3,078 research outputs found
A JWST/NIRCam Study of Key Contributors to Reionization: The Star-forming and Ionizing Properties of UV-faint Galaxies
Spitzer/IRAC imaging has revealed that the brightest galaxies
often exhibit young ages and strong nebular line emission, hinting at high
ionizing efficiency among early galaxies. However, IRAC's limited sensitivity
has long hindered efforts to study the fainter, more numerous population often
thought largely responsible for reionization. Here we use CEERS JWST/NIRCam
data to characterize 116 UV-faint (median M)
galaxies. The SEDs are typically dominated by young (10-50 Myr), low-mass
() stellar populations, and we find no need for
extremely high stellar masses (). Considering previous
studies of UV-bright (M) galaxies, we find evidence
for a strong (5-10) increase in specific star formation rate toward
lower luminosities (median sSFR=103 Gyr in CEERS). The larger sSFRs
imply a more dominant contribution from OB stars in the relatively numerous
UV-faint population, perhaps suggesting that these galaxies are very efficient
ionizing agents (median erg Hz). In spite of their
much larger sSFRs, we find no significant increase in [OIII]H EWs
towards fainter M (median 780 ). If confirmed,
this may indicate that a substantial fraction of our CEERS galaxies possess
extremely low metallicities (3% ) where [OIII] emission is
suppressed. Alternatively, high ionizing photon escape fractions or bursty star
formation histories can also weaken the nebular lines in a subset of our CEERS
galaxies. While the majority of our objects are very blue (median
), we identify a significant tail of very dusty galaxies
() at 0.5 which may contribute significantly
to the star formation rate density.Comment: Accepted in MNRAS. Updated to use the most recent NIRCam zeropoints.
There are no significant changes to the conclusions relative to v
Calibrating the Star Formation Rate at z=1 from Optical Data
We present a star-formation rate calibration based on optical data that is
consistent with average observed rates in both the red and blue galaxy
populations at z~1. The motivation for this study is to calculate SFRs for
DEEP2 Redshift Survey galaxies in the 0.7<z<1.4 redshift range, but our results
are generally applicable to similar optically-selected galaxy samples without
requiring UV or IR data. Using SFRs fit from UV/optical SEDs in the AEGIS
survey, we explore the behavior of restframe B-band magnitude, observed [OII]
luminosity, and restframe (U-B) color with SED-fit SFR for both red sequence
and blue cloud galaxies. We find that a SFR calibration can be calculated for
all z~1 DEEP2 galaxies using a simultaneous fit in M_B and restframe colors
with residual errors that are within the SFR measurement error. The resulting
SFR calibration produces fit residual errors of 0.3 dex RMS scatter for the
full color-independent sample with minimal correlated residual error in L[OII]
or stellar mass. We then compare the calibrated z~1 SFRs to two diagnostics
that use L[OII] as a tracer in local galaxies and correct for dust extinction
at intermediate redshifts through either galaxy B-band luminosity or stellar
mass. We find that a L[OII] - M_B SFR calibration commonly used in the
literature agrees well with our calculated SFRs after correcting for the
average B-band luminosity evolution in L* galaxies. However, we find better
agreement with a local L[OII]-based SFR calibration that includes stellar mass
to correct for reddening effects, indicating that stellar mass is a better
tracer of dust extinction for all galaxy types and less affected by systematic
evolution than galaxy luminosity from z=1 to the current epoch.Comment: 16 pages, 15 figures, emulateapj format, to be submitted to Ap
The XMM Cluster Survey: The Stellar Mass Assembly of Fossil Galaxies
This paper presents both the result of a search for fossil systems (FSs)
within the XMM Cluster Survey and the Sloan Digital Sky Survey and the results
of a study of the stellar mass assembly and stellar populations of their fossil
galaxies. In total, 17 groups and clusters are identified at z < 0.25 with
large magnitude gaps between the first and fourth brightest galaxies. All the
information necessary to classify these systems as fossils is provided. For
both groups and clusters, the total and fractional luminosity of the brightest
galaxy is positively correlated with the magnitude gap. The brightest galaxies
in FSs (called fossil galaxies) have stellar populations and star formation
histories which are similar to normal brightest cluster galaxies (BCGs).
However, at fixed group/cluster mass, the stellar masses of the fossil galaxies
are larger compared to normal BCGs, a fact that holds true over a wide range of
group/cluster masses. Moreover, the fossil galaxies are found to contain a
significant fraction of the total optical luminosity of the group/cluster
within 0.5R200, as much as 85%, compared to the non-fossils, which can have as
little as 10%. Our results suggest that FSs formed early and in the highest
density regions of the universe and that fossil galaxies represent the end
products of galaxy mergers in groups and clusters. The online FS catalog can be
found at http://www.astro.ljmu.ac.uk/~xcs/Harrison2012/XCSFSCat.html.Comment: 30 pages, 50 figures. ApJ published version, online FS catalog added:
http://www.astro.ljmu.ac.uk/~xcs/Harrison2012/XCSFSCat.htm
Evolution of the Most Massive Galaxies to z=0.6: I. A New Method for Physical Parameter Estimation
We use principal component analysis (PCA) to estimate stellar masses, mean
stellar ages, star formation histories (SFHs), dust extinctions and stellar
velocity dispersions for ~290,000 galaxies with stellar masses greater than
$10^{11}Msun and redshifts in the range 0.4<z<0.7 from the Baryon Oscillation
Spectroscopic Survey (BOSS). We find the fraction of galaxies with active star
formation first declines with increasing stellar mass, but then flattens above
a stellar mass of 10^{11.5}Msun at z~0.6. This is in striking contrast to
z~0.1, where the fraction of galaxies with active star formation declines
monotonically with stellar mass. At stellar masses of 10^{12}Msun, therefore,
the evolution in the fraction of star-forming galaxies from z~0.6 to the
present-day reaches a factor of ~10. When we stack the spectra of the most
massive, star-forming galaxies at z~0.6, we find that half of their [OIII]
emission is produced by AGNs. The black holes in these galaxies are accreting
on average at ~0.01 the Eddington rate. To obtain these results, we use the
stellar population synthesis models of Bruzual & Charlot (2003) to generate a
library of model spectra with a broad range of SFHs, metallicities, dust
extinctions and stellar velocity dispersions. The PCA is run on this library to
identify its principal components over the rest-frame wavelength range
3700-5500A. We demonstrate that linear combinations of these components can
recover information equivalent to traditional spectral indices such as the
4000A break strength and HdA, with greatly improved S/N. This method is able to
recover physical parameters such as stellar mass-to-light ratio, mean stellar
age, velocity dispersion and dust extinction from the relatively low S/N BOSS
spectra. We examine the sensitivity of our stellar mass estimates to the input
parameters in our model library and the different stellar population synthesis
models.Comment: 20 pages, 18 Figures, submitted to MNRA
A critical look at the mass-metallicity-star formation rate relation in the local universe. I. An improved analysis framework and confounding systematics
It has been proposed that the mass-metallicity relation of galaxies exhibits
a secondary dependence on star formation rate (SFR), and that the resulting
M-Z-SFR relation may be redshift-invariant, i.e., "fundamental." However,
conflicting results on the character of the SFR dependence, and whether it
exists, have been reported. To gain insight into the origins of the conflicting
results, we (a) devise a non-parametric, astrophysically motivated analysis
framework based on the offset from the star-forming ("main") sequence at a
given stellar mass (relative specific SFR), (b) apply this methodology and
perform a comprehensive re-analysis of the local M-Z-SFR relation, based on
SDSS, GALEX, and WISE data, and (c) study the impact of sample selection, and
of using different metallicity and SFR indicators. We show that metallicity is
anti-correlated with specific SFR regardless of the indicators used. We do not
find that the relation is spurious due to correlations arising from biased
metallicity measurements, or fiber aperture effects. We emphasize that the
dependence is weak/absent for massive galaxies (), and that the
overall scatter in the M-Z-SFR relation does not greatly decrease from the M-Z
relation. We find that the dependence is stronger for the highest SSFR galaxies
above the star-forming sequence. This two-mode behavior can be described with a
broken linear fit in 12+log(O/H) vs. log (SFR), at a given .
Previous parameterizations used for comparative analysis with higher redshift
samples that do not account for the more detailed behavior of the local M-Z-SFR
relation may incorrectly lead to the conclusion that those samples follow a
different relationship.Comment: ApJ. Several minor correction
Astrometry and geodesy with radio interferometry: experiments, models, results
Summarizes current status of radio interferometry at radio frequencies
between Earth-based receivers, for astrometric and geodetic applications.
Emphasizes theoretical models of VLBI observables that are required to extract
results at the present accuracy levels of 1 cm and 1 nanoradian. Highlights the
achievements of VLBI during the past two decades in reference frames, Earth
orientation, atmospheric effects on microwave propagation, and relativity.Comment: 83 pages, 19 Postscript figures. To be published in Rev. Mod. Phys.,
Vol. 70, Oct. 199
CLASSY III: The Properties of Starburst-Driven Warm Ionized Outflows
We report the results of analyses of galactic outflows in a sample of 45
low-redshift starburst galaxies in the COS Legacy Archive Spectroscopic SurveY
(CLASSY), augmented by five additional similar starbursts with COS data. The
outflows are traced by blueshifted absorption-lines of metals spanning a wide
range of ionization potential. The high quality and broad spectral coverage of
CLASSY data enable us to disentangle the absorption due to the static ISM from
that due to outflows. We further use different line multiplets and doublets to
determine the covering fraction, column density, and ionization state as a
function of velocity for each outflow. We measure the outflow's mean velocity
and velocity width, and find that both correlate in a highly significant way
with the star-formation rate, galaxy mass, and circular velocity over ranges of
four orders-of-magnitude for the first two properties. We also estimate outflow
rates of metals, mass, momentum, and kinetic energy. We find that, at most,
only about 20% of silicon created and ejected by supernovae in the starburst is
carried in the warm phase we observe. The outflows' mass-loading factor
increases steeply and inversely with both circular and outflow velocity
(log-log slope -1.6), and reaches for dwarf galaxies. We find
that the outflows typically carry about 10 to 100% of the momentum injected by
massive stars and about 1 to 20% of the kinetic energy. We show that these
results place interesting constraints on, and new insights into, models and
simulations of galactic winds.Comment: 34 pages, 16 figures, 6 tables, submitted to Ap
The Eighth Data Release of the Sloan Digital Sky Survey: First Data from SDSS-III
The Sloan Digital Sky Survey (SDSS) started a new phase in August 2008, with
new instrumentation and new surveys focused on Galactic structure and chemical
evolution, measurements of the baryon oscillation feature in the clustering of
galaxies and the quasar Ly alpha forest, and a radial velocity search for
planets around ~8000 stars. This paper describes the first data release of
SDSS-III (and the eighth counting from the beginning of the SDSS). The release
includes five-band imaging of roughly 5200 deg^2 in the Southern Galactic Cap,
bringing the total footprint of the SDSS imaging to 14,555 deg^2, or over a
third of the Celestial Sphere. All the imaging data have been reprocessed with
an improved sky-subtraction algorithm and a final, self-consistent photometric
recalibration and flat-field determination. This release also includes all data
from the second phase of the Sloan Extension for Galactic Understanding and
Evolution (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars
at both high and low Galactic latitudes. All the more than half a million
stellar spectra obtained with the SDSS spectrograph have been reprocessed
through an improved stellar parameters pipeline, which has better determination
of metallicity for high metallicity stars.Comment: Astrophysical Journal Supplements, in press (minor updates from
submitted version
Measuring food preference and reward: application and cross-cultural adaptation of the leeds food preference questionnaire in human experimental research
Decisions about what we eat play a central role in human appetite and energy balance. Measuring food reward and its underlying components of implicit motivation (wanting) and explicit sensory pleasure (liking) is therefore important in understanding which foods are preferred in a given context and at a given moment in time. Among the different methods used to measure food reward, the Leeds Food Preference Questionnaire (LFPQ) is a well-established tool that has been widely used in the scientific field for over 10 years. The original LFPQ measures explicit liking and implicit wanting for the same visual food stimuli varying along two nutritional dimensions: fat (high or low) and taste (sweet or savoury/non-sweet). With increasing use of the LFPQ (in original or adapted forms) across different cultural and scientific contexts, there is a need for a set of recommendations for effective execution as well as cultural and nutritional adaptations of the tool. This paper aims to describe the current status of the LFPQ for researchers new to the methodology, and to provide standards of good practice that can be adopted for its cultural adaptation and use in the laboratory or clinic. This paper details procedures for the creation and validation of appropriate food stimuli; implementation of the tool for sensitive measures of food reward; and interpretation of the main end-points of the LFPQ. Following these steps will facilitate comparisons of findings between studies and lead to a better understanding of the role of food reward in human eating behaviour
CLASSY VIII: Exploring the Source of Ionization with UV ISM diagnostics in local High- Analogs
In the current JWST era, rest-frame UV spectra play a crucial role in
enhancing our understanding of the interstellar medium (ISM) and stellar
properties of the first galaxies in the epoch of reionization (EoR, ).
Here, we compare well-known and reliable optical diagrams sensitive to the main
ionization source (i.e., star formation, SF; active galactic nuclei, AGN;
shocks) to UV counterparts proposed in the literature - the so-called ``UV-BPT
diagrams'' - using the HST COS Legacy Archive Spectroscopic SurveY (CLASSY),
the largest high-quality, high-resolution and broad-wavelength range atlas of
far-UV spectra for 45 local star-forming galaxies. In particular, we explore
where CLASSY UV line ratios are located in the different UV diagnostic plots,
taking into account state-of-the-art photoionization and shock models and, for
the first time, the measured ISM and stellar properties (e.g., gas-phase
metallicity, ionization parameter, carbon abundance, stellar age). We find that
the combination of C III] 1907,9 He II and O III]
1666 can be a powerful tool to separate between SF, shocks and AGN at
sub-solar metallicities. We also confirm that alternative diagrams without O
III] 1666 still allow us to define a SF-locus with some caveats.
Diagrams including C IV 1548,51 should be taken with caution
given the complexity of this doublet profile. Finally, we present a discussion
detailing the ISM conditions required to detect UV emission lines, visible only
in low gas-phase metallicity (12+log(O/H) ) and high ionization
parameter (log() ) environments. Overall, CLASSY and our UV
toolkit will be crucial in interpreting the spectra of the earliest galaxies
that JWST is currently revealing.Comment: 31 pages, submitted to ApJ, comments welcom
- …