text
stringlengths 89
2.49k
| category
stringclasses 19
values |
|---|---|
Disentangling the near infrared continuum spectral components of the
inner 500 pc of Mrk 573: two-dimensional maps: We present a near infrared study of the spectral components of the continuum
in the inner 500$\times$500 pc$^2$ of the nearby Seyfert galaxy Mrk573 using
adaptive optics near-infrared integral field spectroscopy with the instrument
NIFS of the Gemini North Telescope at a spatial resolution of $\sim$50 pc. We
performed spectral synthesis using the {\sc starlight} code and constructed
maps for the contributions of different age components of the stellar
population: young ($age\leq100$ Myr), young-intermediate ($100<age\leq700$
Myr), intermediate-old ($700$ Myr $<age\leq2$ Gyr) and old ($age>2$ Gyr) to the
near-IR K-band continuum, as well as their contribution to the total stellar
mass. We found that the old stellar population is dominant within the inner 250
pc, while the intermediate age components dominate the continuum at larger
distances. A young stellar component contributes up to $\sim$20% within the
inner $\sim$70 pc, while hot dust emission and featureless continuum components
are also necessary to fit the nuclear spectrum, contributing up to 20% of the
K-band flux there. The radial distribution of the different age components in
the inner kiloparsec of Mrk573 is similar to those obtained by our group for
the Seyfert galaxies Mrk1066, Mrk1157 and NGC1068 in previous works using a
similar methodology. Young stellar populations ($\leq$100 Myr) are seen in the
inner 200-300 pc for all galaxies contributing with $\ge$20% of the K-band
flux, while the near-IR continuum is dominated by the contribution of
intermediate-age stars ($t=$100 Myr-2 Gyr) at larger distances. Older stellar
populations dominate in the inner 250 pc. | astro-ph_GA |
A southern hemisphere survey of the 5780 and 6284 Å diffuse
interstellar bands: correlation with the extinction: We present a new database of 5780.5 and 6283.8 {\AA} DIB measurements and
also study their correlation with the reddening. The database is based on
high-resolution, high-quality spectra of early-type nearby stars located in the
southern hemisphere at an average distance of 300 pc. Equivalent widths of the
two DIBs were determined by means of a realistic continuum fitting and
synthetic atmospheric transmissions. For all stars that possess a precise
measurement of their color excess, we compare the DIBs and the extinction. We
find average linear relationships of the DIBS and the color excess that agree
well with those of a previous survey of northern hemisphere stars closer than
550 pc. This similarity shows that there is no significant spatial dependence
of the average relationship in the solar neighborhood within $\simeq$ 600 pc. A
noticeably different result is our higher degree of correlation of the two DIBs
with the extinction. We demonstrate that it is simply due to the lower
temperature and intrinsic luminosity of our targets. Using cooler target stars
reduces the number of outliers, especially for nearby stars, confirming that
the radiation field of UV bright stars has a significant influence on the DIB
strength. We have used the cleanest data to compute updated DIB shapes. | astro-ph_GA |
CO luminosity function from Herschel-selected galaxies and the
contribution of AGN: We derive the CO luminosity function (LF) for different rotational
transitions (i.e. (1-0), (3-2), (5-4)) starting from the Herschel LF by
Gruppioni et al. and using appropriate $L'_{\rm CO} - L_{\rm IR}$ conversions
for different galaxy classes. Our predicted LFs fit the data so far available
at $z\approx0$ and $2$. We compare our results with those obtained by
semi-analytical models (SAMs): while we find a good agreement over the whole
range of luminosities at $z\approx0$, at $z\approx1$ and $z\approx2$ the
tension between our LFs and SAMs in the faint and bright ends increases. We
finally discuss the contribution of luminous AGN
($L_{X}>10^{44}\,\rm{erg\,s^{-1}}$) to the bright end of the CO LF concluding
that they are too rare to reproduce the actual CO luminosity function at
$z\approx2$. | astro-ph_GA |
ATCA observations of SiO masers in the Galactic center: We present the Australia Telescope Compact Array (ATCA) observations of the
SiO masers in the Galactic center in transitions of v=1, J=2--1 at 86 GHz and
v=1, J=1--0 at 43 GHz. Two 86-GHz SiO masers were detected within the central
parsec, and they are associated with IRS 10EE and IRS 15NE, respectively. We
detected eighteen 43-GHz SiO masers within a projected separation of <2 pc from
Sagittarius A* (Sgr A*), among which seven masers are newly discovered from our
observations. This raises the total number of 43-GHz SiO masers within the
central 4 parsecs of the GC region to 22. Simultaneous observations at 86 and
43 GHz showed that the intensity of 43-GHz SiO maser is ~3 times higher than
that of 86-GHz maser in IRS 10EE (an OH/IR star), while the integrated flux of
the SiO maser emission at 43 GHz is comparable with that at 86~GHz in IRS~15NE
(an ordinary Mira variable). These results are consistent with previous
observations of massive late-type stars in the Galaxy in which the 86-GHz SiO
maser is in general weaker than the 43-GHz SiO maser in OH/IR stars, while the
two transitions are comparably strong in Mira stars. | astro-ph_GA |
Star clusters near and far; tracing star formation across cosmic time: Star clusters are fundamental units of stellar feedback and unique tracers of
their host galactic properties. In this review, we will first focus on their
constituents, i.e.\ detailed insight into their stellar populations and their
surrounding ionised, warm, neutral, and molecular gas. We, then, move beyond
the Local Group to review star cluster populations at various evolutionary
stages, and in diverse galactic environmental conditions accessible in the
local Universe. At high redshift, where conditions for cluster formation and
evolution are more extreme, we are only able to observe the integrated light of
a handful of objects that we believe will become globular clusters. We
therefore discuss how numerical and analytical methods, informed by the
observed properties of cluster populations in the local Universe, are used to
develop sophisticated simulations potentially capable of disentangling the
genetic map of galaxy formation and assembly that is carried by globular
cluster populations. | astro-ph_GA |
Ionized gas in the NGC 3077 galaxy: The nearby dwarf galaxy NGC 3077 is known for its peculiar morphology, which
includes numerous dust lanes and emission-line regions. The interstellar medium
in this galaxy is subject to several perturbing factors. These are primarily
the central starburst and tidal structures in the M 81 group. We present a
comprehensive study of the state of ionization, kinematics, and chemical
composition of ionized gas in NGC 3077, including both star-forming regions and
diffuse ionized gas (DIG) at the periphery. We study gas motions in the
H$\alpha$ line via high-resolution ($R\approx15\,000$) 3D spectroscopy with the
scanning Fabry-Perot interferometer installed into SCORPIO-2 instrument
attached to the 6-m telescope of the SAO RAS. Images in the main optical
emission lines were acquired with MaNGaL photometer with a tunable filter at
the 2.5-m telescope of the Caucasian Mountain Observatory of SAI MSU. We also
used SCORPIO-2 to perform long-slit spectroscopy of the galaxy with a
resolution of $R\approx1\,000$. Our estimate of the gas metallicity,
$Z=0.6Z_\odot$, is significantly lower than the earlier determination, but
agrees with the "luminosity--metallicity" dependence. Spatially resolved
diagnostic diagrams of the emission-line ratios do not show correlations
between the gas ionization state and its velocity dispersion, and this is most
likely due to strong ionization by young stars, whereas the contribution of
shocks to the excitation of emission lines is less important. We also studied
the locations of multicomponent H$\alpha$ profiles and provide arguments
suggesting that they are mostly associated with individual kinematic components
along the line of sight and not with expanding shells as it was believed
earlier. We also observe there a combination of wind outflow from star-forming
regions and accretion from interstellar gas clouds in the M 81 group. | astro-ph_GA |
A comprehensive view of the Virgo Stellar Stream: Radial velocities and metallicities have been measured for 82 RR Lyrae
identified by the QUEST survey in the direction of the Virgo constellation.
Distributed over 90 sq. deg. of the sky, they lie from 4 to 23 kpc from the
Sun. Using an algorithm for finding groups in phase space and modeling the
smooth halo component in the region, we identified the 5 most significant RRLS
groups. We have examined the SEKBO and the Catalina catalog of RRLS (Prior et
al. 2009, and Drake et al. 2013), as well as the bright QUEST RRLS sample
(Vivas et al. in prep.), the catalogs of Blue Horizontal Branch stars compiled
by Sirko et al (2004) and Brown et al (2008, 2010) and the catalog of Red Giant
stars from the Spaghetti survey, for stars that may be related to the QUEST
RRLS groups. The most significant group of RRLS is the Virgo Stellar Stream
(VSS, Duffau et al 2006), group A, which is composed of at least 10 RRLS and 3
BHB stars. It has a mean distance of 19.6 kpc and a mean radial velocity Vgsr =
128 km/s, as estimated from its RRLS members. With the revised velocities
reported here, there is no longer an offset in velocity between the RRLS in the
VSS and the prominent peak in the velocities of main-sequence turnoff stars
reported by Newberg et al (2007) in the same direction and at a similar
distance (S297+63-20.5). The location in phase space of two other groups (F,H)
suggests a possible connection with the VSS, which cannot be discarded at this
point, although the turnoff colors of the VSS and group H, as identified from
Newberg et al. (2007), suggest they might be composed of different populations.
Two more groups (B,D), are found at mean distances of 19 and 5.7 kpc, and mean
radial velocities of -94 and 32 km/s. None of our groups seems to relate to Sgr
streams. The excess of stars observed in Virgo appears to be composed of
several halo substructures along the same line of sight. | 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 |
Spectro-photometric decomposition of galaxy structural components: Galaxies are complex systems made up of different structural components such
as bulges, discs, and bars. Understanding galaxy evolution requires unveiling,
independently, their history of stellar mass and metallicity assembly. We
introduce C2D, a new algorithm to perform spectro-photometric multi-component
decompositions of integral field spectroscopy (IFS) datacubes. The galaxy
surface-brightness distribution at each wavelength (quasi-monochromatic image)
is fitted using GASP2D, a 2D photometric decomposition code. As a result, C2D
provides both a characteristic one-dimensional spectra and a full datacube with
all the spatial and spectral information for every component included in the
fit. We show the basic steps of the C2D spectro-photometric fitting procedure,
tests on mock datacubes demonstrating its reliability, and a first application
of C2D to a sample of three early-type galaxies (ETGs) observed within the
CALIFA survey. The resulting datacubes from C2D are processed through the
PIPE3D pipeline obtaining both the stellar populations and ionised gas
properties of bulges and discs. This paper presents an overview of the
potential of C2D+PIPE3D to unveil the formation and evolution of galaxies. | astro-ph_GA |
Angular Momentum of Dwarf Galaxies: We present measurements of baryonic mass Mb and specific angular momentum
(sAM) jb in 14 rotating dwarf Irregular (dIrr) galaxies from the LITTLE THINGS
sample. These measurements, based on 21cm kinematic data from the Very Large
Array and stellar mass maps from the Spitzer Space Telescope, extend previous
AM measurements by more than two orders of magnitude in Mb. The dwarf galaxies
show systematically higher jb values than expected from the jb~Mb^{2/3} scaling
of spiral galaxies, representative of a scale-free galaxy formation scenario.
This offset can be explained by decreasing baryon mass fractions fM=Mb Mdyn
(where Mdyn is the dynamical mass) with decreasing Mb (for Mb<10^{11}Msun). We
find that the sAM of neutral atomic hydrogen HI alone is about 2.5 times higher
than that of the stars. The M-j relation of HI is significantly steeper than
that of the stars, as a direct consequence of the systematic variation of the
HI fraction with Mb. | astro-ph_GA |
The Imprint of Reionization on the Star Formation Histories of Dwarf
Galaxies: We explore the impact of cosmic reionization on nearby isolated dwarf
galaxies using a compilation of SFHs estimated from deep HST data and a
cosmological hydrodynamical simulation of the Local Group. The nearby dwarfs
show a wide diversity of star formation histories; from ancient systems that
have largely completed their star formation $\sim 10$ Gyr ago to young dwarfs
that have formed the majority of their stars in the past $\sim 5$ Gyr to
two-component systems characterized by the overlap of comparable numbers of old
and young stars. Taken as an ensemble, star formation in nearby dwarfs dips to
lower-than-average rates at intermediate times ($4<t$/Gyr $<8$), a feature that
we trace in the simulation to the effects of cosmic reionization. Reionization
heats the gas and drives it out of the shallow potential wells of low mass
halos, affecting especially those below a sharp mass threshold that corresponds
to a virial temperature of $\sim 2 \times 10^4 $ $\mathrm{K}$ at $z_{\rm
reion}$.
The loss of baryons leads to a sharp decline in the star forming activity of
early-collapsing systems, which, compounded by feedback from early star
formation, empties halos of gas and leaves behind systems where a single old
stellar component prevails. In halos below the threshold at $z_{\rm reion}$,
reionization heating leads to a delay in the onset of star formation that lasts
until the halo grows massive enough to allow some of the remaining gas to cool
and form stars. Young stellar components therefore dominate in dwarfs whose
halos assemble late and thus form few stars before reionization. Two-component
systems may be traced to late mergers of individual examples of the two
aforementioned cases. The relative dearth of intermediate-age stars in nearby
dwarfs might thus be the clearest signature yet identified of the imprint of
cosmic reionization on the star formation history of dwarf galaxies. | astro-ph_GA |
The Transition Region between Brightest Cluster Galaxies and
Intra-Cluster Light in Galaxy Groups and Clusters: We take advantage of a state-of-art semi analytic model of galaxy formation,
and the model presented in \citet{contini21a}, to investigate the mass
distribution of Brightest Cluster Galaxies (BCGs) and Intra-Cluster Light (ICL)
by addressing two points: (1) the region of transition between a BCG dominated
distribution and an ICL dominated one, and; (2) the relation between the total
BCG+ICL mass and the ICL one alone. We find the transition radius to be
independent of both BCG+ICL and halo masses, with an average of 60$\pm$40 kpc,
in good agreement with previous observational measurements, but given the large
scatter, it can be considered as a sort of physical separation between the two
components only on cluster scale. From the analysis of $M_{ICL}-M_{BCG+ICL}$
relation, we build a method able to extract the ICL mass directly from the
knowledge of the BCG+ICL one. Given the large scatter on low mass systems, such
method under/overpredicts the true value of the ICL in a significant way, up to
a factor of three in the worst cases. On the other hand, for $\log
M_{BCG+ICL}>12$ or $\log M_{Halo}>14$, the difference between the true value
and the one extracted from the $M_{ICL}-M_{BCG+ICL}$ relation ranges between
$\pm$30\%. We therefore suggest this relation as a reliable test for
observational works aiming to isolate the ICL from the BCG, for systems hosted
by haloes on cluster scale. | astro-ph_GA |
The DiskMass Survey. VIII. On the Relationship Between Disk Stability
and Star Formation: We study the relationship between the stability level of late-type galaxy
disks and their star-formation activity using integral-field gaseous and
stellar kinematic data. Specifically, we compare the two-component (gas+stars)
stability parameter from Romeo & Wiegert (Q_RW), incorporating stellar
kinematic data for the first time, and the star-formation rate estimated from
21cm continuum emission. We determine the stability level of each disk
probabilistically using a Bayesian analysis of our data and a simple dynamical
model. Our method incorporates the shape of the stellar velocity ellipsoid
(SVE) and yields robust SVE measurements for over 90% of our sample. Averaging
over this subsample, we find a meridional shape of sigma_z/sigma_R =
0.51^{+0.36}_{-0.25} for the SVE and, at 1.5 disk scale lengths, a stability
parameter of Q_RW = 2.0 +/- 0.9. We also find that the disk-averaged
star-formation-rate surface density (Sigma-dot_e,*) is correlated with the
disk-averaged gas and stellar mass surface densities (Sigma_e,g and Sigma_e,*)
and anti-correlated with Q_RW. We show that an anti-correlation between
Sigma-dot_e,* and Q_RW can be predicted using empirical scaling relations, such
that this outcome is consistent with well-established statistical properties of
star-forming galaxies. Interestingly, Sigma-dot_e,* is not correlated with the
gas-only or star-only Toomre parameters, demonstrating the merit of calculating
a multi-component stability parameter when comparing to star-formation
activity. Finally, our results are consistent with the Ostriker et al. model of
self-regulated star-formation, which predicts
Sigma-dot_e,*/Sigma_e,g/sqrt(Sigma_e,*). Based on this and other theoretical
expectations, we discuss the possibility of a physical link between disk
stability level and star-formation rate in light of our empirical results. | astro-ph_GA |
Survey of Gravitationally-lensed Objects in HSC Imaging (SuGOHI). II.
Environments and Line-of-Sight Structure of Strong Gravitational Lens
Galaxies to z ~ 0.8: We investigate the local and line-of-sight overdensities of strong
gravitational lens galaxies using wide-area multiband imaging from the Hyper
Suprime-Cam Subaru Strategic Program. We present 41 new definite or probable
lens candidates discovered in Data Release 2 of the survey. Using a combined
sample of 87 galaxy-scale lenses out to a lens redshift of $z_{\mathrm{L}} \sim
0.8$, we compare galaxy number counts in lines of sight toward known and
newly-discovered lenses in the survey to those of a control sample consisting
of random lines of sight. We also compare the local overdensity of lens
galaxies to a sample of "twin" galaxies that have a similar redshift and
velocity dispersion to test whether lenses lie in different environments from
similar non-lens galaxies. We find that lens fields contain higher number
counts of galaxies compared to the control fields, but this effect arises from
the local environment of the lens. Once galaxies in the lens plane are removed,
the lens lines of sight are consistent with the control sample. The local
environments of the lenses are overdense compared to the control sample, and
are slightly overdense compared to those of the twin sample, although the
significance is marginal. There is no significant evidence of the evolution of
the local overdensity of lens environments with redshift. | astro-ph_GA |
A Photodissociation Region study of NGC 4038: We present a model of the photodissociation regions of NGC 4038, which is
part of the Antennae galaxies. We have considered one-dimensional slabs of
uniform density all having a maximum $A_V=10\,{\rm mag}$, interacting with
plane-parallel radiation. The density range in our simulations spans four
orders of magnitude ($100\le n\le 10^6\,{\rm cm}^{-3}$) and the UV field
strength spans more than three orders of magnitude ($10\le\chi\le10^{4.5}$
multiples of the ${\rm Draine}$ field), from which we generated a grid of about
1400 simulations. We compare our results with Herschel SPIRE-FTS, CSO and
ISO-LWS observations of eight CO transition lines ($J=1-0$ to $8-7$) and the
[CI] 609\mu m and [OI] 146\mu m fine structure lines. We find that the
molecular and atomic emission lines trace different gas components of NGC 4038,
thus single emission models are insufficient to reproduce the observed values.
In general, low-$J$ CO transition lines correspond to either low density
regions interacting with low UV field strengths, or high density regions
interacting with high UV field strengths. Higher $J$ CO transition lines are
less dependent on the UV field strength and are fitted by gas with density
$n\sim10^{4.5}-10^{5.2}\,{\rm cm}^{-3}$. We find that the observed fine
structure line ratio of [CI] 609\mu m/[OI] 146\mu m is reproduced by clouds
subject to weaker UV fields compared to the CO lines. We make estimates of the
$X_{\rm CO}$ factor which relates the CO emission with the column density of
molecular hydrogen, and find that it is less than the canonical Milky Way
value. | astro-ph_GA |
The H$α$ broadband photometric reverberation mapping of four
Seyfert 1 galaxies: Broadband photometric reverberation mapping (PRM) have been investigated for
AGNs in recent years, but mostly on accretion disk continuum RM. Due to the
small fraction of broad emission lines in the broadband, PRM for emission lines
is very challenging. Here we present an ICCF-Cut method for broadband PRM to
obtain the H$\alpha$ broad line lag and apply it to four Seyfert 1 galaxies,
MCG+08-11-011, NGC 2617, 3C 120 and NGC 5548. All of them have high quality
broadband lightcurves with daily/sub-daily cadence, which enables us to extract
H$\alpha$ lightcurves from the line band by subtracting the contributions from
the continuum and host galaxy. Their extracted H$\alpha$ lightcurves are
compared with the lagged continuum band lightcurves, as well as the lagged
H$\beta$ lightcurves obtained by spectroscopic RM (SRM) at the same epochs. The
consistency of these lightcurves and the comparison with the SRM H$\beta$ lags
provide supports to the H$\alpha$ lags of these AGNs, in a range from 9 to 19
days, obtained by the ICCF-Cut, JAVELIN and $\chi^2$ methods. The simulations
to evaluate the reliability of H$\alpha$ lags and the comparisons between SRM
H$\beta$ and PRM H$\alpha$ lags indicate that the consistency of the ICCF-Cut,
JAVELIN and $\chi^2$ results can ensure the reliability of the derived
H$\alpha$ lags. These methods may be used to estimate the broad line region
sizes and black hole masses of a large sample of AGNs in the large multi-epoch
high cadence photometric surveys such as LSST in the future. | astro-ph_GA |
Cosmological simulations of dwarfs: the need for ISM physics beyond SN
feedback alone: The dominant feedback mechanism in low mass haloes is usually assumed to take
the form of massive stars exploding as supernovae (SNe). We perform very high
resolution cosmological zoom-in simulations of five dwarf galaxies to z = 4
with our mechanical SN feedback model. This delivers the correct amount of
momentum corresponding to the stage of the SN remnant evolution resolved, and
has been shown to lead to realistic dwarf properties in isolated simulations.
We find that in 4 out of our 5 simulated cosmological dwarfs, SN feedback has
insufficient impact resulting in excessive stellar masses, extremely compact
sizes and central super-solar stellar metallicities. The failure of the SN
feedback in our dwarfs is physical in nature within our model and is the result
of the build up of very dense gas in the early universe due to mergers and
cosmic inflows prior to the first SN occurring. We demonstrate that our results
are insensitive to resolution (provided that it is high enough), details of the
(spatially uniform) UV background and reasonable alterations within our star
formation prescription. We therefore conclude that the ability of SNe to
regulate dwarf galaxy properties is dependent on other physical processes, such
as turbulent pressure support, clustering and runaway of SN progenitors and
other sources of stellar feedback. | astro-ph_GA |
The evolutionary tracks of young massive star clusters: Stars mostly form in groups consisting of a few dozen to several ten thousand
members. For 30 years, theoretical models provide a basic concept of how such
star clusters form and develop: they originate from the gas and dust of
collapsing molecular clouds. The conversion from gas to stars being incomplete,
the left over gas is expelled, leading to cluster expansion and stars becoming
unbound. Observationally, a direct confirmation of this process has proved
elusive, which is attributed to the diversity of the properties of forming
clusters. Here we take into account that the true cluster masses and sizes are
masked, initially by the surface density of the background and later by the
still present unbound stars. Based on the recent observational finding that in
a given star-forming region the star formation efficiency depends on the local
density of the gas, we use an analytical approach combined with \mbox{N-body
simulations, to reveal} evolutionary tracks for young massive clusters covering
the first 10 Myr. Just like the Hertzsprung-Russell diagram is a measure for
the evolution of stars, these tracks provide equivalent information for
clusters. Like stars, massive clusters form and develop faster than their
lower-mass counterparts, explaining why so few massive cluster progenitors are
found. | astro-ph_GA |
ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: The Infrared
Excess of UV-selected z=2-10 galaxies as a function of UV-continuum Slope and
Stellar Mass: We make use of deep 1.2mm-continuum observations (12.7microJy/beam RMS) of a
1 arcmin^2 region in the Hubble Ultra Deep Field to probe dust-enshrouded star
formation from 330 Lyman-break galaxies spanning the redshift range z=2-10 (to
~2-3 Msol/yr at 1sigma over the entire range). Given the depth and area of
ASPECS, we would expect to tentatively detect 35 galaxies extrapolating the
Meurer z~0 IRX-beta relation to z>~2 (assuming T_d~35 K). However, only 6
tentative detections are found at z>~2 in ASPECS, with just three at >3sigma.
Subdividing z=2-10 galaxies according to stellar mass, UV luminosity, and
UV-continuum slope and stacking the results, we only find a significant
detection in the most massive (>10^9.75 Msol) subsample, with an infrared
excess (IRX=L_{IR}/L_{UV}) consistent with previous z~2 results. However, the
infrared excess we measure from our large selection of sub-L* (<10^9.75 Msol)
galaxies is 0.11(-0.42)(+0.32) and 0.14(-0.14)(+0.15) at z=2-3 and z=4-10,
respectively, lying below even an SMC IRX-beta relation (95% confidence). These
results demonstrate the relevance of stellar mass for predicting the IR
luminosity of z>~2 galaxies. We furthermore find that the evolution of the
IRX-stellar mass relationship depends on the evolution of the dust temperature.
If the dust temperature increases monotonically with redshift (as (1+z)^0.32)
such that T_d~44-50 K at z>=4, current results are suggestive of little
evolution in this relationship to z~6. We use these results to revisit recent
estimates of the z>~3 SFR density. One less obvious implication is in
interpreting the high Halpha EWs seen in z~5 galaxies: our results imply that
star-forming galaxies produce Lyman-continuum photons at twice the efficiency
(per unit UV luminosity) as implied in conventional models. Star-forming
galaxies can then reionize the Universe, even if the escape fraction is <10%. | astro-ph_GA |
Powerful H2 Line Cooling in Stephan's Quintet II. Group-wide Gas and
Shock Modeling of the Warm H2 and a Comparison with [CII]157.7um Emission and
Kinematics: We map for the first time the two-dimensional H_2 excitation of warm
intergalactic gas in Stephan's Quintet on group-wide (50 x 35 kpc^2) scales to
quantify the temperature, mass and warm-H_2 mass fraction as a function of
position using Spitzer. Molecular gas temperatures are seen to rise (to T >
700K) and the slope of the power--law density-temperature relation flattens
along the main ridge of the filament, defining the region of maximum heating.
We also performed MHD modeling of the excitation properties of the warm gas, to
map the velocity structure and energy deposition rate of slow and fast
molecular shocks. Slow magnetic shocks were required to explain the power
radiated from the lowest--lying rotational states of H_2, and strongly support
the idea that energy cascades down to small scales and low velocities from the
fast collision of NGC 7318b with group-wide gas. The highest levels of heating
of the warm H_2 is strongly correlated with the large-scale stirring of the
medium as measured by [CII] spectroscopy with Herschel. H_2 is also seen
associated with a separate bridge which extends towards the Seyfert nucleus in
NGC 7319, both from Spitzer and CARMA CO observations. This opens up the
possibility that both galaxy collisions and AGN outflows can turbulently heat
gas on large-scales in compact groups. The observations provide a laboratory
for studying the effects of turbulent energy dissipation on group-wide scales
that may provide clues about the heating and cooling of gas at high-z in early
galaxy and protogalaxy formation. | astro-ph_GA |
Probing star formation and feedback in dwarf galaxies. Integral field
view of the blue compact galaxy Tololo 1937-423: (Abridged) Blue compact galaxies (BCG) are gas-rich, low-mass, small systems
that form stars at unusually high rates. This makes them excellent laboratories
for investigating the process of star-formation (SF) at galactic scales and the
effects of massive stellar feedback on the interstellar (and intergalactic)
medium.
We analyzed the BCG Tololo 1937-423 using optical integral field spectroscopy
with VIMOS at the Very Large Telescope to probe its morphology, stellar
content, nebular excitation and ionization properties, and the kinematics of
its warm ionized gas.
We found that Tololo 1937-423 is currently undergoing an extended starburst,
with nine major $H\alpha$ clumps. The galaxy presents a single continuum peak
that is not cospatial with any knot in emission lines, indicating at least two
relatively recent episodes of SF. The inhomogeneous dust distribution reaches
its maximum roughly at the position of the continuum peak. We found shocked
regions in the galaxy outer regions and at the edges of the SF knots. The
oxygen abundance is similar in all the SF regions, suggesting a chemically
homogeneous ionized interstellar medium over spatial scales of several kpc. The
ionized gas kinematics displays an overall regular rotation around a
northwest-southeast axis.
The morphology of the galaxy and the two different episodes of SF suggest a
scenario of triggered (induced by supernova shock waves) SF acting in Tololo
1937-423. The inferred ages for the different SF episodes (~13-80 Myr for the
central post-starburst and 5-7 Myr for the ongoing SF) are consistent with
triggered SF, with the most recent SF episode caused by the collective effect
of stellar winds and supernova explosions from the central post-starburst. The
velocity dispersion pattern, with higher velocity dispersions found at the
edges of the SF regions, and shocked regions in the galaxy, also favor this
scenario. | astro-ph_GA |
Identification of High-Redshift Galaxy Overdensities in GOODS-N and
GOODS-S: We conduct a systematic search for high-redshift galaxy overdensities at $4.9
< z_{\,\mathrm{spec}} < 8.9$ in both the GOODS-N and GOODS-S fields using
JWST/NIRCam imaging from JADES and JEMS in addition to JWST/NIRCam wide field
slitless spectroscopy from FRESCO. High-redshift galaxy candidates are
identified using HST+JWST photometry spanning $\lambda = 0.4-5.0\
\mu\mathrm{m}$. We confirmed the redshifts for roughly a third of these
galaxies using JWST/FRESCO spectroscopy over $\lambda = 3.9-5.0\ \mu\mathrm{m}$
through identification of either $\mathrm{H} \alpha$ or
$\left[\mathrm{OIII}\right]\lambda5008$ around the best-fit photometric
redshift. The rest-UV magnitudes and continuum slopes of these galaxies were
inferred from the photometry: the brightest and reddest objects appear in more
dense environments and thus are surrounded by more galaxy neighbors than their
fainter and bluer counterparts, suggesting accelerated galaxy evolution within
overdense environments. We find $17$ significant ($\delta_{\mathrm{gal}} \geq
3.04$, $N_{\mathrm{galaxies}} \geq 4$) galaxy overdensities across both fields
($7$ in GOODS-N and $10$ in GOODS-S), including the two highest redshift
spectroscopically confirmed galaxy overdensities to date at $\left<
z_{\mathrm{\,spec}} \right> = 7.955$ and $\left< z_{\mathrm{\,spec}} \right> =
8.222$ (representing densities around $\sim 6$ and $\sim 12$ times that of a
random volume). We estimate the total halo mass of these large-scale structures
to be $11.5 \leq \mathrm{log}_{10}\left(M_{\mathrm{halo}}/M_{\odot}\right) \leq
13.4$ using an empirical stellar mass to halo mass relation, which are likely
underestimates as a result of incompleteness. These protocluster candidates are
expected to evolve into massive galaxy clusters with
$\mathrm{log}_{10}\left(M_{\mathrm{halo}}/M_{\odot}\right) \gtrsim 14$ by $z =
0$. | astro-ph_GA |
The pattern speeds of vertical breathing waves: We measure and compare the pattern speeds of vertical breathing, vertical
bending, and spiral density waves in two isolated N-body+SPH simulations, using
windowed Fourier transforms over 1 Gyr time intervals. We show that the pattern
speeds of the breathing waves match those of the spirals but are different from
those of the bending waves. We also observe matching pattern speeds between the
bar and breathing waves. Our results not only strengthen the case that,
throughout the disc, breathing motions are driven by spirals but indeed that
the breathing motions are part and parcel of the spirals. | astro-ph_GA |
Disk Evolution in W5: Intermediate Mass Stars at 2-5 Myr: We present the results of a survey of young intermediate mass stars (age
$<$~5 Myr, 1.5 $<M_{\star} \leq $ 15 $M_{\odot}$) in the W5 massive star
forming region. We use combined optical, near-infrared and {\it Spitzer} Space
Telescope photometry and optical spectroscopy to define a sample of stars of
spectral type A and B and examine their infrared excess properties. We find
objects with infrared excesses characteristic of optically thick disks, i.e.
Herbig AeBe stars. These stars are rare: $<$1.5% of the entire spectroscopic
sample of A and B stars, and absent among stars more massive than 2.4
$M_\odot$. 7.5% of the A and B stars possess infrared excesses in a variety of
morphologies that suggest their disks are in some transitional phase between an
initial, optically thick accretion state and later evolutionary states. We
identify four morphological classes based on the wavelength dependence of the
observed excess emission above theoretical photospheric levels: (a) the
optically thick disks; (b) disks with an optically thin excess over the
wavelength range 2 to 24 $\micron$, similar to that shown by Classical Be
stars; (c) disks that are optically thin in their inner regions based on their
infrared excess at 2-8 $\micron$ and optically thick in their outer regions
based on the magnitude of the observed excess emission at 24 $\micron$; (d)
disks that exhibit empty inner regions (no excess emission at $\lambda$ $\leq$
8 $\micron$) and some measurable excess emission at 24 $\micron$. A sub-class
of disks exhibit no significant excess emission at $\lambda \leq$ 5.8
$\micron$, have excess emission only in the {\it Spitzer} 8 $\micron$ band and
no detection at 24 $\micron$. We discuss these spectral energy distribution
(SED) types, suggest physical models for disks exhibiting these emission
patterns and additional observations to test these theories. | astro-ph_GA |
Star Formation in a Strongly Magnetized Cloud: We study star formation in the Center Ridge 1 (CR1) clump in the Vela C giant
molecular cloud, selected as a high column density region that shows the lowest
level of dust continuum polarization angle dispersion, likely indicating that
the magnetic field is relatively strong. We observe the source with the ALMA
7m-array at 1.05~mm and 1.3~mm wavelengths, which enable measurements of dust
temperature, core mass and astrochemical deuteration. A relatively modest
number of eleven dense cores are identified via their dust continuum emission,
with masses spanning from 0.17 to 6.7 Msun. Overall CR1 has a relatively low
compact dense gas fraction compared with other typical clouds with similar
column densities, which may be a result of the strong magnetic field and/or the
very early evolutionary stage of this region. The deuteration ratios, Dfrac, of
the cores, measured with N2H+(3-2) and N2D+(3-2) lines, span from 0.011 to
0.85, with the latter being one of the highest values yet detected. The level
of deuteration appears to decrease with evolution from prestellar to
protostellar phase. A linear filament, running approximately parallel with the
large scale magnetic field orientation, is seen connecting the two most massive
cores, each having CO bipolar outflows aligned orthogonally to the filament.
The filament contains the most deuterated core, likely to be prestellar and
located midway between the protostars. The observations permit measurement of
the full deuteration structure of the filament along its length, which we
present. We also discuss the kinematics and dynamics of this structure, as well
as of the dense core population. | astro-ph_GA |
A near-infrared study of the obscured 3C129 galaxy cluster: We present a catalogue of 261 new infrared selected members of the 3C129
galaxy cluster. The cluster, located at $z \approx$ 0.02, forms part of the
Perseus-Pisces filament and is obscured at optical wavelengths due to its
location in the zone of avoidance. We identified these galaxies using the $J-$
and $K-$band imaging data provided by the UKIDSS Galactic Plane Survey within
an area with a radius of $1.1^{\circ}$ centred on the X-ray emission of the
cluster at $\ell, b \approx 160.52^{\circ}, 0.27^{\circ}$. A total of 26 of the
identified galaxy members have known redshifts 24 of which are from our 2016
Westerbork HI survey and two are from optical spectroscopy. An analysis of the
galaxy density at the core of the 3C129 cluster shows it to be less dense than
the Coma and Norma clusters, but comparable to the galaxy density in the core
of the Perseus cluster. From an assessment of the spatial and velocity
distributions of the 3C129 cluster galaxies that have redshifts, we derived a
velocity of $cz = 5227 \pm 171$ km/s and $\sigma = 1097 \pm 252$ km/s for the
main cluster, with a substructure in the cluster outskirts at $cz = 6923 \pm
71$ km/s with $\sigma = 422 \pm 100$ km/s. The presence of this substructure is
consistent with previous claims based on the X-ray analysis that the cluster is
not yet virialised and may have undergone a recent merger. | astro-ph_GA |
Outflow and metallicity in the broad-line region of low-redshift active
galactic nuclei: Outflows in active galactic nuclei (AGNs) are crucial to understand in
investigating the co-evolution of supermassive black holes (SMBHs) and their
host galaxies since outflows may play an important role as an AGN feedback
mechanism. Based on the archival UV spectra obtained with HST and IUE, we
investigate outflows in the broad-line region (BLR) in low-redshift AGNs (z <
0.4) through the detailed analysis of the velocity profile of the CIV emission
line. We find a dependence of the outflow strength on the Eddington ratio and
the BLR metallicity in our low-redshift AGN sample, which is consistent with
the earlier results obtained for high-redshift quasars. These results suggest
that the BLR outflows, gas accretion onto SMBH, and past star-formation
activity in the host galaxies are physically related in low-redshift AGNs as in
powerful high-redshift quasars. | astro-ph_GA |
The Role of Non-ionizing Radiation Pressure in Star Formation: The
Stability of Cores and Filaments: Stars form when filaments and dense cores in molecular clouds fragment and
collapse due to self-gravity. In the most basic analyses of gravitational
stability, the competition between self-gravity and thermal pressure sets the
critical (i.e. maximum stable) mass of spheres and the critical line density of
cylinders. Previous work has considered additional support from magnetic fields
and turbulence. Here, we consider the effects of non-ionizing radiation,
specifically the inward radiation pressure force that acts on dense structures
embedded in an isotropic radiation field. Using hydrostatic, isothermal models,
we find that irradiation lowers the critical mass and line density for
gravitational collapse, and can thus act as a trigger for star formation. For
structures with moderate central densities, $\sim10^3$ cm$^{-3}$, the
interstellar radiation field in the Solar vicinity has an order unity effect on
stability thresholds. For more evolved objects with higher central densities, a
significant lowering of stability thresholds requires stronger irradiation, as
can be found closer to the Galactic center or near stellar associations. Even
when strong sources of ionizing radiation are absent or extincted, our study
shows that interstellar irradiation can significantly influence the star
formation process. | astro-ph_GA |
CO in OH/IR stars close to the Galactic centre: Aims: A pilot project has been carried out to measure circumstellar CO
emission from three OH/IR stars close to the Galactic centre. The intention was
to find out whether it would be possible to conduct a large-scale survey for
mass-loss rates using, for example, the Atacama Large Millimeter Array (ALMA).
Such a survey would increase our understanding of the evolution of the Galactic
bulge.
Methods: Two millimetre-wave instruments were used: the Nobeyama Millimeter
Array at 115 GHz and the Submillimeter Array at 230 GHz. An interferometer is
necessary as a `spatial filter' in this region of space because of the
confusion with interstellar CO emission.
Results: Towards two of the stars, CO emission was detected with positions
and radial velocities coinciding within the statistical errors with the
corresponding data of the associated OH sources. However, for one of the stars
the line profile is not what one expects for an unresolved expanding
circumstellar envelope. We believe that this CO envelope is partially resolved
and that this star therefore is a foreground star not belonging to the bulge.
Conclusions: The results of the observations have shown that it is possible
to detect line profiles of circumstellar CO from late-type stars both within
and in the direction of the Galactic bulge. ALMA will be able to detect CO
emission in short integrations with sensitivity sufficient to estimate
mass-loss rates from a large number of such stars. | astro-ph_GA |
Herschel Observations of the T Cha Transition Disk: Constraining the
Outer Disk Properties: T Cha is a nearby (d = 100 pc) transition disk known to have an optically
thin gap separating optically thick inner and outer disk components. Huelamo et
al. (2011) recently reported the presence of a low-mass object candidate within
the gap of the T Cha disk, giving credence to the suspected planetary origin of
this gap. Here we present the Herschel photometry (70, 160, 250, 350, and 500
micron) of T Cha from the "Dust, Ice, and Gas in Time" (DIGIT) Key Program,
which bridges the wavelength range between existing Spitzer and millimeter data
and provide important constraints on the outer disk properties of this
extraordinary system. We model the entire optical to millimeter wavelength
spectral energy distribution (SED) of T Cha (19 data points between 0.36 and
3300 micron without any major gaps in wavelength coverage). T Cha shows a steep
spectral slope in the far-IR, which we find clearly favors models with outer
disks containing little or no dust beyond 40 AU. The full SED can be modeled
equally well with either an outer disk that is very compact (only a few AU
wide) or a much larger one that has a very steep surface density profile. That
is, T Cha's outer disk seems to be either very small or very tenuous. Both
scenarios suggest a highly unusual outer disk and have important but different
implications for the nature of T Cha. Spatially resolved images are needed to
distinguish between the two scenarios. | astro-ph_GA |
Enhanced X-ray Emission from the Most Radio-Powerful Quasar in the
Universe's First Billion Years: We present deep (265 ks) Chandra X-ray observations of PSO
J352.4034$-$15.3373, a quasar at z=5.831 that, with a radio-to-optical flux
ratio of R>1000, is one of the radio-loudest quasars in the early universe and
is the only quasar with observed extended radio jets of kpc-scale at $z \gtrsim
6$. Modeling the X-ray spectrum of the quasar with a power law, we find a best
fit of $\Gamma = 1.99^{+0.29}_{-0.28}$, leading to an X-ray luminosity of
$L_{2-10} = 1.26^{+0.45}_{-0.33} \times 10^{45}\ {\rm erg}\ {\rm s}^{-1}$ and
an X-ray to UV brightness ratio of $\alpha_{\rm OX} = -1.36 \pm 0.11$. We
identify a diffuse structure 50 kpc (${\sim}8^{\prime\prime}$) to the NW of the
quasar along the jet axis that corresponds to a $3\sigma$ enhancement in the
angular density of emission and can be ruled out as a background fluctuation
with a probability of P=0.9985. While with few detected photons the spectral
fit of the structure is uncertain, we find that it has a luminosity of
$L_{2-10}\sim10^{44}\ {\rm erg}\ {\rm s}^{-1}$. These observations therefore
potentially represent the most distant quasar jet yet seen in X-rays. We find
no evidence for excess X-ray emission where the previously-reported radio jets
are seen (which have an overall linear extent of $0.^{\prime\prime}28$), and a
bright X-ray point source located along the jet axis to the SE is revealed by
optical and NIR imaging to not be associated with the quasar. | astro-ph_GA |
Imprints of interaction processes in the globular cluster system of NGC
3640: We present a wide-field study of the globular cluster systems (GCS) of the
elliptical galaxy NGC 3640 and its companion NGC 3641, based on observations
from Gemini Multi-Object Spectrograph/Gemini. NGC 3640 is a shell galaxy which
presents a complex morphology, which previous studies have indicated as the
sign of a recent 'dry' merger, although whether its nearest neighbour could
have influenced these substructures remains an open question. In this work, we
trace the spatial distribution of the globular clusters (GCs) as well as their
colour distribution, finding a potential bridge of red GCs that connects NGC
3640 to its less massive companion, and signs that the blue GCs were spatially
disturbed by the event that created the shells. | astro-ph_GA |
The Carina Project. VIII. The α-element abundances: We have performed a new abundance analysis of Carina Red Giant (RG) stars
from spectroscopic data collected with UVES (high resolution) and
FLAMES/GIRAFFE (high and medium resolution) at ESO/VLT. The former sample
includes 44 RGs, while the latter consists of 65 (high) and ~800 (medium
resolution) RGs, covering a significant fraction of the galaxy's RG branch
(RGB), and red clump stars. To improve the abundance analysis at the faint
magnitude limit, the FLAMES/GIRAFFE data were divided into ten surface gravity
and effective temperature bins. The spectra of the stars belonging to the same
gravity/temperature bin were stacked. This approach allowed us to increase by
at least a factor of five the signal-to-noise ratio in the faint limit
(V>20.5mag). We took advantage of the new photometry index cU,B,I introduced by
Monelli et al. (2014), as an age and probably a metallicity indicator, to split
stars along the RGB. These two stellar populations display distinct [Fe/H] and
[Mg/H] distributions: their mean Fe abundances are -2.15$\pm$0.06dex
(sig=0.28), and -1.75$\pm$0.03dex (sig=0.21), respectively. The two iron
distributions differ at the 75% level. This supports preliminary results by
Lemasle et al. (2012) and by Monelli et al. (2014). Moreover, we found that the
old and intermediate-age stellar populations have mean [Mg/H] abundances of
-1.91$\pm$0.05dex (sig=0.22) and -1.35$\pm$0.03dex (sig=0.22); these differ at
the 83% level. Carina's {\alpha}-element abundances agree, within 1sigma, with
similar abundances for field Halo stars and for cluster (Galactic, Magellanic)
stars. The same outcome applies to nearby dwarf spheroidals and ultra-faint
dwarf galaxies, in the iron range covered by Carina stars. Finally, we found
evidence of a clear correlation between Na and O abundances, thus suggesting
that Carina's chemical enrichment history is quite different than in the
globular clusters. | astro-ph_GA |
On the carriers of the 3.4-micrometer absorption and emission bands, and
their evolution: Based on the results of chemical analysis and simulation of kerogens and
immature coals, a large number of chemical structures carrying the 3.4-mum
feature were studied by means of computer simulation codes. Further selection
criteria were the integrated strength of the absorption lines in the aliphatic
stretchings wavelength band, weak IR activity in the aromatic stretching band
and absence of notable activity outside the astronomical UIBs (Unidentified
Infrared Bands). Most of the structures that were retained can be classed as
branched, short and oxygen-bridged CH_{2} chains, and naphtenic chains.
Combinations of their absorption spectra deliver spectra comparable to those
observed in the sky. Absorption spectra were derived from Normal Mode Analysis.
Emission spectra of the same structures were computed by monitoring their
overall dipole moment as they vibrate freely in vacuum after excitation. These
spectra were then combined in suitable proportions, together with those of
aromatic structures, so as to simulate various typical near IR emission spectra
observed in the sky. | astro-ph_GA |
Gentle heating by mixing in cooling flow clusters: We analyze three-dimensional hydrodynamical simulations of the interaction of
jets and the bubbles they inflate with the intra-cluster medium (ICM), and show
that the heating of the ICM by mixing hot bubble gas with the ICM operates over
tens of millions of years, and hence can smooth the sporadic activity of the
jets. The inflation process of hot bubbles by propagating jets forms many
vortices, and these vortices mix the hot bubble gas with the ICM. The mixing,
hence the heating of the ICM, starts immediately after the jets are launched,
but continues for tens of millions of years. We suggest that the smoothing of
the active galactic nucleus (AGN) sporadic activity by the long-lived vortices
accounts for the recent finding of a gentle energy coupling between AGN heating
and the ICM. | astro-ph_GA |
Probing The Ultraviolet Luminosity Function of the Earliest Galaxies
with the Renaissance Simulations: In this paper, we present the first results from the Renaissance Simulations,
a suite of extremely high-resolution and physics-rich AMR calculations of high
redshift galaxy formation performed on the Blue Waters supercomputer. These
simulations contain hundreds of well-resolved galaxies at $z \sim 25-8$, and
make several novel, testable predictions. Most critically, we show that the
ultraviolet luminosity function of our simulated galaxies is consistent with
observations of high-z galaxy populations at the bright end of the luminosity
function (M$_{1600} \leq -17$), but at lower luminosities is essentially flat
rather than rising steeply, as has been inferred by Schechter function fits to
high-z observations, and has a clearly-defined lower limit in UV luminosity.
This behavior of the luminosity function is due to two factors: (i) the strong
dependence of the star formation rate on halo virial mass in our simulated
galaxy population, with lower-mass halos having systematically lower star
formation rates and thus lower UV luminosities; and (ii) the fact that halos
with virial masses below $\simeq 2 \times 10^8$ M$_\odot$ do not universally
contain stars, with the fraction of halos containing stars dropping to zero at
$\simeq 7 \times 10^6$ M$_\odot$. Finally, we show that the brightest of our
simulated galaxies may be visible to current and future ultra-deep space-based
surveys, particularly if lensed regions are chosen for observation. | astro-ph_GA |
An evolutionary continuum from nucleated dwarf galaxies to star clusters: Systematic studies have revealed hundreds of ultra-compact dwarf galaxies
(UCDs) in the nearby Universe. With half-light radii $r_h$ of approximately
10-100 parsecs and stellar masses $M_*$ $\approx$ $10^6-10^8$ solar masses,
UCDs are among the densest known stellar systems. Although similar in
appearance to massive globular clusters, the detection of extended stellar
envelopes, complex star formation histories, elevated mass-to-light ratio, and
supermassive black holes suggest that some UCDs are remnant nuclear star
clusters of tidally-stripped dwarf galaxies, or even ancient compact galaxies.
However, only a few objects have been found in the transient stage of tidal
stripping, and this assumed evolutionary path has never been fully traced by
observations. Here we show that 106 galaxies in the Virgo cluster have
morphologies that are intermediate between normal, nucleated dwarf galaxies and
single-component UCDs, revealing a continuum that fully maps this morphological
transition, and fills the `size gap' between star clusters and galaxies. Their
spatial distribution and redder color are also consistent with stripped
satellite galaxies on their first few pericentric passages around massive
galaxies. The `ultra-diffuse' tidal features around several of these galaxies
directly show how UCDs are forming through tidal stripping, and that this
evolutionary path can include an early phase as a nucleated ultra-diffuse
galaxy (UDG). These UCDs represent substantial visible fossil remnants of
ancient dwarf galaxies in galaxy clusters, and more low-mass remnants probably
remain to be found. | astro-ph_GA |
Post-Starburst Galaxies in SDSS-IV MaNGA: Post-starburst galaxies, identified by their unusually strong Balmer
absorption lines and weaker than average emission lines, have traditionally
been selected based on their central stellar populations. Here we identify 360
galaxies with post-starburst regions from the MaNGA integral field survey and
classify these galaxies into three types: 31 galaxies with central
post-starburst regions (CPSB), 37 galaxies with off-center ring-like
post-starburst regions (RPSB) and 292 galaxies with irregular post-starburst
regions (IPSB). Focussing on the CPSB and RPSB samples, and comparing their
radial gradients in D$_n$4000, H$\delta_{\rm A}$ and W(H$\alpha$) to control
samples, we find that while the CPSBs have suppressed star formation throughout
their bulge and disk, and clear evidence of rapid decline of star formation in
the central regions, the RPSBs only show clear evidence of recently rapidly
suppressed star formation in their outer regions and an ongoing central
starburst. The radial profiles in mass-weighted age and stellar $v/\sigma$
indicate that CPSBs and RPSBs are not simply different evolutionary stages of
the same event, rather that CPSB galaxies are caused by a significant
disruptive event, while RPSB galaxies are caused by disruption of gas fuelling
to the outer regions. Compared to the control samples, both CPSB and RPSB
galaxies show a higher fraction of interactions/mergers, misaligned gas or bars
that might be the cause of the gas inflows and subsequent quenching. | astro-ph_GA |
MIGHTEE-HI: the HI Size-Mass relation over the last billion years: We present the observed HI size-mass relation of $204$ galaxies from the
MIGHTEE Survey Early Science data. The high sensitivity of MeerKAT allows us to
detect galaxies spanning more than 4 orders of magnitude in HI mass, ranging
from dwarf galaxies to massive spirals, and including all morphological types.
This is the first time the relation has been explored on a blind homogeneous
data set which extends over a previously unexplored redshift range of $0 < z <
0.084$, i.e. a period of around one billion years in cosmic time. The sample
follows the same tight logarithmic relation derived from previous work, between
the diameter ($D_{\rm HI}$) and the mass ($M_{\rm HI}$) of HI discs. We measure
a slope of $0.501\pm 0.008$, an intercept of $-3.252^{+0.073}_{-0.074}$, and an
observed scatter of $0.057$ dex. For the first time, we quantify the intrinsic
scatter of $0.054 \pm 0.003$ dex (${\sim} 10 \%$), which provides a constraint
for cosmological simulations of galaxy formation and evolution. We derive the
relation as a function of galaxy type and find that their intrinsic scatters
and slopes are consistent within the errors. We also calculate the $D_{\rm HI}
- M_{\rm HI}$ relation for two redshift bins and do not find any evidence for
evolution with redshift. These results suggest that over a period of one
billion years in lookback time, galaxy discs have not undergone significant
evolution in their gas distribution and mean surface mass density, indicating a
lack of dependence on both morphological type and redshift. | astro-ph_GA |
The GALAH survey: Elemental abundances in open clusters using joint
effective temperature and surface gravity photometric priors: The ability to measure precise and accurate stellar effective temperatures
($T_{\rm{eff}}$) and surface gravities ($\log(g)$) is essential in determining
accurate and precise abundances of chemical elements in stars. Measuring
$\log(g)$ from isochrones fitted to colour-magnitude diagrams of open clusters
is significantly more accurate and precise compared to spectroscopic $\log(g)$.
By determining the ranges of ages, metallicity, and extinction of isochrones
that fit the colour-magnitude diagram, we constructed a joint probability
distribution of $T_{\rm{eff}}$ and $\log(g)$. The joint photometric probability
shows the complex correlations between $T_{\rm{eff}}$ and $\log(g)$, which
depend on the evolutionary stage of the star. We show that by using this
photometric prior while fitting spectra, we can acquire more precise
spectroscopic stellar parameters and abundances of chemical elements. This
reveals higher-order abundance trends in open clusters like traces of atomic
diffusion. We used photometry and astrometry provided by the \textit{Gaia} DR3
catalogue, Padova isochrones, and Galactic Archaeology with HERMES (GALAH) DR4
spectra. We analysed the spectra of 1979 stars in nine open clusters, using
MCMC to fit the spectroscopic abundances of 26 elements, $T_{\rm{eff}}$,
$\log(g)$, $v_{\rm{mic}}$, and $v_{\rm{broad}}$. We found that using
photometric priors improves the accuracy of abundances and $\log(g)$, which
enables us to view higher-order trends of abundances caused by atomic diffusion
in M67 and Ruprecht 147. | astro-ph_GA |
Galactic Orbital Effects on Pulsar Timing: In the currently accepted paradigm, dark matter is hypothesized as an
explanation of the flat rotation curves of galaxies under the assumption of
virialized orbits. The use of millisecond pulsar timing as a probe of Galactic
dark matter content is explored as a means of relaxing this assumption. A
method of inference of the Galactic potential using the frequency derivative
$\dot{\nu}$ is produced, and an estimate for a virialized Galactic rotation
curve is given through direct observation of acceleration. The data set used
includes 210 pulsars with known $\dot{\nu}$ and astrometric properties, a
subset of which also have measured $\ddot{\nu}$. In principle, this enables the
exploration of kinematic effects, but in practice, $\ddot{\nu}$ values are
found to be too imprecise at present to adequately constrain radial velocities
of pulsars. Additionally, surface magnetic field strengths are inferred from
$\dot{\nu}$ and the magnetic spin-down contribution to $\ddot{\nu}$ is
estimated. For several pulsars the radial velocity is known, and the kinematic
contribution to $\ddot{\nu}$ is estimated accordingly. The binary orbital
periods of PSR J1713+0747 and other binary pulsars are also used to constrain
Galactic mass density models. | astro-ph_GA |
Stellar population analysis of MaNGA early-type galaxies: IMF dependence
and systematic effects: We study systematics associated with estimating simple stellar population
(SSP) parameters -- age, metallicity [M/H], $\alpha$-enhancement [$\alpha$/Fe]
and IMF shape -- and associated $M_*/L$ gradients, of elliptical slow rotators
(E-SRs), fast rotators (E-FRs) and S0s from stacked spectra of galaxies in the
MaNGA survey. These systematics arise from (i) how one normalizes the spectra
when stacking; (ii) having to subtract emission before estimating absorption
line strengths; (iii) the decision to fit the whole spectrum or just a few
absorption lines; (iv) SSP model differences (e.g. isochrones, enrichment,
IMF). The MILES+Padova SSP models, fit to the H$_\beta$, $\langle$Fe$\rangle$,
TiO$_{\rm 2SDSS}$ and [MgFe] Lick indices in the stacks, indicate that out to
the half-light radius $R_e$: (a) ages are younger and [$\alpha$/Fe] values are
lower in the central regions but the opposite is true of [M/H]; (b) the IMF is
more bottom-heavy in the center, but is close to Kroupa beyond about $R_e/2$;
(c) this makes $M_*/L$ about $2\times$ larger in the central regions than
beyond $R_e/2$. While the models of Conroy et al. (2018) return similar [M/H]
and [$\alpha$/Fe] profiles, the age and (hence) $M_*/L$ profiles can differ
significantly even for solar abundances and a Kroupa IMF; different responses
to non-solar abundances and IMF parametrization further compound these
differences. There are clear (model independent) differences between E-SRs,
E-FRs and S0s: younger ages and less enhanced [$\alpha$/Fe] values suggest that
E-FRs and S0s are not SSPs, but relaxing this assumption is unlikely to change
their inferred $M_*/L$ gradients significantly. | astro-ph_GA |
Bipolar Outflows out to 10~kpc for Massive Galaxies at Redshift
$z\approx 1$: Galactic outflows are believed to play a critical role in the evolution of
galaxies by regulating their mass build-up and star formation. Theoretical
models assumes bipolar shapes for the outflows that extends well into the
circumgalctic medium (CGM), up to tens of kpc perpendicular to the galaxies.
They have been directly observed in the local Universe in several individual
galaxies, e.g., around the Milky Way and M82. At higher redshifts, cosmological
simulations of galaxy formation predict an increase in the frequency and
efficiency of galactic outflows due to the increasing star formation activity.
Outflows are responsible for removing potential fuel for star formation from
the galaxy, while at the same enriching the CGM and the intergalactic medium.
These feedback processes, although incorporated as key elements of cosmological
simulations, are still poorly constrained on CGM scales. Here we present an
ultra-deep MUSE image of the mean MgII emission surrounding a sample of
galaxies at z~1 that strongly suggests the presence of outflowing gas on
physical scales of more than 10kpc. We find a strong dependence of the detected
signal on the inclination of the central galaxy, with edge-on galaxies clearly
showing enhanced MgII emission along the minor axis, while face-on galaxies
display much weaker and more isotropic emission. We interpret these findings as
supporting the idea that outflows typically have a bipolar cone geometry
perpendicular to the galactic disk. We demonstrate that the signal is not
dominated by a few outliers. After dividing the galaxy sample in subsamples by
mass, the bipolar emission is only detected in galaxies with stellar mass
$\mathrm{M_* \gtrsim 10^{9.5} M_\odot}$. | astro-ph_GA |
Metal flows of the circumgalactic medium, and the metal budget in
galactic halos: We present an analysis of the flow of metals through the circumgalactic
medium (CGM) in the Feedback in Realistic Environments (FIRE) simulations of
galaxy formation, ranging from isolated dwarfs to $L*$ galaxies. We find that
nearly all metals produced in high-redshift galaxies are carried out in winds
that reach $0.25 R_{\rm vir}$. When measured at $0.25 R_{\rm vir}$ the
metallicity of outflows is slightly higher than the interstellar medium (ISM)
metallicity. Many metals thus reside in the CGM. Cooling and recycling from
this reservoir determine the metal budget in the ISM. The outflowing metal flux
decreases by a factor of $\sim2-5$ between $0.25 R_{\rm vir}$ and $R_{\rm
vir}$. Furthermore, outflow metallicity is typically lower at $R_{\rm vir}$
owing to dilution of the remaining outflow by metal-poor material swept up from
the CGM. The inflow metallicity at $R_{\rm vir}$ is generally low, but outflow
and inflow metallicities are similar in the inner halo. At low redshift,
massive galaxies no longer generate outflows that reach the CGM, causing a
divergence in CGM and ISM metallicity. Dwarf galaxies continue to generate
outflows, although they preferentially retain metal ejecta. In all but the
least massive galaxy considered, a majority of the metals are within the halo
at $z=0$. We measure the fraction of metals in CGM, ISM and stars, and quantify
the thermal state of CGM metals in each halo. The total amount of metals in the
low-redshift CGM of two simulated $L*$ galaxies is consistent with estimates
from the COS halos survey, while for the other two it appears to be lower. | astro-ph_GA |
Increasing the Scientific Return of Stellar Orbits at the Galactic
Center: We report a factor of $\sim$3 improvement in Keck Laser Guide Star Adaptive
Optics (LGSAO) astrometric measurements of stars near the Galaxy's supermassive
black hole (SMBH). By carrying out a systematic study of M92, we have produced
a more accurate model for the camera's optical distortion. Updating our
measurements with this model, and accounting for differential atmospheric
refraction, we obtain estimates of the SMBH properties that are a factor of
$\sim$2 more precise, and most notably, increase the likelihood that the black
hole is at rest with respect to the nuclear star cluster. These improvements
have also allowed us to extend the radius to which stellar orbital parameter
estimates are possible by a factor of 2. | astro-ph_GA |
The Presence of Weak Active Galactic Nuclei in High Redshift Star
Forming Galaxies: We present [OIII 5007A] observations of the star forming galaxy HDF-BMZ1299
(z=1.598) using Keck Observatory's Adaptive Optics system with the
near-infrared integral field spectrograph OSIRIS. Using previous Halpha and
[NII] measurements of the same source, we are able for the first time to use
spatially resolved observations to place a high-redshift galaxy's substructure
on a traditional HII diagnostic diagram. We find that HDF-BMZ1299's spatially
concentrated nebular ratios in the central ~1.5 kiloparsec (0."2) are best
explained by the presence of an AGN: log([NII]/Halpha)=-0.22+/-0.05 and 2sigma
limit of log([OIII]/Hbeta)>0.26. The dominant energy source of this galaxy is
star formation, and integrating a single aperture across the galaxy yields
nebular ratios that are composite spectra from both AGN and HII regions. The
presence of an embedded AGN in HDF-BMZ1299 may suggest a potential
contamination in a fraction of other high-redshift star forming galaxies, and
we suggest that this may be a source of the "elevated" nebular ratios
previously seen in seeing-limited metallicity studies. HDF-BMZ1299's estimated
AGN luminosity is L_Halpha = 3.7e41 erg/s and L_[OIII] = 5.8e41 erg/s, making
it one of the lowest luminosity AGN discovered at this early epoch. | astro-ph_GA |
CO, H2O, H2O+ line and dust emission in a z = 3.63 strongly lensed
starburst merger at sub-kiloparsec scales: Using ALMA, we report high angular-resolution observations of the redshift
z=3.63 galaxy, G09v1.97, one of the most luminous strongly lensed galaxies
discovered by the H-ATLAS survey. We present 0"2-0"4 resolution images of the
rest-frame 188 and 419$\mu$m dust continuum and the CO(6-5), H2O(211-202) and
J=2 H2O+ line emission. We also report the detection of H$_2^{18}$O in this
source. The dust continuum and molecular gas emission are resolved into a
nearly complete ~1"5 diameter Einstein ring plus a weaker image in the center,
which is caused by a special dual deflector lensing configuration. The observed
line profiles of the CO, H2O and H2O+ lines are strikingly similar. In the
source plane, we reconstruct the dust continuum images and the spectral cubes
of the line emission at sub-kpc scales. The reconstructed dust emission in the
source plane is dominated by a compact disk with an effective radius of 0.7kpc
plus an overlapping extended disk with a radius twice as large. While the
average magnification for the dust continuum is $\mu$~10-11, the magnification
of the line emission varies 5 to 22 across different velocity components. The
emission lines have similar spatial and kinematic distributions. The molecular
gas and dust content reveal that G09v1.97 is a gas-rich major merger in its
pre-coalescence phase. Both of the merging companions are intrinsically ULIRGs
with LIR reaching $\gtrsim 4\times10^{12}L_\odot$, and the total LIR of
G09v1.97 is $1.4\times10^{13}L_\odot$. The approaching southern galaxy shows no
obvious kinematic structure with a semi-major half-light radius a_s=0.4kpc,
while the receding galaxy resembles an a_s=1.2kpc rotating disk. The two
galaxies are separated by a projected distance of 1.3kpc, bridged by weak line
emission that is co-spatially located with the cold-dust-emission peak,
suggesting a large amount of cold ISM in the interacting region. (abridged) | astro-ph_GA |
Planetary Nebula Candidates Uncovered with the HASH Research Platform: A detailed examination of new high quality radio catalogues (e.g. Cornish) in
combination with available mid-infrared (MIR) satellite imagery (e.g. Glimpse)
has allowed us to find 70 new planetary nebula (PN) candidates based on
existing knowledge of their typical colors and fluxes. To further examine the
nature of these sources, multiple diagnostic tools have been applied to these
candidates based on published data and on available imagery in the HASH (Hong
Kong/ AAO/ Strasbourg H{\alpha} planetary nebula) research platform. Some
candidates have previously-missed optical counterparts allowing for
spectroscopic follow-up. Indeed, the single object spectroscopically observed
so far has turned out to be a bona fide PN. | astro-ph_GA |
New insights on the recoiling/binary black hole candidate J0927+2943 via
molecular gas observations: The peculiar QSO J0927+2943 shows multiple sets of emission lines in its
optical spectrum. This signature has been interpreted as the relative motion
between a black hole, either recoiling or bound in a binary system, and its
host galaxy, or as a superposition of two galaxies along the line of sight. In
order to test these scenarios, we have collected 2mm CO(2-1) observations using
the IRAM Plateau de Bure Interferometer, and optical images and spectroscopy at
the Calar Alto observatory. Together with archival HST images, these data
provide unique insights on the nature of this system. The recoiling/binary
black hole scenarios are ruled out by the clear detection of a galactic-scale
molecular gas reservoir at the same redshift of the QSO broad lines. The
observations presented here also disfavour the superposition model, although
with less constraints. Thus, the origin of the second, bright set of narrow
emission lines in J0927+2943 is still unknown. | astro-ph_GA |
AGN feedback duty cycle in Planck SZ selected clusters using Chandra
observations: We present a systematic study of X-ray cavities using archival Chandra
observations of nearby galaxy clusters selected by their Sunyaev-Zel'dovich
(SZ) signature in the Planck survey, which provides a nearly unbiased
mass-selected sample to explore the entire AGN feedback duty cycle. Based on
X-ray image analysis, we report that 30 of the 164 clusters show X-ray
cavities, which corresponds to a detection fraction of 18%. After correcting
for spatial resolution to match the high-$z$ SPT-SZ sample, the detection
fraction decreases to 9%, consistent with the high-z sample, hinting that the
AGN feedback has not evolved across almost 8 Gyrs. Our finding agrees with the
lack of evolution of cool-core clusters fraction. We calculate the cavity
power, P_{\rm cav}, and find that most systems of our sample have enough AGN
heating to offset the radiative losses of the intracluster medium. | astro-ph_GA |
Binary Frequencies in Globular Clusters: Binary stars are predicted to have an important role in the evolution of
globular clusters, so we obtained binary fractions for 35 globular clusters
that were imaged in the F606W and F814W with the ACS on the Hubble Space
Telescope. When compared to the values of prior efforts (Sollima et al. 2007;
Milone et al. 2012), we find significant discrepancies, despite each group
correcting for contamination effects and having performed the appropriate
reliability tests. The most reliable binary fractions are obtained when
restricting the binary fraction to q > 0.5. Our analysis indicates that the
range of the binary fractions is nearly an order of magnitude for the lowest
dynamical ages, suggesting that there is a broad distribution in the binary
fraction at globular cluster formation. Dynamical effects also appears to
decrease the core binary fractions by a factor of two over a Hubble time, but
this is a weak relationship. We confirm a correlation from previous work that
the binary fraction within the core radius decreases with cluster age,
indicating that younger clusters formed with higher binary fractions. The
strong radial gradient in the binary fraction with cluster radius appears to be
a consequence of dynamical interactions. It is often not present in dynamically
young clusters but nearly always present in dynamically old clusters. | astro-ph_GA |
Origin of reduced dynamical friction by dark matter halos with net
prograde rotation: We provide an explanation for the reduced dynamical friction on galactic bars
in spinning dark matter halos. Earlier work based on linear theory predicted an
increase in dynamical friction when dark halos have a net forward rotation,
because prograde orbits couple to bars with greater strength than retrograde
orbits. Subsequent numerical studies, however, found the opposite trend:
dynamical friction weakens with increasing spin of the halo. We revisit this
problem and demonstrate that linear theory in fact correctly predicts a reduced
torque in forward-rotating halos. We show that shifting the halo mass from
retrograde to prograde phase space generates a positive gradient in the
distribution function near the origin of the z-angular momentum (Lz=0), which
results in a resonant transfer of Lz to the bar, making the net dynamical
friction weaker. While this effect is subdominant for the major resonances,
including the corotation resonance, it leads to a significant positive torque
on the bar for the series of direct radial resonances, as these resonances are
strongest at Lz=0. The overall dynamical friction from spinning halos is shown
to decrease with the halo's spin, in agreement with the secular behavior of
N-body simulations. We validate our linear calculation by computing the
nonlinear torque from individual resonances using the angle-averaged
Hamiltonian. | astro-ph_GA |
Multi-Element Abundance Measurements from Medium-Resolution Spectra. IV.
Alpha Element Distributions in Milky Way Dwarf Satellite Galaxies: We derive the star formation histories of eight dwarf spheroidal (dSph) Milky
Way satellite galaxies from their alpha element abundance patterns. Nearly 3000
stars from our previously published catalog (Paper II) comprise our data set.
The average [alpha/Fe] ratios for all dSphs follow roughly the same path with
increasing [Fe/H]. We do not observe the predicted knees in the [alpha/Fe] vs.
[Fe/H] diagram, corresponding to the metallicity at which Type Ia supernovae
begin to explode. Instead, we find that Type Ia supernova ejecta contribute to
the abundances of all but the most metal-poor ([Fe/H] < -2.5) stars. We have
also developed a chemical evolution model that tracks the star formation rate,
Types II and Ia supernova explosions, and supernova feedback. Without metal
enhancement in the supernova blowout, massive amounts of gas loss define the
history of all dSphs except Fornax, the most luminous in our sample. All six of
the best-fit model parameters correlate with dSph luminosity but not with
velocity dispersion, half-light radius, or Galactocentric distance. | astro-ph_GA |
High-quality strong lens candidates in the final Kilo Degree survey
footprint: We present 97 new high-quality strong lensing candidates found in the final
$\sim 350\,\rm deg^2$, that completed the full $\sim 1350\,\rm deg^2$ area of
the Kilo-Degree Survey (KiDS). Together with our previous findings, the final
list of high-quality candidates from KiDS sums up to 268 systems. The new
sample is assembled using a new Convolutional Neural Network (CNN) classifier
applied to $r$-band (best seeing) and $g,~r,~i$ color-composited images
separately. This optimizes the complementarity of the morphology and color
information on the identification of strong lensing candidates. We apply the
new classifiers to a sample of luminous red galaxies (LRGs) and a sample of
bright galaxies (BGs) and select candidates that received a high probability to
be a lens from the CNN ($P_{\rm CNN}$). In particular, setting $P_{\rm
CNN}>0.8$ for the LRGs, the $1$-band CNN predicts 1213 candidates, while the
$3$-band classifier yields 1299 candidates, with only $\sim$30\% overlap. For
the BGs, in order to minimize the false positives, we adopt a more conservative
threshold, $P_{\rm CNN} >0.9$, for both CNN classifiers. This results in 3740
newly selected objects. The candidates from the two samples are visually
inspected by 7 co-authors to finally select 97 "high-quality" lens candidates
which received mean scores larger than 6 (on a scale from 0 to 10). We finally
discuss the effect of the seeing on the accuracy of CNN classification and
possible avenues to increase the efficiency of multi-band classifiers, in
preparation of next-generation surveys from ground and space. | astro-ph_GA |
Rapid dynamical mass segregation and properties of fractal star clusters: We investigate the evolution of young star clusters using N-body simulations.
We confirm that subvirial and fractal-structured clusters will dynamically mass
segregate on a short timescale (within 0.5 Myr). We adopt a modified
minimum-spanning-tree (MST) method to measure the degree of mass segregation,
demonstrating that the stars escaping from a cluster's potential are important
for the temporal dependence of mass segregation in the cluster. The form of the
initial velocity distribution will also affect the degree of mass segregation.
If it depends on radius, the outer parts of the cluster would expand without
undergoing collapse. In velocity space, we find 'inverse mass segregation,'
which indicates that massive stars have higher velocity dispersions than their
lower-mass counterparts. | astro-ph_GA |
The Universe is at Most 88% Neutral at z=10.6: Recent observations of GN-z11 with JWST have revealed a Ly$\alpha$ emission
line with an equivalent width of 18$\pm 2$ angstroms. At z=10.6, this galaxy is
expected to lie in the heart of reionization. We use a series of inhomogeneous
reionization simulations to derive the distribution of the Ly$\alpha$ EW after
traveling through the neutral intergalactic medium with varying average neutral
gas fraction, $x_{HI}$. We use these distribution to place an upper limit of
$x_{HI} < $ 0.88 at z=10.6 at 95% confidence level. We compare our upper limit
to different reionization history models, which include the recently identified
enhancement at the bright end of the luminosity function at z>8. We find that
models in which faint galaxies have higher escape fraction compared to bright
galaxies are favored by the new data. | astro-ph_GA |
Ionization compression impact on dense gas distribution and star
formation, Probability density functions around H ii regions as seen by
Herschel: Ionization feedback should impact the probability distribution function (PDF)
of the column density around the ionized gas. We aim to quantify this effect
and discuss its potential link to the Core and Initial Mass Function (CMF/IMF).
We used in a systematic way Herschel column density maps of several regions
observed within the HOBYS key program: M16, the Rosette and Vela C molecular
cloud, and the RCW 120 H ii region. We fitted the column density PDFs of all
clouds with two lognormal distributions, since they present a double-peak or
enlarged shape in the PDF. Our interpretation is that the lowest part of the
column density distribution describes the turbulent molecular gas while the
second peak corresponds to a compression zone induced by the expansion of the
ionized gas into the turbulent molecular cloud. The condensations at the edge
of the ionized gas have a steep compressed radial profile, sometimes
recognizable in the flattening of the power-law tail. This could lead to an
unambiguous criterion able to disentangle triggered from pre-existing star
formation. In the context of the gravo-turbulent scenario for the origin of the
CMF/IMF, the double peaked/enlarged shape of the PDF may impact the formation
of objects at both the low-mass and the high-mass end of the CMF/IMF. In
particular a broader PDF is required by the gravo-turbulent scenario to fit
properly the IMF with a reasonable initial Mach number for the molecular cloud.
Since other physical processes (e.g. the equation of state and the variations
among the core properties) have already been suggested to broaden the PDF, the
relative importance of the different effects remains an open question. | astro-ph_GA |
Exploring AGN - starburst coexistence in galaxies at z$\sim$ 0.8 by the
[OIII]4959+5007/[OIII]4363 line ratio: We analyze by detailed modelling the spectra observed from the sample
galaxies at z$\sim$0.8 presented by Ly et al (2015), constraining the models by
the [OIII]5007+4959/[OIII]4363 line ratios. Composite models accounting for
shock and photoionization by AGN or starburst are adopted. O/H are about solar
for all the objects, except for a few AGN clouds with O/H= 0.3 -0.5 solar.
Starburst models reproduce most of the data within the observational errors.
About half of the object spectra are well fitted by an accreting AGN. Some
galaxies show multiple radiation sources, such as starburst+AGN, or a double
AGN. | astro-ph_GA |
A Photometric and Kinematic Analysis of UDG1137+16 (dw1137+16): Probing
Ultra-Diffuse Galaxy Formation in a Group Environment: The dominant physical formation mechanism(s) for ultra-diffuse galaxies
(UDGs) is still poorly understood. Here, we combine new, deep imaging from the
Jeanne Rich Telescope with deep integral field spectroscopy from the Keck II
telescope to investigate the formation of UDG1137+16 (dw1137+16). Our new
analyses confirm both its environmental association with the low density UGC
6594 group, along with its large size of 3.3 kpc and status as a UDG. The new
imaging reveals two distinct stellar components for UDG1137+16, indicating that
a central stellar body is surrounded by an outer stellar envelope undergoing
tidal interaction. Both the components have approximately similar stellar
masses. From our integral field spectroscopy we measure a stellar velocity
dispersion within the half-light radius (15 $\pm$ 4 $\mathrm{km\ s^{-1}}$) and
find that UDG1137+16 is similar to some other UDGs in that it is likely dark
matter dominated. Incorporating literature measurements, we also examine the
current state of UDG observational kinematics. Placing these data on the
central stellar velocity dispersion -- stellar mass relation, we suggest there
is little evidence for UDG1137+16 being created through a strong tidal
interaction. Finally, we investigate the constraining power current dynamical
mass estimates (from stellar and globular cluster velocity dispersions) have on
the total halo mass of UDGs. As most are measured within the half-light radius,
they are unable to accurately constrain UDG total halo masses. | astro-ph_GA |
Physical properties of circumnuclear ionising clusters. II. NGC 7469: Circumnuclear star forming regions (CNSFR) are massive clusters found close
to galactic nuclei. These entities give us an excellent opportunity to study
star formation in environments with high metallicity and to relate it with
active galactic nuclei. Our principal aim is to derive the physical properties
and dynamical masses of the CNSFRs in the two rings of the spiral NGC 7469,
categorized as a Luminous Infrared Galaxy (ULIRG) and hosting a Seyfert 1
nucleus. We have used archival data obtained with the MUSE spectrograph
attached to one of the ESO VLT telescopes and we have applied the techniques
shown in the first paper of the series. Regions in the studied galaxy show
large sizes which can be explained by the stellar winds produced by WR stars.
The inner ring regions seem to be more compact than the outer ones, showing
higher electron densities and filling factors. The young stellar population of
the clusters has contributions of ionising populations with ages around 5 Ma
and its masses constitute less than a 1\% of the total mass of each cluster.
The inner ring regions which are close to the active galactic nucleus probably
are the only ones that have enough mass to survive the action of the AGN. They
constitute the $\sim$ 90 \% of the total inner ring mass. | astro-ph_GA |
First images of the molecular gas around a born-again star revealed by
ALMA: Born-again stars allow probing stellar evolution in human timescales and
provide the most promising path for the formation of hydrogen-deficient
post-asymptotic giant branch objects, but their cold and molecular components
remain poorly explored. Here we present ALMA observations of V605 Aql that
unveil for the first time the spatio-kinematic distribution of the molecular
material associated to a born-again star. Both the continuum and molecular line
emission exhibit a clumpy ring-like structure with a total extent of
$\approx$1$^{\prime\prime}$ in diameter. The bulk of the molecular emission is
interpreted as being produced in a radially-expanding disk-like structure with
an expansion velocity v$_{\rm exp}$$\sim$90 km s$^{-1}$ and an inclination
$i$$\approx$60$^{\circ}$ with respect to the line-of-sight. The observations
also reveal a compact high-velocity component, v$_{\rm exp}$$\sim$280 km
s$^{-1}$, that is aligned perpendicularly to the expanding disk. This component
is interpreted as a bipolar outflow with a kinematical age $\tau$$\lesssim$20
yr, which could either be material that is currently being ejected from V605
Aql, or it is being dragged from the inner parts of the disk by a stellar wind.
The dust mass of the disk is in the range $M_{\rm
dust}$$\sim$0.2-8$\times$10$^{-3}$ M$_{\odot}$, depending on the dust
absorption coefficient. The mass of the CO is $M_{\rm
CO}$$\approx$1.1$\times10^{-5}$ $M_{\odot}$, which is more than three orders of
magnitude larger than the mass of the other detected molecules. We estimate a
$^{12}$C/$^{13}$C ratio of 5.6$\pm$0.6, which is consistent with the single
stellar evolution scenario in which the star experienced a very late thermal
pulse instead of a nova-like event as previously suggested. | astro-ph_GA |
An [$α$/Fe]-enhanced thick disk in a Milky Way Analogue: The Milky Way disk consists of two prominent components - a thick,
alpha-rich, low-metallicity component and a thin, metal-rich, low-alpha
component. External galaxies have been shown to contain thin and thick disk
components, but whether distinct components in the [$\alpha$/Fe]-[Z/H] plane
exist in other Milky Way-like galaxies is not yet known. We present VLT-MUSE
observations of UGC 10738, a nearby, edge-on Milky Way-like galaxy. We
demonstrate through stellar population synthesis model fitting that UGC 10738
contains alpha-rich and alpha-poor stellar populations with similar spatial
distributions to the same components in the Milky Way. We discuss how the
finding that external galaxies also contain chemically distinct disk components
may act as a significant constraint on the formation of the Milky Way's own
thin and thick disk. | astro-ph_GA |
Galactic Orbits of Globular Clusters in the Region of the Galactic Bulge: Galactic orbits have been constructed over long time intervals for ten
globular clusters located near the Galactic center. A model with an axially
symmetric gravitational potential for the Galaxy was initially applied, after
which a non-axially symmetric potential corresponding to the central bar was
added. Variations in the trajectories of all these globular clusters in the XY
plane due to the influence of the bar were detected. These were greatest for
the cluster Terzan 4 in the meridional (RZ) plane. The globular clusters Terzan
1, Terzan 2, Terzan 4, Terzan 9, NGC 6522, and NGC 6558 always remained within
the Galactic bulge, no farther than 4 kpc from the Galactic center. | astro-ph_GA |
Cosmic rays in molecular clouds probed by H$_{2}$ rovibrational lines --
Perspectives for the James Webb Space Telescope: Cosmic rays (CRs) at sub-TeV energies play a fundamental role in the chemical
and dynamical evolution of molecular clouds, as they control the ionisation,
dissociation, and excitation of H$_{2}$. Their characterisation is important
both for the interpretation of observations and for the development of
theoretical models. The methods used so far for estimating the CR ionisation
rate ($\zeta$) in molecular clouds have several limitations due to
uncertainties in the adopted chemical networks. We refine and extend the method
proposed by Bialy (2020) to estimate $\zeta$ by observing rovibrational
transitions of H$_{2}$ at near-infrared wavelengths, which are mainly excited
by secondary CR electrons. Combining models of interstellar CR propagation and
attenuation with the calculation of the expected secondary electron spectrum
and updated H$_{2}$ excitation cross sections by electron collisions, we derive
the intensity of the four H$_{2}$ rovibrational transitions observable in
dense, cold gas: (1-0)O(2), (1-0)Q(2), (1-0)S(0), and (1-0)O(4). The proposed
method allows the estimation of $\zeta$ for a given observed line intensity and
H$_{2}$ column density. We are also able to deduce the shape of the low-energy
CR proton spectrum impinging upon the molecular cloud. We present a look-up
plot and a web-based application that can be used to constrain the low-energy
spectral slope of the interstellar CR proton spectrum. We comment on the
capability of the James Webb Space Telescope to detect these near-infrared
H$_{2}$ lines, making it possible to derive for the first time spatial
variation of $\zeta$ in dense gas. Besides the implications for the
interpretation of the chemical-dynamic evolution of a molecular cloud, it will
be possible to test competing models of CR propagation and attenuation in the
interstellar medium, as well as compare CR spectra in different Galactic
regions. | astro-ph_GA |
A Gaia based photometric and kinematic analysis of the old open cluster
King 11: This paper presents an investigation of an old age open cluster King 11 using
Gaia's Early Data Release 3 (EDR3) data. Considering the stars with membership
probability ($P_{\mu}$) $> 90\%$, we identified 676 most probable cluster
members within the cluster's limiting radius. The mean proper motion (PM) for
King 11 is determined as: $\mu_{x}=-3.391\pm0.006$ and $\mu_{y}=-0.660\pm0.004$
mas yr$^{-1}$. The blue straggler stars (BSS) of King 11 show a centrally
concentrated radial distribution. The values of limiting radius, age, and
distance are determined as 18.51 arcmin, 3.63$\pm$0.42 Gyr and $3.33\pm0.15$
kpc, respectively. The cluster's apex coordinates ($A=267.84^{\circ} \pm
1.01^{\circ}$, $D=-27.48^{\circ} \pm 1.03^{\circ}$) are determined using the
apex diagram (AD) method and verified using the ($\mu_U$,$\mu_T$) diagram. We
also obtained the orbit that the cluster follows in the Galaxy and estimated
its tentative birthplace in the disk. The resulting spatial velocity of King 11
is 60.2 $\pm$ 2.16 km s$^{-1}$. A significant oscillation along the
$Z$-coordinate up to 0.556$\pm$0.022~kpc is determined. | astro-ph_GA |
Star formation in the outskirts of DDO 154: A top-light IMF in a nearly
dormant disc: We present optical photometry of Hubble Space Telescope (HST) ACS/WFC data of
the resolved stellar populations in the outer disc of the dwarf irregular
galaxy DDO 154. The photometry reveals that young main sequence stars are
almost absent from the outermost HI disc. Instead, most are clustered near the
main stellar component of the galaxy. We constrain the stellar initial mass
function (IMF) by comparing the luminosity function of the main sequence stars
to simulated stellar populations assuming a constant star formation rate over
the dynamical timescale. The best-fitting IMF is deficient in high mass stars
compared to a canonical Kroupa IMF, with a best-fit slope $\alpha = -2.45$ and
upper mass limit $M_U = 16\ M_{\odot}$. This top-light IMF is consistent with
predictions of the Integrated Galaxy-wide IMF theory. Combining the HST images
with HI data from The HI Nearby Galaxy Survey Treasury (THINGS) we determine
the star formation law (SFL) in the outer disc. The fit has a power law
exponent $N = 2.92 \pm0.22$ and zero point $A=4.47 \pm 0.65 \times 10^{-7} \
M_{\odot} \ \text{yr}^{-1} \ \text{kpc}^{-2}$. This is depressed compared to
the Kennicutt-Schmidt Star Formation Law, but consistent with weak star
formation observed in diffuse HI environments. Extrapolating the SFL over the
outer disc implies that there could be significant star formation occurring
that is not detectable in H$\alpha$. Last, we determine the Toomre stability
parameter $Q$ of the outer disc of DDO 154 using the THINGS HI rotation curve
and velocity dispersion map. 72% of the HI in our field has $Q\leq 4$ and this
incorporates 96% of the observed MS stars. Hence 28% of the HI in the field is
largely dormant. | astro-ph_GA |
The nuclear properties and extended morphologies of powerful radio
galaxies: the roles of host galaxy and environment: Powerful radio galaxies exist as either compact or extended sources, with the
extended sources traditionally classified by their radio morphologies as
Fanaroff--Riley (FR) type I and II sources. FRI/II and compact radio galaxies
have also been classified by their optical spectra into two different types:
high excitation (HERG; quasar-mode) and low excitation (LERG; jet-mode). We
present a catalogue of visual morphologies for a complete sample of $>$1000
1.4-GHz-selected extended radio sources from the Sloan Digital Sky Survey. We
study the environment and host galaxy properties of FRI/II and compact sources,
classified into HERG/LERG types, in order to separate and distinguish the
factors that drive the radio morphological variations from those responsible
for the spectral properties. Comparing FRI LERGs with FRII LERGs at fixed
stellar mass and radio luminosity, we show that FRIs typically reside in richer
environments and are hosted by smaller galaxies with higher mass surface
density; this is consistent with extrinsic effects of jet disruption driving
the FR dichotomy. Using matched samples of HERGs and LERGs, we show that HERG
host galaxies are more frequently star-forming, with more evidence for
disk-like structure than LERGs, in accordance with currently-favoured models of
fundamentally different fuelling mechanisms. Comparing FRI/II LERGs with
compact LERGs, we find the primary difference is that compact objects typically
harbour less massive black holes. This suggests that lower-mass black holes may
be less efficient at launching stable radio jets, or do so for shorter times.
Finally, we investigate rarer sub-classes: wide-angle tail, head-tail,
FR-hybrid and double-double sources. | astro-ph_GA |
Preliminary results of using k-Nearest Neighbours Regression to estimate
the redshift of radio selected datasets: In the near future, all-sky radio surveys are set to produce catalogues of
tens of millions of sources with limited multi-wavelength photometry.
Spectroscopic redshifts will only be possible for a small fraction of these
new-found sources. In this paper, we provide the first in-depth investigation
into the use of k-Nearest Neighbours Regression for the estimation of redshift
of these sources. We use the Australia Telescope Large Area Survey radio data,
combined with the Spitzer Wide-Area Infrared Extragalactic Survey infra-red,
the Dark Energy Survey optical and the Australian Dark Energy Survey
spectroscopic survey data. We then reduce the depth of photometry to match what
is expected from upcoming Evolutionary Map of the Universe survey, testing
against both data sets. To examine the generalisation of our methods, we test
one of the sub-fields of Australia Telescope Large Area Survey against the
other. We achieve an outlier rate of ~10% across all tests, showing that the
k-Nearest Neighbours regression algorithm is an acceptable method of estimating
redshift, and would perform better given a sample training set with uniform
redshift coverage. | astro-ph_GA |
The WISSH quasars project XI. The mean Spectral Energy Distribution and
Bolometric Corrections of the most luminous quasars: Hyper-luminous Quasi-Stellar Objects (QSOs) represent the ideal laboratory to
investigate Active Galactic Nuclei (AGN) feedback mechanism since their
formidable energy release causes powerful winds at all scales and thus the
maximum feedback is expected.
We aim at deriving the mean Spectral Energy Distribution (SED) of a sample of
85 WISE-SDSS Selected Hyper-luminous (WISSH) quasars. Since the SED provides a
direct way to investigate the AGN structure, our goal is to understand if
quasars at the bright end of the luminosity function have peculiar properties
compared to the bulk of the population. We built a mean intrinsic SED after
correcting for the dust extinction, absorption and emission lines and
intergalactic medium absorption. We also derived bolometric, IR band and
monochromatic luminosities together with bolometric corrections at lambda =
5100 A and 3 micron. We define a new relation for the 3 micron bolometric
correction. We find that the mean SED of hyper-luminous WISSH QSOs is different
from that of less luminous sources, i.e. a relatively lower X-ray emission and
a near and mid IR excess which can be explained assuming a larger dust
contribution. WISSH QSOs have stronger emission from both warm and very hot
dust, the latter being responsible for shifting the typical dip of the AGN SED
from 1.3 to 1.1 micron. We also derived the mean SEDs of two sub-samples
created according to the presence of Broad Absorption Lines and equivalent
width of CIV line. We confirm that BALs are X-ray weak and that they have a
reddened UV-optical continuum. We also find that BALs tend to have stronger
emission from the hot dust component. This analysis suggests that
hyper-luminous QSOs have a peculiar SED compared to less luminous objects. It
is therefore critical to use SED templates constructed exclusively from very
bright quasars samples when dealing with particularly luminous sources. | astro-ph_GA |
Period-Luminosity Relations for Galactic classical Cepheids in the Sloan
bands: We present the first period-luminosity (PL) and period-Wesenheit (PW)
relations in the Sloan-Pans-STARRS gP1rP1iP1 bands for classical fundamental
mode Cepheids in the Milky Way. We used a relatively modest number of 76 stars
for the PL and 84-85 stars for the PW relations calibration. The data for the
project were collected with the network of 40-cm telescopes of Las Cumbres
Observatory, and Gaia Data Release 3 parallaxes were used for the calculations.
These gri-band PL and PW relations calibrations will be a useful tool for
distance determinations in the era of large sky surveys using the Sloan
photometric system, especially with the near-future start of the Large Synoptic
Survey of Space and Time (LSST). | astro-ph_GA |
AGN-driven Cold Gas Outflow of NGC 1068 Characterized by
Dissociation-Sensitive Molecules: Recent developments in (sub-)millimeter facilities have drastically changed
the amount of information obtained from extragalactic spectral scans. In this
paper, we present a feature extraction technique using principal component
analysis (PCA) applied to arcsecond-resolution (1.0-2.0 arcsec = 72-144 pc)
spectral scan datasets for the nearby type-2 Seyfert galaxy, NGC 1068, using
Band 3 of the Atacama Large Millimeter/submillimeter Array. We apply PCA to 16
well-detected molecular line intensity maps convolved to a common 150 pc
resolution. In addition, we include the [SIII]/[SII] line ratio and [CI]
$^3P_1$-$^3P_0$ maps in the literature, both of whose distributions show
remarkable resemblance with that of a kpc-scale biconical outflow from the
central AGN. We identify two prominent features: (1) central concentration at
the circumnuclear disk (CND) and (2) two peaks across the center that coincide
with the biconical outflow peaks. The concentrated molecular lines in the CND
are mostly high-dipole molecules (e.g., H$^{13}$CN, HC$_3$N, and HCN). Line
emissions from molecules known to be enhanced in irradiated interstellar
medium, CN, C$_2$H, and HNC, show similar concentrations and extended
components along the bicone, suggesting that molecule dissociation is a
dominant chemical effect of the cold molecular outflow of this galaxy. Although
further investigation should be made, this scenario is consistent with the
faintness or absence of the emission lines from CO isotopologues, CH$_3$OH, and
N$_2$H$^+$, in the outflow, which are easily destroyed by dissociating photons
and electrons. | astro-ph_GA |
Extremely inverted peaked spectrum radio sources: We report our ongoing search for extremely inverted spectrum compact radio
galaxies, for which the defining feature in the radio spectrum is not the
spectral peak, but instead the slope of the spectrum (alpha) in the
high-opacity (i.e., lower frequency) part of the radio spectrum. Specifically,
our focus is on the spectral regime with spectral index, alpha >+2.5. The
motivation for our study is, firstly, extragalactic sources with such extreme
spectral index are extremely rare, because of the unavailability of right
combination of sensitivity and resolution over a range of low frequencies. The
second reason is more physically motivated, since alpha = +2.5 is the maximum
slope theoretically possible for a standard radio source emitting synchrotron
radiation. Therefore such sources could be the test-bed for some already
proposed alternative scenarios for synchrotron self-absorption (SSA), like the
free-free absorption (FFA) highlighting the importance of jet-ISM interaction
in the radio galaxy evolution. | astro-ph_GA |
Discovery of a very Lyman-$α$-luminous quasar at z=6.62: Distant luminous quasars provide important information on the growth of the
first supermassive black holes, their host galaxies and the epoch of
reionization. The identification of quasars is usually performed through
detection of their Lyman-$\alpha$ line redshifted to $\sim$ 0.9 microns at
z>6.5. Here, we report the discovery of a very Lyman-$\alpha$ luminous quasar,
PSO J006.1240+39.2219 at redshift z=6.618, selected based on its red colour and
multi-epoch detection of the Lyman-$\alpha$ emission in a single near-infrared
band. The Lyman-$\alpha$-line luminosity of PSO J006.1240+39.2219 is unusually
high and estimated to be 0.8$\times$10$^{12}$ Solar luminosities (about 3% of
the total quasar luminosity). The Lyman-$\alpha$ emission of PSO
J006.1240+39.2219 shows fast variability on timescales of days in the quasar
rest frame, which has never been detected in any of the known high-redshift
quasars. The high luminosity of the Lyman-$\alpha$ line, its narrow width and
fast variability resemble properties of local Narrow-Line Seyfert 1 galaxies
which suggests that the quasar is likely at the active phase of the black hole
growth accreting close or even beyond the Eddington limit. | astro-ph_GA |
Lens galaxies in the Illustris simulation: power-law models and the bias
of the Hubble constant from time-delays: A power-law density model, i.e., $\rho(r) \propto r^{-\gamma'}$ has been
commonly employed in strong gravitational lensing studies, including the
so-called time-delay technique used to infer the Hubble constant $H_0$.
However, since the radial scale at which strong lensing features are formed
corresponds to the transition from the dominance of baryonic matter to dark
matter, there is no known reason why galaxies should follow a power law in
density. The assumption of a power law artificially breaks the mass-sheet
degeneracy, a well-known invariance transformation in gravitational lensing
which affects the product of Hubble constant and time delay and can therefore
cause a bias in the determination of $H_0$ from the time-delay technique. In
this paper, we use the Illustris hydrodynamical simulations to estimate the
amplitude of this bias, and to understand how it is related to observational
properties of galaxies. Investigating a large sample of Illustris galaxies that
have velocity dispersion $\sigma_{SIE}$>160 km/s at redshifts below $z=1$, we
find that the bias on $H_0$ introduced by the power-law assumption can reach
20%-50%, with a scatter of $10\%-30\%$ (rms). However, we find that by
selecting galaxies with an inferred power-law model slope close to isothermal,
it is possible to reduce the bias on $H_0$ to <5%, and the scatter to <10%.
This could potentially be used to form less biased statistical samples for
$H_0$ measurements in the upcoming large survey era. | astro-ph_GA |
Magnetic field measurement in TMC-1C using 22.3 GHz CCS Zeeman splitting: Measurement of magnetic fields in dense molecular clouds is essential for
understanding the fragmentation process prior to star formation. Radio
interferometric observations of CCS 22.3 GHz emission, from the starless core
TMC-1C, have been carried out with the Karl G. Jansky Very Large Array to
search for Zeeman splitting of the line in order to constrain the magnetic
field strength. Toward a region offset from the dust peak, we report a
detection of the Zeeman splitting of the CCS 2_1 - 1_0 transition, with an
inferred magnetic field of ~2 mG. If we interpret the dust peak to be the core
of TMC-1C, and the region where we have made a detection of the magnetic field
to be the envelope, then our observed value for the magnetic field is
consistent with a subcritical mass-to-flux ratio envelope around a core with
supercritical mass-to-flux ratio. The ambipolar diffusion timescale for the
formation of the core is consistent with the relevant timescale based on
chemical modeling of the TMC-1C core. This work demonstrates the potential of
deep CCS observation to carry out future measurements of magnetic field
strengths in dense molecular clouds and, in turn, understand the role of the
magnetic field in star formation. | astro-ph_GA |
Kinematics and Mass Modeling of Messier 33: Halpha observations: As part of a long-term project to revisit the kinematics and dynamics of the
large disc galaxies of the Local Group, we present the first deep, wide-field
(42' x 56') 3D-spectroscopic survey of the ionized gas disc of Messier 33.
Fabry-Perot interferometry has been used to map its Ha distribution and
kinematics at unprecedented angular resolution (<3'') and resolving power
(12600), with the 1.6m telescope at the Observatoire du Mont Megantic. The
ionized gas distribution follows a complex, large-scale spiral structure,
unsurprisingly coincident with the already-known spiral structures of the
neutral and molecular gas discs. The kinematical analysis of the velocity field
shows that the rotation center of the Ha disc is distant from the photometric
center by 170 pc (sky projected distance) and that the kinematical major-axis
position angle and disc inclination are in excellent agreement with photometric
values. The Ha rotation curve agrees very well with the HI rotation curves for
0 < R < 6.5 kpc, but the Ha velocities are 10-20 km/s higher for R > 6.5 kpc.
The reason for this discrepancy is not well understood. The velocity dispersion
profile is relatively flat around 16 km/s, which is at the low end of velocity
dispersions of nearby star-forming galactic discs. A strong relation is also
found between the Ha velocity dispersion and the Ha intensity. Mass models were
obtained using the Ha rotation curve but, as expected, the dark matter halo's
parameters are not very well constrained since the optical rotation curve only
extends out to 8 kpc. | astro-ph_GA |
Mid Infrared View of the High Mass Star Formation Region W51A: In this paper we present the results of a mid infrared study of G49.5-0.4, or
W51A, part of the massive starbirth complex W51. Combining public data from the
$Spitzer$ IRAC camera, and Gemini mid infrared camera T-ReCS at 7.73, 9.69,
12.33 and 24.56 \micron, with spatial resolution of $\sim$0.5\arcsec, we have
identified the mid infrared counterparts of 8 ultracompact HII regions, showing
that two radio sources are deeply embedded in molecular clouds and another is a
cloud of ionized gas. From the T-ReCS data we have unveiled the central core of
W51 region, revealing massive young stellar candidates. We modeled the spectral
energy distribution of the detected sources suggesting the embedded objects are
sources with spectral types ranging from B3 to O5, but the majority of the fits
indicate stellar objects with B1 spectral types. We also present an extinction
map of IRS~2, showing that a region with lower extinction corresponds to the
region where a proposed jet of gas has impacted the foreground cloud. From this
map, we also derived the total extinction towards the enigmatic source IRS~2E,
which amounts to $\sim$60 magnitudes in the $V$ band. We calculated the color
temperature due to thermal emission of the circumstellar dust of the detected
sources; the temperatures are in the interval of $\sim$100 -- 150 K, which
corresponds to the emission of dust located at 0.1 pc from the central source.
Finally, we show a possible mid infrared counterpart of a detected source at mm
wavelengths that was found by \cite{zap08,zap09} to be a massive young stellar
object undergoing a high accretion rate. | astro-ph_GA |
How the power spectrum of dust continuum images may hide the presence of
a characteristic filament width: Herschel observations of interstellar clouds support a paradigm for star
formation in which filaments play a central role. One of the foundations of
this paradigm is the finding, based on studies of the radial column density
profiles, that nearby filaments share a common inner width of ~0.1 pc. The
existence of a characteristic filament width has been questioned, however, as
it seems inconsistent with the scale-free nature of the power spectrum of cloud
images.
In an effort to clarify the origin of this apparent discrepancy, we examined
the power spectra of the Herschel 250 micron images of the Polaris, Aquila, and
Taurus clouds and performed a number of simple numerical experiments by
injecting synthetic filaments in both the Herschel images and synthetic
background images.
We constructed several populations of synthetic filaments of 0.1 pc width
with realistic area filling factors ($A_{\rm fil}$) and distributions of column
density contrasts ($\delta_c$). After adding synthetic filaments to the
Herschel images, we re-computed the image power spectra and compared the
results with the original, essentially scale-free power spectra. We used the
$\chi^2$ variance of the residuals between the best power-law fit and the
output power spectrum as a diagnostic of the presence of a significant
departure from a scale-free power spectrum.
We found that the $\chi^2$ variance depends primarily on the combined
parameter $\delta_c^2\, A_{\rm fil}$. Analysis of the real Herschel data shows
that the observed filamentary structure contributes only 1/5 of the power in
the power spectra at angular frequencies where an effect of the characteristic
filament width is expected.
We conclude that the scale-free power spectra of Herschel images remain
consistent with the existence of a characteristic filament width ~0.1 pc and do
not invalidate the conclusions drawn from studies of the filament profiles. | astro-ph_GA |
An accurate low-redshift measurement of the cosmic neutral hydrogen
density: Using a spectral stacking technique, we measure the neutral hydrogen (HI)
properties of a sample of galaxies at $z < 0.11$ across 35 pointings of the
Westerbork Synthesis Radio Telescope (WSRT). The radio data contains 1,895
galaxies with redshifts and positions known from the Sloan Digital Sky Survey
(SDSS). We carefully quantified the effects of sample bias, aperture used to
extract spectra, sidelobes and weighting technique and use our data to provide
a new estimate for the cosmic HI mass density. We find a cosmic HI mass density
of $\Omega_{\rm HI} = (4.02 \pm 0.26)\times 10^{-4} h_{70}^{-1}$ at $\langle
z\rangle = 0.066$, consistent with measurements from blind HI surveys and other
HI stacking experiments at low redshifts. The combination of the small
interferometer beam size and the large survey volume makes our result highly
robust against systematic effects due to confusion at small scales and cosmic
variance at large scales. Splitting into three sub-samples with $\langle
z\rangle$ = 0.038, 0.067 and 0.093 shows no significant evolution of the HI gas
content at low redshift. | astro-ph_GA |
Stellar Velocity Dispersion in Mergers: The Effects of Dust and Star
Formation: We investigate the effects of stellar evolution and dust on measurements of
stellar velocity dispersion in mergers of disk galaxies. $N$-body simulations
and radiative transfer analysis software are used to obtain mass-weighted and
flux-weighted measurements of stellar velocity dispersion. We find that the
distribution of dust with respect to the distribution of young stars in such
systems is more important than the total degree of attenuation. The presence of
dust typically causes flux-weighted measurements of stellar velocity dispersion
to be elevated with respect to mass-weighted measurements because dust
preferentially obscures young stars, which tend to be dynamically cooler than
older stellar populations in such systems. In exceptional situations, in which
young stars are not preferentially obscured by dust, flux-weighted velocity
dispersion measurements tend to be negatively offset with respect to
mass-weighted measurements because the dynamically cool young stellar
populations are more luminous, per unit mass, than older stellar populations.
Our findings provide a context for comparing observationally-obtained
measurements of velocity dispersion with measurements of velocity dispersion
obtained from galaxy merger simulations. | astro-ph_GA |
Linking Compact Dwarf Starburst Galaxies in the RESOLVE Survey to
Downsized Blue Nuggets: We identify and characterize compact dwarf starburst (CDS) galaxies in the
RESOLVE survey, a volume-limited census of galaxies in the local universe, to
probe whether this population contains any residual ``blue nuggets,'' a class
of intensely star-forming compact galaxies first identified at high redshift
$z$. Our 50 low-$z$ CDS galaxies are defined by dwarf masses (stellar mass $M_*
< 10^{9.5}$ M$_{\odot}$), compact bulged-disk or spheroid-dominated
morphologies (using a quantitative criterion, $\mu_\Delta > 8.6$), and specific
star formation rates above the defining threshold for high-$z$ blue nuggets
($\log$ SSFR [Gyr$^{-1}] > -0.5$). Across redshifts, blue nuggets exhibit three
defining properties: compactness relative to contemporaneous galaxies, abundant
cold gas, and formation via compaction in mergers or colliding streams. Those
with halo mass below $M_{\rm halo} \sim 10^{11.5}$ M$_{\odot}$ may in theory
evade permanent quenching and cyclically refuel until the present day. Selected
only for compactness and starburst activity, our CDS galaxies generally have
$M_{\rm halo} \lesssim 10^{11.5}$ M$_{\odot}$ and gas-to-stellar mass ratio
$\gtrsim$1. Moreover, analysis of archival DECaLS photometry and new 3D
spectroscopic observations for CDS galaxies reveals a high rate of photometric
and kinematic disturbances suggestive of dwarf mergers. The SSFRs, surface mass
densities, and number counts of CDS galaxies are compatible with theoretical
and observational expectations for redshift evolution in blue nuggets. We argue
that CDS galaxies represent a maximally-starbursting subset of traditional
compact dwarf classes such as blue compact dwarfs and blue E/S0s. We conclude
that CDS galaxies represent a low-$z$ tail of the blue nugget phenomenon formed
via a moderated compaction channel that leaves open the possibility of disk
regrowth and evolution into normal disk galaxies. | astro-ph_GA |
Bivariate Luminosity Function of Galaxy Pairs: We measure the bivariate luminosity function (BLF) of galaxy pairs and use it
to probe and characterize the galaxy-galaxy interaction between pair members.
The galaxy pair sample is selected from the main galaxy sample of Sloan Digital
Sky Survey and supplied with a significant number of redshifts from the LAMOST
spectral and GAMA surveys. We find the BLFs depend on the projected distance
$d_{\text{p}}$ between pair members. At large separation $d_{\text{p}} > 150
h^{-1}\ \text{kpc}$, the BLF degenerates into a luminosity function (LF) of
single galaxies, indicating few interactions between pair members. At $100
h^{-1}\ \text{kpc} \leq d_{\text{p}} \leq 150 h^{-1}\ \text{kpc}$, the BLF
starts to show the correlation between pair members, in the sense that the
shape of the conditional luminosity function (CLF) of one member galaxy starts
to depend on the luminosity of the other member galaxy. Specifically, the CLF
with a brighter companion has a steeper faint-end slope, which becomes even
more significant at $50 h^{-1}\ \text{kpc} \leq d_{\text{p}} \leq 100 h^{-1}\
\text{kpc}$. This behavior is consistent with the scenario, \textit{and also is
the observational evidence}, that dynamic friction drives massive major merger
pairs to merge more quickly. At close distance $d_{\text{p}} \leq 50 h^{-1}\
\text{kpc}$, besides the merging time-scale effect, the BLF also shows an
overall brightening of $\Delta M_r \geq 0.04$ mag, which reveals the enhanced
star formation of the close-pair phase. By combining another statistical
conclusion that the star formation rate of late-type galaxies in close pairs is
enhanced at a level of about 40\%, we further conclude that the average
starburst time-scale of close pairs is as long as 0.4 Gyr. | astro-ph_GA |
How do disks and planetary systems in high-mass open clusters differ
from those around field stars?: Only star clusters that are sufficiently compact and massive survive largely
unharmed beyond 10 Myr. However, their compactness means a high stellar density
which can lead to strong gravitational interactions between the stars. As young
stars are often initially surrounded by protoplanetary disks and later on
potentially by planetary systems, the question arises to what degree these
strong gravitational interactions influence planet formation and the properties
of planetary systems. Here, we perform simulations of the evolution of compact
high-mass clusters like Trumpler 14 and Westerlund 2 from the embedded to the
gas-free phase and study the influence of stellar interactions. We concentrate
on the development of the mean disk size in these environments. Our simulations
show that in high-mass open clusters $80-90\%$ of all disks/planetary systems
should be smaller than 50 AU just due to the strong stellar interactions in
these environments. Already in the initial phases, 3-4 close fly-bys lead to
typical disk sizes within the range of 18-27 AU. Afterwards, the disk sizes are
altered only to a small extent. Our findings agree with the recent observation
that the disk sizes in the once dense environment of the Upper Scorpio OB
association, NGC~2362, and h/$\chi$Persei are at least three times smaller in
size than, for example, in Taurus. We conclude that the observed planetary
systems in high-mass open clusters should also be on average smaller than those
found around field stars; in particular, planets on wide orbits are expected to
be extremely rare in such environments. | astro-ph_GA |
The Mass Distributions of Starless and Protostellar Cores in Gould Belt
Clouds: Using data from the SCUBA Legacy Catalogue (850 um) and Spitzer Space
Telescope (3.6 - 70 um), we explore dense cores in the Ophiuchus, Taurus,
Perseus, Serpens, and Orion molecular clouds. We develop a new method to
discriminate submillimeter cores found by SCUBA as starless or protostellar,
using point source photometry from Spitzer wide field surveys. First, we
identify infrared sources with red colors associated with embedded young
stellar objects (YSOs). Second, we compare the positions of these
YSO-candidates to our submillimeter cores. With these identifications, we
construct new, self-consistent starless and protostellar core mass functions
(CMFs) for the five clouds. We find best fit slopes to the high-mass end of the
CMFs of -1.26 +/- 0.20, -1.22 +/- 0.06, -0.95 +/- 0.20, and -1.67 +/- 0.72 for
Ophiuchus, Taurus, Perseus, and Orion, respectively. Broadly, these slopes are
each consistent with the -1.35 power-law slope of the Salpeter IMF at higher
masses, but suggest some differences. We examine a variety of trends between
these CMF shapes and their parent cloud properties, potentially finding a
correlation between the high-mass slope and core temperature. We also find a
trend between core mass and effective size, but we are very limited by
sensitivity. We make similar comparisons between core mass and size with visual
extinction (for A_V >= 3) and find no obvious trends. We also predict the
numbers and mass distributions of cores that future surveys with SCUBA-2 may
detect in each of these clouds. | astro-ph_GA |
On the relation of host properties and environment of AGN galaxies
across the standard optical diagnostic diagram: We study the host properties and environment of active galactic nuclei (AGNs)
galaxies, taken from SDSS-DR12, across the $\text{[O III]}/\text{H}\beta$ vs
$\text{[N II]}/\text{H}\alpha$ diagnostic diagram. We select AGN subsamples
defined as parallel and perpendicular to the star-forming locus on the BPT
diagram based on the Kauffmann et al. and Schawinski et al. criteria. For
parallel subsamples we find that AGN host properties exhibit a morphological
evolution as they become more distant to the star-forming sequence. The local
density environment shows a more evident morphology-density relationship for
subsamples mainly formed by Composite and Spiral galaxies than those containing
LINERs and Seyferts, where the AGN emission is the dominant source. We also
analyse the properties of the five closest AGN neighbours observing no
significant differences in the environment, although the AGN host properties of
every subsample have noticeable variations. The AGNs belonging to perpendicular
subsamples show clear differences on their host properties from left top to
right bottom on the diagram. However, the analysis of the local density
environment do not reflect strong dependency with the host AGN properties. This
result is reinforced by the characteristics of the AGN neighbouring galaxies.
These findings suggest that mixed AGN/star-forming galaxies present
environmental features more similar to that of non-active galaxies. However, as
AGNs at the centre of the more evolved galaxies become the dominant source, the
environment tends to provide suitable conditions for the central black hole
feeding with an increasing content of gas and likelihood of a higher merger
rate. | astro-ph_GA |
Long-term optical spectral monitoring of a changing-look AGN NGC 3516 I:
Continuum and broad-line flux variability: Here we present the long-term optical spectral monitoring of a changing-look
active galactic nuclei (AGN) NGC 3516 that covers 22 years (from 1996 to 2018).
We explore a variability in the broad lines and continuum, finding that the
continuum is changing by more than a factor of 2, while the broad lines are
varying by more than a factor of 10. The minimum of activity is observed in
2014, when the broad lines almost disappeared. We confirm that NGC 3516 is a
changing-look AGN, and the absorption seen in the UV and X-ray may indicate
that there is an obscuring region which is responsible for this.
The line profiles are also changing. The mean profiles of the broad Halpha
and Hbeta lines show shoulder-like structure in the wings, and enhanced peak,
that may indicate a complex BLR. The rms-profiles of both lines seem to have
the same shape and width of around 4200 km/s, indicating practically the same
kinematics in the Halpha and Hbeta emitting regions.
Measured time-lags between the continuum and Halpha and Hbeta broad-line
variability are ~15 and 17 days, respectively, that in combination with the
broad lines width allows us to estimate the NGC 3516 central black hole mass.
We find that the black hole mass is 4.73+-1.40 x 10^7M_sun which is in
agreement with previous estimates. | astro-ph_GA |
Formation of supermassive stars in the first star clusters: The formation of supermassive stars is believed to be an essential
intermediate step for the formation of the massive black hole seeds that become
the supermassive black holes powering the quasars observed in the early
Universe. Numerical simulations have shown that supermassive stars can form in
atomic-cooling halos when protostars reach accretion rates higher than
$\sim10^{-2}$ M$_\odot$ yr$^{-1}$ and fragmentation is suppressed on pc scales.
It is however still uncertain if a supermassive star still emerges when
fragmentation occurs at smaller scales and a cluster of stars is formed
instead. In this work we explore the problem of massive object formation due to
the interplay of collisions and accretion in star clusters at low metallicity.
We model a small embedded cluster of accreting protostars following sub-parsec
scale fragmentation during the collapse of a primordial gas cloud and follow
its evolution by performing $N$-body plus hydrodynamical simulations. Our
results show that supermassive stars with 10$^3$ and 10$^4$ M$_\odot$ are
always formed due to the interplay of collisions and accretion, and in some
cases these objects are part of a binary system. The resulting supermassive
star is surrounded by tens of smaller stars with typical masses in the range
$1$-$100$ M$_\odot$. | astro-ph_GA |
Galactic Disk Bulk Motions as Revealed by the LSS-GAC DR2: We report a detailed investigation of the bulk motions of the nearby Galactic
stellar disk, based on three samples selected from the LSS-GAC DR2: a global
sample containing 0.57 million FGK dwarfs out to $\sim$ 2 kpc, a local subset
of the global sample consisting $\sim$ 5,400 stars within 150 pc, and an
anti-center sample containing $\sim$ 4,400 AFGK dwarfs and red clump stars
within windows of a few degree wide centered on the Galactic anti-center. The
global sample is used to construct a three-dimensional map of bulk motions of
the Galactic disk from the solar vicinity out to $\sim$ 2 kpc with a spatial
resolution of $\sim$ 250 pc. Typical values of the radial and vertical
components of bulk motion range from $-$15 km s$^{-1}$ to 15 km s$^{-1}$, while
the lag behind the circular speed dominates the azimuthal component by up to
$\sim$ 15 km s$^{-1}$. The map reveals spatially coherent, kpc-scale stellar
flows in the disk, with typical velocities of a few tens km s$^{-1}$. Bending-
and breathing-mode perturbations are clearly visible, and vary smoothly across
the disk plane. Our data also reveal higher-order perturbations, such as breaks
and ripples, in the profiles of vertical motion versus height. From the local
sample, we find that stars of different populations exhibit very different
patterns of bulk motion. Finally, the anti-center sample reveals a number of
peaks in stellar number density in the line-of-sight velocity versus distance
distribution, with the nearer ones apparently related to the known moving
groups. The "velocity bifurcation" reported by Liu et al. (2012) at
Galactocentric radii 10--11 kpc is confirmed. However, just beyond this
distance, our data also reveal a new triple-peaked structure. | astro-ph_GA |
Carbon, nitrogen and oxygen abundance gradients in M101 and M31: We present deep spectrophotometry of 18 HII regions in the nearby massive
spiral galaxies M101 and M31. We have obtained direct determinations of
electron temperature in all the nebulae. We detect the CII 4267 line in several
HII regions, permitting to derive the radial gradient of C/H in both galaxies.
We also determine the radial gradients of O/H, N/O, Ne/O, S/O, Cl/O and Ar/O
ratios. As in other spiral galaxies, the C/H gradients are steeper than those
of O/H producing negative slopes of the C/O gradient. The scatter of the
abundances of O with respect to the gradient fittings do not support the
presence of significant chemical inhomogeneities across the discs of the
galaxies, especially in the case of M101. We find trends in the S/O, Cl/O and
Ar/O ratios as a function of O/H in M101 that can be reduced using Te
indicators different from the standard ones for calculating some ionic
abundances. The distribution of the N/O ratio with respect to O/H is rather
flat in M31, similarly to previous findings for the MilkyWay. Using the disc
effective radius, Re, as a normalization parameter for comparing gradients, we
find that the latest estimates of Re for the Milky Way provide an excess of
metallicity in apparent contradiction with the mass-metallicity relation; a
value about two times larger might solve the problem. Finally, using different
abundance ratios diagrams we find that the enrichment timescales of C and N
result to be fairly similar despite their different nucleosynthetic origin. | astro-ph_GA |
Size, shade or shape? The contribution of galaxies of different types to
the star-formation history of the Universe from SDSS-IV MaNGA: By fitting stellar populations to SDSS-IV MaNGA survey observations of ~7000
suitably-weighted individual galaxies, we reconstruct the star-formation
history of the Universe, which we find to be in reasonable agreement with
previous studies. Dividing the galaxies by their present-day stellar mass, we
demonstrate the downsizing phenomenon, whereby the more massive galaxies hosted
the most star-formation at earlier times. Further dividing the galaxy sample by
colour and morphology, we find that a galaxy's present-day colour tells us more
about its historical contribution to the cosmic star formation history than its
current morphology. We show that downsizing effects are greatest among galaxies
currently in the blue cloud, but that the level of downsizing in galaxies of
different morphologies depends quite sensitively on the morphological
classification used, due largely to the difficulty in classifying the smaller
low-mass galaxies from their ground-based images. Nevertheless, we find
agreement that among galaxies with stellar masses
$M_{\star}>6\times10^{9}\,M_{\odot}$, downsizing is most significant in
spirals. However, there are complicating factors. For example, for more massive
galaxies, we find that colour and morphology are predictors of the past star
formation over a longer timescale than in less massive systems. Presumably this
effect is reflecting the longer period of evolution required to alter these
larger galaxies' physical properties, but shows that conclusions based on any
single property don't tell the full story. | astro-ph_GA |
Wide field polarimetry around the Perseus cluster at 350 MHz: This paper investigates the fascinating diffuse polarization structures at
350 MHz that have previously been tentatively attributed to the Perseus cluster
and, more specifically, tries to find out whether the structures are located at
(or near) the Perseus cluster, or in the Milky Way. A wide field, eight point
Westerbork Synthesis Radio Telescope mosaic of the area around the Perseus
cluster was observed in full polarization. The frequency range was 324 to 378
MHz and the resolution of the polarization maps was 2'x3'. The maps were
processed using Faraday rotation measure synthesis to counter bandwidth
depolarization. The RM-cube covers Faraday depths of -384 to +381 rad m^{-2} in
steps of 3 rad m^{-2}. There is emission all over the field at Faraday depths
between -50 and +100 rad m^{-2}. All previously observed structures were
detected. However, no compelling evidence was found supporting association of
those structures with either the Perseus cluster or large scale structure
formation gas flows in the Perseus-Pisces super cluster. On the contrary, one
of the structures is clearly associated with a Galactic depolarization canal at
1.41 GHz. Another large structure in polarized intensity, as well as Faraday
depth at a Faraday depth of +30 rad m^{-2}, coincides with a dark object in
WHAM H-alpha maps at a kinematic distance of 0.5 \pm 0.5 kpc. All diffuse
polarized emission at 350 MHz towards the Perseus cluster is most likely
located within 1 kpc from the Sun. The layers that emit the polarized radiation
are less than 40 pc/B|| thick. | astro-ph_GA |
The interacting late-type host galaxy of the radio-loud narrow-line
Seyfert 1 IRAS 20181-2244: Narrow-line Seyfert 1 galaxies (NLS1s) are a class of active galactic nuclei
(AGN) which are known to be one of the few sources of $\gamma$ rays, which
originate in a relativistic beamed jet. Becuase of their relatively large
distance, a poorly investigated aspect of these jetted NLS1s is their
environment, and in particular their host galaxy. In this work we present the
results of a morphological analysis of the host galaxy of the jetted NLS1 IRAS
20181-2244 observed with the 6.5m Baade Telescope of the Las Campanas
Observatory. The GALFIT analysis ran on the Ks image, along with additional
spectroscopic observations performed with the Nordic Optical Telescope, clearly
revealed the presence of an interacting system of two galaxies. The data
suggest that this NLS1 is hosted by a late-type galaxy, although the result is
not conclusive. This analysis, along with other results in the literature,
might suggest that two populations of jetted NLS1 exist. Further morphological
studies are needed to confirm or disprove this hypothesis. | astro-ph_GA |
Detection of Broad H$α$ Emission Lines in the Late-time Spectra of
a Hydrogen-poor Superluminous Supernova: iPTF13ehe is a hydrogen-poor superluminous supernova (SLSN) at z=0.3434, with
a slow-evolving light curve and spectral features similar to SN2007bi. It rises
within (83-148)days (rest-frame) to reach a peak bolometric luminosity of
1.3x$10^{44}$erg/s, then decays very slowly at 0.015mag. per day. The measured
ejecta velocity is 13000km/s. The inferred explosion characteristics, such as
the ejecta mass (67-220$M_\odot$), the total radiative and kinetic energy
($10^{51}$ & 2x$10^{53}$erg respectively), is typical of a slow-evolving H-poor
SLSN event. However, the late-time spectrum taken at +251days reveals a Balmer
Halpha emission feature with broad and narrow components, which has never been
detected before among other H-poor SLSNe. The broad component has a velocity
width of ~4500km/s and has a ~300km/s blue-ward shift relative to the narrow
component. We interpret this broad H$\alpha$ emission with luminosity of
$\sim$2$\times10^{41}$\,erg\,s$^{-1}$ as resulting from the interaction between
the supernova ejecta and a discrete H-rich shell, located at a distance of
$\sim4\times10^{16}$\,cm from the explosion site. This ejecta-CSM interaction
causes the rest-frame r-band LC to brighten at late times. The fact that the
late-time spectra are not completely absorbed by the shock ionized CSM shell
implies that its Thomson scattering optical depth is likely <1, thus setting
upper limits on the CSM mass <30$M_\odot$ and the volume number density
<4x$10^8cm^{-3}$. Of the existing models, a Pulsational Pair Instability
Supernova model can naturally explain the observed 30$M_\odot$ H-shell, ejected
from a progenitor star with an initial mass of (95-150)$M_\odot$ about 40 years
ago. We estimate that at least $\sim$15\%\ of all SLSNe-I may have late-time
Balmer emission lines. | astro-ph_GA |
The Local Dark Matter Density from SDSS-SEGUE G-dwarfs: We derive the local dark matter density by applying the integrated Jeans
equation method from Silverwood et al. (2016) to SDSS-SEGUE G-dwarf data
processed and presented by B\"udenbender et al. (2015). We use the MultiNest
Bayesian nested sampling software to fit a model for the baryon distribution,
dark matter and tracer stars, including a model for the 'tilt term' that
couples the vertical and radial motions, to the data. The $\alpha$-young
population from B\"udenbender et al. (2015) yields the most reliable result of
$\rho_{\rm DM} = 0.46^{+0.07}_{-0.09}\, {{\rm GeV\, cm}^{-3}} =
0.012^{+0.001}_{-0.002}\, {{\rm M}_\odot \, {\rm pc}^{-3}}$. Our analyses yield
inconsistent results for the $\alpha$-young and $\alpha$-old data, pointing to
problems in the tilt term and its modelling, the data itself, the assumption of
a flat rotation curve, or the effects of disequilibria. | astro-ph_GA |
Variations of Broad Emission Lines from periodicity QSOs under the
interpretation of supermassive binary black holes with misaligned
circumbinary broad line regions: Quasars with periodic light curves are considered as candidates of
supermassive binary black hole (BBH) systems. One way for further confirmations
may be searching for other characteristic signatures, such as those in their
broad emission lines (BELs), if any, which require a thorough understanding on
the response of BELs to the BBH systems. In Ji et al. (2021), we have
investigated the response of circumbinary broad line region (BLR) to the
central active secondary black hole under the relativistic Doppler boosting
(BBH-DB) and intrinsic variation (BBH-IntDB) dominant mechanisms for continuum
variation by assuming the middle plane of the BLR aligned with the BBH orbital
plane. In this paper, we explore how the BEL profiles vary when the BLR is
misaligned from the BBH orbital plane with different offset angles under both
the BBH-DB and BBH-IntDB scenarios. Given a fixed inclination angle of the BBH
orbital plane viewed in edge-on and similar continuum light curves produced by
the two scenarios, increasing offset angles make the initial opening angle of
the circumbinary BLR enlarged due to orbital precession caused by the BBH
system, especially for clouds in the inner region, which result in Lorentz-like
BEL profiles for the BBH-DB model but still Gaussian-like profiles for the
BBH-IntDB model at the vertical BLR case. The amplitude of profile variations
decrease with increasing offset angles for the BBH-DB scenario, while keep
nearly constant for the BBH-IntDB scenario, since the Doppler boosting effect
is motion direction preferred but the intrinsic variation is radiated
isotropically. If the circumbinary BLR is composed of a coplanar and a vertical
components with their number of clouds following the mass ratio of the BBHs,
then the bi-BLR features are more significant for the BBH-IntDB model that
require larger mass ratio to generate similar continuum variation than the
BBH-DB model. | astro-ph_GA |
The Tucana dwarf spheroidal: a distant backsplash galaxy of M31?: We use the APOSTLE Local Group (LG) cosmological hydro-simulations to examine
the properties of "backsplash" galaxies, i.e, dwarfs which were within the
virial boundaries of the Milky Way (MW) or M31 in the past, but are today
outside their virial radius ($r_{200}$). More than half of all dwarfs between
$1-2\,r_{200}$ of each primary are backsplash. More distant backsplash systems,
i.e., those reaching distances well beyond $2\,r_{200}$, are typically close to
apocentre of nearly radial orbits, and, therefore, essentially at rest relative
to their primary. We use this result to investigate which LG dwarfs beyond
$\sim500$ kpc of either primary could be a distant backsplash satellite of MW
or M31. Tucana dSph, one of the few known quiescent LG field dwarfs, at $d_{\rm
M31}\approx1350$ kpc and $d_{\rm MW}\approx880$ kpc, is a promising candidate.
Tucana's radial velocity is consistent with being at rest relative to M31.
Further, Tucana is located close to M33's orbital plane around M31, and simple
orbit integrations indicate that Tucana may have been ejected during an early
pericentric passage of M33 $\sim11$ Gyr ago, a timing which approximately
coincides with Tucana's last episode of star formation. We suggest that Tucana
may have been an early-infalling satellite of M31 or M33, providing a
compelling explanation for its puzzling lack of gas and ongoing star formation
despite its isolated nature. In this scenario, M33 should have completed some
orbits around M31, a result that may help to explain the relative dearth of M33
satellite-candidates identified so far. | astro-ph_GA |
LAGER Ly$α$ Luminosity Function at $z\sim7$, Implications for
Reionization: We present a new measurement of the Ly$\alpha$ luminosity function at
redshift $z=6.9$, finding moderate evolution from $z=5.7$ that is consistent
with a fully or largely ionized $z\sim7$ intergalactic medium. Our result is
based on four fields of the LAGER (Lyman Alpha Galaxies in the Epoch of
Reionization) project. Our survey volume of $6.1\times10^{6}$ Mpc$^{3}$ is
double that of the next largest $z\sim 7$ survey. We combine two new LAGER
fields (WIDE12 and GAMA15A) with two previously reported LAGER fields (COSMOS
and CDFS). In the new fields, we identify $N=95$ new $z=6.9$ Ly$\alpha$
emitters (LAEs); characterize our survey's completeness and reliability; and
compute Ly$\alpha$ luminosity functions. The best-fit Schechter luminosity
function parameters for all four LAGER fields are in good general agreement.
Two fields (COSMOS and WIDE12) show evidence for a bright-end excess above the
Schechter function fit. We find that the Ly$\alpha$ luminosity density declines
at the same rate as the UV continuum LF from $z=5.7$ to $z=6.9$. This is
consistent with an intergalactic medium that was fully ionized as early as
redshift $z\sim 7$, or with a volume-averaged neutral hydrogen fraction of
$x_{HI} < 0.33$ at $1\sigma$. | astro-ph_GA |
Detailed study of the Bootes field using 300-500 MHz uGMRT observations:
Source Properties and radio--infrared correlations: The dominant source of radio continuum emissions at low frequencies is
synchrotron radiation, which originates from star-forming regions in disk
galaxies and from powerful jets produced by active galactic nuclei (AGN). We
studied the Bootes field using the upgraded Giant Meterwave Radio Telescope
(uGMRT) at 400 MHz, achieving a central minimum off-source RMS noise of
35$\mu$Jy beam$^{-1}$ and a catalogue of 3782 sources in $\sim6$ sq. degrees of
the sky. The resulting catalogue was compared to other radio frequency
catalogues, and the corrected normalised differential source counts were
derived. We use standard multi-wavelength techniques to classify the sources in
star-forming galaxies (SFGs), radio-loud (RL) AGN, and radio-quiet (RQ) AGN
that confirm a boost in the SFGs and RQ\,AGN AGN populations at lower flux
levels. For the first time, we investigated the properties of the radio--IR
relations at 400\,MHz in this field. The $L_{\rm 400 MHz}$--$L_{\rm TIR}$
relations for SFGs were found to show a strong correlation with non-linear
slope values of $1.10\pm0.01$, and variation of $q_{\rm TIR}$ with $z$ is given
as, $q_{\rm TIR} = (2.19 \pm 0.07)\ (1+z)^{-0.15 \pm 0.08}$. This indicates
that the non-linearity of the radio--IR relations can be attributed to the mild
variation of $q_{\rm TIR}$ values with $z$. The derived relationships exhibit
similar behaviour when applied to LOFAR at 150 MHz and also at 1.4 GHz. This
emphasises the fact that other parameters like magnetic field evolution with
$z$ or the number densities of cosmic ray electrons can play a vital role in
the mild evolution of $q$ values. | astro-ph_GA |
The Far-IR View of Star and Planet Forming Regions: The far-IR range is a critical wavelength range to characterize the physical
and chemical processes that transform the interstellar material into stars and
planets. Objects in the earliest phases of stellar and planet evolution release
most of their energy at these long wavelengths. In this contribution we briefly
summarise some of the most relevant scientific advances achieved by the
Herschel Space Observatory in the field. We also anticipate those that will be
made possible by the large increase in sensitivity of SPICA cooled telescope.
It is concluded that only through sensitive far-IR observations much beyond
Herschel capabilities we will be able to constrain the mass, the energy budget
and the water content of hundreds of protostars and planet-forming disks. | astro-ph_GA |
X-shaped Radio Galaxies: Optical Properties, Large-scale Environment and
Relationship to Radio Structure: In order to find clues to the origin of the "winged" or "X-shaped" radio
galaxies (XRGs) we investigate here the parent galaxies of a large sample of
106 XRGs for optical-radio axes alignment, interstellar medium, black hole
mass, and large-scale environment. For 41 of the XRGs it was possible to
determine the optical major axis and the primary radio axis and the strong
tendency for the two axes to be fairly close is confirmed. However, several
counter-examples were also found and these could challenge the widely discussed
backflow diversion model for the origin of the radio wings. Comparison with a
well-defined large sample of normal FR II radio galaxies has revealed that: (i)
XRGs possess slightly less massive central black holes than the normal radio
galaxies (average masses being log$M_{\rm BH} \sim$ 8.81 $M_{\odot}$ and 9.07
$M_{\odot}$, respectively); (ii) a much higher fraction of XRGs ($\sim$ 80%)
exhibits red mid-IR colors ($W2 - W3 > 1.5$), indicating a population of young
stars and/or an enhanced dust mass, probably due to relatively recent galaxy
merger(s). A comparison of the large-scale environment (i.e., within $\sim$ 1
Mpc) shows that both XRGs and FRII radio galaxies inhabit similarly poor galaxy
clustering environments (medium richness being 8.94 and 11.87, respectively).
Overall, the origin of XRGs seems difficult to reconcile with a single dominant
physical mechanism and competing mechanisms seem prevalent. | astro-ph_GA |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.