1,778 research outputs found
The Mid-Infrared Luminosities of Normal Galaxies over Cosmic Time
Modern population synthesis models estimate that 50% of the restframe K-band
light is produced by TP-AGB stars during the first Gyr of a stellar population,
with a substantial fraction continuing to be produced by the TP-AGB over a
Hubble time. Between 0.2 and 1.5 Gyr, intermediate mass stars evolve into
TP-AGB C stars which, due to significant amounts of circumstellar dust, emit
half their energy in the mid-IR. We combine these results using published
mid-IR colors of Galactic TP-AGB M and C stars to construct simple models for
exploring the contribution of the TP-AGB to 24micron data as a function of
stellar population age. We compare these empirical models with an ensemble of
galaxies in the CDFS from z=0 to z=2, and with high quality imaging in M81.
Within the uncertainties, the TP-AGB appears responsible for a substantial
fraction of the mid-IR luminosities of galaxies from z=0 to z=2, the maximum
redshift to which we can test our hypothesis, while, at the same time, our
models reproduce much of the detailed structure observed in mid-IR imaging of
M81. The mid-IR is a good diagnostic of star formation over timescales of ~1.5
Gyr, but this implies that on-going star formation rates at z=1 may be
overestimated by factors of ~1.5-6, depending on the nature of star formation
events. Our results, if confirmed through subsequent work, have strong
implications for the star formation rate density of the universe and the growth
of stellar mass over time.Comment: 6 pages, 4 figures, Accepted for publication in Astrophysical Journal
Letter
Integrated spectral energy distributions of binary star composite stellar populations
This paper presents theoretical integrated spectral energy distributions
(SEDs) of binary star composite stellar populations (bsCSPs) in early-type
galaxies, and how the bsCSP model can be used for spectral studies of galaxies.
All bsCSPs are built basing on three adjustable inputs (metallicity, ages of
old and young components). The effects of binary interactions and stellar
population mixture are taken into account. The results show some UV-upturn SEDs
naturally for bsCSPs. The SEDs of bsCSPs are affected obviously by all of three
stellar population parameters, and the effects of three parameters are
degenerate. This suggests that the effects of metallicity, and the ages of the
old (major in stellar mass) and young (minor) components of stellar populations
should be taken into account in SED studies of early-type galaxies. The
sensitivities of SEDs at different wavelengths to the inputs of a stellar
population model are also investigated. It is shown that UV SEDs are sensitive
to all of three stellar population parameters, rather than to only stellar age.
Special wavelength ranges according to some SED features that are relatively
sensitive to stellar metallicity, young-component age, and old-component age of
bsCSPs are found by this work. For example, the shapes of SEDs with wavelength
ranges of 5110-5250AA, 5250--5310AA, 5310--5350AA, 5830--5970AA, 20950--23550AA
are relatively sensitive to the stellar metallicity of bsCSPs. The shapes of
SEDs within 965-985AA, 1005--1055AA, 1205--1245AA are sensitive to
old-component age, while SED features within the wavelength ranges of
2185--2245AA, 2455--2505AA, 2505--2555AA, 2775--2825AA, 2825--2875AA to
young-component age.Comment: 10 pages, 12 figures, Accepted to publish in MNRA
Resolving the Steiner Point Removal Problem in Planar Graphs via Shortcut Partitions
Recently the authors [CCLMST23] introduced the notion of shortcut partition
of planar graphs and obtained several results from the partition, including a
tree cover with trees for planar metrics and an additive embedding into
small treewidth graphs. In this note, we apply the same partition to resolve
the Steiner point removal (SPR) problem in planar graphs: Given any set of
terminals in an arbitrary edge-weighted planar graph , we construct a minor
of whose vertex set is , which preserves the shortest-path distances
between all pairs of terminals in up to a constant factor. This resolves in
the affirmative an open problem that has been asked repeatedly in literature.Comment: Manuscript not intended for publication. The results have been
subsumed by arXiv:2308.00555 from the same author
Clustering of star-forming galaxies detected in mid-infrared with the Spitzer wide-area survey
We discuss the clustering properties of galaxies with signs of ongoing star
formation detected by the Spitzer Space Telescope at 24mum band in the SWIRE
Lockman Hole field. The sample of mid-IR-selected galaxies includes ~20,000
objects detected above a flux threshold of S24mum=310muJy. We adopt
optical/near-IR color selection criteria to split the sample into the
lower-redshift and higher-redshift galaxy populations. We measure the angular
correlation function on scales of theta=0.01-3.5 deg, from which, using the
Limber inversion along with the redshift distribution established for similarly
selected source populations in the GOODS fields (Rodighiero et al. 2010), we
obtain comoving correlation lengths of r0=4.98+-0.28 h^-1 Mpc and r0
=8.04+-0.69 h^-1 Mpc for the low-z (=0.7) and high-z (=1.7) subsamples,
respectively. Comparing these measurements with the correlation functions of
dark matter halos identified in the Bolshoi cosmological simulation (Klypin et
al. 2011}, we find that the high-redshift objects reside in progressively more
massive halos reaching Mtot>3e12 h^-1 Msun, compared to Mtot>7e11 h^-1 Msun for
the low-redshift population. Approximate estimates of the IR luminosities based
on the catalogs of 24mum sources in the GOODS fields show that our high-z
subsample represents a population of "distant ULIRGs" with LIR>10^12Lsun, while
the low-z subsample mainly consists of "LIRGs", LIR~10^11Lsun. The comparison
of number density of the 24mum selected galaxies and of dark matter halos with
derived minimum mass Mtot shows that only 20% of such halos may host
star-forming galaxies.Comment: 15 pages, 12 figure
The Star-Formation Histories of z~2 DOGs and SMGs
The Spitzer Space Telescope has identified a population of ultra-luminous
infrared galaxies (ULIRGs) at z ~ 2 that may play an important role in the
evolution of massive galaxies. We measure the stellar masses of two populations
of Spitzer-selected ULIRGs, both of which have extremely red R-[24] colors
(dust-obscured galaxies, or DOGs) and compare our results with sub-millimeter
selected galaxies (SMGs). One set of 39 DOGs has a local maximum in their
mid-IR spectral energy distribution (SED) at rest-frame 1.6um associated with
stellar emission ("bump DOGs"), while the other set of 51 DOGs has a power-law
dominated mid-IR SED with spectral features typical of obscured AGN ("power-law
DOGs"). We use stellar population synthesis models applied self-consistently to
broad-band photometry in the rest-frame ultra-violet, optical, and
near-infrared of each of these populations and test a variety of stellar
population synthesis codes, star-formation histories (SFHs), and initial mass
functions (IMFs). Assuming a simple stellar population SFH and a Chabrier IMF,
we find that the median and inner quartile stellar masses of SMGs, bump DOGs
and power-law DOGs are given by log(M_*/M_sun) = 10.42_-0.36^+0.42,
10.62_-0.32^+0.36, and 10.71_-0.34^+0.40, respectively. Implementing more
complicated SFHs with multiple age components increases these mass estimates by
up to 0.5 dex. Our stellar mass estimates are consistent with physical
mechanisms for the origin of z~2 ULIRGs that result in high star-formation
rates for a given stellar mass. Such mechanisms are usually driven by a major
merger of two gas-rich systems, rather than smooth accretion of gas and small
satellites.Comment: 17 pages, 7 figures, 3 tables. Plus figures showing SEDs and best-fit
synthesized stellar population model. Accepted to the Ap
The stellar evolution of Luminous Red Galaxies, and its dependence on colour, redshift, luminosity and modelling
We present a series of colour evolution models for Luminous Red Galaxies
(LRGs) in the 7th spectroscopic data release of the Sloan Digital Sky Survey
(SDSS), computed using the full-spectrum fitting code VESPA on high
signal-to-noise stacked spectra. The colour-evolution models are computed as a
function of colour, luminosity and redshift, and we do not a-priori assume that
LRGs constitute a uniform population of galaxies in terms of stellar evolution.
By computing star-formation histories from the fossil record, the measured
stellar evolution of the galaxies is decoupled from the survey's selection
function, which also evolves with redshift. We present these evolutionary
models computed using three different sets of Stellar Population Synthesis
(SPS) codes. We show that the traditional fiducial model of purely passive
stellar evolution of LRGs is broadly correct, but it is not sufficient to
explain the full spectral signature. We also find that higher-order corrections
to this model are dependent on the SPS used, particularly when calculating the
amount of recent star formation. The amount of young stars can be
non-negligible in some cases, and has important implications for the
interpretation of the number density of LRGs within the selection box as a
function of redshift. Dust extinction, however, is more robust to the SPS
modelling: extinction increases with decreasing luminosity, increasing
redshift, and increasing r-i colour. We are making the colour evolution tracks
publicly available at http://www.icg.port.ac.uk/~tojeiror/lrg_evolution/.Comment: 29 pages, 34 figures, re-submitted to MNRAS after addressing the
referee's repor
The VIMOS-VLT Deep Survey: Evolution in the Halo Occupation Number since z 1
We model the evolution of the mean galaxy occupation of dark-matter halos
over the range , using the data from the VIMOS-VLT Deep Survey
(VVDS). The galaxy projected correlation function was computed for a
set of luminosity-limited subsamples and fits to its shape were obtained using
two variants of Halo Occupation Distribution models. These provide us with a
set of best-fitting parameters, from which we obtain the average mass of a halo
and average number of galaxies per halo. We find that after accounting for the
evolution in luminosity and assuming that we are largely following the same
population, the underlying dark matter halo shows a growth in mass with
decreasing redshift as expected in a hierarchical structure formation scenario.
Using two different HOD models, we see that the halo mass grows by 90% over the
redshift interval z=[0.5,1.0]. This is the first time the evolution in halo
mass at high redshifts has been obtained from a single data survey and it
follows the simple form seen in N-body simulations with , and . This provides evidence for a rapid accretion
phase of massive halos having a present-day mass , with a merger event occuring between redshifts of 0.5
and 1.0. Futhermore, we find that more luminous galaxies are found to occupy
more massive halos irrespectively of the redshift. Finally, the average number
of galaxies per halo shows little increase from redshift z 1.0 to z
0.5, with a sharp increase by a factor 3 from z 0.5 to z 0.1,
likely due to the dynamical friction of subhalos within their host halos.Comment: 14 pages, 6 figures, 5 tables. MNRAS accepted
Close Galaxy Pairs at z = 3: A Challenge to UV Luminosity Abundance Matching
We use a sample of z~3 Lyman Break Galaxies (LBGs) to examine close pair
clustering statistics in comparison to LCDM-based models of structure
formation. Samples are selected by matching the LBG number density and by
matching the observed LBG 3-D correlation function of LBGs over the two-halo
term region. We show that UV-luminosity abundance matching cannot reproduce the
observed data, but if subhalos are chosen to reproduce the observed clustering
of LBGs we are able to reproduce the observed LBG pair fraction, (Nc), defined
as the average number of companions per galaxy. This model suggests an over
abundance of LBGs by a factor of ~5 over those observed, suggesting that only 1
in 5 halos above a fixed mass hosts a galaxy with LBG-like UV luminosity
detectable via LBG selection techniques. We find a total observable close pair
fraction of 23 \pm 0.6% (17.7 \pm 0.5%) using a prototypical cylinder radius in
our overdense fiducial model and 8.3 \pm 0.5% (5.6 \pm 0.2%) in an abundance
matched model (impurity corrected). For the matched spectroscopic slit
analysis, we find Ncs = 5.1\pm0.2% (1.68\pm0.02%), the average number of
companions observed serendipitously in our for fiducial slits (abundance
matched), whereas the observed fraction of serendipitous spectroscopic close
pairs is 4.7\pm1.5 per cent using the full LBG sample and 7.1\pm2.3% for a
subsample with higher signal-to-noise ratio. We show that the standard method
of halo assignment fails to reproduce the break in the LBG close pair behavior
at small scale. To reconcile these discrepancies we suggest that a plausible
fraction of LBGs in close pairs with lower mass than our sample experience
interaction-induced enhanced star formation that boosts their luminosity
sufficiently to be detected in observational sample but are not included in the
abundance matched simulation sample.Comment: 18 pages, 12 figures, 1 table, published in MNRA
Comparing six evolutionary population synthesis models through spectral synthesis on galaxies
We compare six popularly used evolutionary population synthesis (EPS) models
(BC03, CB07, Ma05, GALEV, GRASIL, Vazdekis/Miles) through fitting the full
optical spectra of six representative types of galaxies (star-forming and
composite galaxies, Seyfert 2s, LINERs, E+A and early-type galaxies), which are
taken from the Sloan Digital Sky Survey (SDSS). Throughout our paper, we use
the simple stellar populations (SSPs) from each EPS model and the software
STARLIGHT to do our fits. Our main results are: Using different EPS models the
resulted numerical values of contributed light fractions change obviously, even
though the dominant populations are consistent. The stellar population
synthesis does depend on the selection of age and metallicity, while it does
not depend on the stellar evolution track much. The importance of young
populations decreases from star-forming, composite, Seyfert 2, LINER to
early-type galaxies, and E+A galaxies lie between composite galaxies and
Seyfert 2s in most cases. We conclude that different EPS models do derive
different stellar populations, so that it is not reasonable to directly compare
stellar populations estimated from different EPS models. To get reliable
results, we should use the same EPS model for the compared samples.Comment: 13 pages, 4 figures, accepted for publication in A&
Adverse drug reactions and off-label and unlicensed medicines in children: a nested case control study of inpatients in a pediatric hospital
Off-label and unlicensed (OLUL) prescribing has been prevalent in pediatric practice. Using data from a prospective cohort study of adverse drug reactions (ADRs) among pediatric inpatients, we aimed to test the hypothesis that OLUL status is a risk factor for ADRs
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