3,752 research outputs found
The Highly Unusual Chemical Composition of the Hercules Dwarf Spheroidal Galaxy
We report on the abundance analysis of two red giants in the faint Hercules
dwarf spheroidal (dSph) galaxy. These stars show a remarkable deficiency in the
neutron-capture elements, while the hydrostatic alpha-elements (O, Mg) are
strongly enhanced. Our data indicate [Ba/Fe] and [Mg/Fe] abundance ratios of
<-2 dex and ~+0.8 dex, respectively, with essentially no detection of other
n-capture elements. In contrast to the only other dSph star with similar
abundance patterns, Dra 119, which has a very low metallicity at [Fe/H]=-2.95
dex, our objects, at [Fe/H]~-2.0 dex, are only moderately metal poor. The
measured ratio of hydrostatic/explosive alpha-elements indicates that high-mass
(~35 M_sun) Type II supernovae progenitors are the main, if not only,
contributors to the enrichment of this galaxy. This suggests that star
formation and chemical enrichment in the ultrafaint dSphs proceeds
stochastically and inhomogeneously on small scales, or that the IMF was
strongly skewed to high mass stars. The neutron capture deficiencies and the
[Co/Fe] and [Cr/Fe] abundance ratios in our stars are similar to those in the
extremely low metallicity Galactic halo. This suggests that either our stars
are composed mainly of the ejecta from the first, massive, population III stars
(but at moderately high [Fe/H]), or that SN ejecta in the Hercules galaxy were
diluted with ~30 times less hydrogen than typical for extreme metal-poor stars.Comment: 5 pages, 3 figures, accepted by Astrophysical Journal Letter
Faint NUV/FUV Standards from Swift/UVOT, GALEX and SDSS Photometry
At present, the precision of deep ultraviolet photometry is somewhat limited
by the dearth of faint ultraviolet standard stars. In an effort to improve this
situation, we present a uniform catalog of eleven new faint (u sim17)
ultraviolet standard stars. High-precision photometry of these stars has been
taken from the Sloan Digital Sky Survey and Galaxy Evolution Explorer and
combined with new data from the Swift Ultraviolet Optical Telescope to provide
precise photometric measures extending from the Near Infrared to the Far
Ultraviolet. These stars were chosen because they are known to be hot (20,000 <
T_eff < 50,000 K) DA white dwarfs with published Sloan spectra that should be
photometrically stable. This careful selection allows us to compare the
combined photometry and Sloan spectroscopy to models of pure hydrogen
atmospheres to both constrain the underlying properties of the white dwarfs and
test the ability of white dwarf models to predict the photometric measures. We
find that the photometry provides good constraint on white dwarf temperatures,
which demonstrates the ability of Swift/UVOT to investigate the properties of
hot luminous stars. We further find that the models reproduce the photometric
measures in all eleven passbands to within their systematic uncertainties.
Within the limits of our photometry, we find the standard stars to be
photometrically stable. This success indicates that the models can be used to
calibrate additional filters to our standard system, permitting easier
comparison of photometry from heterogeneous sources. The largest source of
uncertainty in the model fitting is the uncertainty in the foreground reddening
curve, a problem that is especially acute in the UV.Comment: Accepted for publication in Astrophysical Journal. 31 pages, 13
figures, electronic tables available from ApJ or on reques
The WiggleZ Dark Energy Survey: Direct constraints on blue galaxy intrinsic alignments at intermediate redshifts
Correlations between the intrinsic shapes of galaxy pairs, and between the
intrinsic shapes of galaxies and the large-scale density field, may be induced
by tidal fields. These correlations, which have been detected at low redshifts
(z<0.35) for bright red galaxies in the Sloan Digital Sky Survey (SDSS), and
for which upper limits exist for blue galaxies at z~0.1, provide a window into
galaxy formation and evolution, and are also an important contaminant for
current and future weak lensing surveys. Measurements of these alignments at
intermediate redshifts (z~0.6) that are more relevant for cosmic shear
observations are very important for understanding the origin and redshift
evolution of these alignments, and for minimising their impact on weak lensing
measurements. We present the first such intermediate-redshift measurement for
blue galaxies, using galaxy shape measurements from SDSS and spectroscopic
redshifts from the WiggleZ Dark Energy Survey. Our null detection allows us to
place upper limits on the contamination of weak lensing measurements by blue
galaxy intrinsic alignments that, for the first time, do not require
significant model-dependent extrapolation from the z~0.1 SDSS observations.
Also, combining the SDSS and WiggleZ constraints gives us a long redshift
baseline with which to constrain intrinsic alignment models and contamination
of the cosmic shear power spectrum. Assuming that the alignments can be
explained by linear alignment with the smoothed local density field, we find
that a measurement of \sigma_8 in a blue-galaxy dominated, CFHTLS-like survey
would be contaminated by at most +/-0.02 (95% confidence level, SDSS and
WiggleZ) or +/-0.03 (WiggleZ alone) due to intrinsic alignments. [Abridged]Comment: 18 pages, 12 figures, accepted to MNRAS; v2 has correction to one
author's name, NO other changes; v3 has minor changes in explanation and
calculations, no significant difference in results or conclusions; v4 has an
additional footnote about model interpretation, no changes to
data/calculations/result
The GALEX Arecibo SDSS Survey. VI. Second Data Release and Updated Gas Fraction Scaling Relations
We present the second data release from the GALEX Arecibo SDSS Survey (GASS),
an ongoing large Arecibo program to measure the HI properties for an unbiased
sample of ~1000 galaxies with stellar masses greater than 10^10 Msun and
redshifts 0.025<z<0.05. GASS targets are selected from the Sloan Digital Sky
Survey (SDSS) spectroscopic and Galaxy Evolution Explorer (GALEX) imaging
surveys, and are observed until detected or until a gas mass fraction limit of
a few per cent is reached. This second data installment includes new Arecibo
observations of 240 galaxies, and marks the 50% of the complete survey. We
present catalogs of the HI, optical and ultraviolet parameters for these
galaxies, and their HI-line profiles. Having more than doubled the size of the
sample since the first data release, we also revisit the main scaling relations
of the HI mass fraction with galaxy stellar mass, stellar mass surface density,
concentration index, and NUV-r color, as well as the gas fraction plane
introduced in our earlier work.Comment: 30 pages, 12 figures. Accepted for publication in A&A. Version with
complete Appendix A available at http://www.mpa-garching.mpg.de/GASS/pubs.php
. GASS released data can be found at
http://www.mpa-garching.mpg.de/GASS/data.ph
Are galaxies with AGN a transition population?
We present the results of an analysis of a well-selected sample of galaxies
with active and inactive galactic nuclei from the Sloan Digital Sky Survey, in
the range 0.01 < z < 0.16. The SDSS galaxy catalogue was split into two classes
of active galaxies, Type~2 AGN and composites, and one set of inactive,
star-forming/passive galaxies. For each active galaxy, two inactive control
galaxies were selected by matching redshift, absolute magnitude, inclination,
and radius. The sample of inactive galaxies naturally divides into a red and a
blue sequence, while the vast majority of AGN hosts occur along the red
sequence. In terms of H-alpha equivalent width, the population of composite
galaxies peaks in the valley between the two modes, suggesting a transition
population. However, this effect is not observed in other properties such as
colour-magnitude space, or colour-concentration plane. Active galaxies are seen
to be generally bulge-dominated systems, but with enhanced H-alpha emission
compared to inactive red-sequence galaxies. AGN and composites also occur in
less dense environments than inactive red-sequence galaxies, implying that the
fuelling of AGN is more restricted in high-density environments. These results
are therefore inconsistent with theories in which AGN host galaxies are a
`transition' population. We also introduce a systematic 3D spectroscopic
imaging survey, to quantify and compare the gaseous and stellar kinematics of a
well-selected, distance-limited sample of up to 20 nearby Seyfert galaxies, and
20 inactive control galaxies with well-matched optical properties. The survey
aims to search for dynamical triggers of nuclear activity and address
outstanding controversies in optical/IR imaging surveys.Comment: 12 pages, 8 figures, accepted by MNRA
A Wide Field Survey of Satellite Galaxies around the Spiral Galaxy M106
We present a wide field survey of satellite galaxies in M106 (NGC 4258)
covering a 1.7\degr \times 2\degr field around M106 using
Canada-France-Hawaii Telescope/MegaCam. We find 16 satellite galaxy candidates
of M106.
Eight of these galaxies are found to be dwarf galaxies that are much smaller
and fainter than the remaining galaxies. Four of these galaxies are new
findings. Surface brightness profiles of 15 out of 16 satellite galaxies can be
represented well by an exponential disk profile with varying scale length. We
derive the surface number density distribution of these satellite galaxies. The
central number density profile (d kpc) is well fitted by a power-law
with a power index of , similar to the expected power index of
isothermal distribution. The luminosity function of these satellites is
represented well by the Schechter function with a faint end slope of
. Integrated photometric properties (total luminosity,
total colour, and disk scale length) and the spatial distribution of these
satellite galaxies are found to be roughly similar to those of the Milky Way
and M31.Comment: Accepted by MNRA
Mid-Infrared Galaxy Luminosity Functions from the AGN and Galaxy Evolution Survey
We present galaxy luminosity functions at 3.6, 4.5, 5.8, and 8.0 micron
measured by combining photometry from the IRAC Shallow Survey with redshifts
from the AGN and Galaxy Evolution Survey of the NOAO Deep Wide-Field Survey
Bootes field. The well-defined IRAC samples contain 3800-5800 galaxies for the
3.6-8.0 micron bands with spectroscopic redshifts and z < 0.6. We obtained
relatively complete luminosity functions in the local redshift bin of z < 0.2
for all four IRAC channels that are well fit by Schechter functions. We found
significant evolution in the luminosity functions for all four IRAC channels
that can be fit as an evolution in M* with redshift, \Delta M* = Qz. While we
measured Q=1.2\pm0.4 and 1.1\pm0.4 in the 3.6 and 4.5 micron bands consistent
with the predictions from a passively evolving population, we obtained
Q=1.8\pm1.1 in the 8.0 micron band consistent with other evolving star
formation rate estimates. We compared our LFs with the predictions of
semi-analytical galaxy formation and found the best agreement at 3.6 and 4.5
micron, rough agreement at 8.0 micron, and a large mismatch at 5.8 micron.
These models also predicted a comparable Q value to our luminosity functions at
8.0 micron, but predicted smaller values at 3.6 and 4.5 micron. We also
measured the luminosity functions separately for early and late-type galaxies.
While the luminosity functions of late-type galaxies resemble those for the
total population, the luminosity functions of early-type galaxies in the 3.6
and 4.5 micron bands indicate deviations from the passive evolution model,
especially from the measured flat luminosity density evolution. Combining our
estimates with other measurements in the literature, we found (53\pm18)% of the
present stellar mass of early-type galaxies has been assembled at z=0.7.Comment: 39 pages, 15 figures, submitted to ApJ (revised following the referee
report
Health services research doctoral core competencies
This manuscript presents an initial description of doctoral level core competencies for health services research (HSR). The competencies were developed by a review of the literature, text analysis of institutional accreditation self-studies submitted to the Council on Education for Public Health, and a consensus conference of HSR educators from US educational institutions. The competencies are described in broad terms which reflect the unique expertise, interests, and preferred learning methods of academic HSR programs. This initial set of core competencies is published to generate further dialogue within and outside of the US about the most important learning objectives and methods for HSR training and to clarify the unique skills of HSR training program graduates
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