dark matter (FDM) has dynamical properties that differ significantly
from cold dark matter (CDM). These dynamical differences are strongly
manifested on the spatial scale of dwarf spheroidal galaxies (dSphs), which
roughly corresponds to the de Broglie wavelength of a canonical mass FDM
particle. We study simulations of a dSph satellite which is tidally perturbed
by its host galaxy, in order to identify dynamical signatures that are unique
to FDM, and to quantify the imprints of such perturbations on an observable
stellar tracer population. We find that a perturbed FDM soliton develops a
long-standing breathing mode, whereas for CDM such a breathing mode quickly
phase-mixes and disappears. We also demonstrate that such signatures become
imprinted on the dynamics of a stellar tracer population, making them
observable with sufficiently precise astrometric measurements. | astro-ph_GA |
Power-law models of totally anisotropic scattering: The interstellar scattering responsible for pulsar parabolic arcs, and for
intra-day variability of compact radio quasars, is highly anisotropic in some
cases. We numerically simulate these observed phenomena using totally
anisotropic, power-law models for the electron density fluctuations which cause
the scattering. By comparing our results to the scattered image of PSR B0834+06
and, independently, to dual-frequency light curves of the quasar PKS1257-326,
we constrain the nature of the scattering media on these lines of sight. We
find that models with spectral indices slightly below \beta=3, including the
one-dimensional Kolmogorov model, are broadly consistent with both data sets.
We confirm that a single physical model suffices for both sources, with the
scattering medium simply being more distant in the case of B0834+06. This
reinforces the idea that intra-day variability and parabolic arcs have a common
cause in a type of interstellar structure which, though obscure, is
commonplace. However, the implied gas pressure fluctuations are large compared
to typical interstellar pressures, and the magnetic stresses are much larger
still. Thus while these scattering media may be commonplace, their underlying
dynamics appear quite extraordinary. | astro-ph_GA |
Effects of feedback on galaxies in the VELA simulations: elongation,
clumps and compaction: The evolution of star-forming galaxies at high redshifts is very sensitive to
the strength and nature of stellar feedback. Using two sets of cosmological,
zoom-in simulations from the VELA suite, we compare the effects of two
different models of feedback: with and without kinetic feedback from the
expansion of supernovae shells and stellar winds. At a fixed halo mass and
redshift, the stellar mass is reduced by a factor of 1-3 in the models with
stronger feedback, so the stellar-mass-halo-mass relation is in better
agreement with abundance matching results. On the other hand, the
three-dimensional shape of low-mass galaxies is elongated along a major axis in
both models. At a fixed stellar mass, Ms<10^10 Msun, galaxies are more
elongated in the strong-feedback case. More massive, star-forming discs with
high surface densities form giant clumps. However, the population of round,
compact, old (age_c > 300 Myr), quenched, stellar (or gas-poor) clumps is
absent in the model with strong feedback. On the other hand, giant star-forming
clumps with intermediate ages (age_c= 100 - 300 Myr) can survive for several
disc dynamical times, independently of feedback strength. The evolution through
compaction followed by quenching in the plane of central surface density and
specific star-formation rate is similar under the two feedback models. | astro-ph_GA |
Is there a relationship between AGN and star formation in IR-bright
AGNs?: We report the relationship between the luminosities of active galactic nuclei
(AGNs) and the rates of star formation (SF) for a sample of 323 far-infrared
(FIR)-detected AGNs. This sample has a redshift range of 0.2 $< z <$ 2.5, and
spans three orders of magnitude in luminosity, ${\rm L_{X} \sim
10^{42-45}}$erg$s^{-1}$. We find that in AGN hosts, the total IR luminosity
(8-1000$\mu$m) has a significant AGN contribution (average$\sim$20%), and we
suggest using the FIR luminosity (30-1000 $\mu$m) as a more reliable star
formation rate (SFR) estimator. We also conclude that monochromatic
luminosities at 60 and 100\,$\mu$\,m are also good SFR indicators with
negligible AGN contributions, and are less sensitive than integrated infrared
luminosities to the shape of the AGN SED, which is uncertain at
$\lambda>$100\micron. Significant bivariate $L_{\rm X}$-$L_{\rm IR}$
correlations are found, which remain significant in the combined sample when
using residual partial correlation analysis to account for the inherent
redshift dependence. No redshift or mass dependence is found for the ratio
between SFR and black hole accretion rate (BHAR), which has a mean and scatter
of log (SFR/BHAR) $=3.1 \pm$ 0.5, agreeing with the local mass ratio between
supermassive black hole and host galaxies. The large scatter in this ratio and
the strong AGN-SF correlation found in these IR-bright AGNs are consistent with
the scenario of an AGN-SF dependence on a common gas supply, regardless of the
evolutionary model. | astro-ph_GA |
CHANG-ES XIII: Transport processes and the magnetic fields of NGC 4666 -
indication of a reversing disk magnetic field: We analyze the magnetic field geometry and the transport processes of the
cosmic rays of the edge-on spiral starburst galaxy NGC 4666 from CHANG-ES radio
continuum data in two frequencies; 6 GHz (C-band) and 1.5 GHz (L-band).
Supplementary X-ray data are used to investigate the hot gas in NGC 4666. We
determine the radio scale heights of total power emission at both frequencies
for this galaxy. We show the magnetic field orientations derived from the
polarization data. Using rotation measure (RM) synthesis we further study the
behavior of the RM values along the disk in C-band to investigate the
large-scale magnetic-field pattern. We use the revised equipartition formula to
calculate a map of the magnetic field strength. Furthermore, we model the
processes of cosmic-ray transport into the halo with the 1D SPINNAKER model.
The extended radio halo of NGC 4666 is box-shaped and is probably produced by
the previously observed supernova-driven superwind. This is supported by our
finding of an advective cosmic-ray transport such as that expected for a
galactic wind. The scaleheight analysis revealed an asymmetric halo above and
below the disk as well as between the two sides of the major axis. A central
point source as well as a bubble structure is seen in the radio data for the
first time. Our X-ray data show a box-shaped hot halo around NGC 4666 and
furthermore confirm the AGN nature of the central source. NGC 4666 has a
large-scale X-shaped magnetic field in the halo, as has been observed in other
edge-on galaxies. The analysis furthermore revealed that the disk of NGC 4666
shows hints of field reversals along its radius, which is the first detection
of this phenomenon in an external galaxy. | astro-ph_GA |
ALMA reveals sequential high-mass star formation in the G9.62+0.19
complex: Stellar feedback from high-mass stars (e.g., H{\sc ii} regions) can strongly
influence the surrounding interstellar medium and regulate star formation. Our
new ALMA observations reveal sequential high-mass star formation taking place
within one sub-virial filamentary clump (the G9.62 clump) in the G9.62+0.19
complex. The 12 dense cores (MM 1-12) detected by ALMA are at very different
evolutionary stages, from starless core phase to UC H{\sc ii} region phase.
Three dense cores (MM6, MM7/G, MM8/F) are associated with outflows. The
mass-velocity diagrams of outflows associated with MM7/G and MM8/F can be well
fitted with broken power laws. The mass-velocity diagram of SiO outflow
associated with MM8/F breaks much earlier than other outflow tracers (e.g., CO,
SO, CS, HCN), suggesting that SiO traces newly shocked gas, while the other
molecular lines (e.g., CO, SO, CS, HCN) mainly trace the ambient gas
continuously entrained by outflow jets. Five cores (MM1, MM3, MM5, MM9, MM10)
are massive starless core candidates whose masses are estimated to be larger
than 25 M$_{\sun}$, assuming a dust temperature of $\leq$ 20 K. The shocks from
the expanding H{\sc ii} regions ("B" \& "C") to the west may have great impact
on the G9.62 clump through compressing it into a filament and inducing core
collapse successively, leading to sequential star formation. Our findings
suggest that stellar feedback from H{\sc ii} regions may enhance the star
formation efficiency and suppress the low-mass star formation in adjacent
pre-existing massive clumps. | astro-ph_GA |
The galaxy counterpart of the high-metallicity and 16 kpc impact
parameter DLA towards Q0918+1636 - a challenge to galaxy formation models?: The quasar Q0918+1636 (z=3.07) has an intervening high-metallicity Damped
Lyman-alpha Absorber (DLA) along the line of sight, at a redshift of z=2.58.
The DLA is located at a large impact parameter of 16.2 kpc, and has an almost
solar metallicity. It is shown, that a novel type of cosmological galaxy
formation models, invoking a new SNII feedback prescription, the Haardt & Madau
(2012) UVB field and explicit treatment of UVB self-shielding, can reproduce
the observed characteristics of the DLA. UV radiation from young stellar
populations in the galaxy, in particular in the photon energy range 10.36-13.61
eV (relating to Sulfur II abundance), are also considered in the analysis. It
is found that a) for L~L* galaxies (at z=2.58), about 10% of the sight-lines
through the galaxies at impact parameter 16.2 kpc will display a Sulfur II
column density N(SII)$>$ 10$^{15.82}$ cm$^{-2}$ (the observed value for the
DLA), and b) considering only cases where a near-solar metallicity will be
detected at 16.2 kpc impact parameter, the probability distribution of galaxy
SFR peaks near the value observed for the DLA galaxy counterpart of ~27
Msun/yr. It is argued, that the bulk of the alpha-elements, like Sulfur, traced
by the high metal column density, b=16.2 kpc absorption lines, were produced by
evolving young stars in the inner galaxy, and later transported outward by
galactic winds. | astro-ph_GA |
Stripped elliptical galaxies as probes of ICM physics: II. Stirred, but
mixed? Viscous and inviscid gas stripping of the Virgo elliptical M89: Elliptical galaxies moving through the intra-cluster medium (ICM) are
progressively stripped of their gaseous atmospheres. X-ray observations reveal
the structure of galactic tails, wakes, and the interface between the galactic
gas and the ICM. This fine-structure depends on dynamic conditions (galaxy
potential, initial gas contents, orbit in the host cluster), orbital stage
(early infall, pre-/post-pericenter passage), as well as on the still
ill-constrained ICM plasma properties (thermal conductivity, viscosity,
magnetic field structure). Paper I describes flow patterns and stages of
inviscid gas stripping. Here we study the effect of a Spitzer-like temperature
dependent viscosity corresponding to Reynolds numbers, Re, of 50 to 5000 with
respect to the ICM flow around the remnant atmosphere. Global flow patterns are
independent of viscosity in this Reynolds number range. Viscosity influences
two aspects: In inviscid stripping, Kelvin-Helmholtz instabilities (KHIs) at
the sides of the remnant atmosphere lead to observable horns or wings.
Increasing viscosity suppresses KHIs of increasing length scale, and thus
observable horns and wings. Furthermore, in inviscid stripping, stripped
galactic gas can mix with the ambient ICM in the galaxy's wake. This mixing is
suppressed increasingly with increasing viscosity, such that viscously stripped
galaxies have long X-ray bright, cool wakes. We provide mock X-ray images for
different stripping stages and conditions. While these qualitative results are
generic, we tailor our simulations to the Virgo galaxy M89 (NGC 4552), where
Re~ 50 corresponds to a viscosity of 10% of the Spitzer level. Paper III
compares new deep Chandra and archival XMM-Newton data to our simulations. | astro-ph_GA |
The Dragon-II simulations -- II. Formation mechanisms, mass, and spin of
intermediate-mass black holes in star clusters with up to 1 million stars: The processes that govern the formation of intermediate-mass black holes
(IMBHs) in dense stellar clusters are still unclear. Here, we discuss the role
of stellar mergers, star-BH interactions and accretion, as well as BH binary
(BBH) mergers in seeding and growing IMBHs in the \textsc{Dragon-II} simulation
database, a suite of 19 direct $N$-body models representing dense clusters with
up to $10^6$ stars. \textsc{Dragon-II} IMBHs have typical masses of $m_{\rm
IMBH} = (100-380)$ M$_\odot$ and relatively large spins $\chi_{\rm IMBH} >
0.6$. We find a link between the IMBH formation mechanism and the cluster
structure. In clusters denser than $3\times 10^5$ M$_\odot$ pc$^{-3}$, the
collapse of massive star collision products represents the dominant IMBH
formation process, leading to the formation of heavy IMBHs ($m_{\rm IMBH} >
200$ M$_\odot$), possibly slowly rotating, that form over times $<5$ Myr and
grow further via stellar accretion and mergers in just $<30$ Myr. BBH mergers
are the dominant IMBH formation channel in less dense clusters, for which we
find that the looser the cluster, the longer the formation time ($10-300$ Myr)
and the larger the IMBH mass, although remaining within $200$ M$_\odot$. Strong
dynamical scatterings and relativistic recoil efficiently eject all IMBHs in
\textsc{Dragon-II} clusters, suggesting that IMBHs in this type of cluster are
unlikely to grow beyond a few $10^2$ M$_\odot$. | astro-ph_GA |
Probing the origin of the two-component structure of broad line region
by reverberation mapping of an extremely variable quasar: The physical origins of quasar components, such as the broad line region
(BLR) and dust torus, remain under debate. To gain insights into them, we
focused on Changing-State Quasars (CSQs) which provide a unique perspective
through structural changes associated with accretion disk state transitions. We
targeted SDSS J125809.31+351943.0, an extremely variable CSQ, to study its
central core structure and kinematics. We conducted reverberation mapping with
optical spectroscopy to explore the structure of the BLR and estimate the black
hole mass. The results from H$\beta$ reverberation mapping indicated a black
hole mass of $10^{9.64^{+0.11}_{-0.20}}\rm{M_\odot}$. Additionally, we analyzed
variations in the optical to X-ray spectral indices, $\alpha_{\rm{ox}}$, before
and after the state transition, to investigate the accretion disk. These
variations in $\alpha_{\rm{ox}}$ and the Eddington ratio (from 0.4 \% to 2.4
\%) exhibitied behavior similar to state transitions observed in X-ray binary
systems. Spectral analysis of H$\beta$ revealed a predominantly double-peaked
profile during dim periods, transitioning to include a single-peaked component
as the quasar brightened, suggesting that H$\beta$ contains a mixture of two
components. Each of these components has its distinct characteristics: the
first is a double-peaked profile that remains stable despite changes in the
accretion rate, while the second is a variable single-peaked profile. Using
time lags from reverberation mapping, we estimated the spatial relationships
between these BLR components, the accretion disk, and the dust torus. Our
results suggest that the BLR consists of two distinct components, each
differing in location and origin. | astro-ph_GA |
Unraveling the Complex Structure of AGN-driven Outflows. VI. Strong
Ionized Outflows in Type 1 AGNs and the Outflow Size-Luminosity Relation: We present spatially resolved gas kinematics, ionization, and energetics of
11 type 1 and 5 type 2 active galactic nuclei (AGNs) with strong ionized gas
outflows at z $<0.3$ using Gemini Multi-Object Spectrograph Integral Field Unit
(GMOS-IFU) data. We find a strongly blueshifted region in [OIII] velocity maps,
representing an approaching cone in biconical outflows, and blueshifted and
redshifted regions in H$\alpha$ velocity maps, which show gravitationally
rotating kinematics. AGN photoionization is dominant in the central region of
most targets, and some of them also show ring-like structures of LINER or
composite that surround the AGN-dominated center. Following our previous
studies, we kinematically determine outflow sizes by the ratio between [OIII]
and stellar velocity dispersion. Outflow sizes of type 1 AGNs follow the same
kinematic outflow size-[OIII] luminosity relation obtained from the type 2 IFU
sample in Kang & Woo and Luo (updated slope $0.29\pm0.04$), while they are
limited to the central kpc scales, indicating the lack of global impact of
outflows on the interstellar medium. Small mass outflow rates and large star
formation rates of the combined sample support that there is no evidence of
rapid star formation quenching by outflows, which is consistent with the
delayed AGN feedback. | astro-ph_GA |
MAHALO Deep Cluster Survey II. Characterizing massive forming galaxies
in the Spiderweb protocluster at z=2.2: This paper is the second in a series presenting the results of our deep
H$\alpha$-line survey towards protoclusters at $z>2$, based on narrow-band
imaging with the Subaru Telescope. This work investigates massive galaxies in a
protocluster region associated with a radio galaxy (PKS 1138$-$262), the
Spiderweb galaxy, at $z=2.2$. Our 0.5 mag deeper narrow-band imaging than
previous surveys collects a total of 68 H$\alpha$ emitters (HAE). 17 out of the
68 are newly discovered protocluster members. First, a very high characteristic
stellar mass of M$_\star^\ast=10^{11.73}$ M$_\odot$ is measured from a
Schechter function fit to the mass distribution of HAEs. Together with the
Chandra X-ray data, we find that four out of six massive HAEs
(M$_\star>10^{11}$ M$_\odot$) show bright X-ray emission, suggesting that they
host active galactic nuclei (AGNs). Their mass estimates, therefore, would be
affected by the nuclear emission from AGNs. Notably, the X-ray detected HAEs
are likely positioned near the boundary between star-forming and quiescent
populations in the rest-frame $UVJ$ plane. Moreover, our deep narrow-band data
succeed in probing the bright H$\alpha$ (+[Nii]) line nebula of the Spiderweb
galaxy extending over $\sim100$ physical kpc. These results suggest that the
massive galaxies in the Spiderweb protocluster are on the way to becoming the
bright red sequence objects seen in local galaxy clusters, where AGNs might
play an essential role in their quenching processes. Though a more statistical
database is needed to build a general picture. | astro-ph_GA |
Molecular Emission from a Galaxy Associated with a z~2.2 Damped
Lyman-alpha Absorber: Using the Atacama Large Millimeter/sub-millimeter Array, we have detected
CO(3-2) line and far-infrared continuum emission from a galaxy associated with
a high-metallicity ([M/H] = -0.27) damped Ly-alpha absorber (DLA) at z
=2.19289. The galaxy is located 3.5" away from the quasar sightline,
corresponding to a large impact parameter of 30 kpc at the DLA redshift. We use
archival Very Large Telescope-SINFONI data to detect Halpha emission from the
associated galaxy, and find that the object is dusty, with a dust-corrected
star formation rate of 110 +60 -30 Msun/yr. The galaxy's molecular mass is
large, Mmol = (1.4 +- 0.2) x 10^11 x (\alpha_CO/4.3) x (0.57/r_31) Msun,
supporting the hypothesis that high-metallicity DLAs arise predominantly near
massive galaxies. The excellent agreement in redshift between the CO(3-2) line
emission and low-ion metal absorption (~40 km/s) disfavors scenarios whereby
the gas probed by the DLA shows bulk motion around the galaxy. We use Giant
Metrewave Radio Telescope HI 21cm absorption spectroscopy to find that the HI
along the DLA sightline must be warm, with a stringent lower limit on the spin
temperature of T_s > 1895 x (f/0.93) K. The detection of CI absorption in the
DLA, however, also indicates the presence of cold neutral gas. To reconcile
these results requires that the cold components in the DLA contribute little to
the HI column density, yet contain roughly 50% of the metals of the absorber,
underlining the complex multi-phase nature of the gas surrounding high-z
galaxies. | astro-ph_GA |
Where stars form: inside-out growth and coherent star formation from HST
Halpha maps of 2676 galaxies across the main sequence at z~1: We present Ha maps at 1kpc spatial resolution for star-forming galaxies at
z~1, made possible by the WFC3 grism on HST. Employing this capability over all
five 3D-HST/CANDELS fields provides a sample of 2676 galaxies. By creating deep
stacked Halpha (Ha) images, we reach surface brightness limits of
1x10^-18\erg\s\cm^2\arcsec^2, allowing us to map the distribution of ionized
gas out to >10kpc for typical L* galaxies at this epoch. We find that the
spatial extent of the Ha distribution increases with stellar mass as
r(Ha)[kpc]=1.5(Mstars/10^10Msun)^0.23. Furthermore, the Ha emission is more
extended than the stellar continuum emission, consistent with inside-out
assembly of galactic disks. This effect, however, is mass dependent with
r(Ha)/r(stars)=1.1(M/10^10Msun)^0.054, such that at low masses r(Ha)~r(stars).
We map the Ha distribution as a function of SFR(IR+UV) and find evidence for
`coherent star formation' across the SFR-M plane: above the main sequence, Ha
is enhanced at all radii; below the main sequence, Ha is depressed at all
radii. This suggests that at all masses the physical processes driving the
enhancement or suppression of star formation act throughout the disks of
galaxies. It also confirms that the scatter in the star forming main sequence
is real and caused by variations in the star formation rate at fixed mass. At
high masses (10^10.5<M/Msun<10^11), above the main sequence, Ha is particularly
enhanced in the center, plausibly building bulges and/or supermassive black
holes. Below the main sequence, the star forming disks are more compact and a
strong central dip in the EW(Ha), and the inferred specific star formation
rate, appears. Importantly though, across the entirety of the SFR-M plane, the
absolute star formation rate as traced by Ha is always centrally peaked, even
in galaxies below the main sequence. | astro-ph_GA |
The Vista Variables in the Via Lactea (VVV) ESO Public Survey: Current
Status and First Results: Vista Variables in the Via Lactea (VVV) is an ESO Public Survey that is
performing a variability survey of the Galactic bulge and part of the inner
disk using ESO's Visible and Infrared Survey Telescope for Astronomy (VISTA).
The survey covers 520 deg^2 of sky area in the ZYJHK_S filters, for a total
observing time of 1929 hours, including ~ 10^9 point sources and an estimated ~
10^6 variable stars. Here we describe the current status of the VVV Survey, in
addition to a variety of new results based on VVV data, including light curves
for variable stars, newly discovered globular clusters, open clusters, and
associations. A set of reddening-free indices based on the ZYJHK_S system is
also introduced. Finally, we provide an overview of the VVV Templates Project,
whose main goal is to derive well-defined light curve templates in the near-IR,
for the automated classification of VVV light curves. | astro-ph_GA |
Clues on the Missing Sources of Reionization from Self-consistent
Modeling of Milky Way and Dwarf Galaxy Globular Clusters: Globular clusters are unique tracers of ancient star formation. We determine
the formation efficiencies of globular clusters across cosmic time by modeling
the formation and dynamical evolution of the globular cluster population of a
Milky Way type galaxy in hierarchical cosmology, using the merger tree from the
Via Lactea II simulation. All of the models are constrained to reproduce the
observed specific frequency and initial mass function of globular clusters in
isolated dwarfs. Globular cluster orbits are then computed in a time varying
gravitational potential after they are either accreted from a satellite halo or
formed in situ, within the Milky Way halo. We find that the Galactocentric
distances and metallicity distribution of globular clusters are very sensitive
to the formation efficiencies of globular clusters as a function of redshift
and halo mass. Our most accurate models reveal two distinct peaks in the
globular cluster formation efficiency at z~2 and z~7-12 and prefer a formation
efficiency that is mildly increasing with decreasing halo mass, the opposite of
what expected for feedback-regulated star formation. This model accurately
reproduces the positions, velocities, mass function, metallicity distribution,
and age distribution of globular clusters in the Milky Way and predicts that ~
40% formed in situ, within the Milky Way halo, while the other ~ 60% were
accreted from about 20 satellite dwarf galaxies with Vc > 30 km/s, and about
29% or all globular clusters formed at redshifts z > 7. These results further
strengthen the notion that globular cluster formation was an important mode of
star formation in high-redshift galaxies and likely played a significant role
in the reionization of the intergalactic medium | astro-ph_GA |
A massive mess: When a large dwarf and a Milky Way-like galaxy merge: Circa 10 billion years ago the Milky Way merged with a massive satellite,
Gaia-Enceladus. To gain insight into the properties of its debris we analyse in
detail the suite of simulations from Villalobos & Helmi (2008), which includes
an experiment that produces a good match to the kinematics of nearby halo stars
inferred from Gaia data. We compare the kinematic distributions of stellar
particles in the simulations and study the distribution of debris in orbital
angular momentum, eccentricity and energy, and its relation to the mass-loss
history of the simulated satellite. We confirm that Gaia-Enceladus probably
fell in on a retrograde, 30$^\circ$ inclination orbit. We find that while 75%
of the debris in our preferred simulation has large eccentricity ($> 0.8$),
roughly 9% has eccentricity smaller than 0.6. Star particles lost early have
large retrograde motions, and a subset of these have low eccentricity. Such
stars would be expected to have lower metallicities as they stem from the
outskirts of the satellite, and hence naively they could be confused with
debris associated with a separate system. These considerations seem to apply to
some of the stars from the postulated Sequoia galaxy. When a massive discy
galaxy merges, it leaves behind debris with a complex phase-space structure, a
large range of orbital properties, and a range of chemical abundances.
Observationally, this results in substructures with very different properties,
which can be misinterpreted as implying independent progeny. Detailed chemical
abundances of large samples of stars and tailored hydrodynamical simulations
are critical to resolving such conundrums. | astro-ph_GA |
Correlations of gas, dust and young stellar populations in the spiral
galaxy NGC 7331: Molecular clouds (MCs) in galaxies are complex places with many phases. It
is, therefore, essential to study the physics and kinematics of the MCs using
multiple emission lines. We probe the physics of the molecular gas and dust in
the nearby spiral galaxy NGC 7331 using multiple emission lines, i.e. carbon
monoxide (CO), 24{\mu}m and far-ultraviolet (FUV) data. 14 positions were
targeted across the gaseous disc of NGC 7331. We found that CO intensities, gas
mass, gas surface density, and 24{\mu}m-to-FUV flux ratio (i.e. the extinction)
increase up to about 40 arcsec from the centre and then start to decrease.
There is a positive correlation between most of the pair of parameters studied
(except FUV flux density). The beam-averaged physical parameters on the eastern
side of the disc show higher median values than those on the western side. Our
results indicate that the star formation activity, stellar populations and
overall physical properties of the ISM are different on either side of the
disc. Our study provides notable insights into the complex nature of the
interstellar medium (ISM) in galaxies and has the potential to provoke future
higher-resolution studies yet to come. | astro-ph_GA |
Kinematics of the Atomic ISM in M33 on 80 pc scales: We present new L-band ($1\mbox{--}2$ GHz) observations of the nearby spiral
galaxy M33 with 80 pc resolution obtained with the Karl G. Jansky Very Large
Array. The HI observations, combined with HI measurements from the Green Bank
Telescope, improve the spectral resolution and sensitivity ($2.8$ K rms noise
in a $0.2$ km s$^{-1}$ channel) compared to previous observations. We find
individual profiles are usually non-Gaussian, harbouring line wings, multiple
components, and asymmetries. Given this spectral complexity, we quantify the
motions in the atomic ISM through moment analysis of the spectra and fits to
aligned, stacked profiles. The measured value of the HI line width depends
strongly on the method used, with the velocity stacked profiles aligned to the
peak velocity giving the minimum value of $\sigma = 7$ km s$^{-1}$ and all
other methods giving higher values ($\sigma\sim10$ km s$^{-1}$). All
measurements of the line width show a shallow radial trend, with $\sigma$
decreasing by $\sim2$ km s$^{-1}$ from $R_{\rm gal}=0$ to $R_{\rm gal}=8$ kpc.
We consider a number of energy sources that might maintain the line width
against turbulent dissipation, but no single source is adequate. We find excess
emission relative to a Gaussian in the stacked profile line wings, ranging from
9% to 26% depending on how the spectra are aligned. By splitting the line wings
into symmetric and asymmetric components, we find that the lagging rotational
disk accounts for one-third of the line wing flux. We also find emission far
from the rotation axis of the galaxy in multiple discrete HI clouds, including
a filament with a projected length of $\sim8$ kpc. | astro-ph_GA |
A 2-3 mm high-resolution molecular line survey towards the centre of the
nearby spiral galaxy NGC 6946: The complex physical, kinematic, and chemical properties of galaxy centres
make them interesting environments to examine with molecular line emission. We
present new $2-4$" (${\sim}75{-}150$ pc at $7.7$ Mpc) observations at 2 and 3
mm covering the central $50$" (${\sim}1.9$ kpc) of the nearby double-barred
spiral galaxy NGC 6946 obtained with the IRAM Plateau de Bure Interferometer.
We detect spectral lines from ten molecules: CO, HCN, HCO$^+$, HNC, CS,
HC$_3$N, N$_2$H$^+$, C$_2$H, CH$_3$OH, and H$_2$CO. We complemented these with
published 1mm CO observations and 33 GHz continuum observations to explore the
star formation rate surface density ${\Sigma_{\mathrm{SFR}}}$ on 150 pc scales.
In this paper, we analyse regions associated with the inner bar of NGC 6946 $-$
the nuclear region (NUC), the northern (NBE), and southern inner bar end (SBE)
and we focus on short-spacing corrected bulk (CO) and dense gas tracers (HCN,
HCO$^+$, and HNC). We find that HCO$^+$ correlates best with
${\Sigma_{\mathrm{SFR}}}$, but the dense gas fraction ($f_{\mathrm{dense}}$)
and star formation efficiency of the dense gas (${\mathrm{SFE_{dense}}}$) fits
show different behaviours than expected from large-scale disc observations.The
SBE has a higher ${\Sigma_{\mathrm{SFR}}}$, $f_{\mathrm{dense}}$, and shocked
gas fraction than the NBE. We examine line ratio diagnostics and find a higher
CO(2-1)/CO(1-0) ratio towards NBE than for the NUC. Moreover, comparison with
existing extragalactic datasets suggests that using the HCN/HNC ratio to probe
kinetic temperatures is not suitable on kiloparsec and sub-kiloparsec scales in
extragalactic regions. Lastly, our study shows that the HCO$^+$/HCN ratio might
not be a unique indicator to diagnose AGN activity in galaxies. | astro-ph_GA |
Is a recently discovered HI cloud near M94 a starless dark matter halo?: Observations with the Five-Hundred-Meter Aperture Spherical Telescope have
revealed the presence of a marginally-resolved source of 21 cm emission from a
location $\sim50'$ from the M94 galaxy, without a stellar counterpart down to
the surface brightness limit of the DESI Imaging Legacy Survey ($\sim29.15$ mag
arcsec$^{-2}$ in the $g$ band). The system (hereafter Cloud-9) has round column
density isocontours and a line width consistent with thermal broadening from
gas at $T\sim2\times10^4$ $K$. These properties are unlike those of previously
detected dark HI clouds and similar to the expected properties of
REionization-Limited-HI Cloud (RELHICs), namely, starless dark matter (DM)
halos filled with gas in hydrostatic equilibrium and in thermal equilibrium
with the cosmic ultraviolet background. At the distance of M94, $d\sim4.7$ Mpc,
we find that Cloud-9 is consistent with being a RELHIC inhabiting a
Navarro-Frenk-White (NFW) DM halo of mass, $M_{200}\sim5\times10^{9}$
$M_{\odot}$, and concentration, $c_{\rm NFW}\sim13$. Although the agreement
between the model and observations is good, Cloud-9 appears to be slightly, but
systematically, more extended than expected for $\Lambda$CDM RELHICs. This may
imply either that Cloud-9 is much closer than implied by its recessional
velocity, $v_{\rm CL9}\sim300$ km s$^{-1}$, or that its halo density profile is
flatter than NFW, with a DM mass deficit greater than a factor of $10$ at radii
$r\lesssim1$ kpc. Further observations may aid in constraining these scenarios
better and help elucidate whether Cloud-9 is the first ever observed RELHIC, a
cornerstone prediction of the $\Lambda$CDM model on the smallest scales. | astro-ph_GA |
The Galaxy in Context: Structural, Kinematic and Integrated Properties: Our Galaxy, the Milky Way, is a benchmark for understanding disk galaxies. It
is the only galaxy whose formation history can be studied using the full
distribution of stars from white dwarfs to supergiants. The oldest components
provide us with unique insight into how galaxies form and evolve over billions
of years. The Galaxy is a luminous (L-star) barred spiral with a central
box/peanut bulge, a dominant disk, and a diffuse stellar halo. Based on global
properties, it falls in the sparsely populated "green valley" region of the
galaxy colour-magnitude diagram. Here we review the key integrated, structural
and kinematic parameters of the Galaxy, and point to uncertainties as well as
directions for future progress. Galactic studies will continue to play a
fundamental role far into the future because there are measurements that can
only be made in the near field and much of contemporary astrophysics depends on
such observations. | astro-ph_GA |
A Uniformly Selected, Southern-Sky 6dF, Optical AGN Catalog: We have constructed a catalog of active galactic nuclei (AGNs) with $z <
0.13$, based on optical spectroscopy, from the parent sample of galaxies in the
6dF galaxy survey (Final Release of 6dFGS), a census of the Southern
hemisphere. This work is an extension of our all sky AGN catalog \citet [ZCF,
here after]{ZCF19}. The ZCF is based on 43,533 galaxies with $\rm K_s \leq$
11.75 ($z \leq 0.09$) in the 2MASS Redshift Survey (2MRS). The parent catalog
of this work, the 6dF catalog, consists of 136,304 publicly available digital
spectra for 125,071 galaxies with $\rm Dec \leq 0^\circ$ and $\rm K_s \leq
12.65$ (median $z = 0.053$). Our AGN catalog consists of 3109 broad line AGNs
and 12,156 narrow line AGNs which satisfy the \citet{Kauffmann03} criteria, of
which 3865 also satisfy the \citet{Kewley01} criteria. We also provide emission
line widths, fluxes, flux errors, and signal-to-noise ratios of all the
galaxies in our spectroscopic sample, allowing users to customize the selection
criteria. In addition, we provide AGN likelihood for the rest of galaxies based
on the availability and quality of their spectra. These likelihood values can
be used for rigorous statistical analyses. | astro-ph_GA |
Effects of baryonic and dark matter substructure on the Pal 5 stream: Gravitational encounters between small-scale dark matter substructure and
cold stellar streams in the Milky Way halo lead to density perturbations in the
latter, making streams an effective probe for detecting dark matter
substructure. The Pal 5 stream is one such system for which we have some of the
best data. However, Pal 5 orbits close to the center of the Milky Way and has
passed through the Galactic disk many times, where its structure can be
perturbed by baryonic structures such as the Galactic bar and giant molecular
clouds (GMCs). In order to understand how these baryonic structures affect Pal
5's density, we present a detailed study of the effects of the Galactic bar,
spiral structure, GMCs, and globular clusters on the Pal 5 stream. We estimate
the effect of each perturber on the stream density by computing its power
spectrum and comparing it to the power induced by a CDM-like population of dark
matter subhalos. We find that the bar and GMCs can each individually create
power that is comparable to the observed power on large scales, leaving little
room for dark matter substructure, while spirals are subdominant on all scales.
On degree scales, the power induced by the bar is small, but GMCs create
small-scale density variations that are similar in amplitude to the dark-matter
induced variations but otherwise indistinguishable from it. These results
demonstrate that Pal 5 is a poor system for constraining the dark matter
substructure fraction and that observing streams further out in the halo will
be necessary to confidently detect dark matter subhalos. | astro-ph_GA |
Probing $z \gtrsim 6$ massive black holes with gravitational waves: We investigate the coalescence of massive black hole ($M_{\rm BH}\gtrsim
10^{6}~\rm M_{\odot}$) binaries (MBHBs) at $6<z<10$ by adopting a suite of
cosmological hydrodynamical simulations of galaxy formation, zoomed-in on
biased ($ >3 \sigma$) overdense regions ($M_h\sim 10^{12}~\rm M_{\odot}$ dark
matter halos at $z = 6$) of the Universe. We first analyse the impact of
different resolutions and AGN feedback prescriptions on the merger rate,
assuming instantaneous mergers. Then, we compute the halo bias correction
factor due to the overdense simulated region. Our simulations predict merger
rates that range between 3 - 15 $\rm yr^{-1}$ at $z\sim 6$, depending on the
run considered, and after correcting for a bias factor of $\sim 20-30$.
For our fiducial model, we further consider the effect of delay in the MBHB
coalescence due to dynamical friction. We find that 83 per cent of MBHBs will
merge within the Hubble time, and 21 per cent within 1 Gyr, namely the age of
the Universe at $z > 6$. We finally compute the expected properties of the
gravitational wave (GW) signals and find the fraction of LISA detectable events
with high signal-to-noise ratio (SNR $>$ 5) to range between 66-69 per cent.
However, identifying the electro-magnetic counterpart of these events remains
challenging due to the poor LISA sky localization that, for the loudest signals
($\mathcal M_c\sim 10^6~\rm M_{\odot}$ at $z=6$), is around 10 $\rm deg^2$. | astro-ph_GA |
The impact of black hole feedback on the UV luminosity and stellar mass
assembly of high-redshift galaxies: We employ the Delphi semi-analytical model to study the impact of black hole
growth on high-redshift galaxies, both in terms of the observed UV luminosity
and of the star formation rate. To do this, firstly, we assess the contribution
of AGN to the total galaxy UV luminosity as a function of stellar mass and
redshift. We find that for $M_{UV} < -24$ mag and $z \approx 5 - 6$ the
galaxies for which the black hole UV luminosity outshines the stellar UV
emission become the majority, and we estimate their duty cycle. Secondly, we
study the evolution of the AGN and stellar luminosity functions (LFs), finding
that it is driven both by changes in their characteristic luminosities (i.e.
evolution of the intrinsic brightness of galaxies) and in their normalizations
(i.e. evolution of the number densities of galaxies), depending on the
luminosity range considered. Finally, we follow the mass assembly history for
three different halo mass bins, finding that the magnitude of AGN-driven
outflows depends on the host halo mass. We show that AGN feedback is most
effective when the energy emitted by the accreting black hole is approximately
$1\%$ of the halo binding energy, and that this condition is met in galaxies in
halos with $M_h \sim 10^{11.75} M_\odot$ at $z=4$. In such cases, AGN feedback
can drive outflows that are up to 100 times more energetic than SN-driven
outflows, and the star formation rate is a factor of three lower than for
galaxies of the same mass without black hole activity. | astro-ph_GA |
Restoration of the Tully-Fisher Relation by Statistical Rectification: I employ the Lucy rectification algorithm to recover the
inclination-corrected distribution of local disk galaxies in the plane of
absolute magnitude ($M_i$) and HI velocity width ($W_{20}$). By considering the
inclination angle as a random variable with a known probability distribution,
the novel approach eliminates one major source of uncertainty in studies of the
Tully-Fisher relation: inclination angle estimation from axial ratio.
Leveraging the statistical strength derived from the entire sample of 28,264
HI-selected disk galaxies at $z < 0.06$ from the Arecibo Legacy Fast ALFA
(ALFALFA) survey, I show that the restored distribution follows a sharp
correlation that is approximately a power law between $-16 > M_i > -22$: $M_i =
M_0 - 2.5\beta \ [\log(W_{\rm 20}/250 {\rm km/s})]$, with $M_0 = -19.77\pm0.04$
and $\beta = 4.39\pm0.06$. At the brighter end ($M_i < -22$), the slope of the
correlation decreases to $\beta \approx 3.3$, confirming previous results.
Because the method accounts for measurement errors, the intrinsic dispersion of
the correlation is directly measured: $\sigma(\log W_{20}) \approx 0.06$ dex
between $-17 > M_i > -23$, while $\sigma(M_i)$ decreases from $\sim$0.8 in slow
rotators to $\sim$0.4 in fast rotators. The statistical rectification method
holds significant potential, especially in the studies of
intermediate-to-high-redshift samples, where limited spatial resolution hinders
precise measurements of inclination angles. | astro-ph_GA |
Magnetized Kelvin-Helmholtz instability in the presence of a radiation
field: The purpose of this study is to analyze the dynamical role of a radiation
field on the growth rate of the unstable Kelvin - Helmholtz (KH) perturbations.
As a first step toward this purpose, the analyze is done in a general way,
irrespective of applying the model to a specific astronomical system. The
transition zone between the two layers of the fluid is ignored. Then, we
perform a linear analysis and by imposing suitable boundary conditions and
considering a radiation field, we obtain appropriate dispersion relation.
Unstable modes are studied by solving the dispersion equation numerically, and
then growth rates of them are obtained. By analyzing our dispersion relation,
we show that for a wide range of the input parameters, the radiation field has
a destabilizing effect on KH instability. In eruptions of the galaxies or
supermassive stars, the radiation field is dynamically important and because of
the enhanced KH growth rates in the presence of the radiation; these eruptions
can inject more momentum and energy into their environment and excite more
turbulent motions. | astro-ph_GA |
A 10,000 Years Old Explosion in DR21: Sensitive high angular resolution ($\sim$ 2$"$) CO(2-1) line observations
made with the Submillimeter Array (SMA) of the flow emanating from the
high-mass star forming region DR21 located in the Cygnus X molecular cloud are
presented. These new interferometric observations indicate that this well known
enigmatic outflow appears to have been produced by an explosive event that took
place about 10,000 years ago, and that might be related with the disintegration
of a massive stellar system, as the one that occurred in Orion BN/KL 500 years
ago, but about 20 times more energetic. This result therefore argues in favor
of the idea that the disintegration of young stellar systems perhaps is a
frequent phenomenon present during the formation of the massive stars. However,
many more theoretical and observational studies are still needed to confirm our
hypothesis. | astro-ph_GA |
Constraints on Spin of a Supermassive Black Hole in Quasars with Big
Blue Bump: We determined the spin value of supermassive black hole (SMBH) in active
galactic nuclei (AGN) with investigated ultraviolet-to-optical spectral energy
distribution, presented in the sample of Shang et al. (2005). The estimates of
the spin values have been produced at the base of the standard geometrically
thin accretion disk model and with using the results of the polarimetric
observations. The polarimetric observations are very important for determining
the inclination angle of AGN disk. We presented the results of our
determinations of the radiation efficiency of the accretion flow and values of
the spins of SMBHs, that derives the coefficient of radiation efficiency. The
majority of SMBHs of AGNs from Shang et al. (2005) sample are to be the Kerr
black holes with the high spin value. | astro-ph_GA |
$Ω_{\rm bar}$ in NGC 5597 from VLA HI 21 cm Observations: We report Very Large Array B-configuration observations of the atomic
hydrogen 21 cm line emission from the barred disk galaxy NGC 5597 at an angular
resolution of 7.1" x 4.2". Using the resonance method, and assuming the ratio
of the corotation radius to the semi-major axis of the stellar bar is unity
($\mathcal{R} \equiv R_{\rm CR}/a_{\rm bar} = 1$), we estimate the angular
pattern speed of the stellar bar to be, $\Omega_{{\rm bar}} \sim 15.3$ km
s$^{-1}$ kpc$^{-1}$. This constant value for $\Omega_{\rm bar}$ crosses
$\Omega_{\rm gas} + \kappa(R)/4$ at a distance $\sim 6.73$ kpc which would
correspond to the spatial location of the north spiral structure near an outer
m=4 resonance. This value of $\Omega_{\rm bar}$ is similar to the values
estimated for other bright nearby barred galaxies that exhibit circumnuclear
rings (near ILR) or outer rings (near OLR). | astro-ph_GA |
Hidden giants in JWST's PEARLS: An ultra-massive z=4.26 sub-millimeter
galaxy that is invisible to HST: We present a multi-wavelength analysis using SMA, JCMT, NOEMA, JWST, HST, and
SST of two dusty strongly star-forming galaxies, 850.1 and 850.2, seen through
the massive cluster lens A1489. These SMA-located sources both lie at z=4.26
and have bright dust continuum emission, but 850.2 is a UV-detected Lyman-break
galaxy, while 850.1 is undetected at <2um, even with deep JWST/NIRCam
observations. We investigate their stellar, ISM, and dynamical properties,
including a pixel-level SED analysis to derive sub-kpc-resolution stellar-mass
and Av maps. We find that 850.1 is one of the most massive and highly obscured,
Av~5, galaxies known at z>4 with M*~10^11.8 Mo (likely forming at z>6), and
850.2 is one of the least massive and least obscured, Av~1, members of the z>4
dusty star-forming population. The diversity of these two dust-mass-selected
galaxies illustrates the incompleteness of galaxy surveys at z>3-4 based on
imaging at <2um, the longest wavelengths feasible from HST or the ground. The
resolved mass map of 850.1 shows a compact stellar mass distribution,
Re(mass)~1kpc, but its expected evolution to z~1.5 and then z~0 matches both
the properties of massive, quiescent galaxies at z~1.5 and ultra-massive
early-type galaxies at z~0. We suggest that 850.1 is the central galaxy of a
group in which 850.2 is a satellite that will likely merge in the near future.
The stellar morphology of 850.1 shows arms and a linear bar feature which we
link to the active dynamical environment it resides within. | astro-ph_GA |
The better half -- Asymmetric star-formation due to ram pressure in the
EAGLE simulations: We use the EAGLE simulations to study the effects of the intra-cluster medium
(ICM) on the spatially resolved star-formation activity in galaxies. We study
three cases of galaxy asymmetry dividing each galaxy in two halves using the
plane (i) perpendicular to the $\rm \texttt{velocity}$ direction,
differentiating the galaxy part approaching to the cluster center, hereafter
dubbed as the "leading half", and the opposite one "trailing half", (ii)
perpendicular to the $\rm \texttt{radial}$ position of the satellite to the
centre of the cluster, (iii) that maximizes the star-formation rate ($\rm SFR$)
difference between the two halves. For (i), we find an enhancement of the $\rm
SFR$, star formation efficiency ($\rm SFE$), and interstellar medium pressure
in the leading half with respect to the trailing one and normal star-forming
galaxies in the EAGLE simulation, and a clear overabundance of gas particles in
their trailing. These results suggest that ram pressure (RP) is boosting the
star formation by gas compression in the leading half, and transporting the gas
to the trailing half. This effect is more pronounced in satellites of
intermediate stellar masses $\rm 10^{9.5-10.5} M_{\odot}$, with gas masses
above $\rm 10^{9} M_{\odot}$, and located within one virial radius or in the
most massive clusters. In (iii) we find an alignment between the velocity and
the vector perpendicular to the plane that maximizes the $\rm SFR$ difference
between the two halves. It suggests that finding this plane in real galaxies
can provide insights into the velocity direction. | astro-ph_GA |
The TREX Survey: Kinematical Complexity Throughout M33's Stellar Disk
and Evidence for a Stellar Halo: We present initial results from a large spectroscopic survey of stars
throughout M33's stellar disk. We analyze a sample of 1667 red giant branch
(RGB) stars extending to projected distances of $\sim 11$ kpc from M33's center
($\sim 18$ kpc, or $\sim 10$ scale lengths, in the plane of the disk). The
line-of-sight velocities of RGB stars show the presence of two kinematical
components. One component is consistent with rotation in the plane of M33's HI
disk and has a velocity dispersion ($\sim 19$ km s$^{-1}$) consistent with that
observed in a comparison sample of younger stars, while the second component
has a significantly higher velocity dispersion. A two-component fit to the RGB
velocity distribution finds that the high dispersion component has a velocity
dispersion of $59.3^{+2.6}_{-2.5}$ km s$^{-1}$ and rotates very slowly in the
plane of the disk (consistent with no rotation at the $<1.5\sigma$ level),
which favors interpreting it as a stellar halo rather than a thick disk
population. A spatial analysis indicates that the fraction of RGB stars in the
high-velocity-dispersion component decreases with increasing radius over the
range covered by the spectroscopic sample. Our spectroscopic sample establishes
that a significant high-velocity-dispersion component is present in M33's RGB
population from near M33's center to at least the radius where M33's HI disk
begins to warp at 30$'$ ($\sim 7.5$ kpc) in the plane of the disk. This is the
first detection and spatial characterization of a kinematically hot stellar
component throughout M33's inner regions. | astro-ph_GA |
CO Multi-line Imaging of Nearby Galaxies (COMING). III. Dynamical effect
on molecular gas density and star formation in the barred spiral galaxy NGC
4303: We present the results of $^{12}$CO($J$=1-0) and $^{13}$CO($J$=1-0)
simultaneous mappings toward the nearby barred spiral galaxy NGC 4303 as a part
of the CO Multi-line Imaging of Nearby Galaxies (COMING) project. Barred spiral
galaxies often show lower star-formation efficiency (SFE) in their bar region
compared to the spiral arms. In this paper, we examine the relation between the
SFEs and the volume densities of molecular gas $n(\rm{H}_2)$ in the eight
different regions within the galactic disk with CO data combined with archival
far-ultraviolet and 24 $\mu$m data. We confirmed that SFE in the bar region is
lower by 39% than that in the spiral arms. Moreover, velocity-alignment
stacking analysis was performed for the spectra in the individual regions. The
integrated intensity ratios of $^{12}$CO to $^{13}$CO ($R_{12/13}$) range from
10 to 17 as the results of stacking. Fixing a kinetic temperature of molecular
gas, $n(\rm{H}_2)$ was derived from $R_{12/13}$ via non-local thermodynamic
equilibrium (non-LTE) analysis. The density $n(\rm{H}_2)$ in the bar is lower
by 31-37% than that in the arms and there is a rather tight positive
correlation between SFEs and $n(\rm{H}_2)$, with a correlation coefficient of
$\sim 0.8$. Furthermore, we found a dependence of $n(\rm{H}_2)$ on the velocity
dispersion of inter-molecular clouds ($\Delta V/ \sin i$). Specifically,
$n(\rm{H}_2)$ increases as $\Delta V/ \sin i$ increases when $\Delta V/ \sin i
< 100$ km s$^{-1}$. On the other hand, $n(\rm{H}_2)$ decreases as $\Delta V/
\sin i$ increases when $\Delta V/ \sin i > 100$ km s$^{-1}$. These relations
indicate that the variations of SFE could be caused by the volume densities of
molecular gas, and the volume densities could be governed by the dynamical
influence such as cloud-cloud collisions, shear and enhanced inner-cloud
turbulence. | astro-ph_GA |
Photometric and kinematical analysis of Koposov 12 and Koposov 43 open
clusters: We present a photometric and kinematical analysis of two and poorly studied
open clusters; Koposov 12 (FSR 802) and Koposov 43 (FSR 848) by using
cross-matched data from PPMXL and Gaia DR2 catalog. We use astrometric
parameters to identify 285 and 310 cluster members for Koposov 12 and Koposov
43, respectively. Using the extracted member candidates and isochrone fitting
to near-infrared (J, H, Ks) and Gaia DR2 bands (G, GBP, GRP), and Color
Magnitude Diagrams (CMDs), we have estimated ages: log (age/yr) = 9.00 +/- 0.20
and 9.50 +/- 0.20, and distances d = 1850 +/- 43 pc and 2500 +/- 50 pc for
Koposov 12 and Koposov 43, respectively, assuming Solar metallicity (Z=0.019).
The estimated masses of the cluster derived using initial mass function and
synthetic CMD are 364 +/- 19 M_sun and 352 +/- 19 M_sun. We have also computed
their velocity ellipsoid parameters based on (3x3) matrix elements (mu_ij). | astro-ph_GA |
Observations contradict galaxy size and surface brightness predictions
that are based on the expanding universe hypothesis: In a non-expanding universe surface brightness is independent of distance or
redshift, while in an expanding universe it decreases rapidly with both.
Similarly, for objects of the same luminosity, the angular radius of an object
in a non-expanding universe declines with redshift, while in an expanding
universe this radius increases for redshifts z>1.25. The author and colleagues
have previously shown that data for the surface brightness of disk galaxies are
compatible with a static universe with redshift linearly proportional to
distance at all z (SEU hypothesis). In this paper we examine the more
conventional hypothesis that the universe is expanding, but that the actual
radii of galaxies of a given luminosity increase with time (decrease with z),
as others have proposed. We show that the radii data for both disk and
elliptical galaxies are incompatible with any of the published size-evolution
predictions based on an expanding universe. We find that all the physical
mechanisms proposed for size evolution, such as galaxy mergers, lead to
predictions that are in quantitative contradiction with either the radius data
or other data sets, such as the observed rate of galaxy mergers. In addition,
we find that when the effect of telescope resolution is taken into account, the
r-z relationships for disk and elliptical galaxies are identical. Both are
excellently fit by SEU predictions. An overall comparison of cosmological
models requires examining all available data-sets, but for this data-set there
is a clear contradiction of predictions based on an expanding universe
hypothesis. | astro-ph_GA |
Semi-Supervised Domain Adaptation for Cross-Survey Galaxy Morphology
Classification and Anomaly Detection: In the era of big astronomical surveys, our ability to leverage artificial
intelligence algorithms simultaneously for multiple datasets will open new
avenues for scientific discovery. Unfortunately, simply training a deep neural
network on images from one data domain often leads to very poor performance on
any other dataset. Here we develop a Universal Domain Adaptation method
DeepAstroUDA, capable of performing semi-supervised domain alignment that can
be applied to datasets with different types of class overlap. Extra classes can
be present in any of the two datasets, and the method can even be used in the
presence of unknown classes. For the first time, we demonstrate the successful
use of domain adaptation on two very different observational datasets (from
SDSS and DECaLS). We show that our method is capable of bridging the gap
between two astronomical surveys, and also performs well for anomaly detection
and clustering of unknown data in the unlabeled dataset. We apply our model to
two examples of galaxy morphology classification tasks with anomaly detection:
1) classifying spiral and elliptical galaxies with detection of merging
galaxies (three classes including one unknown anomaly class); 2) a more
granular problem where the classes describe more detailed morphological
properties of galaxies, with the detection of gravitational lenses (ten classes
including one unknown anomaly class). | astro-ph_GA |
Near-infrared spectroscopy of 5 ultra-massive galaxies at 1.7 < z < 2.7: We present the results of a pilot near-infrared (NIR) spectroscopic campaign
of five very massive galaxies ($\log(\text{M}_\star/\text{M}_\odot)>11.45$) in
the range of $1.7<z<2.7$. We measure an absorption feature redshift for one
galaxy at $z_\text{spec}=2.000\pm0.006$. For the remaining galaxies, we combine
the photometry with the continuum from the spectra to estimate continuum
redshifts and stellar population properties. We define a continuum redshift
($z_{\rm cont}$ ) as one in which the redshift is estimated probabilistically
using EAZY from the combination of catalog photometry and the observed
spectrum. We derive the uncertainties on the stellar population synthesis
properties using a Monte Carlo simulation and examine the correlations between
the parameters with and without the use of the spectrum in the modeling of the
spectral energy distributions (SEDs). The spectroscopic constraints confirm the
extreme stellar masses of the galaxies in our sample. We find that three out of
five galaxies are quiescent (star formation rate of $\lesssim 1
M_\odot~yr^{-1}$) with low levels of dust obscuration ($A_{\rm V} < 1$) , that
one galaxy displays both high levels of star formation and dust obscuration
(${\rm SFR} \approx 300 M_\odot~{\rm yr}^{-1}$, $A_{\rm V} \approx 1.7$~mag),
and that the remaining galaxy has properties that are intermediate between the
quiescent and star-forming populations. | astro-ph_GA |
X-ray and radio variability in the low luminosity Active Galactic
Nucleus NGC 7213: We present the results of a ~ 3 year campaign to monitor the low luminosity
active galactic nucleus (LLAGN) NGC 7213 in the radio (4.8 and 8.4 GHz) and
X-ray bands (2-10 keV). With a reported X-ray Eddington ratio of 7 x 10^-4
L_Edd, NGC 7213 can be considered to be comparable to a hard state black hole
X-ray binary. We show that a weak correlation exists between the X-ray and
radio light curves. We use the cross-correlation function to calculate a global
time lag between events in the X-ray and radio bands to be 24 +/- 12 days lag
(8.4 GHz radio lagging X-ray), and 40 +/- 13 days lag (4.8 GHz radio lagging
X-ray). The radio-radio light curves are extremely well correlated with a lag
of 20.5 +/- 12.9 days (4.8 GHz lagging 8.4 GHz). We explore the previously
established scaling relationship between core radio and X-ray luminosities and
black hole mass L_{R} \propto M^{0.6-0.8} L_{X}^{0.6}, known as the
`fundamental plane of black hole activity', and show that NGC 7213 lies very
close to the best-fit `global' correlation for the plane as one of the most
luminous LLAGN. With a large number of quasi-simultaneous radio and X-ray
observations, we explore for the first time the variations of a single AGN with
respect to the fundamental plane. Although the average radio and X-ray
luminosities for NGC 7213 are in good agreement with the plane, we show that
there is intrinsic scatter with respect to the plane for the individual data
points. | astro-ph_GA |
On the dark matter haloes inner structure and galaxy morphology: In the present paper, we extend the study of Del Popolo (2010) to determine
the slope of the inner density profile of galaxy haloes with different
morphologies. We study how galaxy morphology changes the relation between the
inner slope of the galaxy halo density profile, $\alpha$, and the stellar mass,
$M_{*}$, or rotation velocity $V_{\rm rot}$. For this, we use the model of Del
Popolo (2009) in combination with observed data from the Romanowsky \& Fall
(2012) sample of elliptical and spiral galaxies, the Local Group sample
compiled by McConnachie (2012), and the simulation results by Cloet-Osselaer et
al. (2014). We find that the slope $\alpha$ flattens monotonically, from
$\alpha \simeq -1 $ at $V_{\rm rot} \simeq 250$ km/s, to $\alpha \simeq 0 $.
After $V_{\rm rot}\simeq 25$ km/s the slope starts to steepen. The steepening
happens in the mass range dominated by non-rotationally supported galaxies
(e.g., dSphs) and depends on the level of offset in the angular momentum of
rotationally and non-rotationally dominated galaxies. The steepening is a
consequence of the decrease in baryons content, and angular momentum in
spheroidal dwarf galaxies. We finally compare our result to the SPH simulations
of Di Cintio. Our result is in qualitatively agreement with their simulations,
with the main difference that the inner slope $\alpha$ at small stellar masses
($M_* \lesssim10^{8} M_{\odot}$) is flatter than that in their simulations. As
a result, the claim that finding a core in dwarf galaxies with masses slightly
smaller than $\simeq 10^6 M_{\odot}$, (as in the Di Cintio, or Governato,
supernovae feedback mechanism) would be a problem for the $\Lambda$CDM model
must be probably revised. | astro-ph_GA |
Accretion onto disk galaxies via hot and rotating CGM inflows: Observed accretion rates onto the Milky-Way and other local spirals fall
short of that required to sustain star formation for cosmological timescales. A
potential avenue for this unseen accretion is an inflow in the volume-filling
hot phase ($\sim10^6$ K) of the circumgalactic medium (CGM), as suggested by
some cosmological simulations. Using hydrodynamic simulations and a new
analytic solution valid in the slow-rotation limit, we show that a hot inflow
spins up as it approaches the galaxy, while remaining hot, subsonic and
quasi-spherical. At the radius of angular momentum support ($\approx15$ kpc for
the Milky-Way) the hot flow flattens into a disk geometry and then cools from
$\sim10^6$ K to $\sim10^4$ K at the disk-halo interface. Cooling affects all
hot gas, rather than just a subset of individual gas clouds, implying that
accretion via hot inflows does not rely on local thermal instability in
contrast with 'precipitation' models for galaxy accretion. Prior to cooling and
accretion the inflow completes $\sim t_{\rm cool}/t_{\rm ff}$ radians of
rotation, where $t_{\rm cool}/t_{\rm ff}$ is the cooling time to free-fall time
ratio in hot gas immediately outside the galaxy. The ratio $t_{\rm cool}/t_{\rm
ff}$ may thus govern the development of turbulence and enhancement of magnetic
fields in gas accreting onto low-redshift spirals. We argue that accretion via
hot inflows can explain the observed truncation of nearby thin stellar disks at
$\approx4$ disk radii. We also show that if rotating hot inflows are common in
Milky-Way size disk galaxies, as predicted, then signatures should be
observable with X-ray telescopes and FRB surveys. | astro-ph_GA |
Gas fractions and depletion times in galaxies with different degrees of
interaction: We study the atomic gas content and the central stellar mass concentration
for a sample of almost 1500 nearby galaxies to investigate the nature of
starbursts and the influence of galaxy-galaxy interactions on star formation
(SF). We used a sample of catalogued interacting and non-interacting galaxies
in the S$^4$G survey - along with archival HI gas masses, stellar masses
($M_{\ast}$), and SF rates from $IRAS$ far-infrared fluxes - and calculate
depletion times and gas fractions. We traced the central stellar mass
concentration from the inner slope of the stellar component of the rotation
curves. Starbursts are defined as galaxies with a factor $>4$ enhanced SF rate
relative to a control sample of non-interacting galaxies which are $\pm 0.2$
dex in stellar mass and $\pm 1$ in $T$-type. Starbursts are mainly early-type
($T\lesssim 5$), massive spiral galaxies ($M_{\ast}\gtrsim 10^{10}M_{\odot}$)
that are not necessarily interacting. For a given stellar mass bin, starbursts
are characterised by lower gas depletion times, similar gas fractions, and
larger central stellar mass concentrations than non-starburst galaxies. The
global distributions of gas fraction and gas depletion time are not
statistically different for interacting and non-interacting galaxies. However,
in the case of currently merging galaxies, the median gas depletion time is a
factor of $0.4 \pm 0.2$ that of control sample galaxies, and their SF rates are
a factor of $1.9 \pm 0.5$ enhanced, even though the median gas fraction is
similar. Starbursts present long-lasting SF in the circumnuclear regions that
causes an enhancement of the central stellar density at $z\approx0$ in both
interacting and non-interacting systems. Starbursts have low gas depletion
timescales, yet similar gas fractions as normal main-sequence galaxies. Galaxy
mergers cause a moderate enhancement of the SF efficiency (Abridged). | astro-ph_GA |
Towards a complete stellar mass function of the Hyades. I. Pan-STARRS1
optical observations of the low-mass stellar content: The Hyades cluster is an ideal target to study the dynamical evolution of a
star cluster over the entire mass range due to its intermediate age and
proximity to the Sun. We wanted to extend the Hyades mass function towards
lower masses down to 0.1 Msol and to use the full three-dimensional spatial
information to characterize the dynamical evolution of the cluster. We
performed a kinematic and photometric selection using the PPMXL and Pan-STARRS1
sky surveys, to search for cluster members up to 30 pc from the cluster centre.
We determined our detection efficiency and field star contamination rate to
derive the cluster luminosity and mass functions down to masses of 0.1 Msol.
The thorough astrometric and photometric constraints minimized the
contamination. A minimum spanning tree algorithm was used to quantify the mass
segregation. We discovered 43 new Hyades member candidates with velocity
perpendicular to the Hyades motion up to 2 km/s. They have mass estimates
between 0.43 and 0.09 Msol, for a total mass of 10 Msol. This doubles the
number of Hyades candidates with masses smaller than 0.15 Msol. We provide an
additional list of 11 possible candidates with velocity perpendicular to the
Hyades motion up to 4 km/s. The cluster is significantly mass segregated. The
extension of the mass function towards lower masses provided an even clearer
signature than estimated in the past. We also identified as likely Hyades
member an L0 dwarf previously assumed to be a field dwarf. Finally we question
the membership of a number of previously published candidates, including a
L2.5-type dwarf. | astro-ph_GA |
Physical Model of Dust Polarization by Radiative Torque Alignment and
Disruption and Implications for Grain Internal Structures: Dust polarization depends on the physical and mechanical properties of dust,
as well as the properties of local environments. To understand how dust
polarization varies with grain mechanical properties and the local environment,
in this paper, we model the wavelength-dependence polarization of starlight and
polarized dust emission by aligned grains by simultaneously taking into account
grain alignment and rotational disruption by radiative torques (RATs). We
explore a wide range of the local radiation field and grain mechanical
properties characterized by tensile strength. We find that the maximum
polarization and the peak wavelength shift to shorter wavelengths as the
radiation strength $U$ increases due to the enhanced alignment of small grains.
Grain rotational disruption by RATs tends to decrease the optical-near infrared
polarization but increases the ultraviolet polarization of starlight due to the
conversion of large grains into smaller ones. In particular, we find that the
submillimeter (submm) polarization degree at $850~\mu \rm m$ ($P_{850}$) does
not increase monotonically with the radiation strength or grain temperature
($T_{d}$), but it depends on the tensile strength of grain materials. Our
physical model of dust polarization can be tested with observations toward
star-forming regions or molecular clouds irradiated by a nearby star, which
have higher radiation intensity than the average interstellar radiation field.
Finally, we compare our predictions of the $P_{850}-T_{d}$ relationship with
{\it Planck} data and find that the observed decrease of $P_{850}$ with $T_{d}$
can be explained when grain disruption by RATs is accounted for, suggesting
that interstellar grains unlikely to have a compact structure but perhaps a
composite one. The variation of the submm polarization with U (or $T_{d}$) can
provide a valuable constraint on the internal structures of cosmic dust. | astro-ph_GA |
A Submillimeter Perspective on the GOODS Fields (SUPER GOODS). V. Deep
450 Micron Imaging: We present deep SCUBA-2 450 micron imaging of the two GOODS fields, achieving
a central rms of 1.14 mJy for the GOODS-N and 1.86 mJy for the GOODS-S. For
each field, we give a catalog of >4-sigma detections (79 and 16 sources,
respectively). We construct the 450 micron number counts, finding excellent
agreement with others from the literature. We match the 450 micron sources to
20 cm data (both fields) and ALMA 870 micron data (GOODS-S) to gauge the
accuracy of the 450 micron positions. We use the extensive redshift information
available on the fields to test how well redshift can be estimated from simple
flux ratios (450 micron/850 micron and 20 cm/850 micron), finding tight
correlations. We provide a catalog of candidate high-redshift submillimeter
galaxies. We look for evolution in dust temperature with redshift by fitting
the spectral energy distributions of the sources, but we do not find any
significant redshift evolution after accounting for the far-infrared
luminosity. We do not find evidence for 450 micron selection picking out warmer
sources than 850 micron selection. We find that a 450 micron selected sample
only adds low-redshift (z<1.5) galaxies beyond an 850 micron sample. | astro-ph_GA |
A new strong-lensing galaxy at z=0.066: Another elliptical galaxy with a
lightweight IMF: We report the discovery of a new low-redshift galaxy-scale gravitational
lens, identified from a systematic search of publicly available MUSE
observations. The lens galaxy, 2MASXJ04035024-0239275, is a giant elliptical at
$z$ = 0.06604 with a velocity dispersion of $\sigma$ = 314 km s$^{-1}$. The
lensed source has a redshift of 0.19165 and forms a pair of bright images
either side of the lens centre. The Einstein radius is 1.5 arcsec, projecting
to 1.8 kpc, which is just one quarter of the galaxy effective radius. After
correcting for an estimated 19 per cent dark matter contribution, we find that
the stellar mass-to-light ratio from lensing is consistent with that expected
for a Milky Way initial mass function (IMF). Combining the new system with
three previously-studied low-redshift lenses of similar $\sigma$, the derived
mean mass excess factor (relative to a Kroupa IMF) is $\langle\alpha\rangle$ =
1.09$\pm$0.08. With all four systems, the intrinsic scatter in $\alpha$ for
massive elliptical galaxies can be limited to $<0.32$, at 90 per cent
confidence. | astro-ph_GA |
Spectrophotometric Redshifts In The Faint Infrared Grism Survey: Finding
Overdensities Of Faint Galaxies: We improve the accuracy of photometric redshifts by including low-resolution
spectral data from the G102 grism on the Hubble Space Telescope, which assists
in redshift determination by further constraining the shape of the broadband
Spectral Energy Disribution (SED) and identifying spectral features. The
photometry used in the redshift fits includes near-IR photometry from
FIGS+CANDELS, as well as optical data from ground-based surveys and HST ACS,
and mid-IR data from Spitzer. We calculated the redshifts through the
comparison of measured photometry with template galaxy models, using the EAZY
photometric redshift code. For objects with F105W $< 26.5$ AB mag with a
redshift range of $0 < z < 6$, we find a typical error of $\Delta z = 0.03 *
(1+z)$ for the purely photometric redshifts; with the addition of FIGS spectra,
these become $\Delta z = 0.02 * (1+z)$, an improvement of 50\%. Addition of
grism data also reduces the outlier rate from 8\% to 7\% across all fields.
With the more-accurate spectrophotometric redshifts (SPZs), we searched the
FIGS fields for galaxy overdensities. We identified 24 overdensities across the
4 fields. The strongest overdensity, matching a spectroscopically identified
cluster at $z=0.85$, has 28 potential member galaxies, of which 8 have previous
spectroscopic confirmation, and features a corresponding X-ray signal. Another
corresponding to a cluster at $z=1.84$ has 22 members, 18 of which are
spectroscopically confirmed. Additionally, we find 4 overdensities that are
detected at an equal or higher significance in at least one metric to the two
confirmed clusters. | astro-ph_GA |
Physical Properties of Massive Compact Starburst Galaxies with Extreme
Outflows: We present results on the nature of extreme ejective feedback episodes and
the physical conditions of a population of massive ($\rm M_* \sim 10^{11}
M_{\odot}$), compact starburst galaxies at z = 0.4-0.7. We use data from
Keck/NIRSPEC, SDSS, Gemini/GMOS, MMT, and Magellan/MagE to measure rest-frame
optical and near-IR spectra of 14 starburst galaxies with extremely high star
formation rate surface densities (mean $\rm \Sigma_{SFR} \sim 3000 \,M_{\odot}
yr^{-1} kpc^{-2}$) and powerful galactic outflows (maximum speeds v$_{98} \sim$
1000-3000 km s$^{-1}$). Our unique data set includes an ensemble of both
emission [OII]$\lambda\lambda$3726,3729, H$\beta$,
[OIII]$\lambda\lambda$4959,5007, H$\alpha$, [NII]$\lambda\lambda$6548,6583, and
[SII]$\lambda\lambda$6716,6731) and absorption MgII$\lambda\lambda$2796,2803,
and FeII$\lambda$2586) lines that allow us to investigate the kinematics of the
cool gas phase (T$\sim$10$^4$ K) in the outflows. Employing a suite of line
ratio diagnostic diagrams, we find that the central starbursts are
characterized by high electron densities (median n$_e \sim$ 530 cm$^{-3}$), and
high metallicity (solar or super-solar). We show that the outflows are most
likely driven by stellar feedback emerging from the extreme central starburst,
rather than by an AGN. We also present multiple intriguing observational
signatures suggesting that these galaxies may have substantial Lyman continuum
(LyC) photon leakage, including weak [SII] nebular emission lines. Our results
imply that these galaxies may be captured in a short-lived phase of extreme
star formation and feedback where much of their gas is violently blown out by
powerful outflows that open up channels for LyC photons to escape. | astro-ph_GA |
The Effect of Many Minor Mergers on the Size Growth of Compact Quiescent
Galaxies: Massive galaxies with a half-mass radius <~ 1kpc are observed in the early
universe (z~>2), but not in the local universe. In the local universe
similar-mass (within a factor of two) galaxies tend to be a factor of 4 to 5
larger. Dry minor mergers are known to drive the evolution of the size of a
galaxy without much increasing the mass, but it is unclear if the growth in
size is sufficient to explain the observations. We test the hypothesis that
galaxies grow through dry minor mergers by simulating merging galaxies with
mass ratios of q=1:1 (equal mass) to q=1:160. In our N-body simulations the
total mass of the parent galaxy doubles. We confirm that major mergers do not
cause a sufficient growth in size. The observation can be explained with
mergers with a mass ratio of q=1:5--1:10. Smaller mass ratios cause a more
dramatic growth in size, up to a factor of ~17 for mergers with a mass ratio of
1:80. For relatively massive minor mergers q ~> 1:20 the mass of the incoming
child galaxies tend to settle in the halo of the parent galaxy. This is caused
by the tidal stripping of the child galaxies by the time they enter the central
portion of the parent. When the accretion of minor galaxies becomes more
continuous, when q <~ 1:40, the foreign mass tends to concentrate more in the
central region of the parent galaxy. We speculate that this is caused by
dynamic interactions between the child galaxies inside the merger remnant and
the longer merging times when the difference in mass is larger. These
interactions cause dynamical heating which results in accretion of mass inside
the galaxy core and a reduction of the parent's circular velocity and density. | astro-ph_GA |
The Abell 85 BCG: a nucleated, core-less galaxy: New high-resolution r band imaging of the brightest cluster galaxy (BCG) in
Abell 85 (Holm 15A) was obtained using the Gemini Multi Object Spectrograph.
These data were taken with the aim of deriving an accurate surface brightness
profile of the BCG of Abell 85, in particular its central region. The new
Gemini data show clear evidence of a previously unreported nuclear emission
that is evident as a distinct light excess in the central kiloparsec of the
surface brightness profile. We find that the light profile is never flat nor
does it present a downward trend towards the center of the galaxy. That is, the
new Gemini data show a different physical reality from the featureless,
"evacuated core" recently claimed for the Abell 85 BCG. After trying different
models, we find that the surface brightness profile of the BCG of Abell 85 is
best fit by a double Sersic model. | astro-ph_GA |
Resolved neutral carbon emission in nearby galaxies: [CI] Lines as Total
Molecular Gas Tracers: We present maps of atomic carbon [CI](1-0) and [CI](2-1) at a linear
resolution ~1kpc scale for a sample of one HII, six LINER, three Seyfert and
five starburst galaxies observed with Herschel. We compare spatial
distributions of two [CI] lines with that of CO(1-0) emission, and find that
both [CI] lines distribute similarly to CO(1-0) emission in most galaxies. We
present luminosity ratio maps of L'_[CI](1-0)/L'_CO(1-0),
L'_[CI](2-1)/L'_CO(1-0), L'_[CI](2-1)/L'_[CI](1-0) (hereafter R_[CI]) and
f_70/f_160. L'_[CI](2-1)/L'_CO(1-0), R_[CI] and f_70/f_160 are centrally peaked
in starbursts; whereas remain relatively constant in LINERs, indicating that
star-forming activity can enhance carbon emission, especially for [CI](2-1). We
explore the correlations between the luminosities of CO(1-0) and [CI] lines,
and find that L'_CO(1-0) correlates tightly and almost linearly with both
L'_[CI](1-0) and L'_[CI](2-1), suggesting that [CI] lines, similar as CO(1-0),
can trace total molecular gas in our resolved galaxies on kpc scales. We
investigate the dependence of L'_[CI](1-0)/L'_CO(1-0), L'_[CI](2-1)/L'_CO(1-0)
and [CI] excitation temperature T_ex on dust temperature T_dust, and find
non-correlation, a weak and modest correlation, respectively. The ratio of
L'_[CI](1-0)/L'_CO(1-0) stays smooth distribution in most galaxies, indicating
that the conversion factor of [CI](1-0) luminosity to H_2 mass (X_[CI](1-0))
changes with CO(1-0) conversion factor (\alpha_CO) proportionally. Under
optically thin and LTE assumptions, we derive a galaxy-wide average carbon
excitation temperature T_ex ~ 19.7 \pm 0.5K and an average neutral carbon
abundance X[CI]/X[H_2] ~2.5 \pm 1.0 * 10^{-5} in our resolved sample, which is
comparable to the usually adopted value of 3*10^{-5}, but ~3 times lower than
the carbon abundance in local (U)LIRGs. We conclude that the carbon abundance
varies in different galaxy types. | astro-ph_GA |
The Impact of an AGN on PAH Emission in Galaxies: the Case of Ring
Galaxy NGC 4138: We present a focused study of radially-resolved varying PAH emission in the
low-luminosity AGN-host NGC 4138 using deep Spitzer/IRS spectral maps. Using
new model PAH spectra, we investigate whether these variations could be
associated with changes to the PAH grain size distribution due to
photodestruction by the AGN. Separately, we model the effects of the varying
radiation field within NGC 4138, and we use this model to predict the
corresponding changes in the PAH emission spectrum. We find that PAH band
ratios are strongly variable with radius in this galaxy with short-to-long
wavelength band ratios peaking in the starburst ring. The changing mix of
starlight appears to have a considerable effect on the trends in these band
ratios, and our radiation model predicts the shapes of these trends. However,
the amplitude of observed variation is ~2.5 times larger than predicted for
some ratios. A cutoff of small grains in the PAH size distribution, as has been
suggested for AGN, together with changes in PAH ionization fraction could
explain the behavior of the shorter bands, but this model fails to reproduce
longer band behaviors. Additionally, we find that short-to-long wavelength PAH
band ratios increase slightly within ~270pc of the center, suggesting that the
AGN may directly influence PAH emission there. | astro-ph_GA |
Green Bank Telescope Observations of ${\bf ^3He^{\bf +}}$: Planetary
Nebulae: We use the Green Bank Telescope to search for $^3He^+$ emission from a sample
of four Galactic planetary nebulae: NGC 3242, NGC 6543, NGC 6826, and NGC 7009.
During the era of primordial nucleosynthesis the light elements $^2H$, $^3He$,
$^4He$, and $^7Li$ were produced in significant amounts and these abundances
have since been modified primarily by stars. Observations of $^3He^+$ in H II
regions located throughout the Milky Way disk reveal very little variation in
the $^3He/H$ abundance ratio -- the "$^3He$ Plateau" -- indicating that the net
effect of $^3He$ production in stars is negligible. This is in contrast to much
higher $^3He/H$ abundance ratios reported for some planetary nebulae. This
discrepancy is known as the "$^3He$ Problem". We use radio recombination lines
observed simultaneously with the $^3He^+$ transition to make a robust
assessment of the spectral sensitivity that these observations achieve. We
detect spectral lines at $\sim$ 1 -- 2 mK intensities, but at these levels
instrumental effects compromise our ability to measure accurate spectral line
parameters. We do not confirm reports of previous detections of $^3He^+$ in NGC
3242 nor do we detect $^3He^+$ emission from any of our sources. This result
calls into question all reported detections of $^3He^+$ emission from any
planetary nebula. The $^3He/H$ abundance upper limit we derive here for NGC
3242 is inconsistent with standard stellar production of $^3He$ and thus
requires that some type of extra mixing process operates in low-mass stars. | astro-ph_GA |
Realistic galaxy images and improved robustness in machine learning
tasks from generative modelling: We examine the capability of generative models to produce realistic galaxy
images. We show that mixing generated data with the original data improves the
robustness in downstream machine learning tasks. We focus on three different
data sets; analytical S\'ersic profiles, real galaxies from the COSMOS survey,
and galaxy images produced with the SKIRT code, from the IllustrisTNG
simulation. We quantify the performance of each generative model using the
Wasserstein distance between the distributions of morphological properties
(e.g. the Gini-coefficient, the asymmetry, and ellipticity), the surface
brightness distribution on various scales (as encoded by the power-spectrum),
the bulge statistic and the colour for the generated and source data sets. With
an average Wasserstein distance (Fr\'echet Inception Distance) of $7.19 \times
10^{-2}\, (0.55)$, $5.98 \times 10^{-2}\, (1.45)$ and $5.08 \times 10^{-2}\,
(7.76)$ for the S\'ersic, COSMOS and SKIRT data set, respectively, our best
models convincingly reproduce even the most complicated galaxy properties and
create images that are visually indistinguishable from the source data. We
demonstrate that by supplementing the training data set with generated data, it
is possible to significantly improve the robustness against domain-shifts and
out-of-distribution data. In particular, we train a convolutional neural
network to denoise a data set of mock observations. By mixing generated images
into the original training data, we obtain an improvement of $11$ and $45$ per
cent in the model performance regarding domain-shifts in the physical pixel
size and background noise level, respectively. | astro-ph_GA |
Boron Abundances in Diffuse Interstellar Clouds: We present a comprehensive survey of B abundances in diffuse interstellar
clouds from HST/STIS observations along 56 Galactic sight lines. Our sample is
the result of a complete search of archival STIS data for the B II resonance
line at 1362 angstroms, with each detection confirmed by the presence of
absorption from other dominant ions at the same velocity. The data probe a
range of astrophysical environments including both high-density regions of
massive star formation as well as low-density paths through the Galactic halo,
allowing us to clearly define the trend of B depletion onto interstellar grains
as a function of gas density. Many extended sight lines exhibit complex
absorption profiles that trace both local gas and gas associated with either
the Sagittarius-Carina or Perseus spiral arm. Our analysis indicates a higher
B/O ratio in the inner Sagittarius-Carina spiral arm than in the vicinity of
the Sun, which may suggest that B production in the current epoch is dominated
by a secondary process. The average gas-phase B abundance in the warm diffuse
ISM is consistent with the abundances determined for a variety of Galactic disk
stars, but is depleted by 60 percent relative to the solar system value. Our
survey also reveals sight lines with enhanced B abundances that potentially
trace recent production of B-11 either by cosmic-ray or neutrino-induced
spallation. Such sight lines will be key to discerning the relative importance
of the two production routes for B-11 synthesis. | astro-ph_GA |
Ultraviolet and optical view of galaxies in the Coma Supercluster: The Coma supercluster (100 Mpc) offers an unprecedented contiguous range of
environments in the nearby Universe. In this paper we present a catalogue of
spectroscopically confirmed galaxies in the Coma supercluster detected in the
ultraviolet (UV) wavebands. We use the arsenal of UV and optical data for
galaxies in the Coma supercluster covering ~ 500 square degrees on the sky to
study their photometric and spectroscopic properties as a function of
environment at various scales. We identify the different components of the
cosmic-web: large-scale filaments and voids using Discrete Persistent
Structures Extractor, and groups and clusters using Hierarchical Density-based
spatial clustering of applications with noise, respectively. We find that in
the Coma supercluster the median emission in Halpha inclines, while the g-r and
FUV-NUV colours of galaxies become bluer moving further away from the spine of
the filaments out to a radius of around 1 Mpc. On the other hand, an opposite
trend is observed as the distance between the galaxy and centre of the nearest
cluster or group decreases. Our analysis supports the hypothesis that
properties of galaxies are not just defined by its stellar mass and large-scale
density, but also by the environmental processes resulting due to the
intrafilament medium whose role in accelerating galaxy transformations needs to
be investigated thoroughly using multi-wavelength data. | astro-ph_GA |
Water vapour masers in long-period variable stars II. The semi-regular
variables R Crt and RT Vir: Within the 'Medicina/Effelsberg H2O maser monitoring program' we have
observed the maser emission of R Crt and RT Vir for more than two decades. To
get insight in the distribution and longevity of maser spots in the
circumstellar envelopes, we have collected interferometric data, taken in the
same period, from the literature.
We confirm short-time variations of individual maser features on timescales
of months to up to 1.5 years. Also decade-long variations of the general
brightness level independent from individual features were seen in both stars.
These are due to brightness variations occurring independently from each other
in selected velocity ranges, and are independent of the optical lightcurves.
Expected drifts in velocity of individual features are usually masked by
blending. However, in RT Vir we found an exceptional case of a feature with a
constant velocity over 7.5 years (<0.06 km/s/yr).
We attribute the long-term brightness variations to the presence of regions
with higher-than-average density in the stellar wind, which host several clouds
which emit maser radiation on the short time scales. These regions typically
need ~20 years to cross the H2O maser shell, where the right conditions to
excite H2O masers are present. The constant velocity feature (11 km/s) is
likely to come from a single maser cloud, which moved through about half of RT
Vir's H2O maser shell without changing velocity. From this we infer that its
path was located in the outer part of the H2O maser shell, where RT Vir's
stellar wind apparently has already reached its terminal outflow velocity. This
conclusion is corroborated by the observation that the highest H2O maser
outflow velocity in RT Vir approaches the terminal outflow velocity as given by
OH and CO observations. This is generally not observed in other semi-regular
variable stars. | astro-ph_GA |
NGC 1261: an $r$-process enhanced globular cluster from the
Gaia-Enceladus event: Our Milky Way (MW) has witnessed a series of major accretion events. One of
the later additions, Gaia-Enceladus, has contributed a considerable mass to the
inner Galaxy, but also generously donated to the outer halo. So far,
associations with present-day MW globular clusters (GCs) have been chiefly
based on their kinematics and ages. Here, we present a chemical abundance study
of the outer halo (R$_{\rm GC}$=18 kpc) GC NGC 1261, which has been suggested
to be an accreted object. We measured 31 species of 29 elements in two stars
from high-resolution Magellan/MIKE spectra and find that the cluster is
moderately metal poor, at [Fe/H]=-1.26. NGC 1261 is moderately
$\alpha$-enhanced to the 0.3-dex level. While from the small sample alone it is
difficult to assert any abundance correlations, the light elements Na,O,Mg, and
Al differ significantly between the two stars in contrast to the majority of
other elements with smaller scatter; this argues in favour of multiple
generations of stars coexisting in this GC. Intriguingly for its metallicity,
NGC 1261 shows heavy element abundances that are consistent with $r$-process
nucleosynthesis and we discuss their origin in various sites. In particular the
Eu overabundance quantitatively suggests that one single $r$-process event,
such as a neutron-star neutron-star merger or a rare kind of supernova, can be
responsible for the stellar enhancement or even the enrichment of the cluster
with the excess $r$-material. Its heavy element pattern makes NGC 1261 resemble
the moderately enhanced r-I stars that are commonly found in the halo and have
been detected in Gaia-Enceladus as well. Therefore, combining all kinematical,
age, and chemical evidence we conclude that NGC 1261 is a chemically intriguing
GC that was born in Gaia-Enceladus and has been subsequently accreted into the
MW halo. [abridged] | astro-ph_GA |
Stellar Black Hole Binary Mergers in Open Clusters: In this paper we study the evolution of a primordial black hole binary (BHB)
in a sample of over 1500 direct-summation $N-$body simulations of small-and
intermediate-size isolated star clusters as proxies of galactic open clusters.
The BHBs have masses in the range of the first LIGO/Virgo detections. Some of
our models show a significant hardening of the BHB in a relatively short time.
Some of them merge within the cluster, while ejected binaries, typically, have
exceedingly long merger timescales. The perturbation of stars around BHB
systems is key to induce their coalescence. The BHBs which merge in the cluster
could be detected with a delay of a few years between space detectors, as
future LISA, and ground-based ones, due to their relatively high eccentricity.
Under our assumptions, we estimate a BHB merger rate of $R_{\rm mrg} \sim 2$
yr$^{-1}$ Gpc$^{-3}$. We see that in many cases the BHB triggers tidal
disruption events which, however, are not linked to the GW emission. Open
cluster-like systems are, hence, a promising environment for GWs from BHBs and
tidal disruptions. | astro-ph_GA |
The Sheet of Giants: Unusual Properties of the Milky Way's Immediate
Neighbourhood: We quantify the shape and overdensity of the galaxy distribution in the
`Local Sheet' within a sphere of $R=8$ Mpc, and compare these properties with
the expectations of the $\Lambda$CDM model. We measure ellipsoidal axis ratios
of $c/a\approx0.16$ and $b/a\approx0.79$, indicating that the distribution of
galaxies in the Local Volume can be approximated by a flattened oblate
ellipsoid, consistent with the `sheet'-like configuration noted in previous
studies. In contrast with previous estimates that the Local Sheet has a density
close to average, we find that the number density of faint and bright galaxies
in the Local Volume is $\approx1.7$ and $\approx5.2$ times denser,
respectively, than the mean number density of galaxies of the same luminosity.
Comparison with simulations shows that the number density contrasts of bright
and faint galaxies within $8$ Mpc alone make the Local Volume a $\approx
2.5\sigma$ outlier in the $\Lambda$CDM cosmology. Our results indicate that the
cosmic neighbourhood of the Milky Way may be unusual for galaxies of similar
luminosity. The impact of the peculiar properties of our neighbourhood on the
properties of the Milky Way and other nearby galaxies is not yet understood and
warrants further study. | astro-ph_GA |
Nuclear regions as seen with LOFAR international baselines: A
high-resolution study of the recurrent activity: Radio galaxies dominate the radio sky and are essential to the galaxy
evolution puzzle. High-resolution studies of statistical samples of radio
galaxies are expected to shed light on the triggering mechanisms of the AGN,
alternating between the phases of activity and quiescence. In this work, we
focus on the sub-arcsec radio structures in the central regions of the 35 radio
galaxies over 6.6 $deg^2$ of the Lockman Hole region. These sources were
previously classified as active, remnant, and candidate restarted radio
galaxies using 150 MHz LOFAR observations. We examine the morphologies and
study the spectral properties of their central regions to explore their
evolutionary stages and revise the criteria used to select the initial sample.
We use the newly available LOFAR 150 MHz image obtained using international
baselines, achieving 0.38'' x 0.30'' resolution, making this the first
systematic study of the nuclear regions at high resolution and low frequency.
We use publicly available images from the FIRST survey at 1.4 GHz and the Karl
G. Jansky VLA Sky Survey at 3 GHz to achieve our goals. In addition, for one
restarted candidate we present new dedicated observations with the VLA at 3
GHz. We have found various morphologies of the central regions of the radio
galaxies in our sample, some resembling miniature double-double radio galaxies.
We also see the beginnings of active jets or distinct detections unrelated to
the large-scale structure. Furthermore, we have found diverse radio spectra in
our sample - flat, steep, or peaked between 150 MHz and 3 GHz, indicative of
the different life-cycle phases. Based on these analyses, we confirm five of
six previously considered restarted candidates and identify three more from the
active sample, supporting previous results suggesting that the restarted phase
can occur after a relatively short remnant phase (i.e. a few tens of millions
of years). | astro-ph_GA |
Quantifying the suppression of the (un)-obscured star formation in
galaxy cluster cores at 0.2$\lesssim$$z$$\lesssim$0.9: We quantify the star formation (SF) in the inner cores
($\mathcal{R}$/$R_{200}$$\leq$0.3) of 24 massive galaxy clusters at
0.2$\lesssim$$z$$\lesssim$0.9 observed by the $Herschel$ Lensing Survey and the
Cluster Lensing and Supernova survey with $Hubble$. These programmes, covering
the rest-frame ultraviolet to far-infrared regimes, allow us to accurately
characterize stellar mass-limited ($\mathcal{M}_{*}$$>$$10^{10}$ $M_{\odot}$)
samples of star-forming cluster members (not)-detected in the mid- and/or
far-infrared. We release the catalogues with the photometry, photometric
redshifts, and physical properties of these samples. We also quantify the SF
displayed by comparable field samples from the Cosmic Assembly Near-infrared
Deep Extragalactic Legacy Survey. We find that in intermediate-$z$ cluster
cores, the SF activity is suppressed with respect the field in terms of both
the fraction ($\mathcal{F}$) of star-forming galaxies (SFG) and the rate at
which they form stars ($\mathcal{SFR}$ and $s\mathcal{SFR} =
\mathcal{SFR}/\mathcal{M}_{*}$). On average, the $\mathcal{F}$ of SFGs is a
factor $\sim$$2$ smaller in cluster cores than in the field. Furthermore, SFGs
present average $\mathcal{SFR}$ and $s\mathcal{SFR}$ typically $\sim$0.3 dex
smaller in the clusters than in the field along the whole redshift range
probed. Our results favour long time-scale quenching physical processes as the
main driver of SF suppression in the inner cores of clusters since
$z$$\sim$0.9, with shorter time-scale processes being very likely responsible
for a fraction of the missing SFG population. | astro-ph_GA |
A galactic-scale origin for stellar clustering: We recently presented a model for the cluster formation efficiency (CFE),
i.e. the fraction of star formation occurring in bound stellar clusters. It
utilizes the idea that the formation of stars and stellar clusters occurs
across a continuous spectrum of ISM densities. Bound stellar clusters naturally
arise from the high-density end of this density spectrum. Due to short
free-fall times, these high-density regions can achieve high star formation
efficiencies (SFEs) and can be unaffected by gas expulsion. Lower-density
regions remain gas-rich and substructured, and are unbound upon gas expulsion.
The model enables the CFE to be calculated using galactic-scale observables. I
present a brief summary of the model physics, assumptions and caveats, and show
that it agrees well with observations. Fortran and IDL routines for calculating
the CFE are publicly available at http://www.mpa-garching.mpg.de/cfe. | astro-ph_GA |
One, Two, Three ... An Explosive Outflow in IRAS 12326$-$6245 revealed
by ALMA: In the last years there has been a substantial increase in the number of the
reported massive and luminous star-forming regions with related explosive
outflows thanks to the superb sensitivity and angular resolution provided by
the new radio, infrared, and optical facilities. Here, we report one more
explosive outflow related with the massive and bright star-forming region IRAS
12326$-$6245 using Band 6 sensitive and high angular resolution ($\sim$0.2$"$)
Atacama Large Millimeter/Submillimeter Array (ALMA) observations. We find over
10 molecular and collimated well-defined streamers, with Hubble-Lemaitre like
expansion motions, and pointing right to the center of a dusty and molecular
shell (reported for the first time here) localized in the northern part of the
UCHII region known as G301.1A. The estimated kinematic age, and energy for the
explosion are $\sim$700 yrs, and 10$^{48}$ erg, respectively. Taking into
account the recently reported explosive outflows together with IRAS
12326$-$6245, we estimate an event rate of once every 90 yr in our Galaxy,
similar to the formation rate of massive stars. | astro-ph_GA |
The nature of the Milky Way's stellar halo revealed by the three
integrals of motion: We developed a new selection method of halo stars in the phase-space
distribution defined by the three integrals of motion in an axisymmetric
Galactic potential, ($E$, $L_z$, $I_3$), where $I_3$ is the third integral of
motion. The method is used to explore the general chemo-dynamical structure of
the halo based on stellar samples from SDSS-SEGUE DR7 and DR16-APOGEE, matched
with Gaia-DR2. We found, (a) halo stars can be separated from disk stars by
selecting over (1) $0 < L_z < 1500$ \kpckms, $(2I_3)^{1/2} > 1000$ \kpckms
(orbital angle $\theta_{\rm orb}$ $>$ 15-20 deg), and $E < -1.5 \times 10^5$
km$^2$ s$^{-2}$, and (2) $L_z < 0$ \kpckms. These selection criteria are free
from kinematical biases introduced by the simple high-velocity cuts adopted in
recent literature; (b) the averaged, or {\it coarse-grained}, halo phased-space
distribution shows a monotonic exponential decrease with increasing $E$ and
$I_3$ like the Michie-Bodenheimer models; (c) the inner stellar halo described
in \citet{carollo2007,carollo2010} is found to comprise a combination of Gaia
Enceladus debris (GE; \citealt{helmi2018}), lowest-$E$ stars (likely in-situ
stars), as well as metal-poor prograde stars missed by the high velocity cuts
selection; (d) the very metal poor outer halo, ([Fe/H] $< -$2.2), exhibits both
retrograde and prograde rotation, with an asymmetric $L_z$ distribution towards
high retrograde motions, and larger $\theta_{\rm orb}$ than those possessed by
the GE dominated inner halo; (e) the Sgr dSph galaxy could induce a long-range
dynamical effect on local halo stars. Implication for the formation of the
stellar halo are also discussed. | astro-ph_GA |
Photoionization Modelling of the Giant Broad-Line Region in NGC 3998: Prior high angular resolution spectroscopic observations of the
Low-ionization nuclear emission-line region (Liner) in NGC 3998 obtained with
the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space
Telescope (HST) revealed a rich UV-visible spectrum consisting of broad
permitted and broad forbidden emission lines. The photoionization code XSTAR is
employed together with reddening-insensitive emission line diagnostics to
constrain a dynamical model for the broad-line region (BLR) in NGC 3998. The
BLR is modelled as a large H$^+$ region ${\sim}$ 7 pc in radius consisting of
dust-free, low density ${\sim}$ 10$^4$ cm$^{-3}$, low metallicity ${\sim}$ 0.01
$Z/Z_\odot$ gas. Modelling the shape of the broad H${\alpha}$ emission line
significantly discriminates between two independent measures of the black hole
mass, favouring the estimate of de Francesco et al. (2006). Interpreting the
broad H${\alpha}$ emission line in terms of a steady-state spherically
symmetric inflow leads to a mass inflow rate of 1.4 ${\times}$ 10$^{-2}$
M$_\odot$/yr, well within the present uncertainty of calculations that attempt
to explain the observed X-ray emission in terms of an advection-dominated
accretion flow (ADAF). Collectively, the model provides an explanation for the
shape of the H${\alpha}$ emission line, the relative intensities and
luminosities for the H Balmer, [O III], and potentially several of the broad UV
emission lines, as well as refining the initial conditions needed for future
modelling of the ADAF. | astro-ph_GA |
Molecular-Cloud-Scale Chemical Composition III: Constraints of Average
Physical Properties through Chemical Models: It is important to understand the origin of molecular line intensities and
chemical composition in the molecular-cloud scale in the Galactic sources
because it serves as a benchmark to compare with the chemical compositions of
extragalactic sources. Recent observations of the 3-mm spectra averaged over
the 10-pc scale show similar spectral pattern among sources for molecular lines
HCN, HCO$^+$, CCH, HNC, HNCO, c-C$_3$H$_2$, CS, SO, N$_2$H$^+$, and CN. To
constrain the average physical property emitting such spectral pattern, we
model molecular spectra using a time-dependent gas-grain chemical model
followed by a radiative transfer calculation. We use a grid of physical
parameters such as the density $n=3 \times 10^2 - 3\times 10^4$ cm$^{-3}$, the
temperature, $T=10-30$ K, the visual extinction $A_{\rm V} = 2,4,10$ mag, the
cosmic-ray ionization rate $\zeta = 10^{-17} - 10^{-16}$ s$^{-1}$, and the
sulfur elemental abundance $S/H = 8\times 10^{-8} - 8\times 10^{-7}$.
Comparison with the observed spectra indicates that spectra are well reproduced
with the relatively low density of $n=(1-3) \times 10^3\,$cm$^{-3}$, $T=10\,$K,
$\zeta = 10^{-17}$ s$^{-1}$, and the short chemistry timescale of $10^5$ yrs.
This short chemistry timescale may indicate that molecular clouds are
constantly affected by the turbulence, and exposed to low-density, low $A_{\rm
V}$ regions that "refreshes" the chemical clock by UV radiation. The relatively
low density obtained is orders of magnitude lower than the commonly-quoted
critical density in the optically thin case. Meanwhile, this range of density
is consistent with results from recent observational analysis of
molecular-cloud-scale mapping. | astro-ph_GA |
Spontaneous Formation of Outflows Powered by Rotating Magnetized
Accretion Flows in a Galactic Center: We investigate how magnetically driven outflows are powered by a rotating,
weakly magnetized accretion flow onto a supermassive black hole using
axisymmetric magnetohydrodynamic simulations. Our proposed model focuses on the
accretion dynamics on an intermediate scale between the Schwarzschild radius
and the galactic scale, which is $\sim$1-100 pc. We demonstrate that a rotating
disk formed on a parsec-scale acquires poloidal magnetic fields via accretion
and this produces an asymmetric bipolar outflow at some point. The formation of
the outflow was found to follow the growth of strongly magnetized regions
around disk surfaces (magnetic bubbles). The bipolar outflow grew continuously
inside the expanding bubbles. We theoretically derived the growth condition of
magnetic bubbles for our model that corresponds to a necessary condition for
outflow growth. We found that the north-south asymmetric structure of the
bipolar outflow originates from the complex motions excited by accreting flows
around the outer edge of the disk. The bipolar outflow comprises multiple
mini-outflows and downflows (failed outflows). The mini-outflows emanate from
the magnetic concentrations (magnetic patches). The magnetic patches exhibit
inward drifting motions, thereby making the outflows unsteady. We demonstrate
that the inward drift can be modeled using a simple magnetic patch model that
considers magnetic angular momentum extraction. This study could be helpful for
understanding how asymmetric and non-steady outflows with complex substructures
are produced around supermassive black holes without the help of strong
radiation from accretion disks or entrainment by radio jets such as molecular
outflows in radio-quiet active galactic nuclei, NGC 1377. | astro-ph_GA |
Simulations of the star-forming molecular gas in an interacting M51-like
galaxy: cloud population statistics: To investigate how molecular clouds react to different environmental
conditions at a galactic scale, we present a catalogue of giant molecular
clouds resolved down to masses of $\sim 10$~M$_{\odot}$ from a simulation of
the entire disc of an interacting M51-like galaxy and a comparable isolated
galaxy. Our model includes time-dependent gas chemistry, sink particles for
star formation and supernova feedback, meaning we are not reliant on star
formation recipes based on threshold densities and can follow the physics of
the cold molecular phase. We extract giant molecular clouds at a given timestep
of the simulations and analyse their properties. In the disc of our simulated
galaxies, spiral arms seem to act merely as snowplows, gathering gas and clouds
without dramatically affecting their properties. In the centre of the galaxy,
on the other hand, environmental conditions lead to larger, more massive
clouds. While the galaxy interaction has little effect on cloud masses and
sizes, it does promote the formation of counter-rotating clouds. We find that
the identified clouds seem to be largely gravitationally unbound at first
glance, but a closer analysis of the hierarchical structure of the molecular
interstellar medium shows that there is a large range of virial parameters with
a smooth transition from unbound to mostly bound for the densest structures.
The common observation that clouds appear to be virialised entities may
therefore be due to CO bright emission highlighting a specific level in this
hierarchical binding sequence. The small fraction of gravitationally bound
structures found suggests that low galactic star formation efficiencies may be
set by the process of cloud formation and initial collapse. | astro-ph_GA |
The nature of sub-millimetre galaxies II: an ALMA comparison of SMG dust
heating mechanisms: We compare the contribution of Active Galactic Nuclei (AGN) and
star-formation towards dust heating in sub-mm galaxies (SMGs). We have used
ALMA at $0."1$ resolution to image a complete flux-limited sample of seven
sub-mm sources previously shown to have spectral energy distributions (SEDs)
that were as well-fitted by obscured AGN as star-forming galaxy templates.
Indeed, two sub-mm sources were known to be quasars from their absorbed X-ray
emission. We find the sub-mm sizes of all SMGs to be small ($\approx1-2$kpc)
and generally $\sim3$ times smaller than any host detected in the
Near-Infra-Red (NIR). In all cases, the five SMGs are comparable in sub-mm size
to the two known quasars and four $z\approx6$ quasars, also observed with ALMA.
We detect no evidence of diffuse spiral arms in this complete sample. We then
convert the Far-Infra-Red (FIR) luminosities to star-formation rate (SFR)
surface densities and find that the SMGs occupy the same range as the known
quasars in our sample. We conclude that in terms of sub-mm size, extent
relative to host and SFR density as well as luminosity and Mid-IR (MIR) colour,
there is little distinction between the SMGs and sub-mm bright quasars.
Finally, we present preliminary evidence that SMGs with higher MIR luminosities
and sub-mm loud quasars tend to have dust components that range to hotter
temperatures than their less luminous SMG counterparts. In light of these
results, we continue to suggest that luminous SMGs may host dust-absorbed
quasars that may simultaneously dominate the FIR and hard X-ray backgrounds. | astro-ph_GA |
Subaru FOCAS IFU observations of two z=0.12 strong-lensing elliptical
galaxies from SDSS MaNGA: We present new observations of two z=0.12 strong-lensing elliptical galaxies,
originally discovered from the SDSS-IV MaNGA survey, using the new FOCAS IFU
spectrograph on the Subaru Telescope. For J1436+4943, our observations confirm
the identification of this system as a multiple-image lens, in a cusp
configuration, with Einstein radius $\theta_{Ein}$=2.0 arcsec. For J1701+3722,
the improved data confirm earlier hints of a complex source plane, with
different configurations evident in different emission lines. The new
observations reveal a previously unseen inner counter-image to the [OIII] arc
found from MaNGA, leading to a smaller revised Einstein radius of
$\theta_{Ein}$=1.6 arcsec. The inferred projected masses within the Einstein
apertures (3.7-4.7kpc) are consistent with being dominated by stars with an
initial mass function (IMF) similar to that of the Milky Way, and a dark matter
contribution of ~35 per cent as supported from cosmological simulations. These
results are consistent with `pure lensing' analyses of lower-redshift lenses,
but contrast with claims for heavier IMFs from combined lensing-and-dynamical
studies of more distant early-type galaxies. | astro-ph_GA |
The Black Hole in the Compact, High-dispersion Galaxy NGC 1271: Located in the Perseus cluster, NGC 1271 is an early-type galaxy with a small
effective radius of 2.2 kpc and a large stellar velocity dispersion of 276 km/s
for its K-band luminosity of 8.9x10^{10} L_sun. We present a mass measurement
for the black hole in this compact, high-dispersion galaxy using observations
from the integral field spectrograph NIFS on the Gemini North telescope
assisted by laser guide star adaptive optics, large-scale integral field unit
observations with PPAK at the Calar Alto Observatory, and Hubble Space
Telescope WFC3 imaging observations. We are able to map out the stellar
kinematics on small spatial scales, within the black hole sphere of influence,
and on large scales that extend out to four times the galaxy's effective
radius. We find that the galaxy is rapidly rotating and exhibits a sharp rise
in the velocity dispersion. Through the use of orbit-based stellar dynamical
models, we determine that the black hole has a mass of (3.0^{+1.0}_{-1.1}) x
10^9 M_sun and the H-band stellar mass-to-light ratio is 1.40^{+0.13}_{-0.11}
M_sun/L_sun (1-sigma uncertainties). NGC 1271 occupies the sparsely-populated
upper end of the black hole mass distribution, but is very different from the
Brightest Cluster Galaxies (BCGs) and giant elliptical galaxies that are
expected to host the most massive black holes. Interestingly, the black hole
mass is an order of magnitude larger than expectations based on the galaxy's
bulge luminosity, but is consistent with the mass predicted using the galaxy's
bulge stellar velocity dispersion. More compact, high-dispersion galaxies need
to be studied using high spatial resolution observations to securely determine
black hole masses, as there could be systematic differences in the black hole
scaling relations between these types of galaxies and the BCGs/giant
ellipticals, thereby implying different pathways for black hole and galaxy
growth. | astro-ph_GA |
A Catalog of Globular Cluster Systems: What Determines the Size of a
Galaxy's Globular Cluster Population?: We present a catalog of 422 galaxies with published measurements of their
globular cluster (GC) populations. Of these, 248 are E galaxies, 93 are S0
galaxies, and 81 are spirals or irregulars. Among various correlations of the
total number of GCs with other global galaxy properties, we find that N_GC
correlates well though nonlinearly with the dynamical mass of the galaxy bulge
M_dyn = 4 \sigma_e^2 R_e /G, where \sigma_e is the central velocity dispersion
and R_e the effective radius of the galaxy light profile. We also present
updated versions of the GC specific frequency S_N and specific mass S_M versus
host galaxy luminosity and baryonic mass. These graphs exhibit the previously
known U-shape: highest S_N or S_M values occur for either dwarfs or
supergiants, but in the midrange of galaxy size (10^9 - 10^10 L_Sun) the GC
numbers fall along a well defined baseline value of S_N ~ 1 or S_M ~ 0.1,
similar among all galaxy types. Along with other recent discussions, we suggest
that this trend may represent the effects of feedback, which systematically
inhibited early star formation at either very low or very high galaxy mass, but
which had its minimum effect for intermediate masses. Our results strongly
reinforce recent proposals that GC formation efficiency appears to be most
nearly proportional to the galaxy halo mass M_halo. The mean "absolute"
efficiency ratio for GC formation that we derive from the catalog data is
M_GCS/M_halo = 6 \times 10^-5. We suggest that the galaxy-to-galaxy scatter
around this mean value may arise in part because of differences in the relative
timing of GC formation versus field-star formation. Finally, we find that an
excellent empirical predictor of total GC population for galaxies of all
luminosities is N_GC \sim (R_e \sigma_e)^1.3$, a result consistent with
Fundamental Plane scaling relations. | astro-ph_GA |
The SEDIGISM survey: a search for molecular outflows: Context. The formation processes of massive stars are still unclear but a
picture is emerging involving accretion disks and molecular outflows in what
appears to be a scaled-up version of low-mass star formation. A census of
outflow activity towards massive star-forming clumps in various evolutionary
stages has the potential to shed light on massive star formation (MSF).
Aims. We conducted an outflow survey towards ATLASGAL clumps using SEDIGISM
data and aimed to obtain a large sample of clumps exhibiting outflows in
different evolutionary stages.
Methods. We identify the high-velocity wings of the 13CO lines toward
ATLASGAL clumps by (1) extracting the simultaneously observed 13CO and C18O
spectra from SEDIGISM, and (2) subtracting Gaussian fits to the scaled C18O
from the 13CO, line after considering opacity broadening.
Results. We have detected high-velocity gas towards 1192 clumps out of a
total sample of 2052, giving an overall detection rate of 58%. Outflow activity
has been detected in the earliest quiescent clumps (i.e., 70$\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 |
Identification of filamentary structures in the environment of
superclusters of galaxies in the Local Universe: The characterization of the internal structure of the superclusters of
galaxies (walls, filaments and knots where the clusters are located) is
paramount for understanding the formation of the Large Scale Structure and for
outlining the environment where galaxies evolved in the last Gyr. (i) To detect
the compact regions of high relative density (clusters and rich groups of
galaxies); (ii) to map the elongated structures of low relative density
(filaments, bridges and tendrils of galaxies); (iii) to characterize the galaxy
populations on filaments and study the environmental effects they are subject
to. We employed optical galaxies with spectroscopic redshifts from the
SDSS-DR13 inside rectangular boxes encompassing the volumes of a sample of 46
superclusters of galaxies, up to z=0.15. Our methodology implements different
classical pattern recognition and machine learning techniques pipelined in the
Galaxy Systems-Finding algorithm and the Galaxy Filaments-Finding algorithm. We
detected in total 2,705 galaxy systems (clusters and groups, of which 159 are
new) and 144 galaxy filaments in the 46 superclusters of galaxies. The
filaments we detected have a density contrast above 3, with a mean value around
10, a radius of about 2.5 Mpc and lengths between 9 and 130 Mpc. Correlations
between the galaxy properties (mass, morphology and activity) and the
environment in which they reside (systems, filaments and the dispersed
component) suggest that galaxies closer to the skeleton of the filaments are
more massive by up to 25% compared to those in the dispersed component; 70 % of
the galaxies in the filament region present early type morphologies and the
fractions of active galaxies (both AGN and SF) seem to decrease as galaxies
approach the filament. These results suggest that preprocessing in large scale
filaments could have significant effects on galaxy evolution. | astro-ph_GA |
Stellar Kinematics and Metallicities in the Ultra-Faint Dwarf Galaxy
Reticulum II: We present Magellan/M2FS, VLT/GIRAFFE, and Gemini South/GMOS spectroscopy of
the newly discovered Milky Way satellite Reticulum II. Based on the spectra of
25 Ret II member stars selected from Dark Energy Survey imaging, we measure a
mean heliocentric velocity of 62.8 +/- 0.5 km/s and a velocity dispersion of
3.3 +/- 0.7 km/s. The mass-to-light ratio of Ret II within its half-light
radius is 470 +/- 210 Msun/Lsun, demonstrating that it is a strongly dark
matter-dominated system. Despite its spatial proximity to the Magellanic
Clouds, the radial velocity of Ret II differs from that of the LMC and SMC by
199 and 83 km/s, respectively, suggesting that it is not gravitationally bound
to the Magellanic system. The likely member stars of Ret II span 1.3 dex in
metallicity, with a dispersion of 0.28 +/- 0.09 dex, and we identify several
extremely metal-poor stars with [Fe/H] < -3. In combination with its
luminosity, size, and ellipticity, these results confirm that Ret II is an
ultra-faint dwarf galaxy. With a mean metallicity of [Fe/H] = -2.65 +/- 0.07,
Ret II matches Segue~1 as the most metal-poor galaxy known. Although Ret II is
the third-closest dwarf galaxy to the Milky Way, the line-of-sight integral of
the dark matter density squared is log J = 18.8 +/- 0.6 Gev^2/cm^5 within 0.2
degrees, indicating that the predicted gamma-ray flux from dark matter
annihilation in Ret II is lower than that of several other dwarf galaxies. | astro-ph_GA |
Large scale clustering measurements with photometric redshifts:
comparing the dark matter halos of X-ray AGN, star-forming and passive
galaxies at z~1: We combine multiwavelength data in the AEGIS-XD and C-COSMOS surveys to
measure the typical dark matter halo mass of X-ray selected AGN
[Lx(2-10keV)>1e42 erg/s] in comparison with far-infrared selected star-forming
galaxies detected in the Herschel/PEP survey (PACS Evolutionary Probe; Lir>1e11
solar) and quiescent systems at z~1. We develop a novel method to measure the
clustering of extragalactic populations that uses photometric redshift
Probability Distribution Functions in addition to any spectroscopy. This is
advantageous in that all sources in the sample are used in the clustering
analysis, not just the subset with secure spectroscopy. The method works best
for large samples. The loss of accuracy because of the lack of spectroscopy is
balanced by increasing the number of sources used to measure the clustering. We
find that X-ray AGN, far-infrared selected star-forming galaxies and passive
systems in the redshift interval 0.6<z<1.4 are found in halos of similar mass,
$\log M_{DMH}/(M_{\odot}\,h^{-1})\approx13.0$. We argue that this is because
the galaxies in all three samples (AGN, star-forming, passive) have similar
stellar mass distributions, approximated by the J-band luminosity. Therefore
all galaxies that can potentially host X-ray AGN, because they have stellar
masses in the appropriate range, live in dark matter haloes of $\log
M_{DMH}/(M_{\odot}\,h^{-1})\approx13.0$ independent of their star-formation
rates. This suggests that the stellar mass of X-ray AGN hosts is driving the
observed clustering properties of this population. We also speculate that
trends between AGN properties (e.g. luminosity, level of obscuration) and large
scale environment may be related to differences in the stellar mass of the host
galaxies. | astro-ph_GA |
New halo stars of the Galactic globular clusters M3 and M13 in the
LAMOST DR1 Catalog: M3 and M13 are Galactic globular clusters with previous reports of
surrounding stellar halos. We present the results of a search for members and
extratidal cluster halo stars within and outside of the tidal radius of these
clusters in the LAMOST Data Release 1. We find seven candidate cluster members
(inside the tidal radius) of both M3 and M13 respectively. In M3 we also
identify eight candidate extratidal cluster halo stars at distances up to ~9.8
times the tidal radius, and in M13 we identify 12 candidate extratidal cluster
halo stars at distances up to ~13.8 times the tidal radius. These results
support previous indications that both M3 and M13 are surrounded by extended
stellar halos, and we find that the GC destruction rates corresponding to the
observed mass loss are generally significantly higher than theoretical studies
predict. | astro-ph_GA |
The formation of Milky Way-mass disk galaxies in the first 500 million
years of a cold dark matter universe: Whether among the myriad tiny proto-galaxies there exists a population with
similarities to present day galaxies is an open question. We show, using
BlueTides, the first hydrodynamic simulation large enough to resolve the
relevant scales, that the first massive galaxies to form are %in fact predicted
to have extensive rotationally-supported disks. Although their morphology
resembles in some ways Milky-way types seen at much lower redshifts, these
high-redshift galaxies are smaller, denser, and richer in gas than their low
redshift counterparts. From a kinematic analysis of a statistical sample of 216
galaxies at redshift $z=8-10$ we have found that disk galaxies make up 70\% of
the population of galaxies with stellar mass $10^{10} M_\odot$ or greater. Cold
Dark Matter cosmology therefore makes specific predictions for the population
of large galaxies 500 million years after the Big Bang. We argue that
wide-field satellite telescopes (e.g. WFIRST) will in the near future discover
these first massive disk galaxies. The simplicity of their structure and
formation history should make possible new tests of cosmology. | astro-ph_GA |
Magnetic fields in the infrared dark cloud G34.43+0.24: We present the B-fields mapped in IRDC G34.43+0.24 using 850\,$\mu$m
polarized dust emission observed with the POL-2 instrument at JCMT. We examine
the magnetic field geometries and strengths in the northern, central, and
southern regions of the filament. The overall field geometry is ordered and
aligned closely perpendicular to the filament's main axis, particularly in
regions containing the central clumps MM1 and MM2, whereas MM3 in the north has
field orientations aligned with its major axis. The overall field orientations
are uniform at large (POL-2 at 14$\arcsec$ and SHARP at 10$\arcsec$) to small
scales (TADPOL at 2.5$\arcsec$ and SMA at 1.5$\arcsec$) in the MM1 and MM2
regions. SHARP/CSO observations in MM3 at 350\,$\mu$m from Tang et al. show a
similar trend as seen in our POL-2 observations. TADPOL observations
demonstrate a well-defined field geometry in MM1/MM2 consistent with MHD
simulations of accreting filaments. We obtained a plane-of-sky magnetic field
strength of 470$\pm$190\,$\mu$G, 100$\pm$40\,$\mu$G, and 60$\pm$34\,$\mu$G in
the central, northern and southern regions of G34, respectively, using the
updated Davis-Chandrasekhar-Fermi relation. The estimated value of field
strength, combined with column density and velocity dispersion values available
in the literature, suggests G34 to be marginally critical with criticality
parameter $\rm \lambda$ values 0.8$\pm$0.4, 1.1$\pm$0.8, and 0.9$\pm$0.5 in the
central, northern, and southern regions, respectively. The turbulent motions in
G34 are sub-Alfv\'{e}nic with Alfv\'{e}nic Mach numbers of 0.34$\pm$0.13,
0.53$\pm$0.30, and 0.49$\pm$0.26 in the three regions. The observed aligned
B-fields in G34.43+0.24 are consistent with theoretical models suggesting that
B-fields play an important role in guiding the contraction of the cloud driven
by gravity. | astro-ph_GA |
The radial gradient of cosmic ray intensity in the Galaxy: The dependence of the cosmic ray intensity on Galactocentric distance is
known to be much less rapid than that to be thought-to-be sources: supernova
remnants. This is an old problem ('the radial gradient problem') which has led
to a number of possible 'scenarios'. Here, we use recent data on the
supernova's radial distribution and correlate it with the measured HII electron
temperature ({\em T}). We examined two models of cosmic ray injection and
acceleration and in both of them the injection efficiency increases with
increasing ambient temperature {\em T}. The increase is expected to vary as a
high power of {\em T} in view of the strong temperature dependence of the tail
of the Maxwell-Boltzmann distribution of particle energies. Writing the
efficiency as proportional to $T^n$ we find $n\approx 8.4$. There is thus, yet
another possible explanation of the radial gradient problem. | astro-ph_GA |
On the quenching of star formation in observed and simulated central
galaxies: Evidence for the role of integrated AGN feedback: In this paper we investigate how massive central galaxies cease their star
formation by comparing theoretical predictions from cosmological simulations:
EAGLE, Illustris and IllustrisTNG with observations of the local Universe from
the Sloan Digital Sky Survey (SDSS). Our machine learning (ML) classification
reveals supermassive black hole mass ($M_{\rm BH}$) as the most predictive
parameter in determining whether a galaxy is star forming or quenched at
redshift $z=0$ in all three simulations. This predicted consequence of active
galactic nucleus (AGN) quenching is reflected in the observations, where it is
true for a range of indirect estimates of $M_{\rm BH}$ via proxies as well as
its dynamical measurements. Our partial correlation analysis shows that other
galactic parameters lose their strong association with quiescence, once their
correlations with $M_{\rm BH}$ are accounted for. In simulations we demonstrate
that it is the integrated power output of the AGN, rather than its
instantaneous activity, which causes galaxies to quench. Finally, we analyse
the change in molecular gas content of galaxies from star forming to passive
populations. We find that both gas fractions ($f_{\rm gas}$) and star formation
efficiencies (SFEs) decrease upon transition to quiescence in the observations
but SFE is more predictive than $f_{\rm gas}$ in the ML passive/star-forming
classification. These trends in the SDSS are most closely recovered in
IllustrisTNG and are in direct contrast with the predictions made by Illustris.
We conclude that a viable AGN feedback prescription can be achieved by a
combination of preventative feedback and turbulence injection which together
quench star formation in central galaxies. | astro-ph_GA |
Empirical derivation of the metallicity evolution with time and radius
using TNG50 Milky Way/Andromeda analogues: Recent works have used a linear birth metallicity gradient to estimate the
evolution of the [Fe/H] profile in the Galactic disk over time, and infer
stellar birth radii (R$_\text{birth}$) from [Fe/H] and age measurements. These
estimates rely on the evolution of [Fe/H] at the Galactic center ([Fe/H](0,
$\tau$)) and the birth metallicity gradient ($\nabla$[Fe/H]($\tau)$) over time
-- quantities that are unknown and inferred under key assumptions. In this
work, we use the sample of Milky Way/Andromeda analogues from the TNG50
simulation to investigate the ability to recover [Fe/H](R, $\tau$) and
R$_\text{birth}$ in a variety of galaxies. Using stellar disk particles, we
test the assumptions required in estimating R$_\text{birth}$, [Fe/H](0,
$\tau$), and $\nabla$[Fe/H]($\tau)$ using recently proposed methods to
understand when they are valid. We show that $\nabla$[Fe/H]($\tau)$ can be
recovered in most galaxies to within 22% from the range in [Fe/H] across age,
with better accuracy for more massive and stronger barred galaxies. We also
find that the true central metallicity is unrepresentative of the genuine disk
[Fe/H] profile; thus we propose to use a projected central metallicity instead.
About half of the galaxies in our sample do not have a continuously enriching
projected central metallicity, with a dilution in [Fe/H] correlating with
mergers. Most importantly, galaxy-specific [Fe/H](R, $\tau$) can be constrained
and confirmed by requiring the R$_\text{birth}$ distributions of mono-age,
solar neighborhood populations to follow inside-out formation. We conclude that
examining trends with R$_\text{birth}$ is valid for the Milky Way disk and
similarly structured galaxies, where we expect R$_\text{birth}$ can be
recovered to within 16% assuming today's measurement uncertainties in TNG50. | astro-ph_GA |
Magnetic and gaseous spiral arms in M83: Isotropic and anisotropic wavelet transforms are used to decompose the images
of the spiral galaxy M83 in various tracers to quantify structures in a range
of scales from 0.2 to 10 kpc. We used radio polarization observations at
{\lambda}6 cm and 13 cm obtained with the VLA, Effelsberg and ATCA telescopes
and APEX sub-mm observations at 870 {\mu}m, which are first published here,
together with maps of the emission of warm dust, ionized gas, molecular gas,
and atomic gas. The spatial power spectra are similar for the tracers of dust,
gas, and total magnetic field, while the spectra of the ordered magnetic field
are significantly different. The wavelet cross-correlation between all material
tracers and total magnetic field is high, while the structures of the ordered
magnetic field are poorly correlated with those of other tracers. -- The
magnetic field configuration in M83 contains pronounced magnetic arms. Some of
them are displaced from the corresponding material arms, while others overlap
with the material arms. The magnetic field vectors at {\lambda}6 cm are aligned
with the outer material arms, while significant deviations occur in the inner
arms and in the bar region, possibly due to non-axisymmetric gas flows. Outside
the bar region, the typical pitch angles of the material and magnetic spiral
arms are very close to each other at about 10{\deg}. The typical pitch angle of
the magnetic field vectors is about 20{\deg} larger than that of the material
spiral arms. One of the main magnetic arms in M83 is displaced from the gaseous
arms, while the other main arm overlaps a gaseous arm. We propose that a
regular spiral magnetic field generated by a mean-field dynamo is compressed in
material arms and partly aligned with them. The interaction of galactic dynamo
action with a transient spiral pattern is a promising mechanism for producing
such complicated spiral patterns as in M83. | astro-ph_GA |
Optical Identification and Spectroscopy of Supernova Remnants in the
Galaxy M51: Using a combination of ground-based and HST imaging, we have constructed a
catalog of 179 supernova remnants (SNRs) and SNR candidates in the nearby
spiral galaxy M51. Follow-up spectroscopy of 66 of the candidates confirms 61
of these as SNRs, and suggests that the vast majority of the unobserved objects
are SNRs as well. A total of 55 of the candidates are coincident with (mostly
soft) X-ray sources identified in deep Chandra observations of M51; searching
the positions of other soft X-ray sources resulted in several additional
possible optical candidates. There are 16 objects in the catalog coincident
with known radio sources. None of the sources with spectra shows the high
velocities (>500 km/s) characteristic of young, ejecta-dominated SNRs like Cas
A; instead, most if not all appear to be middle-aged SNRs. The general
properties of the SNRs, size distribution and spectral characteristics,
resemble those in other nearby spiral galaxies, notably M33, M83, and NGC6946,
where similar samples exist. However, the spectroscopically observed [N
II]:H{\alpha} ratios appear to be significantly higher than in any of these
other galaxies. Although we have explored various ideas to explain the high
ratios in M51, none of the explanations appears to be satisfactory. | astro-ph_GA |
Strongly lensed candidates from the HSC transient survey: We present a lensed quasar search based on the variability of lens systems in
the HSC transient survey. Starting from 101,353 variable objects with i-band
photometry in the HSC transient survey, we used a variability-based lens search
method measuring the spatial extent in difference images to select potential
lensed quasar candidates. We adopted conservative constraints in this
variability selection and obtained 83,657 variable objects as possible lens
candidates. We then ran CHITAH, a lens search algorithm based on the image
configuration, on those 83,657 variable objects, and 2,130 variable objects
were identified as potential lensed objects. We visually inspected the 2,130
variable objects, and seven of them are our final lensed quasar candidates.
Additionally, we found one lensed galaxy candidate as a serendipitous
discovery. Among the eight final lensed candidates, one is the only known
quadruply lensed quasar in the survey field, HSCJ095921+020638. None of the
other seven lensed candidates have been previously classified as a lens nor a
lensed candidate. Three of the five final candidates with available HST images,
including HSCJ095921+020638, show clues of a lensed feature in the HST images.
A tightening of variability selection criteria might result in the loss of
possible lensed quasar candidates, especially the lensed quasars with faint
brightness or narrow separation, without efficiently eliminating the non-lensed
objects; CHITAH is therefore important as an advanced examination to improve
the lens search efficiency through the object configuration. The recovery of
HSCJ095921+020638 proves the effectiveness of the variability-based lens search
method, and this lens search method can be used in other cadenced imaging
surveys, such as the upcoming Rubin Observatory Legacy Survey of Space and
Time. | astro-ph_GA |
The extreme luminosity states of Sagittarius A*: We discuss mm-wavelength radio, 2.2-11.8um NIR and 2-10 keV X-ray light
curves of the super massive black hole (SMBH) counterpart of Sagittarius A*
(SgrA*) near its lowest and highest observed luminosity states. The luminosity
during the low state can be interpreted as synchrotron emission from a
continuous or even spotted accretion disk. For the high luminosity state SSC
emission from THz peaked source components can fully account for the flux
density variations observed in the NIR and X-ray domain. We conclude that at
near-infrared wavelengths the SSC mechanism is responsible for all emission
from the lowest to the brightest flare from SgrA*. For the bright flare event
of 4 April 2007 that was covered from the radio to the X-ray domain, the SSC
model combined with adiabatic expansion can explain the related peak
luminosities and different widths of the flare profiles obtained in the NIR and
X-ray regime as well as the non detection in the radio domain. | astro-ph_GA |
The Three Hundred: $M_{sub}-V_{circ}$ relation: In this study, we investigate a recent finding based on strong lensing
observations, which suggests that the sub-halos observed in clusters exhibit
greater compactness compared to those predicted by $\Lambda$CDM simulations. To
address this discrepancy, we performed a comparative analysis by comparing the
cumulative mass function of sub-halos and the
$M_{\text{sub}}$-$V_{\text{circ}}$ relation between observed clusters and 324
simulated clusters from The Three Hundred project, focusing on re-simulations
using GADGET-X and GIZMO-SIMBA baryonic models. The sub-halos' cumulative mass
function of the GIZMO-SIMBA simulated clusters agrees with observations, while
the GADGET-X simulations exhibit discrepancies in the lower sub-halo mass range
possibly due to its strong SuperNova feedback. Both GADGET-X and GIZMO-SIMBA
simulations demonstrate a redshift evolution of the sub-halo mass function and
the $V_{max}$ function, with slightly fewer sub-halos observed at lower
redshifts. Neither the GADGET-X nor GIZMO-SIMBA(albeit a little closer)
simulated clusters' predictions for the $M_{\text{sub}}$-$V_{\text{circ}}$
relation align with the observational result. Further investigations on the
correlation between sub-halo/halo properties and the discrepancy in the
$M_{\text{sub}}$-$V_{\text{circ}}$ relation reveals that the sub-halo's half
mass radius and galaxy stellar age, the baryon fraction and sub-halo distance
from the cluster's centre, as well as the halo relaxation state play important
roles on this relation. Nevertheless, we think it is still challenging in
accurately reproducing the observed $M_{\text{sub}}$-$V_{\text{circ}}$ relation
in our current hydrodynamic cluster simulation under the standard $\Lambda$CDM
cosmology. | astro-ph_GA |
The Origin of the 300 km s$^{-1}$ Stream Near Segue 1: We present a search for new members of the 300 km s$^{-1}$ stream (300S) near
the dwarf galaxy Segue 1 using wide-field survey data. We identify 11
previously unknown bright stream members in the APOGEE-2 and SEGUE-1 and 2
spectroscopic surveys. Based on the spatial distribution of the high-velocity
stars, we confirm for the first time that this kinematic structure is
associated with a 24$^{\circ}$-long stream seen in SDSS and Pan-STARRS imaging
data. The 300S stars display a metallicity range of $-2.17 < {\rm [Fe/H]} <
-1.24$, with an intrinsic dispersion of 0.21$_{-0.09}^{+0.12}$ dex. They also
have chemical abundance patterns similar to those of Local Group dwarf
galaxies, as well as that of the Milky Way halo. Using the open-source code
galpy to model the orbit of the stream, we find that the progenitor of the
stream passed perigalacticon about 70 Myr ago, with a closest approach to the
Galactic Center of about 4.1 kpc. Using Pan-STARRS DR1 data, we obtain an
integrated stream luminosity of $4 \times 10^3$ L$_{\odot}$. We conclude that
the progenitor of the stream was a dwarf galaxy that is probably similar to the
satellites that were accreted to build the present-day Milky Way halo. | astro-ph_GA |
Can X-rays provide a solution to the abundance discrepancy problem in
photoionised nebulae?: We re-examine the well-known discrepancy between ionic abundances determined
via the analysis of recombination lines (RLs) and collisionally excited lines
(CELs). We show that abundance variations can be mimicked in a {\it chemically
homogeneous} medium by the presence of dense X-ray irradiated regions which
present different ionisation and temperature structures from those of the more
diffuse medium they are embedded in, which is predominantly ionised by
extreme-ultraviolet radiation. The presence of X-ray ionised dense clumps or
filaments also naturally explains the lower temperatures often measured from O
{\sc ii} recombination lines and from the Balmer jump when compared to
temperatures determined by CELs. We discuss the implications for abundances
determined via the analysis of CELs and RLs and provide a simple analytical
procedure to obtain upwards corrections for CEL-determined abundance. While we
show that the abundance discrepancy factor (ADF) and the Balmer Jump
temperature determined from observations of the Orion Nebula can simultaneously
be reproduced by this model (implying upward corrections for CELs by a factor
of 1.15), we find that the required X-ray fluxes exceed the known Orion's
stellar and diffuse X-ray budget, if we assume that the clumps are located at
the edge of the blister. We propose, however, that spatially resolved
observations may be used to empirically test the model, and we outline how the
framework developed in this letter may be applied in the future to objects with
better constrained geometries (e.g. planetary nebulae). | astro-ph_GA |
A catalogue of 74 new open clusters found in Gaia Data-Release 2: Based on astrometric data from Gaia DR2, we employ an unsupervised machine
learning method to blindly search for open star clusters in the Milky Way
within the Galactic latitude range of |b| < 20 degrees. In addition to 2,080
known clusters, 74 new open cluster candidates are found. In this work, we
present the positions, apparent radii, parallaxes, proper motions and member
stars of these candidates
(https://cdsarc.u-strasbg.fr/ftp/vizier.submit//new_OC/). Meanwhile, to obtain
the physical parameters of each candidate cluster, stellar isochrones are fit
to the photometric data. The results show that the apparent radii and the
observed proper motion dispersions of these new candidates are consistent with
those of open clusters previously identified in Gaia DR2. | astro-ph_GA |
Radiation pressure acting on the neutral He atoms in the Heliosphere: The Interstellar Neutral Helium (ISN He) is an important source of
information on the physical state of the Local Interstellar Medium. Radiation
pressure acting on the neutral helium atoms in the heliosphere has always been
neglected, its effect has been considered insignificant compared to
gravitational force. The most advanced numerical models of ISN He take into
account more and more subtle effects, therefore it is important to check if the
effect of radiation pressure is still negligible. In this paper, we use the
most up-to-date version of the Warsaw Test Particle Model (WTPM) to calculate
the expected helium distribution in the heliosphere, and simulate the flux of
ISN He observed by the Interstellar Boundary Explorer (IBEX) and in the future
by the Interstellar Mapping and Acceleration Probe (IMAP). We compare results
calculated with and without radiation pressure during low and high solar
activity. The results show that in the analysis of IBEX-Lo observations the
radiation pressure acting on typical helium causes flux differences at a level
of 1-4% and is comparable to the observational errors. For the more sensitive
IMAP-Lo instrument, there are some regions in the considered observations
configurations where radiation pressure causes potentially statistically
significant changes in the calculated fluxes. The effect can be up to 9% for
the indirect beam and is likely to be higher than the estimated errors.
Therefore, we claim that in the future analysis of the IMAP-Lo observations
radiation pressure acting on ISN He should be considered. | astro-ph_GA |
Are rotating planes of satellite galaxies ubiquitous?: We compare the dynamics of satellite galaxies in the Sloan Digital Sky Survey
to simple models in order to test the hypothesis that a large fraction of
satellites co-rotate in coherent planes. We confirm the previously-reported
excess of co-rotating satellite pairs located near diametric opposition with
respect to the host, but show that this signal is unlikely to be due to
rotating discs (or planes) of satellites. In particular, no overabundance of
co-rotating satellites pairs is observed within $\sim 20^{\circ}-50^{\circ}$ of
direct opposition, as would be expected for planar distributions inclined
relative to the line-of-sight. Instead, the excess co-rotation for satellite
pairs within $\sim 10^{\circ}$ of opposition is consistent with random noise
associated with undersampling of an underlying isotropic velocity distribution.
We conclude that at most $10\%$ of the hosts in our sample harbor co-rotating
satellite planes (as traced by the luminous satellite population). | astro-ph_GA |
Predicting resolved galaxy properties from photometric images using
convolutional neural networks: Multi-band images of galaxies reveal a huge amount of information about their
morphology and structure. However, inferring properties of the underlying
stellar populations such as age, metallicity or kinematics from those images is
notoriously difficult. Traditionally such information is best extracted from
expensive spectroscopic observations. Here we present the $Painting\,
IntrinsiC\, Attributes\, onto\, SDSS\, Objects$ (PICASSSO) project and test the
information content of photometric multi-band images of galaxies. We train a
convolutional neural network on 27,558 galaxy image pairs to establish a
connection between broad-band images and the underlying physical stellar and
gaseous galaxy property maps. We test our machine learning (ML) algorithm with
SDSS $ugriz$ mock images for which uncertainties and systematics are exactly
known. We show that multi-band galaxy images contain enough information to
reconstruct 2d maps of stellar mass, metallicity, age and gas mass, metallicity
as well as star formation rate. We recover the true stellar properties on a
pixel by pixel basis with only little scatter, $\lesssim20\%$ compared to
$\sim50\%$ statistical uncertainty from traditional mass-to-light-ratio based
methods. We further test for any systematics of our algorithm with image
resolution, training sample size or wavelength coverage. We find that galaxy
morphology alone constrains stellar properties to better than $\sim20\%$ thus
highlighting the benefits of including morphology into the parameter
estimation. The machine learning approach can predict maps of high resolution,
only limited by the resolution of the input bands, thus achieving higher
resolution than IFU observations. The network architecture and all code is
publicly available on GitHub. | astro-ph_GA |
First laboratory detection of vibration-rotation transitions of CH$^+$
and $^{13}$CH$^+$ and improved measurement of their rotational transition
frequencies: The long-searched C-H stretches of the fundamental ions CH$^+$ and
$^{13}$CH$^+$ have been observed for the first time in the laboratory. For
this, the state-dependent attachment of He atoms to these ions at cryogenic
temperatures has been exploited to obtain high-resolution rovibrational data.
In addition, the lowest rotational transitions of CH$^+$, $^{13}$CH$^+$ and
CD$^+$ have been revisited and their rest frequency values improved
substantially. | astro-ph_GA |
Fossil group origins X. Velocity segregation in fossil systems: We want to study how the velocity segregation and the radial profile of the
velocity dispersion depend on the prominence of the brightest cluster galaxies
(BCGs). We divide a sample of 102 clusters and groups of galaxies into four
bins of magnitude gap between the two brightest cluster members. We then
compute the velocity segregation in bins of absolute and relative magnitudes.
Moreover, for each bin of magnitude gap we compute the radial profile of the
velocity dispersion. When using absolute magnitudes, the segregation in
velocity is limited to the two brightest bins and no significant difference is
found for different magnitude gaps. However, when we use relative magnitudes, a
trend appears in the brightest bin: the larger the magnitude gap, the larger
the velocity segregation. We also show that this trend is mainly due to the
presence, in the brightest bin, of satellite galaxies in systems with small
magnitude gaps: in fact, if we study separately central galaxies and
satellites, this trend is mitigated and central galaxies are more segregated
than satellites for any magnitude gap. A similar result is found in the radial
velocity dispersion profiles: a trend is visible in central regions (where the
BCGs dominate) but, if we analyse the profile using satellites alone, the trend
disappears. In the latter case, the shape of the velocity dispersion profile in
the centre of systems with different magnitude gaps show three types of
behaviours: systems with the smallest magnitude gaps have an almost flat
profile from the centre to the external regions; systems with the largest
magnitude gaps show a monothonical growth from the low values of the central
part to the flat ones in the external regions; finally, systems with $1.0 <
\Delta m_{12} \le 1.5$ show a profile that peaks in the centres and then
decreases towards the external regions. We suggest that two mechanisms could be
respons.... | astro-ph_GA |
High-Dimensional Dust Mapping: Galactic interstellar dust has a profound impact not only on our observations
of objects throughout the Universe, but also on the morphology, star formation,
and chemical evolution of the Galaxy. The advent of massive imaging and
spectroscopic surveys (particularly in the infrared) places us on the threshold
of being able to map the properties and dynamics of dust and the interstellar
medium (ISM) in three dimensions throughout the Milky Way disk and bulge. These
developments will enable a fundamentally new understanding of dust properties,
including how grains respond to their local environment and how those
environments affect dust attenuation of background objects of interest.
Distance-resolved maps of dust motion also hold great promise for tracing the
flow of interstellar material throughout the Galaxy on a variety of scales,
from bar-streaming motions to the collapse and dissolution of individual
molecular clouds. These advances require optical and infrared imaging of stars
throughout the Galactic midplane, stretching many kiloparsecs from the Sun,
matched with very dense spectroscopic coverage to probe the ISM's fine-grained
structure. | astro-ph_GA |
Formation of Dark Matter Torii Around Supermassive Black Holes Via The
Eccentric Kozai-Lidov Mechanism: We explore the effects of long term secular perturbations on the distribution
of dark matter particles around Supermassive Black Hole (BH) binaries. We show
that in the hierarchical (in separation) three-body problem, one of the BHs and
a dark matter particle form an inner binary. Gravitational perturbations from
the BH companion, on a much wider orbit, can cause the dark matter particle to
reach extremely high eccentricities and even get accreted onto the BH, by what
is known as the Eccentric Kozai-Lidov (EKL) mechanism. We show that this may
produce a torus-like configuration for the dark matter distribution around the
less massive member of the BH binary. We first consider an Intermediate BH
(IMBH) in the vicinity of our Galactic Center, which may be a relic of a past
minor merger. We show that if the IMBH is close enough (i.e., near the stellar
disk) the EKL mechanism is very efficient in exciting the eccentricity of dark
matter particles in near-polar configurations to extremely high values where
they are accreted by the IMBH. We show that this mechanism is even more
effective if the central BH grows in mass, where we have assumed adiabatic
growth. Since near-polar configurations are disrupted, a torus-like shape is
formed. We also show that this behavior is also likely to be relevant for
Supermassive BH binaries. We suggest that if the BHs are spinning, the accreted
dark matter particles may linger in the ergosphere and thereby may generate
self-annihilations and produce an indirect signature of potential interest. | astro-ph_GA |
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