132 research outputs found
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
On the Classification of UGC1382 as a Giant Low Surface Brightness Galaxy
We provide evidence that UGC1382, long believed to be a passive elliptical
galaxy, is actually a giant low surface brightness (GLSB) galaxy which rivals
the archetypical GLSB Malin 1 in size. Like other GLSB galaxies, it has two
components: a high surface brightness disk galaxy surrounded by an extended low
surface brightness (LSB) disk. For UGC1382, the central component is a
lenticular system with an effective radius of 6 kpc. Beyond this, the LSB disk
has an effective radius of ~38 kpc and an extrapolated central surface
brightness of ~26 mag/arcsec^2. Both components have a combined stellar mass of
~8x10^10 M_sun, and are embedded in a massive (10^10 M_sun) low-density (<3
M_sun/pc^2) HI disk with a radius of 110 kpc, making this one of the largest
isolated disk galaxies known. The system resides in a massive dark matter halo
of at least 2x10^12 M_sun. Although possibly part of a small group, its low
density environment likely plays a role in the formation and retention of the
giant LSB and HI disks. We model the spectral energy distributions and find
that the LSB disk is likely older than the lenticular component. UGC1382 has
UV-optical colors typical of galaxies transitioning through the green valley.
Within the LSB disk are spiral arms forming stars at extremely low
efficiencies. The gas depletion time scale of ~10^11 yr suggests that UGC1382
may be a very long term resident of the green valley. We find that the
formation and evolution of the LSB disk is best explained by the accretion of
gas-rich LSB dwarf galaxies.Comment: 17 pages, 16 figures, 4 tables; accepted to the Astrophysical Journa
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
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