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Comparing Simulated Emission from Molecular Clouds Using Experimental
Design: We propose a new approach to comparing simulated observations that enables us
to determine the significance of the underlying physical effects. We utilize
the methodology of experimental design, a subfield of statistical analysis, to
establish a framework for comparing simulated position-position-velocity data
cubes to each other. We propose three similarity metrics based on methods
described in the literature: principal component analysis, the spectral
correlation function, and the Cramer multi-variate two sample similarity
statistic. Using these metrics, we intercompare a suite of mock observational
data of molecular clouds generated from magnetohydrodynamic simulations with
varying physical conditions. Using this framework, we show that all three
metrics are sensitive to changing Mach number and temperature in the simulation
sets, but cannot detect changes in magnetic field strength and initial velocity
spectrum. We highlight the shortcomings of one-factor-at-a-time designs
commonly used in astrophysics and propose fractional factorial designs as a
means to rigorously examine the effects of changing physical properties while
minimizing the investment of computational resources. | astro-ph_GA |
Discovery of the elusive thioketenylium, HCCS+, in TMC-1: We report the detection in TMC-1 of the cation HCCS+ (3Sigma-), which is the
protonated form of the widespread radical CCS. This is the first time that a
protonated radical has been detected in a cold dark cloud. Twenty-six hyperfine
components from twelve rotational transitions have been observed with the Yebes
40m and IRAM 30m radio telescopes. We confidently assign the characteristic
rotational spectrum pattern to HCCS+ based on the good agreement between the
astronomical and theoretical spectroscopic parameters. The column density of
HCCS+ is (1.1+/-0.1)e12 cm-2, and the CCS/HCCS+ abundance ratio is 50+/-10,
which is very similar to that of CS/HCS+ (35+/-8) and CCCS/HCCCS+ (65+/-20).
From a state-of-the-art gas-phase chemical model, we conclude that HCCS+ is
mostly formed by reactions of proton transfer from abundant cations such as
HCO+, H3O+, and H3+ to the radical CCS. | astro-ph_GA |
A New Multi-Tracer Approach to Defining the Spiral arm width in the
Milky Way: We analyze recent observations of the spiral arm width in the Milky Way, as a
function of the galactic radius, and we compare this relation with the
prediction from the density wave theory. We use the following method: in each
spiral arm, we concentrate on the separation (or offset) between the
starforming region (radio masers) near the shock front of a density wave, and
the aged star region (diffuse CO gas) near the potential minimum of a density
wave; we take this separation between these two tracers as the arm width.
New results: we find a typical separation (maser to diffuse CO gas) near 250
+/- 50 pc, and an increase of this separation with galactic radius of about 25
+/- 5 pc per kpc. We note that, as expected, this separation is somewhat
smaller than that found earlier between the dust lane and the aged star region.
Overall, these results supports the basics of a density wave. | astro-ph_GA |
History and destiny of an emerging early-type galaxy: New IFU insights
on the major-merger remnant NGC7252: NGC7252, which is one of the nearest major-merger galaxy remnants, is an
ideal laboratory to study the processes inherent to the transformation of disc
galaxies to ellipticals as observed about ~1Gyr after the collision. We
obtained wide-field IFU spectroscopy with the VLT-VIMOS integral-field
spectrograph covering the central 50"x50" of NGC7252 to map the stellar and
ionised gas kinematics, and the distribution and conditions of the ionised gas,
revealing the extent of ongoing star formation and recent star formation
history. We find that the inner gas disc is not counter-rotating with respect
to the stars and that the stellar kinematics appear complex with a clear
indication of a prolate-like rotation component suggesting a polar merger
configuration. The ongoing star formation rate is 2.2+-0.6 M_sun/yr and implies
a typical depletion time of 2Gyr given the molecular gas content. Furthermore,
the spatially-resolved star formation history suggests a slight radial
dependence, moving outwards at later times. We confirm a large AGN-ionised gas
cloud previously discovered 5kpc south of the nucleus, and find higher
ionisation also at the galaxy centre relative to the surrounding gas disc.
Although the higher ionisation towards the centre is potentially degenerate
within the central star forming ring, it may be associated with a
low-luminosity AGN. Although NGC7252 has been classified as post-starburst
galaxy at the centre, the elliptical-like major-merger remnant still appears
very active. A central kpc-scale gas disc has presumably re-formed quickly
within the last 100Myr after final coalescence. The disc features ongoing star
formation, implying Gyr long timescale to reach the red sequence through gas
consumption alone. While NGC7252 is useful to probe the transformation from
discs to ellipticals, it is not well-suited to study the transformation from
blue to red at this point. | astro-ph_GA |
Tightening the belt: Constraining the mass and evolution in SDC335: Recent ALMA observations identified one of the most massive star-forming
cores yet observed in the Milky Way; SDC335-MM1, within the infrared dark cloud
SDC335.579-0.292. Along with an accompanying core MM2, SDC335 appears to be in
the early stages of its star formation process. In this paper we aim to
constrain the properties of the stars forming within these two massive
millimetre sources. Observations of SDC335 at 6, 8, 23 and 25GHz were made with
the ATCA. We report the results of these continuum measurements, which combined
with archival data, allow us to build and analyse the spectral energy
distributions (SEDs) of the compact sources in SDC335. Three HCHII regions
within SDC335 are identified, two within the MM1 core. For each HCHII region, a
free-free emission curve is fit to the data allowing the derivation of the
sources' emission measure, ionising photon flux and electron density. Using
these physical properties we assign each HCHII region a ZAMS spectral type,
finding two protostars with characteristics of spectral type B1.5 and one with
a lower limit of B1-B1.5. Ancillary data from infrared to mm wavelength are
used to construct free-free component subtracted SEDs for the mm-cores,
allowing calculation of the bolometric luminosities and revision of the
previous gas mass estimates. The measured luminosities for the two mm-cores are
lower than expected from accreting sources displaying characteristics of the
ZAMS spectral type assigned to them. The protostars are still actively
accreting, suggesting that a mechanism is limiting the accretion luminosity, we
present the case for two different mechanisms capable of causing this. Finally,
using the ZAMS mass values as lower limit constraints, a final stellar
population for SDC335 was synthesised finding SDC335 is likely to be in the
process of forming a stellar cluster comparable to the Trapezium Cluster and
NGC6334 I(N). | astro-ph_GA |
Modeling and Analysis of a Spectrum of the Globular Cluster NGC 2419: NGC 2419 is the most distant massive globular cluster in the outer Galactic
halo. It is unusual also due to the chemical peculiarities found in its red
giant stars in recent years. We study the stellar population of this unusual
object using spectra obtained at the 1.93-m telescope of the Haute-Provence
Observatory. At variance with commonly used methods of high-resolution
spectroscopy applicable only to bright stars, we employ spectroscopic
information on the integrated light of the cluster. We carry out population
synthesis modeling of medium-resolution spectra using synthetic stellar
atmosphere models based on a theoretical isochrone corresponding accurately to
the observed color-magnitude diagram. We study the influence of non-Local
Thermodynamic Equilibrium for some chemical elements on our results. The
derived age (12.6 Gyr), [Fe/H]=-2.25 dex, helium content Y=0.25, and abundances
of 12 other chemical elements are in a good qualitative agreement with
published high-resolution spectroscopy estimates for red giant members in the
cluster. On the other hand, the derived element abundance, [alpha/Fe]=0.13 dex
(the mean of [O/Fe], [Mg/Fe] and [Ca/Fe]), differs from the published one
([alpha/Fe] =0.4 dex) for selected red giants in the cluster and may be
explained by a large dispersion in the alpha-element abundances recently
discovered in NGC2419. We suggest that studies of the {\it integrated} light in
the cluster using high-resolution spectrographs in different wavelength regions
will help to understand the nature of these chemical anomalies. | astro-ph_GA |
NGDEEP Epoch 1: Spatially Resolved H$α$ Observations of Disk and
Bulge Growth in Star-Forming Galaxies at $z \sim$ 0.6-2.2 from JWST NIRISS
Slitless Spectroscopy: We study the H$\alpha$ equivalent width, EW(H$\alpha$), maps of 19 galaxies
at $0.6 < z < 2.2$ in the Hubble Ultra Deep Field (HUDF) derived from NIRISS
slitless spectroscopy as part of the Next Generation Deep Extragalactic
Exploratory Public (NGDEEP) Survey. Our galaxies mostly lie on the
star-formation main sequence with a stellar mass range of $\mathrm{10^9 -
10^{11} M_\odot}$, characterized as "typical" star-forming galaxies at these
redshifts. Leveraging deep HST and JWST broad-band images, spanning 0.4-4.8
$\mu$m, we perform spatially-resolved fitting of the spectral energy
distributions (SEDs) for these galaxies and construct specific star formation
rate (sSFR) and stellar-mass-weighted age maps with a spatial resolution of
$\sim$1 kpc. The pixel-to-pixel EW(H$\alpha$) increases with increasing sSFR
and with decreasing age. The average trends are slightly different from the
relations derived from integrated fluxes of galaxies from the literature,
suggesting complex evolutionary trends within galaxies. We quantify the radial
profiles of EW(H$\alpha$), sSFR, and age. The majority (84%) of galaxies show
positive EW(H$\alpha$) gradients in line with the inside-out quenching
scenario. A few galaxies (16%) show inverse (and flat) trends possibly due to
merging or starbursts. We compare the distributions of EW(H$\alpha$) and sSFR
to the star formation history models (SFHs) as a function of galactocentric
radius. We argue that the central regions of galaxies have experienced, at
least one, rapid star-formation episodes, which leads to the formation of the
bulge, while their outer regions (e.g., disks) grow via more smoothly varying
SFHs. These results demonstrate the ability to study resolved star formation in
distant galaxies with JWST NIRISS. | astro-ph_GA |
The chemical structure of young high-mass star-forming clumps: (II)
parsec-scale CO depletion and deuterium fraction of $\rm HCO^+$: The physical and chemical properties of cold and dense molecular clouds are
key to understanding how stars form. Using the IRAM 30 m and NRO 45 m
telescopes, we carried out a Multiwavelength line-Imaging survey of the 70
$\mu$m dark and bright clOuds (MIAO). At a linear resolution of 0.1--0.5 pc,
this work presents a detailed study of parsec-scale CO depletion and $\rm
HCO^+$ deuterium (D-) fractionation toward four sources (G11.38+0.81,
G15.22-0.43, G14.49-0.13, and G34.74-0.12) included in our full sample. In each
source with $\rm T<20$ K and $n_{\rm H}\rm\sim10^4$--$\rm 10^5 cm^{-3}$, we
compared pairs of neighboring 70 $\mu$m bright and dark clumps and found that
(1) the $\rm H_2$ column density and dust temperature of each source show
strong spatial anticorrelation; (2) the spatial distribution of CO isotopologue
lines and dense gas tracers, such as 1--0 lines of $\rm H^{13}CO^+$ and $\rm
DCO^+$, are anticorrelated; (3) the abundance ratio between $\rm C^{18}O$ and
$\rm DCO^+$ shows a strong correlation with the source temperature; (4) both
the $\rm C^{18}O$ depletion factor and D-fraction of $\rm HCO^+$ show a robust
decrease from younger clumps to more evolved clumps by a factor of more than 3;
and (5) preliminary chemical modeling indicates chemical ages of our sources
are ${\sim}8\times10^4$ yr, which is comparable to their free-fall timescales
and smaller than their contraction timescales, indicating that our sources are
likely dynamically and chemically young. | astro-ph_GA |
Revisiting the alignment of radio galaxies in the ELAIS-N1 field: Aims. Previous studies reported an alignment of the major axes of radio
galaxies on various angular scales. Here, we study the alignment of radio
galaxies in the ELAIS-N1 Low Frequency ARray (LOFAR) deep field, which covers
an area of 25 $\rm deg^2$. \newline Methods. The low noise level of about 20$
\rm ~ \mu Jy/beam$ of the LOFAR deep field observations at 150 MHz enabled the
identification of 447 extended ($> 30 \rm ''$) radio galaxies for which we have
measured the major axis position angle. We found that 95\% of these sources
have either photometric or spectroscopic redshifts, which we then used for a
three-dimensional analysis. \newline Results. We show the distribution of the
position angles of radio galaxies in the ELAIS-N1 field and perform multiple
statistical tests to check whether the radio galaxies are randomly oriented. We
found that the distribution of position angles is consistent with being
uniform. Two peaks around position angles of 50 and 140$\rm~ deg$ are spurious
and are not caused by an alignment, as shown by a 3D analysis. In conclusion,
our results do not support a 2D or 3D alignment of radio galaxies on scales
smaller than $\sim 4 \rm ~ deg$. | astro-ph_GA |
The Thirteenth Data Release of the Sloan Digital Sky Survey: First
Spectroscopic Data from the SDSS-IV Survey MApping Nearby Galaxies at Apache
Point Observatory: The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) began
observations in July 2014. It pursues three core programs: APOGEE-2, MaNGA, and
eBOSS. In addition, eBOSS contains two major subprograms: TDSS and SPIDERS.
This paper describes the first data release from SDSS-IV, Data Release 13
(DR13), which contains new data, reanalysis of existing data sets and, like all
SDSS data releases, is inclusive of previously released data. DR13 makes
publicly available 1390 spatially resolved integral field unit observations of
nearby galaxies from MaNGA, the first data released from this survey. It
includes new observations from eBOSS, completing SEQUELS. In addition to
targeting galaxies and quasars, SEQUELS also targeted variability-selected
objects from TDSS and X-ray selected objects from SPIDERS. DR13 includes new
reductions of the SDSS-III BOSS data, improving the spectrophotometric
calibration and redshift classification. DR13 releases new reductions of the
APOGEE-1 data from SDSS-III, with abundances of elements not previously
included and improved stellar parameters for dwarf stars and cooler stars. For
the SDSS imaging data, DR13 provides new, more robust and precise photometric
calibrations. Several value-added catalogs are being released in tandem with
DR13, in particular target catalogs relevant for eBOSS, TDSS, and SPIDERS, and
an updated red-clump catalog for APOGEE. This paper describes the location and
format of the data now publicly available, as well as providing references to
the important technical papers that describe the targeting, observing, and data
reduction. The SDSS website, http://www.sdss.org, provides links to the data,
tutorials and examples of data access, and extensive documentation of the
reduction and analysis procedures. DR13 is the first of a scheduled set that
will contain new data and analyses from the planned ~6-year operations of
SDSS-IV. | astro-ph_GA |
Is there a maximum mass for black holes in galactic nuclei?: The largest observed supermassive black holes (SMBHs) have a mass of M_BH ~
10^{10} M_sun, nearly independent of redshift, from the local (z~0) to the
early (z>6) Universe. We suggest that the growth of SMBHs above a few 10^{10}
M_sun is prevented by small-scale accretion physics, independent of the
properties of their host galaxies or of cosmology. Growing more massive BHs
requires a gas supply rate from galactic scales onto a nuclear region as high
as >10^3 M_sun/yr. At such a high accretion rate, most of the gas converts to
stars at large radii (~10-100 pc), well before reaching the BH. We adopt a
simple model (Thompson et al. 2005) for a star-forming accretion disk, and find
that the accretion rate in the sub-pc nuclear region is reduced to the smaller
value of at most a few M_sun/yr. This prevents SMBHs from growing above
~10^{11} M_sun in the age of the Universe. Furthermore, once a SMBH reaches a
sufficiently high mass, this rate falls below the critical value at which the
accretion flow becomes advection dominated. Once this transition occurs, BH
feeding can be suppressed by strong outflows and jets from hot gas near the BH.
We find that the maximum SMBH mass, given by this transition, is between
M_{BH,max} ~ (1-6) * 10^{10} M_sun, depending primarily on the efficiency of
angular momentum transfer inside the galactic disk, and not on other properties
of the host galaxy. | astro-ph_GA |
Machine Learning for Galactic Archaeology: A chemistry-based neural
network method for identification of accreted disc stars: We develop a method ('Galactic Archaeology Neural Network', GANN) based on
neural network models (NNMs) to identify accreted stars in galactic discs by
only their chemical fingerprint and age, using a suite of simulated galaxies
from the Auriga Project. We train the network on the target galaxy's own local
environment defined by the stellar halo and the surviving satellites. We
demonstrate that this approach allows the detection of accreted stars that are
spatially mixed into the disc. Two performance measures are defined - recovery
fraction of accreted stars, and the probability that a star with a positive
(accreted) classification is a true-positive result, P(TP). As the NNM output
is akin to an assigned probability, we are able to determine positivity based
on flexible threshold values that can be adjusted easily to refine the
selection of presumed-accreted stars. We find that GANN identifies accreted
disc stars within simulated galaxies, with high recovery fraction and/or high
P(TP). We also find that stars in Gaia-Enceladus-Sausage (GES) mass systems are
over 50% recovered by our NNMs in the majority (18/24) of cases. Additionally,
nearly every individual source of accreted stars is detected at 10% or more of
its peak stellar mass in the disc. We also demonstrate that a conglomerated
NNM, trained on the halo and satellite stars from all of the Auriga galaxies
provides the most consistent results, and could prove to be an intriguing
future approach as our observational capabilities expand. | astro-ph_GA |
A population of ultraviolet-dim protoclusters detected in absorption: Galaxy protoclusters, which will eventually grow into the massive clusters we
see in the local universe, are usually traced by locating overdensities of
galaxies. Large spectroscopic surveys of distant galaxies now exist, but their
sensitivity depends mainly on a galaxy's star formation activity and dust
content rather than its mass. Tracers of massive protoclusters that do not rely
on their galaxy constituents are therefore needed. Here we report observations
of Lyman-$\alpha$ absorption in the spectra of a dense grid of background
galaxies, which we use to locate a substantial number of candidate
protoclusters at redshifts 2.2-2.8 via their intergalactic gas. We find that
the structures producing the most absorption, most of which were previously
unknown, contain surprisingly few galaxies compared to the dark matter content
of their analogs in cosmological simulations. Nearly all are expected to be
protoclusters, and we infer that half of their expected galaxy members are
missing from our survey because they are unusually dim at rest-frame
ultraviolet wavelengths. We attribute this to an unexpectedly strong and early
influence of the protocluster environment on the evolution of these galaxies
that reduced their star formation or increased their dust content. | astro-ph_GA |
Two step ejection of massive stars and the issue of their formation in
isolation: In this paper we investigate the combined effect of massive binary ejection
from star clusters and a second acceleration of a massive star during a
subsequent supernova explosion. We call this the "two-step-ejection" scenario.
The main results are: i) Massive field stars produced via the two-step-ejection
process can not in the vast majority of cases be traced back to their parent
star clusters. These stars can be mistakenly considered as massive stars formed
in isolation. ii) The expected O star fraction produced via the
two-step-ejection process is of the order of 1-4 per cent, in quantitative
agreement with the observed fraction of candidates for isolated-O-star
formation. iii) Stars ejected via the two-step-ejection process can get a
higher final velocity (up to 1.5-2 times higher) than the pre-supernova
velocity of the massive-star binary. | astro-ph_GA |
The chemical evolution of galaxies with a variable IGIMF: Standard analytical chemical evolution modelling of galaxies has been
assuming the stellar initial mass function (IMF) to be invariant and fully
sampled allowing fractions of massive stars to contribute even in dwarf
galaxies with very low star formation rates (SFRs). Recent observations show
the integrated galactic initial mass function (IGIMF) of stars, i.e. the
galaxy-wide IMF, to become systematically top-heavy with increasing SFR. This
has been predicted by the IGIMF theory, which is here used to develop the
analytical theory of the chemical evolution of galaxies. This theory is
non-linear and requires the iterative solution of implicit integral equations
due to the dependence of the IGIMF on the metallicity and on the SFR. It is
shown that the mass-metallicity relation of galaxies emerges naturally,
although at low masses the theoretical predictions overestimate the
observations by 0.3--0.4 dex. A good agreement with the observation can be
obtained only if gas flows are taken into account. In particular, we are able
to reproduce the mass--metallicity relation observed by Lee et al. (2006) with
modest amounts of infall and with an outflow rate which decreases as a function
of the galactic mass. The outflow rates required to fit the data are
considerably smaller than required in models with invariant IMFs. | astro-ph_GA |
Galaxy stellar mass assembly: the difficulty matching observations and
semi-analytical predictions: Semi-analytical models (SAMs) are currently the best way to understand the
formation of galaxies within the cosmic dark-matter structures. While they
fairly well reproduce the local stellar mass functions, correlation functions
and luminosity functions, they fail to match observations at high redshift (z >
3) in most cases, particularly in the low-mass range. The inconsistency between
models and observations indicates that the history of gas accretion in
galaxies, within their host dark-matter halo, and the transformation of gas
into stars, are not well followed. Hereafter, we briefly present a new version
of the GalICS semi-analytical model. We explore the impacts of classical
mechanisms, such as supernova feedback or photoionization, on the evolution of
the stellar mass assembly. Even with a strong efficiency, these two processes
cannot explain the observed stellar mass function and star formation rate
distribution and some other relations. We thus introduce an ad-hoc modification
of the standard paradigm, based on the presence of a \textit{no-star-forming}
gas component, and a concentration of the star-forming gas in galaxy discs. The
main idea behind the existence of the no-star-forming gas reservoir is that
only a fraction of the total gas mass in a galaxy is available to form stars.
The reservoir generates a delay between the accretion of the gas and the star
formation process. This new model is in much better agreement with the
observations of the stellar mass function in the low-mass range than the
previous models, and agrees quite well with a large set of observations,
including the redshift evolution of the specific star formation rate. However,
it predicts a large fraction of no-star-forming baryonic gas, potentially
larger than observed, even if its nature has still to be examined in the
context of the missing baryon problem. | astro-ph_GA |
A First Look at Galaxy Flyby Interactions. II. Do Flybys matter?: In the second paper of this series, we present results from cosmological
simulations on the demographics of flyby interactions to gauge their potential
impact on galaxy evolution. In a previous paper, we demonstrated that flybys --
an interaction where two independent halos inter-penetrate but detach at a
later time and do not merge -- occur much more frequently than previously
believed. In particular, we found that the frequency of flybys increases at low
redshift and is comparable to or even greater than the frequency of mergers for
halos $\gtrsim 10^{11} M_\odot/h$. In this paper, we classify flybys according
to their orbits and the level of perturbation exacted on both the halos
involved. We find that the majority of flybys penetrate deeper than $\sim
R_{half}$ of the primary and have an initial relative speed $\sim 1.6\times
V_{vir}$ of the primary. The typical flyby mass-ratio is $\sim 0.1$ at high $z$
for all halos, while at low $z$, massive primary halos undergo flybys with
small secondary halos. We estimate the perturbation from the flyby on both the
primary and the secondary and find that a typical flyby is mostly
non-perturbative for the primary halo. However, since a massive primary
experiences so many flybys at any given time, they are nearly continually a
victim of a perturbative event. In particular, we find flybys that cause $\sim
1\%$ change in the binding energy of a primary halo occurs $\gtrsim 1 $
Gyr$^{-1}$ for halos $> 10^{10} M_\odot/h$ for $z \lesssim 4$. Secondary halos,
on the other hand, are highly perturbed by the typical encounter, experiencing
a change in binding energy of nearly order unity. Our results imply that flybys
can drive a significant part of galaxy transformation at moderate to lower
redshifts ($z \lesssim 4$). We touch on implications for observational surveys,
mass-to-light ratios, and galaxy assembly bias. | astro-ph_GA |
Relativistic dynamics of stars near a supermassive black hole: General relativistic precession limits the ability of gravitational
encounters to increase the eccentricity $e$ of orbits near a supermassive black
hole (SBH). This "Schwarzschild barrier" (SB) has been shown to play an
important role in the orbital evolution of stars like the galactic center
S-stars. However, the evolution of orbits below the SB, $e>e_\mathrm{SB}$, is
not well understood; the main current limitation is the computational
complexity of detailed simulations. Here we present an $N$-body algorithm that
allows us to efficiently integrate orbits of test stars around a SBH including
general relativistic corrections to the equations of motion and interactions
with a large ($\gtrsim 10^3$) number of field stars. We apply our algorithm to
the S-stars and extract diffusion coefficients describing the evolution in
angular momentum $L$. We identify three angular momentum regimes, in which the
diffusion coefficients depend in functionally different ways on $L$. Regimes of
lowest and highest $L$ are well-described in terms of non-resonant relaxation
(NRR) and resonant relaxation (RR), respectively. In addition, we find a new
regime of "anomalous relaxation" (AR). We present analytic expressions, in
terms of physical parameters, that describe the diffusion coefficients in all
three regimes, and propose a new, empirical criterion for the location of the
SB in terms of the $L$-dependence of the diffusion coefficients. Subsequently
we apply our results to obtain the steady-state distribution of angular
momentum for orbits near a SBH. | astro-ph_GA |
Statistical association between the candidate repeating FRB 20200320A
and a galaxy group: We present results from angular cross-correlations between select samples of
CHIME/FRB repeaters and galaxies in three photometric galaxy surveys, which
have shown correlations with the first CHIME/FRB catalog containing repeating
and nonrepeating sources: WISE$\times$SCOS, DESI-BGS, and DESI-LRG. We find a
statistically significant correlation ($p$-value $<0.001$, after accounting for
look-elsewhere factors) between a sample of repeaters with extragalactic
dispersion measure DM $>395$ pc cm$^{-3}$ and WISE$\times$SCOS galaxies with
redshift $z>0.275$. We demonstrate that the correlation arises surprisingly
because of a statistical association between FRB 20200320A (extragalactic DM
$\approx550$ pc cm$^{-3}$) and a galaxy group in the same dark matter halo at
redshift $z\approx0.32$. We estimate that the host halo, along with an
intervening halo at redshift $z\approx0.12$, accounts for at least $\sim$$30\%$
of the extragalactic DM. Our results strongly motivate incorporating galaxy
group and cluster catalogs into direct host association pipelines for FRBs with
$\lesssim$$1'$ localization precision, effectively utilizing the two-point
information to constrain FRB properties such as their redshift and DM
distributions. In addition, we find marginal evidence for a negative
correlation at 99.4% CL between a sample of repeating FRBs with baseband data
(median extragalactic DM $=354$ pc cm$^{-3}$) and DESI-LRG galaxies with
redshift $0.3\le z<0.45$, suggesting that the repeaters might be more prone
than apparent nonrepeaters to propagation effects in FRB-galaxy correlations
due to intervening free electrons over angular scales
$\sim$$0\mbox{$.\!\!^\circ$}5$. | astro-ph_GA |
Spatial Decorrelation of Young Stars and Dense Gas as a Probe of the
Star Formation-Feedback Cycle in Galaxies: The spatial decorrelation of dense molecular gas and young stars observed on
$\lesssim 1$ kiloparsec scales in nearby galaxies indicates rapid dispersal of
star-forming regions by stellar feedback. We explore the sensitivity of this
decorrelation to different processes controlling the structure of the
interstellar medium, the abundance of molecular gas, star formation, and
feedback in a suite of simulations of an isolated dwarf galaxy with structural
properties similar to NGC300 that self-consistently model radiative transfer
and molecular chemistry. Our fiducial simulation reproduces the magnitude of
decorrelation and its scale dependence measured in NGC300, and we show that
this agreement is due to different aspects of feedback, including H$_2$
dissociation, gas heating by the locally variable UV field, early mechanical
feedback, and supernovae. In particular, early radiative and mechanical
feedback affects the correlation on $\lesssim 100$ pc scales, while supernovae
play a significant role on $\gtrsim 100$ pc scales. The correlation is also
sensitive to the choice of the local star formation efficiency per freefall
time, $\epsilon_{\rm ff}$, which provides a strong observational constraint on
$\epsilon_{\rm ff}$ when the global star formation rate is independent of its
value. Finally, we explicitly show that the degree of correlation between the
peaks of molecular gas and star formation density is directly related to the
distribution of the lifetimes of star-forming regions. | astro-ph_GA |
NOEMA spatially resolved view of the multi-phase outflow in
IRAS17020+4544: a shocked wind in action?: The Narrow Line Seyfert 1 Galaxy IRAS17020+4544 is one of the few AGN where a
galaxy-scale energy-conserving outflow was revealed. This paper reports on
NOEMA observations addressed to constrain the spatial scale of the CO emission
in outflow. The molecular outflowing gas is resolved in five components tracing
approaching and receding gas, all located at a distance of 2-3~kpc on the West
and East side of the active nucleus. This high velocity gas (up to v_out=~1900
km/s) is not coincident with the rotation pattern of the CO gas in the host
galaxy disk. The estimated mass outflow rate shows that with a global mass
output of $\dot{M}_{H_2}$=~139$\pm$20$~M_\odot$~yr$^{-1}$, this powerful
galaxy-scale outflow is consistent with the wind conserving its energy, and
with a momentum rate boost of a factor of ~30 compared to the momentum rate of
the nuclear X-ray wind. Preliminary results from ancillary X-ray (Chandra) and
radio images (e-MERLIN) are reported. While the nature of the radio source is
not conclusive, the Chandra image may tentatively trace extended emission, as
expected by an expanding bubble of hot X-ray gas. The outcome of the NOEMA
analysis and of past and ongoing publications dedicated to the description of
the outflow multi-band phenomenology in IRAS17020+4544 concur to provide
compelling reasons to postulate that an outflow shocking with the galaxy
interstellar medium is driving the multi-phase wind in this peculiar AGN. | astro-ph_GA |
Subaru Hyper Suprime-Cam Survey of Cygnus OB2 Complex -- I:
Introduction, Photometry and Source Catalog: Low mass star formation inside massive clusters is crucial to understand the
effect of cluster environment on processes like circumstellar disk evolution,
planet and brown dwarf formation. The young massive association of Cygnus OB2,
with a strong feedback from massive stars, is an ideal target to study the
effect of extreme environmental conditions on its extensive low-mass
population. We aim to perform deep multi-wavelength studies to understand the
role of stellar feedback on the IMF, brown dwarf fraction and circumstellar
disk properties in the region. We introduce here, the deepest and widest
optical photometry of 1.5$^\circ$ diameter region centred at Cygnus OB2 in
r$_{2}$, i$_{2}$, z and Y-filters using Subaru Hyper Suprime-Cam (HSC). This
work presents the data reduction, source catalog generation, data quality
checks and preliminary results about the pre-main sequence sources. We obtain
713,529 sources in total, with detection down to $\sim$ 28 mag, 27 mag, 25.5
mag and 24.5 mag in r$_{2}$, i$_{2}$, z and Y-band respectively, which is
$\sim$ 3 - 5 mag deeper than the existing Pan-STARRS and GTC/OSIRIS photometry.
We confirm the presence of a distinct pre-main sequence branch by statistical
field subtraction of the central 18$^\prime$ region. We find the median age of
the region as $\sim$ 5 $\pm$ 2 Myrs with an average disk fraction of $\sim$
9$\%$. At this age, combined with A$_V$ $\sim$ 6 - 8 mag, we detect sources
down to a mass range $\sim$ 0.01 - 0.17 M$_\odot$. The deep HSC catalog will
serve as the groundwork for further studies on this prominent active young
cluster. | astro-ph_GA |
Constraints on the non-thermal desorption of methanol in the cold core
LDN 429-C: Cold cores are an early step of star formation, characterized by densities >
10$^4$ cm$^{-3}$, low temperatures (< 15 K), and very low external UV
radiation. We investigate the physico-chemical processes at play to tracing the
origin of molecules that are predominantly formed via reactions on dust grain
surfaces. We observed the cold core LDN 429-C with the NOEMA interferometer and
the IRAM 30m single dish telescope in order to obtain the gas-phase abundances
of key species, including CO and CH$_3$OH. Comparing the observed gas phase of
methanol to its solid phase previously observed with Spitzer allows us to put
quantitative constraints on the efficiency of the non-thermal desorption of
this species. With physical parameters determined from available Herschel data,
we computed abundance maps of 11 detected molecules with a non-local thermal
equilibrium radiative transfer model. These observations allowed us to probe
the molecular abundances as a function of density and visual extinction, with
the variation in temperature being restrained between 12 and 18 K. We then
compared the observed abundances to the predictions of the Nautilus
astrochemical model. We find that all molecules have lower abundances at high
densities and visual extinctions with respect to lower density regions, except
for methanol. Comparing these observations with a grid of chemical models based
on the local physical conditions, we were able to reproduce these observations,
allowing only the parameter time to vary. Comparing the observed gas-phase
abundance of methanol with previous measurements of the methanol ice, we
estimate a non-thermal desorption efficiency between 0.002% and 0.09%,
increasing with density. The apparent increase in the desorption efficiency
cannot be reproduced by our model unless the yield of cosmic-ray sputtering is
altered due to the ice composition varying as a function of density. | astro-ph_GA |
Low-Redshift Lyman Limit Systems as Diagnostics of Cosmological Inflows
and Outflows: We use cosmological hydrodynamic simulations with stellar feedback from the
FIRE project to study the physical nature of Lyman limit systems (LLSs) at z<1.
At these low redshifts, LLSs are closely associated with dense gas structures
surrounding galaxies, such as galactic winds, dwarf satellites, and cool
inflows from the intergalactic medium. Our analysis is based on 14 zoom-in
simulations covering the halo mass range M_h~10^9-10^13 Msun at z=0, which we
convolve with the dark matter halo mass function to produce cosmological
statistics. We find that the majority of cosmologically-selected LLSs are
associated with halos in the mass range 10^10 < M_h < 10^12 Msun. The incidence
and HI column density distribution of simulated absorbers with columns 10^16.2
< N_HI < 2x10^20 cm^-2 are consistent with observations. High-velocity outflows
(with radial velocity exceeding the halo circular velocity by a factor >~2)
tend to have higher metallicities ([X/H] ~ -0.5) while very low metallicity
([X/H] < -2) LLSs are typically associated with gas infalling from the
intergalactic medium. However, most LLSs occupy an intermediate region in
metallicity-radial velocity space, for which there is no clear trend between
metallicity and radial kinematics. Metal-enriched inflows arise in the FIRE
simulations as a result of galactic winds that fall back onto galaxies at low
redshift. The overall simulated LLS metallicity distribution has a mean
(standard deviation) [X/H] = -0.9 (0.4) and does not show significant evidence
for bimodality, in contrast to recent observational studies but consistent with
LLSs arising from halos with a broad range of masses and metallicities. | astro-ph_GA |
Detection of Cosmic Fullerenes in the Almahata Sitta Meteorite: Are They
an Interstellar Heritage?: Buckminsterfullerene, C60 , is the largest molecule observed to date in
interstellar and circumstellar environments. The mechanism of formation of this
molecule is actively debated. Despite targeted searches in primitive
carbonaceous chondrites, no unambiguous detection of C60 in a meteorite has
been reported to date. Here we report the first firm detection of fullerenes,
from C30 to at least C100 , in the Almahata Sitta (AhS) polymict ureilite
meteorite. This detection was achieved using highly sensitive laser desorption
laser ionization mass spectrometry. Fullerenes have been unambiguously detected
in seven clasts of AhS ureilites. Molecular family analysis shows that
fullerenes are from a different reservoir compared to the polycyclic aromatic
hydrocarbons detected in the same samples. The fullerene family correlates best
with carbon clusters, some of which may have been formed by the destruction of
solid carbon phases by the impacting laser. We show that the detected
fullerenes are not formed in this way. We suggest that fullerenes are an
intrinsic component of a specific carbon phase that has yet to be identified.
The nondetection of fullerenes in the Murchison and Allende bulk samples, while
using the same experimental conditions, suggests that this phase is absent or
less abundant in these primitive chondrites. The former case would support the
formation of fullerenes by shock-wave processing of carbonaceous phases in the
ureilite parent body. However, there are no experimental data to support this
scenario. This leaves open the possibility that fullerenes are an interstellar
heritage and a messenger of interstellar processes. | astro-ph_GA |
Luminous Quasars Do Not Live in the Most Overdense Regions of Galaxies
at z~4: We present the cross-correlation between 151 luminous quasars ($M_{
\mathrm{UV}} < -26$) and 179 protocluster candidates at $z \sim 3.8$, extracted
from the Wide imaging survey ($ \sim 121~ $deg$^2$) performed with a part of
the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). We find that only two
out of 151 quasars reside in regions that are more overdense compared to the
average field at $ > 4 \sigma $. The distributions of the distance between
quasars and the nearest protoclusters and the significance of the overdensity
at the position of quasars are statistically identical to those found for
$g$-dropout galaxies, suggesting that quasars tend to reside in almost the same
environment as star-forming galaxies at this redshift. Using stacking analysis,
we find that the average density of $g$-dropout galaxies around quasars is
slightly higher than that around $g$-dropout galaxies on $1.0 - 2.5$ pMpc
scales, while at $ < 0.5$ pMpc that around quasars tends to be lower. We also
find that quasars with higher UV-luminosity or with more massive black holes
tend to avoid the most overdense regions, and that the quasar near zone sizes
are anti-correlated with overdensity. These findings are consistent with a
scenario in which the luminous quasar at $z \sim4 $ resides in structures that
are less massive than those expected for the progenitors of today's rich
clusters of galaxies, and possibly that luminous quasars may be suppressing
star formation in their close vicinity. | astro-ph_GA |
Galaxies M32 and NGC 5102 Confirm a Near-infrared Spectroscopic
Chronometer: We present near infrared (NIR) IRTF/SpeX spectra of the intermediate-age
galaxy M32 and the post-starburst galaxy NGC 5102. We show that features from
thermally-pulsing asymptotic giant branch (TP-AGB) and main sequence turn-off
(MSTO) stars yield similar ages to those derived from optical spectra. The
TP-AGB can dominate the NIR flux of a coeval stellar population between ~0.1
and ~2 Gyr, and the strong features of (especially C-rich) TP-AGB stars are
useful chronometers in integrated light studies. Likewise, the Paschen series
in MSTO stars is stongly dependent on age and is an indicator of a young
stellar component in integrated spectra. We define four NIR spectroscopic
indices to measure the strength of absorption features from both C-rich TP-AGB
stars and hydrogen features in main sequence stars, in a preliminary effort to
construct a robust chronometer that probes the contributions from stars in
different evolutionary phases. By comparing the values of the indices measured
in M32 and NGC 5102 to those in the Maraston (2005) stellar population
synthesis models for various ages and metallicities, we show that model
predictions for the ages of the nuclei of M32 and NGC 5102 agree with previous
results obtained from integrated optical spectroscopy and CMD analysis of the
giant branches. The indices discriminate between an intermediate age population
of ~3-4 Gyr, a younger population of <1 Gyr, and can also detect the signatures
of very young (<100 Myr) populations. | astro-ph_GA |
EMPRESS. VI. Outflows Investigated in Low-Mass Galaxies with
$M_*=10^4-10^7~M_\odot$: Weak Feedback in Low-Mass Galaxies?: We study emission line profiles of 21 nearby low-mass
($M_*=10^4-10^7~M_\odot$) galaxies in deep medium-high resolution spectra taken
with Magellan/MagE. These low-mass galaxies are actively star-forming systems
with high specific star-formation rates of
$\mathrm{sSFR}\sim100-1000~\mathrm{Gyr}^{-1}$ that are well above the
star-formation main sequence and its extrapolation. We identify broad-line
components of H$\alpha$ and [OIII]$\lambda 5007$ emission in 14 out of the 21
galaxies that cannot be explained by the MagE instrumental profile or the
natural broadening of line emission. We conduct double Gaussian profile fitting
to the emission of the 14 galaxies, and find that the broad-line components
have line widths significantly larger than those of the narrow-line components,
indicative of galactic outflows. The board-line components have moderately
large line widths of $\sim 100$ km s$^{-1}$. We estimate the maximum outflow
velocities $v_\mathrm{max}$ and obtain values of $\simeq 60-200$ km s$^{-1}$,
which are found to be comparable to or slightly larger than the escape
velocities. Positive correlations of $v_\mathrm{max}$ with star-formation
rates, stellar masses, and circular velocities, extend down into this low-mass
regime. Broad- to narrow-line flux ratios BNRs are generally found to be
smaller than those of massive galaxies. The small $v_\mathrm{max}$ and BNRs
suggest that the mass loading factors $\eta$ can be as small as 0.1 - 1 or
below, in contrast to the large $\eta$ of energy-driven outflows predicted by
numerical simulations. | astro-ph_GA |
Dynamics of Starbursting Dwarf Galaxies. III. A HI study of 18 nearby
objects: We investigate the dynamics of starbursting dwarf galaxies, using both new
and archival HI observations. We consider 18 nearby galaxies that have been
resolved into single stars by HST observations, providing their star formation
history and total stellar mass. We find that 9 objects have a
regularly-rotating HI disk, 7 have a kinematically disturbed HI disk, and 2
show unsettled HI distributions. Two galaxies (NGC 5253 and UGC 6456) show a
velocity gradient along the minor axis of the HI disk, that we interpret as
strong radial motions. For galaxies with a regularly rotating disk we derive
rotation curves, while for galaxies with a kinematically disturbed disk we
estimate the rotation velocities in their outer parts. We derive baryonic
fractions within about 3 optical scale lengths and find that, on average,
baryons constitute at least 30$\%$ of the total mass. Despite the star
formation having injected $\sim$10$^{56}$ ergs in the ISM in the last $\sim$500
Myr, these starbursting dwarfs have both baryonic and gas fractions similar to
those of typical dwarf irregulars, suggesting that they did not eject a large
amount of gas out of their potential wells. | astro-ph_GA |
The Velocity Statistics of Turbulent Clouds in the Presence of Gravity,
Magnetic fields, Radiation, and Outflow Feedback: The interaction of turbulence, magnetic fields, self-gravity, and stellar
feedback within molecular clouds is crucial for understanding star formation.
We study the effects of self-gravity and outflow feedback on the properties of
the turbulent velocity via the structure function over length scales from
$\sim$ 0.01 pc to 2 pc. We analyze a series of three-dimensional,
magnetohydrodynamical (MHD) simulations of star cluster formation. We find
outflow feedback can change the scaling of velocity fluctuations but still
roughly being in between Kolmogorov and Burgers turbulence. We observe that
self-gravity and protostellar outflows increase the velocity fluctuations over
all length scales. Outflows can amplify the velocity fluctuations by up to a
factor of $\sim$7 on scales $\sim$ 0.01 - 0.2 pc and drive turbulence up to a
scale of $\sim$ 1 pc. The amplified velocity fluctuations provide more support
against gravity and enhance fragmentation on small scales. The self-gravity's
effect is more significant on smaller dense clumps and it increases the
fraction of the compressive velocity component up to a scale of $\sim$ 0.2 pc.
However, outflow feedback drives both solenoidal and compressive modes, but it
induces a higher fraction of solenoidal modes relative to compressive modes.
Thus, with outflows, the dense core ends up with a slightly higher fraction of
solenoidal modes. We find that the compressible fraction is fairly constant
with about 1/3 on scales $\sim$ 0.1 - 0.2 pc. The combined effect of enhanced
velocity dispersion and reduced compressive fraction contributes to a reduction
in the star formation rate. | astro-ph_GA |
General spherical anisotropic Jeans models of stellar kinematics:
including proper motions and radial velocities: Cappellari (2008) presented a flexible and efficient method to model the
stellar kinematics of anisotropic axisymmetric and spherical stellar systems.
The spherical formalism could be used to model the line-of-sight velocity
second moments allowing for essentially arbitrary radial variation in the
anisotropy and general luminous and total density profiles. Here we generalize
the spherical formalism by providing the expressions for all three components
of the projected second moments, including the two proper motion components. A
reference implementation is now included in the public JAM package available at
http://purl.org/cappellari/software | astro-ph_GA |
Formation channels of slowly rotating early-type galaxies: We study the evidence for a diversity of formation processes in early-type
galaxies by presenting the first complete volume-limited sample of slow
rotators with both integral-field kinematics from the ATLAS3D Project and high
spatial resolution photometry from the Hubble Space Telescope. Analysing the
nuclear surface brightness profiles of 12 newly imaged slow rotators, we
classify their light profiles as core-less, and place an upper limit to the
core size of ~10 pc. Considering the full magnitude and volume-limited ATLAS3D
sample, we correlate the presence or lack of cores with stellar kinematics,
including the proxy for the stellar angular momentum and the velocity
dispersion within one half-light radius, stellar mass, stellar age,
$\alpha$-element abundance, and age and metallicity gradients. More than half
of the slow rotators have core-less light profiles, and they are all less
massive than $10^{11}$ Msun. Core-less slow rotators show evidence for
counter-rotating flattened structures, have steeper metallicity gradients, and
a larger dispersion of gradient values than core slow rotators. Our results
suggest that core and core-less slow rotators have different assembly
processes, where the former are the relics of massive dissipation-less merging
in the presence of central supermassive black holes. Formation processes of
core-less slow rotators are consistent with accretion of counter-rotating gas
or gas-rich mergers of special orbital configurations, which lower the final
net angular momentum of stars, but support star formation. We also highlight
core fast rotators as galaxies that share properties of core slow rotators and
core-less slow rotators. Formation processes similar to those for core-less
slow rotators can be invoked to explain the assembly of core fast rotators,
with the distinction that these processes form or preserve cores.[Abridged] | astro-ph_GA |
Polarised radio filaments outside the Galactic plane: We used data from the \wmap satellite at 23, 33 and 41 GHz to study the
diffuse polarised emission over the entire sky. The emission originates mostly
from filamentary structures with well-ordered magnetic fields. Some of these
structures have been known for decades in radio continuum maps. Their origin is
not clear and there are many filaments that are visible for the first time. We
have identified and studied 11 filaments. The polarisation fraction of some of
them can be as high as 40\%, which is a signature of a well ordered magnetic
field. The polarisation spectral indices, averaged over 18 regions in the sky
is $\beta = -3.06 \pm 0.02$, consistent with synchrotron radiation. There are
significant variations in $\beta$ over the sky ($\Delta\beta\approx0.2$).
We explore the link between the large-scale filaments and the local ISM,
using the model of an expanding shell in the solar vicinity. We compared
observed polarisation angles with the predictions from the model and found good
agreement. This strongly suggests that many large scale filaments and loops are
nearby structures. This is important in the context of the Galactic magnetic
field as these structures are normally included in global models, neglecting
the fact that they might be local. We also studied the level of contamination
added by the diffuse filaments to the CMB polarisation power spectra. We
conclude that, even though these filaments present low radio brightness, a
careful removal will be necessary for future all-sky CMB polarisation analysis. | astro-ph_GA |
The KMOS Cluster Survey (KCS) I: The fundamental plane and the formation
ages of cluster galaxies at redshift $1.4<z<1.6$: We present the analysis of the fundamental plane (FP) for a sample of 19
massive red-sequence galaxies ($M_{\star} >4\times10^{10} M_{\odot}$) in 3
known overdensities at $1.39<z<1.61$ from the KMOS Cluster Survey, a guaranteed
time program with spectroscopy from the K-band Multi-Object Spectrograph (KMOS)
at the VLT and imaging from the Hubble Space Telescope. As expected, we find
that the FP zero-point in $B$ band evolves with redshift, from the value 0.443
of Coma to $-0.10\pm0.09$, $-0.19\pm0.05$, $-0.29\pm0.12$ for our clusters at
$z=1.39$, $z=1.46$, and $z=1.61$, respectively. For the most massive galaxies
($\log M_{\star}/M_{\odot}>11$) in our sample, we translate the FP zero-point
evolution into a mass-to-light-ratio $M/L$ evolution finding $\Delta \log
M/L_{B}=(-0.46\pm0.10)z$, $\Delta \log M/L_{B}=(-0.52\pm0.07)z$, to $\Delta
\log M/L_{B}=(-0.55\pm0.10)z$, respectively. We assess the potential
contribution of the galaxies structural and stellar velocity dispersion
evolution to the evolution of the FP zero-point and find it to be $\sim$6-35 %
of the FP zero-point evolution. The rate of $M/L$ evolution is consistent with
galaxies evolving passively. By using single stellar population models, we find
an average age of $2.33^{+0.86}_{-0.51}$ Gyr for the $\log
M_{\star}/M_{\odot}>11$ galaxies in our massive and virialized cluster at
$z=1.39$, $1.59^{+1.40}_{-0.62}$ Gyr in a massive but not virialized cluster at
$z=1.46$, and $1.20^{+1.03}_{-0.47}$ Gyr in a protocluster at $z=1.61$. After
accounting for the difference in the age of the Universe between redshifts, the
ages of the galaxies in the three overdensities are consistent within the
errors, with possibly a weak suggestion that galaxies in the most evolved
structure are older. | astro-ph_GA |
Deuterium fractionation of nitrogen hydrides: detections of NHD and
ND$_2$: Although ammonia is an abundant molecule commonly observed towards the dense
interstellar medium, it has not yet been established whether its main formation
route is from gas-phase ion-molecule reactions or grain-surface hydrogen
additions on adsorbed nitrogen atoms. Deuterium fractionation can be used as a
tool to constrain formation mechanisms. High abundances of deuterated molecules
are routinely observed in the dense interstellar medium, with the ratio between
deuterated molecules and the main isotopologue enhanced by several orders of
magnitude with respect to the elemental D/H ratio. In the case of ammonia, the
detection of its triply deuterated isotopologue hints at high abundances of the
deuterated intermediate nitrogen radicals, ND, NHD and ND$_2$. So far however,
only ND has been detected in the interstellar medium. In this paper, to
constrain the formation of ammonia, we aim at determining the NHD/NH$_2$ and
ND$_2$/NHD abundance ratios, and compare them with the predictions of both pure
gas-phase and grain-surface chemical models. We searched for the fundamental
rotational transitions of NHD and ND$_2$ towards the class 0 protostar
IRAS16293-2422, towards which NH, NH$_2$ and ND had been previously detected.
Both NHD and ND$_2$ are detected in absorption towards the source. The relative
abundance ratios NH$_2$ : NHD : ND$_2$ are close to 8 : 4 : 1. These ratios can
be reproduced by our gas-phase chemical model within a factor of two-three.
Statistical ratios as expected from grain-surface chemistry are also consistent
with our data. Further investigations of the ortho-to-para ratio in ND$_2$ ,
both theoretical and observational, could bring new constraints to better
understand nitrogen hydride chemistry. | astro-ph_GA |
NGC5694: another extra-galactic globular cluster: We discuss the chemical composition of six giant stars of the outer Halo
globular cluster NGC5694, through the analysis of UVES@FLAMES high-resolution
spectra. The cluster has an average iron content [Fe/H]=--1.83+-0.01,
solar-scaled [alpha/Fe] ratios and a very low Ba abundance
([Ba/Fe]=--0.71+-0.06). These anomalous abundance patterns are different from
those observed in other Halo globular clusters but similar to those of the
metal-poor stars in typical dwarf spheroidal galaxies. These findings suggest
an extra-galactic origin for NGC5694, likely from a dwarf spheroidal galaxy. | astro-ph_GA |
Polarisation properties of Milky-Way-like galaxies: (Abridged) We study the polarisation properties, magnetic field strength, and
synchrotron emission scale-height of Milky-Way-like galaxies in comparison with
other spiral galaxies. We use our 3D-emission model of the Milky Way Galaxy for
viewing the Milky Way from outside at various inclinations as spiral galaxies
are observed. When seen edge-on the synchrotron emission from the Milky Way has
an exponential scale-height of about 0.74 kpc, which is much smaller than the
values obtained from previous models. We find that current analysis methods
overestimate the scale-height of synchrotron emission of galaxies by about 10%
at an inclination of 80 degree and about 40% at an inclination of 70 degree
because of contamination from the disk. The observed RMs for face-on galaxies
derived from high-frequency polarisation measurements approximate to the
Faraday depths (FDs) when scaled by a factor of two. For edge-on galaxies, the
observed RMs are indicative of the orientation of the large-scale magnetic
field, but are not well related with the FDs. Assuming energy equipartition
between the magnetic field and particles for the Milky Way results in an
average magnetic-field strength, which is about two times larger than the
intrinsic value for a K factor of 100. The number distribution of the
integrated polarisation percentages of a large sample of unresolved
Milky-Way-like galaxies peaks at about 4.2% at 4.8 GHz and at about 0.8% at
1.4GHz. Integrated polarisation angles rotated by 90 degree align very well
with the position angles of the major axes, implying that unresolved galaxies
do not have intrinsic RMs. | astro-ph_GA |
Intrinsic shapes of Brightest Cluster Galaxies: We discuss the statistical distribution of galaxy shapes and viewing angles
under the assumption of triaxiality by deprojecting observed Surface Brightness
(SB) profiles of 56 Brightest Cluster Galaxies coming from a recently published
large deep-photometry sample. For the first time, we address this issue by
directly measuring axis ratio profiles without limiting ourselves to a
statistical analysis of average ellipticities. We show that these objects are
strongly triaxial, with triaxiality parameters 0.39 $ \leq T \leq $ 0.72, have
on average axis ratios $< p(r) > = $ 0.84 and $< q(r) > =$ 0.68, and are more
spherical in the central regions but flatten out at large radii. Measured
shapes in the outskirts agree well with the shapes found for simulated massive
galaxies and their dark matter halos from both the IllustrisTNG and the
Magneticum simulations, possibly probing the nature of dark matter. In
contrast, both simulations fail to reproduce the observed inner regions of
BCGs, producing too flattened objects. | astro-ph_GA |
Slingshot Mechanism for Clusters: Gas Density Regulates Star Density in
the Orion Nebula Cluster (M42): We characterize the stellar and gas volume density, potential, and
gravitational field profiles in the central $\sim$ 0.5 pc of the Orion Nebula
Cluster (ONC), the nearest embedded star cluster (or rather, proto-cluster)
hosting massive star formation available for detailed observational scrutiny.
We find that the stellar volume density is well characterized by a Plummer
profile $\rho_{stars}(r) = 5755\,{\rm M}_{\odot}\,{\rm
pc}^{-3}\,(1+(r/a)^2)^{-5/2}$, where $a = 0.36$ pc. The gas density follows a
cylindrical power law $\rho_{gas}(R) = 25.9\,{\rm M}_{\odot}\,{\rm
pc}^{-3}\,(R/{\rm pc})^{-1.775}$. The stellar density profile dominates over
the gas density profile inside $r\,\sim\,1$ pc. The gravitational field is
gas-dominated at all radii, but the contribution to the total field by the
stars is nearly equal to that of the gas at $r\,\sim\,a$. This fact alone
demonstrates that the proto-cluster cannot be considered a gas-free system or a
virialized system dominated by its own gravity. The stellar proto-cluster core
is dynamically young, with an age of $\sim$ 2-3 Myr, a 1D velocity dispersion
of $\sigma_{\rm obs} = 2.6$ km s$^{-1}$, and a crossing time of $\sim$ 0.55
Myr. This timescale is almost identical to the gas filament oscillation
timescale estimated recently by Stutz & Gould (2016). This provides strong
evidence that the proto-cluster structure is regulated by the gas filament. The
proto-cluster structure may be set by tidal forces due to the oscillating
filamentary gas potential. Such forces could naturally suppress low density
stellar structures on scales $\gtrsim\,a$. The analysis presented here leads to
a new suggestion that clusters form by an analog of the "slingshot mechanism"
previously proposed for stars. | astro-ph_GA |
Gas contents of galaxy groups from thermal Sunyaev-Zel'dovich effects: A matched filter technique is applied to the Planck all-sky Compton
y-parameter map to measure the thermal Sunyaev-Zel'dovich (tSZ) effect produced
by galaxy groups of different halo masses selected from large redshift surveys
in the low-z Universe. Reliable halo mass estimates are available for all the
groups, which allows us to bin groups of similar halo masses to investigate how
the tSZ effect depends on halo mass over a large mass range. Filters are
simultaneously matched for all groups to minimize projection effects. We find
that the integrated y-parameter and the hot gas content it implies are
consistent with the predictions of the universal pressure profile model only
for massive groups above $10^{14}\,{\rm M}_\odot$, but much lower than the
model prediction for low-mass groups. The halo mass dependence found is in good
agreement with the predictions of a set of simulations that include strong AGN
feedback, but simulations including only supernova feedback significantly over
predict the hot gas contents in galaxy groups. Our results suggest that hot gas
in galaxy groups is either effectively ejected or in phases much below the
virial temperatures of the host halos. | astro-ph_GA |
Statistical properties and correlation length in star-forming molecular
clouds: II. Gravitational potential and virial parameter: In the first article of this series, we have used the ergodic theory to
assess the validity of a statistical approach to characterize various
properties of star-forming molecular clouds (MCs) from a limited number of
observations or simulations. This allows the proper determination of confidence
intervals for various volumetric averages of statistical quantities obtained
form observations or numerical simulations.
In this joint paper, we apply the same formalism to a different kind of
(observational or numerical) study of MCs. Indeed, as observations cannot fully
unravel the complexity of the inner density structure of star forming clouds,
it is important to know whether global observable estimates, such as the total
mass and size of the cloud, can give an accurate estimation of various key
physical quantities that characterize the dynamics of the cloud. Of prime
importance is the correct determination of the total gravitational (binding)
energy and virial parameter of a cloud. We show that, whereas for clouds that
are not in a too advanced stage of star formation, such as Polaris or Orion B,
the knowledge of only their mass and size is sufficient to yield an accurate
determination of the aforementioned quantities from observations (i.e. in real
space). In contrast, we show that this is no longer true for numerical
simulations in a periodic box. We derive a relationship for the ratio of the
virial parameter in these two respective cases. | astro-ph_GA |
Proper Motions of Stellar Streams Discovered in the Dark Energy Survey: We cross-match high-precision astrometric data from Gaia DR2 with accurate
multi-band photometry from the Dark Energy Survey (DES) DR1 to confidently
measure proper motions for nine stellar streams in the DES footprint: Aliqa
Uma, ATLAS, Chenab, Elqui, Indus, Jhelum, Phoenix, Tucana III, and Turranburra.
We determine low-confidence proper motion measurements for four additional
stellar streams: Ravi, Wambelong, Willka Yaku, and Turbio. We find evidence for
a misalignment between stream tracks and the systemic proper motion of streams
that may suggest a systematic gravitational influence from the Large Magellanic
Cloud. These proper motions, when combined with radial velocity measurements,
will allow for detailed orbit modeling which can be used to constrain
properties of the LMC and its affect on nearby streams, as well as global
properties of the Milky Way's gravitational potential. | astro-ph_GA |
The Ties that Bind? Galactic Magnetic Fields and Ram Pressure Stripping: One process affecting gas-rich cluster galaxies is ram pressure stripping,
i.e. the removal of galactic gas through direct interaction with the
intracluster medium. Galactic magnetic fields may have an important impact on
the stripping rate and tail structure. We run the first magnetohydrodynamic
simulations of ram pressure stripping that include a galactic magnetic field,
using 159 pc resolution throughout our entire domain in order to resolve mixing
throughout the tail. We find very little difference in the total amount of gas
removed from the unmagnetized and magnetized galaxies, although a magnetic
field with a radial component will initially accelerate stripped gas more
quickly. In general, we find that magnetic fields in the disk lead to slower
velocities in the stripped gas near the disk and faster velocities farther from
the disk. We also find that magnetic fields in the galactic gas lead to larger
unmixed structures in the tail. Finally, we discuss whether ram pressure
stripped tails can magnetize the ICM. We find that the total magnetic energy
density grows as the tail lengthens, likely through turbulence. There are
microGauss-strength fields in the tail in all of our MHD runs, which survive to
at least 100 kpc from the disk (the edge of our simulated region), indicating
that the area-filling factor of magnetized tails in a cluster could be large. | astro-ph_GA |
Time Variation of Fine-Structure Constant Constrained by [O III]
Emission-Lines at 1.1<z<3.7: [O III]$\lambda\lambda$4960,5008 doublet are often the strongest narrow
emission lines in starburst galaxies and quasi-stellar objects (QSOs), and thus
are a promising probe to possible variation of the fine-structure constant
$\alpha$ over cosmic time. Previous such studies using QSOs optical spectra
were limited to $z<1$. In this work, we constructed a sample of 40 spectra of
Ly$\alpha$ emitting galaxies (LAEs) and a sample of 46 spectra of QSOs at
$1.09<z<3.73$ using the VLT/X-Shooter near-infrared spectra publicly available.
We measured the wavelength ratios of the two components of the spin-orbit
doublet and accordingly calculated $\alpha(z)$ using two methods. Analysis on
all of the 86 spectra yielded $\Delta\alpha/\alpha=(-3\pm6)\times10^{-5}$ with
respect to the laboratory $\alpha$ measurements, consistent with no variation
over the explored time interval. If assuming a uniform variation rate, we
obtained $\alpha^{-1}{\rm d}\alpha/{\rm d}t = (-3\pm6)\times10^{-15}$ yr$^{-1}$
within the last 12 Gyrs. Extensive tests indicate that $\alpha$ variation could
be better constrained using starburst galaxies' spectra than using QSO spectra
in future studies. | astro-ph_GA |
HH 223: a parsec-scale H2 outflow in the star-forming region L723: The dark cloud Lynds 723 (L723) is a low-mass star-forming region where one
of the few known cases of a quadrupolar CO outflow has been reported. Two
recent works have found that the radio continuum source VLA 2, towards the
centre of the CO outflow, is actually a multiple system of young stellar
objects (YSOs). Several line-emission nebulae that lie projected on the
east-west CO outflow were detected in narrow-band Halpha and [SII] images. The
spectra of the knots are characteristic of shock-excited gas (Herbig-Haro
spectra), with supersonic blueshifted velocities, which suggests an optical
outflow also powered by the VLA 2 YSO system of L723. We imaged a field of ~5'
X 5' centred on HH 223, which includes the whole region of the quadrupolar CO
outflow with nir narrow-band filters . The H2 line-emission structures appear
distributed over a region of 5.5' (0.5 pc for a distance of 300 pc) at both
sides of the VLA 2 YSO system, with an S-shape morphology, and are projected
onto the east-west CO outflow. Most of them were resolved in smaller knotty
substructures. The [FeII] emission only appears associated with HH 223. An
additional nebular emission from the continuum in Hc and Kc appears associated
with HH 223-K1, the structure closest to the VLA 2 YSO system, and could be
tracing the cavity walls. We propose that the H2 structures form part of a
large-scale near-infrared outflow, which is also associated with the VLA 2 YSO
system. The current data do not allow us to discern which of the YSOs of VLA 2
is powering this large scale optical/near-infrared outflow. | astro-ph_GA |
No Redshift Evolution in the Broad Line Region Metallicity up to z=7.54:
Deep NIR Spectroscopy of ULAS J1342+0928: We present deep (9 hours) Gemini-N/GNIRS near-infrared spectroscopic
observations of ULAS J1342+0928, a luminous quasar at z=7.54. Various broad
emission lines were detected, as well as the underlying continuum and iron
forests over the rest-frame wavelength 970-2930A. There is a clear trend that
higher-ionization emission lines show larger blueshifts with CIV1549 exhibiting
5510^{+240}_{-110} km s-1 blueshift with respect to the systematic redshift
from the far-infrared [CII] 158um emission line. Those high ionization lines
have wide profiles with FWHM more than 10000 km s-1. A modest blueshift of
340^{+110}_{-80} km s-1 is also seen in MgII, the lowest ionization line
identified in the spectrum. The updated MgII-based black hole mass of
M_BH=9.1_{-1.3}^{+1.4} x 10^8 M_sun and the Eddington ratio of
L_bol/L_Edd=1.1_{-0.2}^{+0.2} confirm that ULAS J1342+0928 is powered by a
massive and actively accreting black hole. There is no significant difference
in the emission line ratios such as SiIV/CIV and AlIII/CIV when compared to
lower-redshift quasars in a similar luminosity range, which suggests early
metal pollution of the broad-line-region clouds. This trend also holds for the
FeII/MgII line ratio, known as a cosmic clock that traces the iron enrichment
in the early universe. Different iron templates and continuum fitting ranges
were used to explore how the FeII/MgII measurement changes as a function of
spectral modeling. Quasars at even higher redshift or at fainter luminosity
range (L_bol<10^46 erg s-1) are needed to probe the sites of early metal
enrichment and a corresponding change in the FeII/MgII ratio. | astro-ph_GA |
Probing WHIM around Galaxy Clusters with Fast Radio Bursts and the
Sunyaev-Zel'dovich effect: We propose a new method to probe the Warm Hot Intergalactic Medium (WHIM)
beyond the virial radius (R_200) of a cluster of galaxies, where X-ray
observations are not easily achievable. In this method, we use dispersion
measures (DMs) of Fast Radio Bursts (FRBs) that appear behind the cluster and
the Sunyaev-Zel'dovich (SZ) effect towards the cluster. The DMs reflect the
density of the intracluster medium (ICM) including the WHIM. If we observe a
sufficient number of FRBs in the direction of the cluster, we can derive the
density profile from the DMs. Similarly, we can derive the pressure profile
from the SZ effect. By combining the density and the pressure profiles, the
temperature profile can be obtained. Based on mock observations of nearby
clusters, we find that the density of the WHIM can be determined even at > 2
R_200 from the cluster center when FRB observations with the Square Kilometre
Array (SKA) become available. The temperature can be derived out to r~ 1.5
R_200, and the radius is limited by the current sensitivity of SZ observations. | astro-ph_GA |
New Determination of Fundamental Properties of Palomar 5 Using Deep DESI
Imaging Data: The legacy imaging surveys for the Dark Energy Spectroscopic Instrument
project provides multiplecolor photometric data, which are about 2 mag deeper
than the SDSS. In this study, we redetermine the fundamental properties for an
old halo globular cluster of Palomar 5 based on these new imaging data,
including structure parameters, stellar population parameters, and luminosity
and mass functions. These characteristics, together with its tidal tails, are
key for dynamical studies of the cluster and constraining the mass model of the
Milky Way. By fitting the King model to the radial surface density profile of
Palomar 5, we derive the core radius of $r_c$ = 2.96' $\pm$ 0.11', tidal radius
of $r_t$ = 17.99' $\pm$ 1.49', and concentration parameter of $c$ = 0.78 $\pm$
0.04. We apply a Bayesian analysis method to derive the stellar population
properties and get an age of 11.508 $\pm$ 0.027 Gyr, metallicity of [Fe/H] =
-1.798 $\pm$ 0.014, reddening of $E(B-V)$ = 0.0552 $\pm$ 0.0005, and distance
modulus of $(m-M)_0$ = 16.835 $\pm$ 0.006. The main-sequence luminosity and
mass functions for both the cluster center, and tidal tails are investigated.
The luminosity and mass functions at different distances from the cluster
center suggest that there is obvious spatial mass segregation. Many faint
low-mass stars have been evaporated at the cluster center and the tidal tails
are enhanced by low-mass stars. Both the concentration and relaxation times
suggest that Palomar 5 is a totally relaxed system. | astro-ph_GA |
Magnetic field structure in the Flattened Envelope and Jet in the young
protostellar system HH 211: HH 211 is a young Class 0 protostellar system, with a flattened envelope, a
possible rotating disk, and a collimated jet. We have mapped it with the
Submillimeter Array in 341.6 GHz continuum and SiO J=8-7 at ~ 0.6 resolution.
The continuum traces the thermal dust emission in the flattened envelope and
the possible disk. Linear polarization is detected in the continuum in the
flattened envelope. The field lines implied from the polarization have
different orientations, but they are not incompatible with current
gravitational collapse models, which predict different orientation depending on
the region/distance. Also, we might have detected for the first time polarized
SiO line emission in the jet due to the Goldreich-Kylafis effect. Observations
at higher sensitivity are needed to determine the field morphology in the jet. | astro-ph_GA |
The Distance and Peculiar Velocity of the Norma cluster (ACO 3627) using
the Near-Infrared $J$ and $K_s$-band Fundamental Plane Relations: We report distance measurements for the Norma cluster based on the
near-infrared $J$- and $K_s$-band Fundamental Plane (FP) relations. Our
simultaneous $J$ and $K_s$-band photometry analyses were performed using 31
early-type galaxies in the nearby Norma cluster obtained using the 1.4 m
InfraRed Survey Facility (IRSF) at the South African Astronomical Observatory.
Our final $K_s$-band FP sample consists of 41 early-type galaxies from the
Norma cluster observed using the IRSF and the New Technology Telescope (NTT) at
the European Southern Observatory. This is the largest cluster sample used for
peculiar velocity studies in the Great Attractor region to date. From the
$K_s$-band FP, we find a distance to the Norma cluster of $4915 \pm 121$ km
s$^{-1}$. The implied peculiar velocity for Norma is $44 \pm 151$ km s$^{-1}$
which further supports a small peculiar velocity for the Norma cluster. | astro-ph_GA |
The evolution of the galaxy content of dark matter haloes: We use the halo occupation distribution (HOD) framework to characterise the
predictions from two independent galaxy formation models for the galactic
content of dark matter haloes and its evolution with redshift. Our galaxy
samples correspond to a range of fixed number densities defined by stellar mass
and span $0 \le z \le 3$. We find remarkable similarities between the model
predictions. Differences arise at low galaxy number densities which are
sensitive to the treatment of heating of the hot halo by active galactic
nuclei. The evolution of the form of the HOD can be described in a relatively
simple way, and we model each HOD parameter using its value at $z=0$ and an
additional evolutionary parameter. In particular, we find that the ratio
between the characteristic halo masses for hosting central and satellite
galaxies can serve as a sensitive diagnostic for galaxy evolution models. Our
results can be used to test and develop empirical studies of galaxy evolution
and can facilitate the construction of mock galaxy catalogues for future
surveys. | astro-ph_GA |
A Multi-Scale Study of Star Formation in Messier 33: For the Local Group Scd galaxy M 33 this paper presents a multi-scale study
of the relationship between the monochromatic star formation rate (SFR)
estimator based on 12 $\mu$m emission and the total SFR estimator based on a
combination of far-ultraviolet and 24 $\mu$m emission. We show the 12 $\mu$m
emission to be a linear estimator of total SFR on spatial scales from 782 pc
down to 49 pc, over almost four magnitudes in SFR. These results therefore
extend to sub-kpc length scales the analogous results from other studies for
global length scales. We use high-resolution HI and $^{12}\mathrm{CO}(J=2-1)$
image sets from the literature to compare the star formation to the neutral
gas. For the full range of length scales we find well-defined power-law
relationships between 12 $\mu$m-derived SFR surface densities and neutral gas
surface densities. For the H$_\mathrm{2}$ gas component almost all correlations
are consistent with being linear. No evidence is found for a breakdown in the
star formation law at small length scales in M 33 reported by other authors. We
show that the average star formation efficiency in M 33 is roughly $10^{-9}$
yr$^{-1}$ and that it remains constant down to giant molecular cloud length
scales. Toomre and shear-based models of the star formation threshold are shown
to inaccurately account for the star formation activity in the inner disc of M
33. Finally, we clearly show that the HI saturation limit of $\approx 9$
M$_{\odot}$ pc$^{-2}$ reported in the literature for other galaxies is not an
intrinsic property of M 33 - it is systematically introduced as an artefact of
spatially smoothing the data. | astro-ph_GA |
Gravitational Encounters and the Evolution of Galactic Nuclei. IV.
Captures Mediated by Gravitational-Wave Energy Loss: Direct numerical integrations of the two-dimensional Fokker-Planck equation
are carried out for compact objects orbiting a supermassive black hole (SBH) at
the center of a galaxy. As in Papers I-III, the diffusion coefficients
incorporate the effects of the lowest-order post-Newtonian corrections to the
equations of motion. In addition, terms describing the loss of orbital energy
and angular momentum due to the 5/2-order post-Newtonian terms are included. In
the steady state, captures are found to occur in two regimes that are clearly
differentiated in terms of energy, or semimajor axis; these two regimes are
naturally characterized as "plunges" (low binding energy) and "EMRIs," or
extreme-mass-ratio inspirals (high binding energy). The capture rate, and the
distribution of orbital elements of the captured objects, are presented for two
steady-state models based on the Milky Way: one with a relatively high density
of remnants and one with a lower density. In both models, but particularly in
the second, the steady-state energy distribution and the distribution of
orbital elements of the captured objects are substantially different than if
the Bahcall-Wolf energy distribution were assumed. The ability of classical
relaxation to soften the blocking effects of the Schwarzschild barrier is
quantified.These results, together with those of Papers I-III, suggest that a
Fokker-Planck description can adequately represent the dynamics of collisional
loss cones in the relativistic regime. | astro-ph_GA |
The SAMI Galaxy Survey: the third and final data release: We have entered a new era where integral-field spectroscopic surveys of
galaxies are sufficiently large to adequately sample large-scale structure over
a cosmologically significant volume. This was the primary design goal of the
SAMI Galaxy Survey. Here, in Data Release 3 (DR3), we release data for the full
sample of 3068 unique galaxies observed. This includes the SAMI cluster sample
of 888 unique galaxies for the first time. For each galaxy, there are two
primary spectral cubes covering the blue (370-570nm) and red (630-740nm)
optical wavelength ranges at spectral resolving power of R=1808 and 4304
respectively. For each primary cube, we also provide three spatially binned
spectral cubes and a set of standardized aperture spectra. For each galaxy, we
include complete 2D maps from parameterized fitting to the emission-line and
absorption-line spectral data. These maps provide information on the gas
ionization and kinematics, stellar kinematics and populations, and more. All
data are available online through Australian Astronomical Optics (AAO) Data
Central. | astro-ph_GA |
Stellar population synthesis based modelling of the Milky Way using
asteroseismology of dwarfs and subgiants from Kepler: Early attempts to apply asteroseismology to study the Galaxy have already
shown unexpected discrepancies for the mass distribution of stars between the
Galactic models and the data; a result that is still unexplained. Here, we
revisit the analysis of the asteroseismic sample of dwarf and subgiant stars
observed by Kepler and investigate in detail the possible causes for the
reported discrepancy. We investigate two models of the Milky Way based on
stellar population synthesis, Galaxia and TRILEGAL. In agreement with previous
results, we find that TRILEGAL predicts more massive stars compared to Galaxia,
and that TRILEGAL predicts too many blue stars compared to 2MASS observations.
Both models fail to match the distribution of the stellar sample in $(\log
g,T_{\rm eff})$ space, pointing to inaccuracies in the models and/or the
assumed selection function. When corrected for this mismatch in $(\log g,T_{\rm
eff})$ space, the mass distribution calculated by Galaxia is broader and the
mean is shifted toward lower masses compared to that of the observed stars.
This behaviour is similar to what has been reported for the Kepler red giant
sample. The shift between the mass distributions is equivalent to a change of
2\% in $\nu_{\rm max}$, which is within the current uncertainty in the
$\nu_{\rm max}$ scaling relation. Applying corrections to the $\Delta \nu$
scaling relation predicted by the stellar models makes the observed mass
distribution significantly narrower, but there is no change to the mean. | astro-ph_GA |
Note on fundamental physics tests from black hole imaging: Comment on
"Hunting for extra dimensions in the shadow of Sagittarius A$^*$": Several works over the past years have discussed the possibility of testing
fundamental physics using Very Long Baseline Interferometry horizon-scale black
hole (BH) images, such as the Event Horizon Telescope (EHT) images of M87$^*$
and Sagittarius A$^*$ (Sgr A$^*$), using the size $r_{\rm sh}$ and deviation
from circularity $\Delta \mathcal{C}$ of the BH shadow. For the case of the EHT
image of Sgr A$^*$, limits on $\Delta \mathcal{C}$ are not available due to the
sparse interferometric coverage of the 2017 observations, alongside the short
variability timescale of Sgr A$^*$ compared to M87$^*$. Concerning this point,
we comment on the results of a recent preprint which purports to have derived
new limits on extra dimensions using the deviation from circularity of Sgr
A$^*$'s shadow. The latter is quoted to be $\lesssim 10\%$ as with M87$^*$,
based on the "similarity" of the two shadows: however, this is an incorrect
assumption, invalidating the subsequent results. In the immediate future, the
simplest tests of fundamental physics from Sgr A$^*$'s image will therefore
mostly have to rely on $r_{\rm sh}$, whereas additional observables such as the
photon ring and azimuthal angle lapse should soon be available and allow for
novel tests. | astro-ph_GA |
Ultra-compact Embedded Clusters in the Galactic Plane: We have identified a previously unrecognized population of very compact,
embedded low-mass Galactic stellar clusters. These tight (r$ \approx $0.14 pc)
groupings appear as bright singular objects at the few arcsec resolution of the
Spitzer Space Telescope at 8 and 24 $\mu$m but become resolved in the
sub-arcsecond UKIDSS images. They average six stars per cluster surrounded by
diffuse infrared emission and coincide with 100 -- 300 M$_{\sun}$ clumps of
molecular material within a larger molecular cloud. The magnitudes of the
brightest stars are consistent with mid- to early-B stars anchoring $\sim$80
M$_{\sun}$ star clusters. Their evolutionary descendants are likely to be
Herbig Ae/Be pre-main sequence clusters. These ultra-compact embedded clusters
(UCECs) may fill part of the low-mass void in the embedded cluster mass
function. We provide an initial catalog of 18 UCECs drawn from infrared
Galactic Plane surveys. | astro-ph_GA |
Collisional excitation of methyl (iso)cyanide by He atoms: rate
coefficients and isomerism effects: Among all closed-shell species observed in molecular clouds, molecules with
C$_{3v}$ symmetry play a crucial role, as their rotational spectroscopy allows
them to behave as a gas thermometer. In the interstellar medium, methyl cyanide
(CH$_3$CN) is the second most abundant of those (after ammonia, NH$_3$). Its
isomer, methyl isocyanide (CH$_3$NC) is less abundant but has been detected in
many astrophysical sources. In order to assess their absolute and relative
abundances, it is essential to understand their collisional excitation
properties. This paper reports the calculation of rate coefficients for
rotational excitation of CH$_3$CN and CH$_3$NC molecules with He atoms, from
low (5 K) to moderate (100 K) temperatures. We include the first 74 and 66
rotational states of both $para$ and $ortho$ symmetries of CH$_3$CN and
CH$_3$NC, respectively. A propensity for $\Delta j=2$ transitions is observed
in the case of CH$_3$CN-He collisions, whereas in the case of CH$_3$NC-He a
propensity for $\Delta j=1$ is observed for transitions involving low values of
$j$ and at low temperatures, while a propensity for $\Delta j=2$ is observed
for higher values of $j$ and at high temperatures. A comparison of rate
coefficients shows differences up to a factor of 3, depending on temperature
and on the $ortho$/$para$ symmetries for dominant transitions. This confirms
the importance of having specific collisional data for each isomer. We also
examined the effect of these new rates on the CH$_3$CN and CH$_3$NC excitation
in molecular clouds by performing radiative transfer calculations of the
excitation and brightness temperatures for several detected lines. | astro-ph_GA |
Delving deep: a population of extremely dusty dwarfs observed by JWST: We take advantage of the NIRCam photometric observations available as part of
the Cosmic Evolution Early Release Science survey (CEERS) to identify and
analyse very red sources in an effort to discover very dusty star forming
galaxies. We select red galaxies as objects with a S/N>3 at 4.4 $\mu$m and a
S/N<2 in all JWST and HST filters at $\lambda\leq2\mu$m, which corresponds to
[F200W]-[F444W]>1.2 considering CEERS depths. This selection is ideal to
identify very dusty (Av>1 mag) galaxies with stellar masses between $10^6$ to
$10^{10}\, \rm M_{\odot}$ at z<5, more massive dusty galaxies at z=5-18 and
galaxies at z>18 due to the Lyman absorption, independently of their dust
extinction. Our sample of F200W-dropouts contains no strong candidates at
z>6.5, instead it consists almost completely (~81%) of z<2 low-mass galaxies,
with a median stellar mass of $10^{7.3} \rm M_{\odot}$. These galaxies show an
exceptional dust extinction with median value of Av=4.9 mag, completely
unexpected given their low stellar mass. The remaining galaxies, which are at
z<6.5, show similar large dust extinction (Av>1), but they are generally more
massive $>10^{7.5}\rm M_{\odot}$. | astro-ph_GA |
Spin Temperature and Density of Cold and Warm HI in the Galactic Disk -
Hidden HI -: We present a method to determine the spin temperature $T_{\rm S}$ and volume
density $n$ of HI gas simultaneously along the tangent-point circle of galactic
rotation in the Milky Way by using the least-$\chi^2$ method. The best-fit
$T_{\rm S}$ is shown to range either in $T_{\rm S}=100-120$ K or in $1000-3000$
K, indicating that the gas is either in cold HI phase with high density and
large optical depth, or in warm HI with low density and small optical depth.
Averaged values at $3\le R \le 8$ kpc are obtained to be $T_{\rm S}=106.7 \pm
16.0$ K and $n=1.53\pm 0.86$ H cm$^{-3}$ for cold HI, and $1720 \pm 1060$ K and
$0.38 \pm 0.10$ H cm$^{-3}$ for warm HI, where $R=8\ |\sin \ l|$ kpc is the
galacto-centric distance along the tangent-point circle. The cold HI appears in
spiral arms and rings, whereas warm HI in the inter-arm regions. The cold HI is
denser by a factor of $\sim 4$ than warm HI. The present analysis has revealed
the hidden HI mass in cold and optically thick phase in the galactic disk. The
total HI mass inside the solar circle is shown to be greater by a factor of $2
- 2.5$ than the current estimation by optically thin assumption. | astro-ph_GA |
Rotation Curve Anomaly and Galactic Warp in M51: We revisit the anomaly of rotation curve in the nearly face-on galaxy M51
that shows an apparently faster decrease of rotation velocity than the
Keplerian law in the outer disk, further showing apparent counter rotation in
the outermost HI disk. We interpret this anomaly as due to warping of the
galactic disk, and determined the warping structure of M51's disk using the
tilted-ring method, assuming that the intrinsic rotation curve is normal. It is
shown that the disk is nearly flat in the inner disk at a constant inclination
angle, but the disk suddenly bends at radius 7.5 kpc by about 27$\deg$. The
inclination angle, then, decreases monotonically outward reaching a perfect
face-on ring at 18 kpc, beyond which the disk is warped in the opposite sense
to the inner disk, resulting in apparent counter rotation. | astro-ph_GA |
No correlation of the Lyman continuum escape fraction with spectral
hardness: The properties that govern the production and escape of hydrogen ionizing
photons (Lyman continuum, LyC; with energies >13.6 eV) in star-forming galaxies
are still poorly understood, but they are key to identifying and characterizing
the sources that reionized the Universe. Here we empirically explore the
relationship between the hardness of ionizing radiation and the LyC leakage in
a large sample of low-$z$ star-forming galaxies from the recent Hubble Space
Telescope Low-$z$ Lyman Continuum Survey. Using Sloan Digital Sky Survey stacks
and deep XShooter observations, we investigate the hardness of the ionizing
spectra ($Q_{\rm He^+}/Q_{\rm H}$) between 54.4 eV (He$^{+}$) and 13.6 eV (H)
from the optical recombination lines HeII 4686A and H$\beta$ 4861A for galaxies
with LyC escape fractions spanning a wide range, $f_{\rm esc} \rm (LyC) \simeq
0 - 90\%$. We find that the observed intensity of HeII/H$\beta$ is primarily
driven by variations in the metallicity, but is not correlated with LyC
leakage. Both very strong ($<f_{\rm esc} \rm (LyC)> \simeq 0.5$) and nonleakers
($ < f_{\rm esc} \rm (LyC) > \simeq 0$) present similar observed intensities of
HeII/H$\beta$ at comparable metallicity, between $\simeq 0.01$ and $\simeq
0.02$ for $12 + \log({\rm O/H}) > 8.0$ and $<8.0$, respectively. Our results
demonstrate that $Q_{\rm He^+}/Q_{\rm H}$ does not correlate with $f_{\rm esc}
\rm (LyC)$, which implies that strong LyC emitters do not show harder ionizing
spectra than nonleakers at similar metallicity. | astro-ph_GA |
Evolution of spatio-kinematic structures in star-forming regions: are
Friends of Friends worth knowing?: The Friends of Friends algorithm identifies groups of objects with similar
spatial and kinematic properties, and has recently been used extensively to
quantify the distributions of gas and stars in young star-forming regions. We
apply the Friends of Friends algorithm to $N$-body simulations of the dynamical
evolution of subvirial (collapsing) and supervirial (expanding) star-forming
regions. We find that the algorithm picks out a wide range of groups (1 -- 25)
for statistically identical initial conditions, and cannot distinguish between
subvirial and supervirial regions in that we obtain similar mode and median
values for the number of groups it identifies. We find no correlation between
the number of groups identified initially and either the initial or subsequent
spatial and kinematic tracers of the regions' evolution, such as the amount of
spatial substructure, dynamical mass segregation, or velocity dispersion. We
therefore urge caution in using the Friends of Friends algorithm to quantify
the initial conditions of star formation. | astro-ph_GA |
Testing PDR models against ISO fine structure line data for
extragalactic sources: Far-infrared [C ii] 158 micron, [O i] 145 micron and [O i] 63 micron fine
structure emission line fluxes were measured from archival Infrared Space
Observatory Long Wavelength Spectrometer spectra of 46 extragalactic sources,
with 28 sources providing detections in all three lines. For 12 of the sources,
the contribution to the [C ii] 158 micron line flux from H ii regions could be
estimated from their detected [N ii] 122 micron line fluxes. The measured [C
ii]/[O i] and [O i] 63/145 micron line flux ratios were compared with those
from a grid of PDR models previously computed using the UCL PDR code.
Persistent offsets between the observed and modelled line ratios could be
partly attributed to the effects of [O i] 63 micron self-absorption. Using the
SMMOL code, we calculated model [O i] line profiles and found that the strength
of the [O i] 63 micron line was reduced by 20-80%, depending on the PDR
parameters. We conclude that high PDR densities and radiation field strengths,
coupled with the effects of [O i] 63 micron self-absorption, are likely to
provide the best match to the observed line flux ratios. | astro-ph_GA |
Spatially resolved observations of outflows in the radio loud AGN of UGC
8782: We use optical Integral Field Spectroscopy (IFU) to study the gas emission
structure and kinematics in the inner 3.4$\times$4.9 kpc$^2$ region of the
galaxy UGC 8782 (3C 293), host of a radio loud Active Galactic Nucleus (AGN).
The observations were performed with the GMOS-IFU on the Gemini North
telescope, resulting in a spatial resolution of $\sim725$ pc at the distance of
the galaxy. While the stars present ordered rotation following the orientation
of the large scale disc, the gas shows a disturbed kinematics. The
emission-line profiles present two kinematic components: a narrow
($\sigma\lesssim200$ km s$^{-1}$) component associated with the gas in the disc
of the galaxy and a broad ($\sigma\gtrsim200$ km s$^{-1}$) component produced
by gas outflows. Emission-line ratio diagrams indicate that the gas in the disc
is excited by the AGN radiation field, while the emission of the outflow
includes additional contribution of shock excitation due to the interaction of
the radio jet with the environment gas. Deviations from pure rotation, of up to
30 km s$^{-1}$, are observed in the disc component and likely produced by a
previous merger event. The broad component is blueshifted by $\sim150-500$ km
s$^{-1}$ relative to the systemic velocity of the galaxy in all locations. We
construct radial profiles of the mass outflow rate and kinetic power of the
ionized gas outflows, which have the maximum values at $\sim1$ kpc from the
nucleus with peak values of $\dot{M}_{\rm out,\Delta R}=0.5\pm0.1$ M$_\odot$
yr$^{-1}$ and $\dot{K}_{\rm out,\Delta R} =$(6.8$\pm$1.1)$\times$10$^{41}$ erg
s$^{-1}$. The kinetic coupling efficiency of these outflows is in the range of
1$-$3 per cent, indicating that they could be powerful enough to affect the
star formation in the host galaxy as predicted by theoretical simulations. | astro-ph_GA |
Studies of Anomalous Microwave Emission (AME) with the SKA: In this chapter, we will outline the scientific motivation for studying
Anomalous Microwave Emission (AME) with the SKA. AME is thought to be due to
electric dipole radiation from small spinning dust grains, although thermal
fluctuations of magnetic dust grains may also contribute. Studies of this
mysterious component would shed light on the emission mechanism, which then
opens up a new window onto the interstellar medium (ISM). AME is emitted mostly
in the frequency range $\sim 10$--100\,GHz, and thus the SKA has the potential
of measuring the low frequency side of the AME spectrum, particularly in band
5. Science targets include dense molecular clouds in the Milky Way, as well as
extragalactic sources. We also discuss the possibility of detecting rotational
line emission from Poly-cyclic Aromatic Hydrocarbons (PAHs), which could be the
main carriers of AME. Detecting PAH lines of a given spacing would allow for a
definitive identification of specific PAH species. | astro-ph_GA |
A Carbon-rich Mira variable in a globular cluster: A stellar merger: The membership of Matsunaga's variable 1, a carbon-rich, mass-losing, Mira
variable, in the globular cluster Lynga 7 is discussed on the basis of radial
velocities. We conclude that it is a member, the first known C-Mira in a
globular cluster. Since such a variable is expected to have an age of $\sim
1-2$ Gyr and an initial mass of $\sim 1.5$ solar masses, we conclude that this
star must be the product of a stellar merger. | astro-ph_GA |
Extraplanar gas in Edge-on Galaxies traced by SOFIA observations of [C
II]: Bursts of localized star formation in galaxies can levitate material from
their midplanes. Spiral galaxies that are edge-on allow clear distinction of
material that is levitated off the galaxies' midplanes. We used SOFIA to
measure the vertical distribution of [C II] 157.7 micron line emission for two
nearby, edge-on galaxies, NGC 891 and NGC 5907. We find that for the central
region and actively-star-forming regions in the northern portion of NGC 891,
and for NGC 5907, a thin (0.3 kpc) disk is supplemented by a thick disk with an
exponential scale height of about 2 kpc. The [C II] is far more extended than
mid-infrared emission (0.1 kpc, tracing present-day massive star formation) but
not as extended as the H I (100 kpc, tracing low-metallicity
circum/inter-galactic matter). The extraplanar [C II] may arise in walls of
chimneys that connect the disk to the halo. | astro-ph_GA |
The Mass-Concentration Relation and the Stellar-to-Halo Mass Ratio in
the CFHT Stripe 82 Survey: We present a new measurement of the mass-concentration relation and the
stellar-to-halo mass ratio over the halo mass range $5\times 10^{12}$ to
$2\times 10^{14}M_{\odot}$. To achieve this, we use weak lensing measurements
from the CFHT Stripe 82 Survey (CS82), combined with the central galaxies from
the redMaPPer cluster catalogue and the LOWZ/CMASS galaxy sample of the Sloan
Digital Sky Survey-III Baryon Oscillation Spectroscopic Survey Tenth Data
Release. The stacked lensing signals around these samples are modelled as a sum
of contributions from the central galaxy, its dark matter halo, and the
neighboring halos, as well as a term for possible centering errors. We measure
the mass-concentration relation: $c_{200c}(M)=A(\frac{M_{200c}}{M_0})^{B}$ with
$A=5.24\pm1.24, B=-0.13\pm0.10$ for $0.2<z<0.4$ and $A=6.61\pm0.75,
B=-0.15\pm0.05$ for $0.4<z<0.6$. These amplitudes and slopes are completely
consistent with predictions from recent simulations. We also measure the
stellar-to-halo mass ratio for our samples, and find results consistent with
previous measurements from lensing and other techniques. | astro-ph_GA |
Massive Star Formation in the Ultraviolet Observed with the Hubble Space
Telescope: Spectroscopic observations of a massive star formation in the ultraviolet and
their interpretation are reviewed. After a brief historical retrospective, two
well-studied resolved star clusters and the surrounding H II regions are
introduced: NGC 2070 in the Large Magellanic Cloud and NGC 604 in M33. These
regions serve as a training set for studies of more distant clusters, which can
no longer be resolved into individual stars. Observations of recently formed
star clusters and extended regions in star-forming galaxies in the nearby
universe beyond the Local Group are presented. Their interpretation relies on
spectral synthesis models. The successes and failures of such models are
discussed, and future directions are highlighted. I present a case study of the
extraordinary star cluster and giant H II region in the blue compact galaxy II
Zw 40. The review concludes with a preview of two upcoming Hubble Space
Telescope programs: ULLYSES, a survey of massive stars in nearby galaxies, and
CLASSY, a study of massive star clusters in star-forming galaxies. | astro-ph_GA |
Reionization with galaxies and active galactic nuclei: In this work we investigate the properties of the sources that reionized the
intergalactic medium (IGM) in the high-redshift Universe. Using a
semi-analytical model aimed at reproducing galaxies and black holes in the
first 1.5 Gyr of the Universe, we revisit the relative role of star formation
and black hole accretion in producing ionizing photons that can escape into the
IGM. Both star formation and black hole accretion are regulated by supernova
feedback, resulting in black hole accretion being stunted in low-mass halos. We
explore a wide range of combinations for the escape fraction of ionizing
photons (redshift-dependent, constant and scaling with stellar mass) from both
star formation ($\langle f_{\rm esc}^{\rm sf} \rangle$) and AGN ($f_{\rm
esc}^{\rm bh}$) to find: (i) the ionizing budget is dominated by stellar
radiation from low stellar mass ($M_*<10^9 {\rm M_\odot}$ ) galaxies at $z>6$
with the AGN contribution (driven by $M_{bh}>10^6 {\rm M_\odot}$ black holes in
$M_* > 10^9 {\rm M_\odot}$ galaxies) dominating at lower redshifts; (ii) AGN
only contribute $10-25\%$ to the cumulative ionizing emissivity by $z=4$ for
the models that match the observed reionization constraints; (iii) if the
stellar mass dependence of $\langle f_{\rm esc}^{\rm sf} \rangle$ is shallower
than $f_{\rm esc}^{\rm bh}$, at $z<7$ a transition stellar mass exists above
which AGN dominate the escaping ionizing photon production rate; (iv) the
transition stellar mass decreases with decreasing redshift. While AGN dominate
the escaping emissivity above the knee of the stellar mass function at $z \sim
6.8$, they take-over at stellar masses that are a tenth of the knee mass by
$z=4$. | astro-ph_GA |
Exploring the SDSS Photometric Galaxies with Clustering Redshifts: We apply clustering-based redshift inference to all extended sources from the
Sloan Digital Sky Survey photometric catalogue, down to magnitude r = 22. We
map the relationships between colours and redshift, without assumption of the
sources' spectral energy distributions (SED). We identify and locate
star-forming, quiescent galaxies, and AGN, as well as colour changes due to
spectral features, such as the 4000 \AA{} break, redshifting through specific
filters. Our mapping is globally in good agreement with colour-redshift tracks
computed with SED templates, but reveals informative differences, such as the
need for a lower fraction of M-type stars in certain templates. We compare our
clustering-redshift estimates to photometric redshifts and find these two
independent estimators to be in good agreement at each limiting magnitude
considered. Finally, we present the global clustering-redshift distribution of
all Sloan extended sources, showing objects up to z ~ 0.8. While the overall
shape agrees with that inferred from photometric redshifts, the clustering
redshift technique results in a smoother distribution, with no indication of
structure in redshift space suggested by the photometric redshift estimates
(likely artifacts imprinted by their spectroscopic training set). We also infer
a higher fraction of high redshift objects. The mapping between the four
observed colours and redshift can be used to estimate the redshift probability
distribution function of individual galaxies. This work is an initial step
towards producing a general mapping between redshift and all available
observables in the photometric space, including brightness, size,
concentration, and ellipticity. | astro-ph_GA |
OMEGA: OSIRIS Mapping of Emission-Line Galaxies in A901/2: This work presents the first results from an ESO Large Programme carried out
using the OSIRIS instrument on the 10m GTC telescope (La Palma). We have
observed a large sample of galaxies in the region of the Abell 901/902 system
(z ~ 0.165) which has been extensively studied as part of the STAGES project.
We have obtained spectrally and spatially resolved H-alpha and [NII] emission
maps for a very large sample of galaxies covering a broad range of
environments. The new data are combined with extensive multi-wavelength
observations which include HST, COMBO-17, Spitzer, Galex and XMM imaging to
study star formation and AGN activity as a function of environment and galaxy
properties such as luminosity, mass and morphology. The ultimate goal is to
understand, in detail, the effect of the environment on star formation and AGN
activity. | astro-ph_GA |
Testing the evolutionary pathways of galaxies and their supermassive
black holes and the impact of feedback from Active Galactic Nuclei via large
multiwavelength datasets: It is still a matter of intense debate how supermassive black holes (SMBH)
grow, and the role played by feedback from active galactic nuclei (AGN) in the
co-evolution of SMBHs and galaxies. To test the coevolution proposed by
theoretical models, we compile a large AGN sample of 5639 X-ray detected AGN,
over a wide redshift range, spanning nearly three orders of magnitude in X-ray
luminosity. The AGN have been detected in the {\it{COSMOS-Legacy}}, the Bo$\rm
\ddot{o}$tes, the XMM-{\it{XXL}} and the eFEDS fields. Using the specific star
formation rate estimates, we split the AGN host galaxies into star forming
(SF), starburst (SB) and quiescent (Q). Our results show that the AGN accretion
is increased in SB systems compared to SF and Q. Our analysis reveals a mild
increase of L$_X$ with M$_*$. The L$_X$/SFR ratio has a weak dependence on
M$_*$, and at fixed M$_*$ it is highest in Q systems. The latter trend is
mostly driven by the significant drop in SFR in the Q state. The measured
strong variations in SFR from the SB/SF to Q mirror those predicted in merger
models with AGN feedback. However, the observed mild variations in L$_X$ are at
variance with the same models. We also study the evolution of SFR for a galaxy
control sample and found that it is very similar to that of X-ray AGN. This
suggests that either AGN play a minor role in the star formation quenching, or
the relative timescales of the two processes are different. | astro-ph_GA |
Practical application of KAM theory to galactic dynamics: II.
Application to weakly chaotic orbits in barred galaxies: Owing to the pioneering work of Contopoulos, a strongly barred galaxy is
known to have irregular orbits in the vicinity of the bar. By definition,
irregular orbits can not be represented by action-angle tori everywhere in
phase space. This thwarts perturbation theory and complicates our understanding
of their role in galaxy structure and evolution. This paper provides a
qualitative introduction to a new method based on KAM theory for investigating
the morphology of regular and irregular orbits based on direct computation of
tori described in Paper 1 and applies it to a galaxy disc bar. Using this
method, we find that much of the phase space inside of the bar radius becomes
chaotic for strong bars, excepting a small region in phase space between the
ILR and corotation resonances for orbits of moderate ellipticity. This helps
explain the preponderance of moderately eccentric bar-supporting orbits as the
bar strength increases. This also suggests that bar strength may be limited by
chaos! The chaos results from stochastic layers that form around primary
resonances owing to separatrix splitting. Most investigations of orbit
regularity are performed using numerical computation of Lyapunov exponents or
related indices. We show that Lyapunov exponents poorly diagnose the degree of
stochasticity in this problem; the island structure in the stochastic sheaths
allow orbit to change morphology while presenting anomalously small Lyapunov
exponent values (i.e. weak chaos). For example, a weakly chaotic orbit may
appear to change its morphology spontaneously, while appearing regular except
during the change itself. The numerical KAM approach sensitively detects these
dynamics and provides a model Hamiltonian for further investigation. It may
underpredict the number of broken tori for strong perturbations. | astro-ph_GA |
Can the observed E/B ratio for dust galactic foreground be explained by
sub-Alfvenic turbulence?: Recent Planck observations of dust polarization in the Galaxy have revealed
that the power in $E$ mode is twice that in $B$ mode. Caldwell et. al. have
formulated a theoretical model in the context of magnetohydrodynamic (MHD)
turbulence and found it problematic to account for this result. In particular,
they concluded that there is a very narrow range of theoretical parameters that
could account for the observation. This poses a problem of whether the accepted
description of MHD turbulence can apply to the interstellar medium. We revisit
the problem and demonstrate that MHD turbulence corresponding to the high
galactic latitudes range of Alfv\'en Mach numbers, i.e. $M_A\lesssim 0.5$, can
successfully explain the available results for the $E$ to $B$ mode ratio. | astro-ph_GA |
LeMMINGs. III. The e-MERLIN Legacy Survey of the Palomar sample.
Exploring the origin of nuclear radio emission in active and inactive
galaxies through the [O III] -- radio connection: What determines the nuclear radio emission in local galaxies? We combine
optical [O III] line emission, robust black hole (BH) mass estimates, and
high-resolution e-MERLIN 1.5-GHz data, from the LeMMINGs survey, of a
statistically-complete sample of 280 nearby, optically active (LINER and
Seyfert) and inactive HII and Absorption line galaxies [ALG]) galaxies. Using
[O III] luminosity ($L_{\rm [O~III]}$) as a proxy for the accretion power,
local galaxies follow distinct sequences in the optical-radio planes of BH
activity, which suggest different origins of the nuclear radio emission for the
optical classes. The 1.5-GHz radio luminosity of their parsec-scale cores
($L_{\rm core}$) is found to scale with BH mass ($M_{\rm BH}$) and [O~III]
luminosity. Below $M_{\rm BH} \sim$10$^{6.5}$ M$_{\odot}$, stellar processes
from non-jetted HII galaxies dominate with $L_{\rm core} \propto M_{\rm
BH}^{0.61\pm0.33}$ and $L_{\rm core} \propto L_{\rm [O~III]}^{0.79\pm0.30}$.
Above $M_{\rm BH} \sim$10$^{6.5}$ M$_{\odot}$, accretion-driven processes
dominate with $L_{\rm core} \propto M_{\rm BH}^{1.5-1.65}$ and $L_{\rm core}
\propto L_{\rm [O~III]}^{0.99-1.31}$ for active galaxies: radio-quiet/loud
LINERs, Seyferts and jetted HII galaxies always display (although low)
signatures of radio-emitting BH activity, with $L_{\rm 1.5\,
GHz}\gtrsim$10$^{19.8}$ W Hz$^{-1}$ and $M_{\rm BH}\gtrsim10^{7}$ M$_{\odot}$,
on a broad range of Eddington-scaled accretion rates ($\dot{m}$). Radio-quiet
and radio-loud LINERs are powered by low-$\dot{m}$ discs launching
sub-relativistic and relativistic jets, respectively. Low-power slow jets and
disc/corona winds from moderately high to high-$\dot{m}$ discs account for the
compact and edge-brightened jets of Seyferts, respectively. Jetted HII galaxies
may host weakly active BHs. Fuel-starved BHs and recurrent activity account for
ALG properties. [abridged] | astro-ph_GA |
3D Asymmetrical motions of the Galactic outer disk with LAMOST K giant
stars: We present a three dimensional velocity analysis of Milky Way disk kinematics
using LAMOST K giant stars and the GPS1 proper motion catalogue. We find that
Galactic disk stars near the anticenter direction (in the range of
Galactocentric distance between $R=8$ and $13$ kpc and vertical position
between $Z=-2$ and $2$ kpc) exhibit asymmetrical motions in the Galactocentric
radial, azimuthal, and vertical components. Radial motions are not zero, thus
departing from circularity in the orbits; they increase outwards within
$R\lesssim 12$ kpc, show some oscillation in the northern ($0 < Z < 2$ kpc)
stars, and have north-south asymmetry in the region corresponding to a
well-known nearby northern structure in the velocity field. There is a clear
vertical gradient in azimuthal velocity, and also an asymmetry that shifts from
a larger azimuthal velocity above the plane near the solar radius to faster
rotation below the plane at radii of 11-12 kpc. Stars both above and below the
plane at $R\gtrsim 9$ kpc exhibit net upward vertical motions. We discuss some
possible mechanisms that might create the asymmetrical motions, such as
external perturbations due to dwarf galaxy minor mergers or dark matter
sub-halos, warp dynamics, internal processes due to spiral arms or the Galactic
bar, and (most likely) a combination of some or all of these components. | astro-ph_GA |
XGAPS: a sub-arcsecond cross-match of Galactic Plane Surveys: We present a sub-arcsecond cross-match of Gaia Data Release 3 (DR3) against
the INT Galactic Plane Surveys (IGAPS) and the United Kingdom Infrared Deep Sky
Survey (UKIDSS). The resulting cross-match of Galactic Plane Surveys (XGAPS)
provides additional precise photometry ($U_{RGO}$, $g$, $r$, $i$, H$\alpha$,
$J$, $H$ and $K$) to the Gaia photometry. In building the catalogue, proper
motions given in Gaia DR3 are wound back to match the epochs of the IGAPS
constituent surveys (INT Photometric \ha Survey of the Northern Galactic Plane,
IPHAS, and the UV-Excess Survey of the northern Galactic plane, UVEX) and
UKIDSS, ensuring high proper motion objects are appropriately cross-matched.
The catalogue contains 33,987,180 sources. The requirement of $>3\sigma$
parallax detection for every included source means that distances out to 1--1.5
kpc are well covered. In producing XGAPS we have also trained a Random Forest
classifier to discern targets with problematic astrometric solutions. Selection
cuts based on the classifier results can be used to clean colour-magnitude and
colour-colour diagrams in a controlled and justified manner, as well as
producing subsets of astrometrically reliable targets. We provide XGAPS as a
111 column table. Uses of the catalogue include the selection of Galactic
targets for multi-object spectroscopic surveys as well as identification of
specific Galactic populations. | astro-ph_GA |
An origin of narrow extended structure in the interstellar medium: an
interstellar contrail created by a fast-moving massive object: We investigate the thermal condensation caused by a massive object that
passes through the interstellar medium with high velocity, and propose a
mechanism for creating a filamentary gaseous object, or interstellar contrail.
Our main result shows that a long interstellar contrail can form with a certain
parameter; a compact object more massive than $10^4\ {\rm M_\odot}$ can make a
filament whose length is larger than $100\ {\rm pc}$. Observation of
interstellar contrails may provide information on the number, masses, and
velocities of fast-moving massive objects, and can be a new method for probing
invisible gravitating sources such as intermediate-mass black holes. | astro-ph_GA |
Invisible Active Galactic Nuclei. II Radio Morphologies & Five New HI 21
cm Absorption Line Detections: We have selected a sample of 80 candidates for obscured radio-loud active
galactic nuclei and presented their basic optical/near-infrared (NIR)
properties in Paper 1. In this paper, we present both high-resolution radio
continuum images for all of these sources and HI 21cm absorption spectroscopy
for a few selected sources in this sample. A-configuration 4.9 and 8.5 GHz VLA
continuum observations find that 52 sources are compact or have substantial
compact components with size <0.5" and flux density >0.1 Jy at 4.9 GHz. The
most compact 36 sources were then observed with the VLBA at 1.4 GHz. One
definite and 10 candidate Compact Symmetric Objects (CSOs) are newly
identified, a detection rate of CSOs ~3 times higher than the detection rate
previously found in purely flux-limited samples. Based on possessing compact
components with high flux densities, 60 of these sources are good candidates
for absorption-line searches. Twenty seven sources were observed for HI 21cm
absorption at their photometric or spectroscopic redshifts with only 6
detections made (one detection is tentative). However, five of these were from
a small subset of six CSOs with pure galaxy optical/NIR spectra and for which
accurate spectroscopic redshifts place the redshifted 21cm line in a RFI-free
spectral window. It is likely that the presence of ubiquitous RFI and the
absence of accurate spectroscopic redshifts preclude HI detections in similar
sources (only one detection out of the remaining 22 sources observed, 14 of
which have only photometric redshifts). Future searches for highly-redshifted
HI and molecular absorption can easily find more distant CSOs among bright,
blank field' radio sources but will be severely hampered by an inability to
determine accurate spectroscopic redshifts for them due to their lack of
rest-frame UV continuum. | astro-ph_GA |
Chemically tagging the Hyades stream: Does it partly originate from the
Hyades cluster?: The Hyades stream has long been thought to be a dispersed vestige of the
Hyades cluster. However, recent analyses of the parallax distribution, of the
mass function, and of the action-space distribution of stream stars have shown
it to be rather composed of orbits trapped at a resonance of a density
disturbance. This resonant scenario should leave a clearly different signature
in the element abundances of stream stars than the dispersed cluster scenario,
since the Hyades cluster is chemically homogeneous. Here, we study the
metalllicty as well as the element abundances of Li, Na, Mg, Fe, Zr, Ba, La,
Ce, Nd, and Eu for a random sample of stars belonging to the Hyades stream, and
compare them with those of stars from the Hyades cluster. From this analysis:
(i) we independently confirm that the Hyades stream cannot be solely composed
of stars originating in the Hyades cluster; (ii) we show that some stars from
the Hyades stream nevertheless have abundances compatible with an origin in the
cluster; (iii) we emphasize that the use of Li as a chemical tag of the cluster
origin of main-sequence stars is very efficient in the range 5500 - 6200 K,
since the Li sequence in the Hyades cluster is very tight; (iv) we show that,
while this evaporated population has a metallicity excess of ~0.2 dex w.r.t.
the local thin disk population, identical to that of the Hyades cluster, the
remainder of the Hyades stream population has still a metallicity excess of
~0.06 to 0.15 dex, consistent with an origin in the inner Galaxy; (v) we show
that the Hyades stream can be interpreted as an inner 4:1 resonance of the
spiral pattern: this then also reproduces an orbital family compatible with the
Sirius stream, and places the origin of the Hyades stream up to 1 kpc inwards
from the solar radius, which might explain the observed metallicity excess of
the stream population. | astro-ph_GA |
Non-similar collapse of singular isothermal spherical molecular cloud
cores with nonzero initial velocities: Theoretically, stars have been formed from the collapse of cores in the
molecular clouds. Historically, the core had been assumed as an singular
isothermal sphere (SIS), and the collapse had been investigated by a
self-similar manner. This is while the rotation and magnetic field lead to
non-symmetric collapse so that a spheroid shape may be occurred. Here, the
resultant of the centrifugal force and magnetic field gradient is assumed to be
in the normal direction of the rotational axis, and its components are supposed
to be a fraction $\beta$ of the local gravitational force. In this research, a
collapsing SIS core is considered to find the importance of the parameter
$\beta$ for oblateness of the mass shells which are above the head of the
expansion wave. We apply the Adomian decomposition method to solve the system
of nonlinear partial differential equations because the collapse does not occur
in a spherical symmetry with self-similar behavior. In this way, we obtain a
semi-analytical relation for the mass infall rate $\dot{M}$ of the shells at
the envelope. Near the rotational axis, the $\dot{M}$ decreases with increasing
of the non-dimensional radius $\xi$, while a direct relation is observed
between $\dot{M}$ and $\xi$ in the equatorial regions. Also, the values of
$\dot{M}$ in the polar regions are greater than the equatorial values, and this
difference is more often at smaller values of $\xi$. Overall, the results show
that before reaching the head of expansion wave, the visible shape of the
molecular cloud cores can evolve to oblate spheroids. The ratio of major to
minor axes of oblate cores increases with increasing the parameter $\beta$, and
its value can approach to the apparently observed elongated shapes of cores in
the maps of molecular clouds such as Taurus and Perseus. | astro-ph_GA |
Relations Between Central Black Hole Mass and Total Galaxy Stellar Mass
in the Local Universe: Scaling relations between central black hole (BH) mass and host galaxy
properties are of fundamental importance to studies of BH and galaxy evolution
throughout cosmic time. Here we investigate the relationship between BH mass
and host galaxy total stellar mass using a sample of 262 broad-line active
galactic nuclei (AGN) in the nearby Universe (z < 0.055), as well as 79
galaxies with dynamical BH masses. The vast majority of our AGN sample is
constructed using Sloan Digital Sky Survey spectroscopy and searching for
Seyfert-like narrow-line ratios and broad H-alpha emission. BH masses are
estimated using standard virial techniques. We also include a small number of
dwarf galaxies with total stellar masses M_stellar < 10^9.5 Msun and a
sub-sample of the reverberation-mapped AGNs. Total stellar masses of all 341
galaxies are calculated in the most consistent manner feasible using
color-dependent mass-to-light ratios. We find a clear correlation between BH
mass and total stellar mass for the AGN host galaxies, with M_BH proportional
to M_stellar, similar to that of early-type galaxies with dynamically-detected
BHs. However, the relation defined by the AGNs has a normalization that is
lower by more than an order of magnitude, with a BH-to-total stellar mass
fraction of M_BH/M_stellar ~ 0.025% across the stellar mass range 10^8 <
M_stellar/Msun < 10^12. This result has significant implications for studies at
high redshift and cosmological simulations in which stellar bulges cannot be
resolved. | astro-ph_GA |
Trigonometric Parallaxes of Four Star-forming Regions in the Distant
Inner Galaxy: We have measured trigonometric parallaxes for four water masers associated
with distant massive young stars in the inner regions of the Galaxy using the
VLBA as part of the BeSSeL Survey. G026.50$+$0.28. is located at the near end
of the Galactic bar, perhaps at the origin of the Norma spiral arm.
G020.77$-$0.05 is in the Galactic Center region and is likely associated with a
far-side extension of the Scutum arm. G019.60$-$0.23 and G020.08$-$0.13 are
likely associated and lie well past the Galactic Center. These sources appear
to be in the Sagittarius spiral arm, but an association with the Perseus arm
cannot be ruled out. | astro-ph_GA |
First laboratory detection of vibration-rotation transitions of CH$^+$
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 |
On the lack of correlation between Mg II 2796, 2803 Angstrom and Lyman
alpha emission in lensed star-forming galaxies: We examine the Mg II 2796, 2803 Angstrom, Lyman alpha, and nebular line
emission in five bright star-forming galaxies at 1.66<z<1.91 that have been
gravitationally lensed by foreground galaxy clusters. All five galaxies show
prominent Mg II emission and absorption in a P Cygni profile. We find no
correlation between the equivalent widths of Mg II and Lyman alpha emission.
The Mg II emission has a broader range of velocities than do the nebular
emission line profiles; the Mg II emission is redshifted with respect to
systemic by 100 to 200 km/s. When present, Lyman alpha is even more redshifted.
The reddest components of Mg II and Lyman alpha emission have tails to 500-600
km/s, implying a strong outflow. The lack of correlation in the Mg II and Lyman
alpha equivalent widths, the differing velocity profiles, and the high ratios
of Mg II to nebular line fluxes together suggest that the bulk of Mg II
emission does not ultimately arise as nebular line emission, but may instead be
reprocessed stellar continuum emission. | astro-ph_GA |
The Lyman Alpha Reference Sample XI: Efficient Turbulence Driven
Lyα Escape and the Analysis of IR, CO and [C II]158 μm: We study the global dust and (molecular) gas content in the Lyman Alpha
Reference Sample (LARS), i.e. 14 local star-forming galaxies. We characterize
their interstellar medium and relate newly derived properties to quantities
relevant for Ly$\alpha$ escape. We observed LARS galaxies with Herschel/PACS,
SOFIA/FIFI-LS, the IRAM 30m telescope and APEX, targeting far-infrared (FIR)
continuum and emission lines of [C II]158$\mu$m, [O I]63$\mu$m, [O III]88$\mu$m
and low-J CO lines. Using Bayesian methods we derive dust model parameters and
estimate total gas masses for all LARS galaxies, taking into account a
metallicity-dependent gas-to-dust ratio. Star formation rates were estimated
from FIR, [C II]158$\mu$m and [O I]63$\mu$m luminosities. LARS covers a wide
dynamic range in the derived properties, with FIR-based star formation rates
from $\sim$0.5-100 $M_{\odot}\ yr^{-1}$, gas fractions between $\sim$15-80% and
gas depletion times ranging from a few hundred Myr up to more than 10 Gyr. The
distribution of LARS galaxies in the $\Sigma_{gas}$ vs. $\Sigma_{SFR}$
(Kennicutt-Schmidt plane) is thus quite heterogeneous. However, we find that
LARS galaxies with the longest gas depletion times, i.e. relatively high gas
surface densities ($\Sigma_{gas}$) and low star formation rate densities
($\Sigma_{SFR}$), have by far the highest Ly$\alpha$ escape fraction. A strong
$\sim$linear relation is found between Ly$\alpha$ escape fraction and the total
gas (HI+H$_2$) depletion time. We argue that the Ly$\alpha$ escape in those
galaxies is driven by turbulence in the star-forming gas that shifts the
Ly$\alpha$ photons out of resonance close to the places where they originate.
We further report on an extreme [C II]158$\mu$m excess in LARS 5, corresponding
to $\sim$14$\pm$3% of the FIR luminosity, i.e. the most extreme [C II]-to-FIR
ratio observed in a non-AGN galaxy to date. | astro-ph_GA |
Appearances can be deceiving: clear signs of accretion in the seemingly
ordinary Sextans dSph: We report the discovery of clear observational signs of past accretion/merger
events in one of the Milky Way satellite galaxies, the Sextans dwarf spheroidal
(dSph). These were uncovered in the spatial distribution, internal kinematics
and metallicity properties of Sextans stars using literature CTIO/DECam
photometric and Magellan/MMFS spectroscopic catalogues. We find the spatial
distribution of stars to vary as a function of the colour/metallicity, being
rather regular and round for the blue (metal-poor) red giant branch and
main-sequence turn-off stars but much more elliptical and irregularly shaped
for the red (metal-rich) ones, with a distinct "shell-like" overdensity in the
northeast side. We also detect kinematic anomalies, in the form of a
"ring-like" feature with a considerably larger systemic line-of-sight velocity
and lower metallicity than the rest of stars; even the photometrically selected
component with a regular looking spatial distribution displays complex
kinematics. With a stellar mass of just $\sim5\times10^{5} M_{\odot}$, Sextans
becomes the smallest galaxy presenting clear observational signs of accretion
to date. | astro-ph_GA |
On the Precision of Full-spectrum Fitting of Stellar Populations. III.
Identifying Age Spreads: In this third paper of a series on the precision of obtaining ages of stellar
populations using the full spectrum fitting technique, we examine the precision
of this technique in deriving possible age spreads within a star cluster. We
test how well an internal age spread can be resolved as a function of cluster
age, population mass fraction, and signal-to-noise (S/N) ratio. For this test,
the two ages (Age (SSP1) and Age (SSP2)) are free parameters along with the
mass fraction of SSP1. We perform the analysis on 118,800 mock star clusters
covering all ages in the range 6.8 < log (age/yr) < 10.2, with mass fractions
from 10% to 90% for two age gaps (0.2 dex and 0.5 dex). Random noise is added
to the model spectra to achieve S/N ratios between 50 to 100 per wavelength
pixel. We find that the mean of the derived Age (SSP1) generally matches the
real Age (SSP1) to within 0.1 dex up to ages around log (age/yr) = 9.5. The
precision decreases for log (age/yr) > 9.6 for any mass fraction or S/N, due to
the similarity of SED shapes for those ages. In terms of the recovery of age
spreads, we find that the derived age spreads are often larger than the real
ones, especially for log(age/yr) < 8.0 and high mass fractions of SSP1.
Increasing the age gap in the mock clusters improves the derived parameters,
but Age (SSP2) is still overestimated for the younger ages. | astro-ph_GA |
An ensemble study of turbulence in extended QSO nebulae at
$z\approx0.5$--1: Turbulent motions in the circumgalactic medium (CGM) play a critical role in
regulating the evolution of galaxies, yet their detailed characterization
remains elusive. Using two-dimensional velocity maps constructed from
spatially-extended [OII] and [OIII] emission, Chen et al. (2023b) measured the
velocity structure functions (VSFs) of four quasar nebulae at
$z\approx\!0.5$--1.1. One of these exhibits a spectacular Kolmogorov relation.
Here we carry out an ensemble study using an expanded sample incorporating four
new nebulae from three additional QSO fields. The VSFs measured for all eight
nebulae are best explained by subsonic turbulence revealed by the line-emitting
gas, which in turn strongly suggests that the cool gas ($T\!\sim\!10^4$ K) is
dynamically coupled to the hot ambient medium. Previous work demonstrates that
the largest nebulae in our sample reside in group environments with clear signs
of tidal interactions, suggesting that environmental effects are vital in
seeding and enhancing turbulence within the gaseous halos, ultimately promoting
the formation of the extended nebulae. No discernible differences are observed
in the VSF properties between radio-loud and radio-quiet QSO fields. We
estimate the turbulent heating rate per unit volume, $Q_{\rm turb}$, in the QSO
nebulae to be $\sim 10^{-26}$--$10^{-22}$ erg cm$^{-3}$ s$^{-1}$ for the cool
phase and $\sim 10^{-28}$--$10^{-25}$ erg cm$^{-3}$ s$^{-1}$ for the hot phase.
This range aligns with measurements in the intracluster medium and star-forming
molecular clouds but is $\sim10^3$ times higher than the $Q_{\rm turb}$
observed inside cool gas clumps on scales $\lesssim1$ kpc using absorption-line
techniques. We discuss the prospect of bridging the gap between emission and
absorption studies by pushing the emission-based VSF measurements to below
$\approx\!10$ kpc. | astro-ph_GA |
A technique to select the most obscured galaxy nuclei: Compact obscured nuclei (CONs) are mainly found in local U/LIRGs. In the
local Universe, these sources are generally selected through the detection of
the HCN-vib (3-2) emission line at submillimetre wavelengths. In this work, we
present a diagnostic method to select deeply buried nuclei based on
mid-infrared (mid-IR) polycyclic aromatic hydrocarbons (PAHs) and continuum
ratios. Using Spitzer/IRS spectra of a representative sample of local ULIRGs
(z<0.27), we examine their PAH and underlying continuum emission ratios. For
deeply embedded sources, we find that the 9.7 micron silicate absorption band
has a particularly pronounced effect on the 11.3 micron PAH feature. The low
flux level in the nuclear silicate absorption band enhances the 11.3 micron PAH
feature contrast (high PAH equivalent width) compared to that of the other PAH
features. The technique has been extended to include the use of the continuum
ratios. However, the latter are affected both by the extinction coming from the
host galaxy as well as the nuclear region, whereas the foreground extinction is
cancelled out when using the PAH equivalent width ratios. We apply our method
to the HERUS and GOALS samples and classify as CON candidates 14 ULIRGs and 10
LIRGs, corresponding to 30% of ULIRGs and 7% of LIRGs from these samples. We
find that the observed continuum ratios of CON-dominated sources can be
explained by assuming torus models with a tapered disk geometry and a smooth
dust distribution. This suggests that the nuclear dusty structure of CONs has
an extremely high dust coverage. We also demonstrate that the use of mid-IR
color-color diagrams is an effective way to select CON-dominated sources at
different redshifts. In particular, the combination of filters of the JWST/MIRI
will enable the selection of CONs out to z~1.5. This will allow extending the
selection of CONs to high redshifts where U/LIRGs are more numerous. | astro-ph_GA |
The Korean 1592--1593 Record of a Guest Star: An `impostor' of the
Cassiopeia A Supernova?: The missing historical record of the Cassiopeia A (Cas A) supernova (SN)
event implies a large extinction to the SN, possibly greater than the
interstellar extinction to the current SN remnant. Here we investigate the
possibility that the guest star that appeared near Cas A in 1592--1593 in
Korean history books could have been an `impostor' of the Cas A SN, i.e., a
luminous transient that appeared to be a SN but did not destroy the progenitor
star, with strong mass loss to have provided extra circumstellar extinction. We
first review the Korean records and show that a spatial coincidence between the
guest star and Cas A cannot be ruled out, as opposed to previous studies. Based
on modern astrophysical findings on core-collapse SN, we argue that Cas A could
have had an impostor and derive its anticipated properties. It turned out that
the Cas A SN impostor must have been bright ($M_V =-14.7 \pm 2.2$ mag) and an
amount of dust with visual extinction of $\ge 2.8\pm 2.2 $ mag should have
formed in the ejected envelope and/or in a strong wind afterwards. The mass
loss needs to have been spherically asymmetric in order to see the light echo
from the SN event but not the one from the impostor event. | astro-ph_GA |
Some optical properties of graphite from IR to millimetric wavelengths: Far infrared(FIR) data on the optical properties of graphite are presently
lacking. An important step towards filling this gap was taken by Kuzmenko et
al. (2008) who measured, on HOPG (Highly Oriented Pyrolitic Graphite) at normal
incidence and from 10 to 300 K, the in-plane dielectric functions from 0.3 to
200 mum, and the reflectance between 0.3 and about 300 mum. We show here how,
using recent developments of the electron theory of graphene, extended to
graphite, it is possible to properly extrapolate the data farther even than
1000 mum, in effect all the way to Direct Current. The plasma frequency as well
as the scattering rate of free electrons are shown to both decrease with T, but
level off near 0 K, in agreement with theory. Along the way, we noticed
significant discrepancies with the well-known and often used derivation of
Philipp (1977) at room temperature, and also with previous data on temperature
dependence and absorbance of graphitic material samples in different physical
forms. Possible reasons for these discrepancies are discussed. Finally, the
absorption efficiency of small graphitic spheres is deduced for the spectral
range from 0.3 to 10000 mum. This may contribute to the discussion on model
dust candidates for recently observed astronomical far infrared emissions. | astro-ph_GA |
Anomalous compressible mode generation by global frame projections of
pure Alfven mode: Alfven wave is the single most important physical phenomenon of
magneto-hydrodynamic turbulence and has far-reaching impact to almost all
studies related to astrophysical magnetic field. Yet the restoration of the
Alfven wave fluctuations from a given magnetic field, aka the local Alfven wave
problem, is never properly addressed in literature albeit its importance.
Previous works model the Alfven wave fluctuation as the perturbation along a
straight-line, constant magnetic field. However, Lazarian & Pogosyan (2012)
suggested that the decomposition of Alfven wave along a straight line, aka. the
global frame decomposition, has a factor of discrepancy to the true local
Alfven wave fluctuation. Here we provide a geometric interpretation on how the
local Alfven wave is related to the global frame through the use of vector
frame formulation. We prove both analytically and numerically that the local
frame Alfven wave is an orthogonal transformation of that of the global frame
and related by the local Alfvenic Mach number. In other words, when we observe
Alfven wave in the global frame of reference, some of the Alfven wave will be
mistaken as compressible waves. The importance of frame choices have a
far-reaching impact to the analytical studies of MHD turbulence. Combining the
frame formalism and the new techniques we can have accurate measurement to some
of the fundamental turbulence properties like the inclination angle of mean
magnetic field relative to the line of sight. | astro-ph_GA |
Aperture and Resolution Effects on Ultraviolet Star-Forming Properties:
Insights from Local Galaxies and Implications for High-Redshift Observations: We present an analysis of the effects of spectral resolution and aperture
scales on derived galaxy properties using far-ultraviolet (FUV) spectra of
local star-forming galaxies from the International Ultraviolet Explorer (R~250,
FOV~10"x20") and Cosmic Origins Spectrograph on the Hubble Space Telescope
(R~15,000, FOV~2.5"). Using these spectra, we measured FUV luminosities,
spectral slopes, dust attenuation, and equivalent widths. We find that galaxies
with one dominant stellar cluster have FUV properties that are independent of
aperture size, while galaxies with multiple bright clusters are sensitive to
the total light fraction captured by the aperture. Additionally, we find
significant correlations between the strength of stellar and interstellar
absorption-lines and metallicity, indicating metallicity-dependent line-driven
stellar winds and interstellar macroscopic gas flows shape the stellar and
interstellar spectral lines, respectively. The observed line-strength versus
metallicity relation of stellar-wind lines agrees with the prediction of
population synthesis models for young starbursts. In particular, measurements
of the strong stellar CIV 1548,1550 line provide an opportunity to determine
stellar abundances as a complement to gas-phase abundances. We provide a
relation between the equivalent width of the CIV line and the oxygen abundance
of the galaxy. We discuss this relation in terms of the stellar-wind properties
of massive stars. As the driving lines in stellar winds are mostly ionized iron
species, the CIV line may eventually offer a method to probe
alpha-element-to-iron ratios in star-forming galaxies once consistent models
with non-solar abundance ratios are available. These results have important
implications for the galaxy-scale, low-resolution observations of high-redshift
galaxies from JWST (R~100-3,500). | astro-ph_GA |
An Analysis of the Shapes of Interstellar Extinction Curves. VI. The
Near-IR Extinction Law: We combine new HST/ACS observations and existing data to investigate the
wavelength dependence of NIR extinction. Previous studies suggest a power-law
form, with a "universal" value of the exponent, although some recent
observations indicate that significant sight line-to-sight line variability may
exist. We show that a power-law model provides an excellent fit to most NIR
extinction curves, but that the value of the power, beta, varies significantly
from sight line-to-sight line. Therefore, it seems that a "universal NIR
extinction law" is not possible. Instead, we find that as beta decreases, R(V)
[=A(V)/E(B-V)] tends to increase, suggesting that NIR extinction curves which
have been considered "peculiar" may, in fact, be typical for different R(V)
values. We show that the power law parameters can depend on the wavelength
interval used to derive them, with the beta increasing as longer wavelengths
are included. This result implies that extrapolating power law fits to
determine R(V) is unreliable. To avoid this problem, we adopt a different
functional form for NIR extinction. This new form mimics a power law whose
exponent increases with wavelength, has only 2 free parameters, can fit all of
our curves over a longer wavelength baseline and to higher precision, and
produces R(V) values which are consistent with independent estimates and
commonly used methods for estimating R(V). Furthermore, unlike the power law
model, it gives R(V)'s that are independent of the wavelength interval used to
derive them. It also suggests that the relation R(V) = -1.36 E(K-V)/E(B-V) -
0.79 can estimate R(V) to +/-0.12. Finally, we use model extinction curves to
show that our extinction curves are in accord with theoretical expectations. | astro-ph_GA |
The Interstellar Medium toward the Galactic Center Source 2MASS
J17470898-2829561: We describe and discuss remarkable infrared spectra, covering key portions of
the $2-5$ $\mu$m wavelength interval, of the probable OH/IR supergiant 2MASS
J17470898$-$2829561 (2M1747), located in direction of the Sgr B molecular cloud
complex within the Central Molecular Zone (CMZ) of the Galaxy. This star was
originally singled out for examination based on its suitability for
spectroscopy of lines of H$_3^+$ in the CMZ. Analysis of the spectra shows that
2M1747 is deeply embedded within Sgr B1, with A$_V$ $\gtrsim$ 100 mag, making
it the only star within Sgr B for which infrared spectra have been obtained at
present, and thereby a unique infrared probe of the dense interstellar medium
within the CMZ. Despite the high extinction, spectra of 2M1747 reveal a veiled
photosphere in the $K$ band and circumstellar gas in the $M$ band, giving clues
as to its nature. Its $ 3.5-4.0$ $\mu$m spectrum contains the strongest
absorption lines of H$_3^+$ observed toward any object to date. The $4.5-4.8$
$\mu$m spectrum has impressively deep and wide absorption lines of interstellar
CO, most of which arise in dense gas within Sgr B1. The $3-5$ $\mu$m spectrum
also contains several solid state absorption features, which are characteristic
of both dense and diffuse clouds, and which raise questions about the
identifications of some of these features. We discuss the nature of the star,
the extinction to it, the extinction law for dust in the CMZ, and the
identifications of the various solid-state features and where they are produced
along this complex line of sight. | astro-ph_GA |
Magnetic Fields, Star Formation Rates and Gas Densities at Sub-kpc
Scales in a Pilot Sample of Nearby Galaxies: We have estimated the magnetic field strengths of a sample of seven galaxies
using their non-thermal synchrotron radio emission at metre wavelengths, and
assuming energy equipartition between magnetic fields and cosmic ray particles.
Spatially resolved star formation rates (SFR) were estimated for the seven
galaxies along with five galaxies studied previously. For the combined sample
of twelve galaxies, the equipartition magnetic fields (B$_\textrm{eq}$) are
correlated with the SFR surface densities ($\Sigma_\textrm{SFR}$) at sub-kpc
scales with B$_\textrm{eq}$ $\propto$ $\Sigma_\textrm{SFR}^ {0.31\pm0.06}$,
consistent with model predictions. We estimated gas densities
($\rho_\textrm{gas}$) for a sub-sample of seven galaxies using archival
observations of the carbon monoxide (CO) rotational transitions and the atomic
hydrogen (HI) 21 cm line and studied the spatially-resolved correlation between
the magnetic fields and $\rho_\textrm{gas}$. Magnetic fields and gas densities
are found to be correlated at sub-kpc scale as B$_\textrm{eq}$ $\propto$
$\rho_\textrm{gas}^{0.40\pm0.09}$. This is broadly consistent with models,
which typically predict B $\propto$ $\rho_\textrm{gas}^{0.5}$. | astro-ph_GA |
Herschel SPIRE-FTS Observations of Excited CO and [CI] in the Antennae
(NGC 4038/39): Warm and Cold Molecular Gas: We present Herschel SPIRE-FTS observations of the Antennae (NGC 4038/39), a
well studied, nearby ($22$ Mpc) ongoing merger between two gas rich spiral
galaxies. We detect 5 CO transitions ($J=4-3$ to $J=8-7$), both [CI]
transitions and the [NII]$205\mu m$ transition across the entire system, which
we supplement with ground based observations of the CO $J=1-0$, $J=2-1$ and
$J=3-2$ transitions, and Herschel PACS observations of [CII] and [OI]$63\mu m$.
Using the CO and [CI] transitions, we perform both a LTE analysis of [CI], and
a non-LTE radiative transfer analysis of CO and [CI] using the radiative
transfer code RADEX along with a Bayesian likelihood analysis. We find that
there are two components to the molecular gas: a cold ($T_{kin}\sim 10-30$ K)
and a warm ($T_{kin} \gtrsim 100$ K) component. By comparing the warm gas mass
to previously observed values, we determine a CO abundance in the warm gas of
$x_{CO} \sim 5\times 10^{-5}$. If the CO abundance is the same in the warm and
cold gas phases, this abundance corresponds to a CO $J=1-0$ luminosity-to-mass
conversion factor of $\alpha_{CO} \sim 7 \ M_{\odot}{pc^{-2} \ (K \ km \
s^{-1})^{-1}}$ in the cold component, similar to the value for normal spiral
galaxies. We estimate the cooling from H$_2$, [CII], CO and [OI]$63\mu m$ to be
$\sim 0.01 L_{\odot}/M_{\odot}$. We compare PDR models to the ratio of the flux
of various CO transitions, along with the ratio of the CO flux to the
far-infrared flux in NGC 4038, NGC 4039 and the overlap region. We find that
the densities recovered from our non-LTE analysis are consistent with a
background far-ultraviolet field of strength $G_0\sim 1000$. Finally, we find
that a combination of turbulent heating, due to the ongoing merger, and
supernova and stellar winds are sufficient to heat the molecular gas. | astro-ph_GA |
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