82 research outputs found
Spitzer observations of a gravitationally lensed quasar, QSO 2237+0305
The four-image gravitationally lensed quasar QSO 2237+0305 is microlensed by
stars in the lens galaxy. The amplitude of microlensing variability can be used
to infer the relative size of the quasar as a function of wavelength; this
provides a test of quasar models. Toward this end, we present Spitzer Space
Telescope Infrared Spectrograph and Infrared Array Camera (IRAC) observations
of QSO 2237+0305, finding the following. (1) The infrared (IR) spectral energy
distribution (SED) is similar to that of other bright radio-quiet quasars,
contrary to an earlier claim. (2) A dusty torus model with a small opening
angle fits the overall shape of the IR SED well, but the quantitative agreement
is poor due to an offset in wavelength of the silicate feature. (3) The flux
ratios of the four lensed images can be derived from the IRAC data despite
being unresolved. We find that the near-IR fluxes are increasingly affected by
microlensing toward shorter wavelengths. (4) The wavelength dependence of the
IRAC flux ratios is consistent with the standard quasar model in which an
accretion disk and a dusty torus both contribute near 1 micron in the rest
frame. This is also consistent with recent IR spectropolarimetry of nearby
quasars
The UV, Optical, and IR Properties of SDSS Sources Detected by GALEX
We discuss the UV, optical, and IR properties of the SDSS sources detected by
GALEX as part of its All-sky Imaging Survey Early Release Observations.
Virtually all of the GALEX sources in the overlap region are detected by SDSS.
GALEX sources represent ~2.5% of all SDSS sources within these fields and about
half are optically unresolved. Most unresolved GALEX/SDSS sources are bright
blue turn-off thick disk stars and are typically detected only in the GALEX
near-UV band. The remaining unresolved sources include low-redshift quasars,
white dwarfs, and white dwarf/M dwarf pairs, and these dominate the optically
unresolved sources detected in both GALEX bands.
Almost all the resolved SDSS sources detected by GALEX are fainter than the
SDSS 'main' spectroscopic limit. These sources have colors consistent with
those of blue (spiral) galaxies (u-r<2.2), and most are detected in both GALEX
bands. Measurements of their UV colors allow much more accurate and robust
estimates of star-formation history than are possible using only SDSS data.
Indeed, galaxies with the most recent (<20 Myr) star formation can be robustly
selected from the GALEX data by requiring that they be brighter in the far-UV
than in the near-UV band. However, older starburst galaxies have UV colors
similar to AGN, and thus cannot be selected unambiguously on the basis of GALEX
fluxes alone.
With the aid of 2MASS data, we construct and discuss median 10 band
UV-optical-IR spectral energy distributions for turn-off stars, hot white
dwarfs, low-redshift quasars, and spiral and elliptical galaxies. We point out
the high degree of correlation between the UV color and the contribution of the
UV flux to the UV-optical-IR flux of galaxies detected by GALEX.Comment: 35 pages, 11 figures, 3 tables; to appear in the AJ. PS with better
figures available from http://www.astro.washington.edu/agueros/pub
The ACS Nearby Galaxy Survey Treasury IV. The Star Formation History of NGC 2976
We present resolved stellar photometry of NGC 2976 obtained with the Advanced
Camera for Surveys (ACS) as part of the ACS Nearby Galaxy Survey Treasury
(ANGST) program. The data cover the radial extent of the major axis of the disk
out to 6 kpc, or ~6 scale lengths. The outer disk was imaged to a depth of
M_F606W ~ 1, and an inner field was imaged to the crowding limit at a depth of
M_F606W ~ -1. Through detailed analysis and modeling of these CMDs we have
reconstructed the star formation history of the stellar populations currently
residing in these portions of the galaxy, finding similar ancient populations
at all radii but significantly different young populations at increasing radii.
In particular, outside of the well-measured break in the disk surface
brightness profile, the age of the youngest population increases with distance
from the galaxy center, suggesting that star formation is shutting down from
the outside-in. We use our measured star formation history, along with H I
surface density measurements, to reconstruct the surface density profile of the
disk during previous epochs. Comparisons between the recovered star formation
rates and reconstructed gas densities at previous epochs are consistent with
star formation following the Schmidt law during the past 0.5 Gyrs, but with a
drop in star formation efficiency at low gas densities, as seen in local
galaxies at the present day. The current rate and gas density suggest that
rapid star formation in NGC 2976 is currently in the process of ceasing from
the outside-in due to gas depletion. This process of outer disk gas depletion
and inner disk star formation was likely triggered by an interaction with the
core of the M81 group >~1 Gyr ago that stripped the gas from the galaxy halo
and/or triggered gas inflow from the outer disk toward the galaxy center.Comment: 22 pages, 14 figures, 2 tables, accepted for publication by Ap
The ACS Nearby Galaxy Survey Treasury
The ACS Nearby Galaxy Survey Treasury (ANGST) is a systematic survey to
establish a legacy of uniform multi-color photometry of resolved stars for a
volume-limited sample of nearby galaxies (D<4 Mpc). The survey volume
encompasses 69 galaxies in diverse environments, including close pairs, small &
large groups, filaments, and truly isolated regions. The galaxies include a
nearly complete range of morphological types spanning a factor of ~10^4 in
luminosity and star formation rate. The survey data consists of images taken
with ACS on HST, supplemented with archival data and new WFPC2 imaging taken
after the failure of ACS. Survey images include wide field tilings covering the
full radial extent of each galaxy, and single deep pointings in uncrowded
regions of the most massive galaxies in the volume. The new wide field imaging
in ANGST reaches median 50% completenesses of m_F475W=28.0 mag, m_F606W=27.3
mag, and m_F814W=27.3 mag, several magnitudes below the tip of the red giant
branch (TRGB). The deep fields reach magnitudes sufficient to fully resolve the
structure in the red clump. The resulting photometric catalogs are publicly
accessible and contain over 34 million photometric measurements of >14 million
stars. In this paper we present the details of the sample selection, imaging,
data reduction, and the resulting photometric catalogs, along with an analysis
of the photometric uncertainties (systematic and random), for both the ACS and
WFPC2 imaging. We also present uniformly derived relative distances measured
from the apparent magnitude of the TRGB.Comment: 54 pages, including 24 pages of figures and 16 pages of tables.
Project website and data available at http://www.nearbygalaxies.org/ . Data
is also available through MAST. Scheduled to appear in the Astrophysical
Journal Supplements. (Replaced to fix several figures that were damaged
during compression
The ACS Nearby Galaxy Survey Treasury I. The Star Formation History of the M81 Outer Disk
The ACS Nearby Galaxy Survey Treasury (ANGST) is a large Hubble Space
Telescope (HST) Advanced Camera for Surveys (ACS) treasury program to obtain
resolved stellar photometry for a volume-limited sample of galaxies out to 4
Mpc. As part of this program, we have obtained deep ACS imaging of a field in
the outer disk of the large spiral galaxy M81. The field contains the outskirts
of a spiral arm as well as an area containing no current star formation. Our
imaging results in a color-magnitude diagram (CMD) reaching to F814W = 28.8 and
F606W = 29.5, one magnitude fainter than the red clump. Through detailed
modeling of the full CMD, we quantify the age and metallicity distribution of
the stellar populations contained in the field. The mean metallicity in the
field is -1<[M/H]<0 and only a small fraction of stars have ages <~1 Gyr. The
results show that most of the stars in this outer disk field were formed by z~1
and that the arm structure at this radius has a lifetime of >~100 Myr. We
discuss the measured evolution of the M81 disk in the context of surveys of
high-redshift disk galaxies and deep stellar photometry of other nearby
galaxies. All of these indicate that massive spiral disks are mostly formed by
z~1 and that they have experienced rapid metal enrichment.Comment: 26 pages, 2 tables, 18 figures, accepted for publication in A
Genome-wide association study of generalized anxiety symptoms in the Hispanic Community Health Study/Study of Latinos
Although generalized anxiety disorder (GAD) is heritable and aggregates in families, no genomic loci associated with GAD have been reported. We aimed to discover potential loci by conducting a genome-wide analysis of GAD symptoms in a large, population-based sample of Hispanic/Latino adults. Data came from 12,282 participants (aged 18–74) in the Hispanic Community Health Study/Study of Latinos. Using a shorted Spielberger Trait Anxiety measure, we analyzed: (1) a total trait anxiety score based on summing responses to all ten items; and (2) a GAD symptoms score restricted to the three items tapping diagnostic features of GAD as defined by DSM-V. We first calculated the heritability due to common variants (h2SNP) and then conducted a genome-wide association study (GWAS) of GAD symptoms. Replication was attempted in three independent Hispanic cohorts (Multi-Ethnic Study of Atherosclerosis, Women’s Health Initiative, Army STARRS). The GAD symptoms score showed evidence of modest heritability (7.2%; p=0.03), while the total trait anxiety score did not (4.97%; p=0.20). One genotyped SNP (rs78602344) intronic to Thrombospondin 2 (THBS2) was nominally associated (p=4.18×10−8) in the primary analysis adjusting for psychiatric medication use and significantly associated with the GAD symptoms score in the analysis excluding medication users (p=4.18×10−8). However, meta-analysis of the replication samples did not support this association. Although GWAS revealed a genome-wide significant locus in this sample, we were unable to replicate this finding. Evidence for heritability was also only detected for GAD symptoms, and not the trait anxiety measure, suggesting differential genetic influences within the domain of trait anxiety
Genetic variation near IRS 1 is associated with adiposity and a favorable metabolic profile in U.S.Hispanics/Latinos: IRS1Variation, Adiposity, and Metabolic Profile
We examined associations of IRS1 genetic variation with adiposity and metabolic profile in US Hispanic/Latino individuals of diverse backgrounds
Genome-wide Association Study of Platelet Count Identifies Ancestry-Specific Loci in Hispanic/Latino Americans
Platelets play an essential role in hemostasis and thrombosis. We performed a genome-wide association study of platelet count in 12,491 participants of the Hispanic Community Health Study/Study of Latinos by using a mixed-model method that accounts for admixture and family relationships. We discovered and replicated associations with five genes (ACTN1, ETV7, GABBR1-MOG, MEF2C, and ZBTB9-BAK1). Our strongest association was with Amerindian-specific variant rs117672662 (p value = 1.16 × 10−28) in ACTN1, a gene implicated in congenital macrothrombocytopenia. rs117672662 exhibited allelic differences in transcriptional activity and protein binding in hematopoietic cells. Our results underscore the value of diverse populations to extend insights into the allelic architecture of complex traits
- …