113 research outputs found
UVOT Measurements of Dust and Star Formation in the SMC and M33
When measuring star formation rates using ultraviolet light, correcting for
dust extinction is a critical step. However, with the variety of dust
extinction curves to choose from, the extinction correction is quite uncertain.
Here, we use Swift/UVOT to measure the extinction curve for star-forming
regions in the SMC and M33. We find that both the slope of the curve and the
strength of the 2175 Angstrom bump vary across both galaxies. In addition, as
part of our modeling, we derive a detailed recent star formation history for
each galaxy.Comment: 6 pages, 5 figures, conference proceedings from Swift: 10 years of
Discovery, held in Rome (2-5 Dec. 2014
The Evolution of the Far-UV Luminosity Function and Star Formation Rate Density of the Chandra Deep Field South from z=0.2-1.2 with Swift/UVOT
We use deep Swift UV/Optical Telescope (UVOT) near-ultraviolet (1600A to
4000A) imaging of the Chandra Deep Field South to measure the rest-frame far-UV
(FUV; 1500A) luminosity function (LF) in four redshift bins between z=0.2 and
1.2. Our sample includes 730 galaxies with u < 24.1 mag. We use two methods to
construct and fit the LFs: the traditional V_max method with bootstrap errors
and a maximum likelihood estimator. We observe luminosity evolution such that
M* fades by ~2 magnitudes from z~1 to z~0.3 implying that star formation
activity was substantially higher at z~1 than today. We integrate our LFs to
determine the FUV luminosity densities and star formation rate densities from
z=0.2 to 1.2. We find evolution consistent with an increase proportional to
(1+z)^1.9 out to z~1. Our luminosity densities and star formation rates are
consistent with those found in the literature, but are, on average, a factor of
~2 higher than previous FUV measurements. In addition, we combine our UVOT data
with the MUSYC survey to model the galaxies' ultraviolet-to-infrared spectral
energy distributions and estimate the rest-frame FUV attenuation. We find that
accounting for the attenuation increases the star formation rate densities by
~1 dex across all four redshift bins.Comment: 20 pages, 8 figures, 6 tables; accepted for publication in Ap
Evolution in the Continuum Morphological Properties of Ly alpha-Emitting Galaxies from Z=3.1 to Z=2.1
We present a rest-frame ultraviolet morphological analysis of 108 z = 2.1 Lyman Alpha Emitters (LAEs) in the Extended Chandra Deep Field South (ECDF-S) and compare it to a similar sample of 171 LAEs at z = 3.1 . Using Hubble Space Telescope (HST) images taken as part of the Galaxy Evolution From Morphology and SEDs survey, Great Observatories Origins Deep Survey, and Hubble Ultradeep Field surveys, we measure the size and photometric component distributions, where photo- metric components are defined as distinct clumps of UV-continuum emission. At both redshifts, the majority of LAEs have observed half-light radii < 2 kpc, but the median half-light radius rises from 0.97 kpc at z = 3.1 to 1.41 kpc at z = 2.1. A similar evolution is seen in the sizes of individual rest-UV components, but there is no evidence for evolution in the number of mUlti-component systems. In the z = 2.1 LAE sample, we see clear correlations between the LAE size and other physical properties derived from its SED. LAEs are found to be larger for galaxies with larger stellar mass, larger star formation rate, and larger dust obscuration, but there is no evidence for a trend between equivalent width and half-light radius at either redshift. The presence of these correlations suggests that a wide range of objects are being selected by LAE surveys at that redshift, including a significant fraction of objects for which a massive and moderately extended population of old stars underlies the young starburst giving rise to the Lya emission
A Large Catalog of Homogeneous Ultra-Violet/Optical GRB Afterglows: Temporal and Spectral Evolution
We present the second Swift Ultra-Violet/Optical Telescope (UVOT) gamma-ray
burst (GRB) afterglow catalog, greatly expanding on the first Swift UVOT GRB
afterglow catalog. The second catalog is constructed from a database containing
over 120,000 independent UVOT observations of 538 GRBs first detected by Swift,
the High Energy Transient Explorer 2 (HETE2), the INTErnational Gamma-Ray
Astrophysics Laboratory (INTEGRAL), the Interplanetary Network (IPN), Fermi,
and Astro-rivelatore Gamma a Immagini Leggero (AGILE). The catalog covers GRBs
discovered from 2005 Jan 17 to 2010 Dec 25. Using photometric information in
three UV bands, three optical bands, and a `white' or open filter, the data are
optimally co-added to maximize the number of detections and normalized to one
band to provide a detailed light curve. The catalog provides positional,
temporal, and photometric information for each burst, as well as Swift Burst
Alert Telescope (BAT) and X-Ray Telescope (XRT) GRB parameters. Temporal slopes
are provided for each UVOT filter. The temporal slope per filter of almost half
the GRBs are fit with a single power-law, but one to three breaks are required
in the remaining bursts. Morphological comparisons with the X-ray reveal that
approximately 75% of the UVOT light curves are similar to one of the four
morphologies identified by Evans et al. (2009). The remaining approximately 25%
have a newly identified morphology. For many bursts, redshift and extinction
corrected UV/optical spectral slopes are also provided at 2000, 20,000, and
200,000 seconds.Comment: 44 pages, 14 figures, to be published in Astrophysical Journal
Supplementa
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