Publications (6)0 Total impact
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Harry I. Teplitz, Marc Rafelski,
Peter Kurczynski,
Nicholas A. Bond,
Norman Grogin,
Anton M. Koekemoer,
Hakim Atek,
Thomas M. Brown,
Dan Coe,
James W. Colbert, [......],
Daniel J. Hanish,
Kyoung-Soo Lee,
Duilia F. de Mello,
Swara Ravindranath,
Russell E. Ryan,
Brian D. Siana,
Claudia Scarlata,
Emmaris Soto,
Elysse N. Voyer,
Arthur M. Wolfe
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ABSTRACT: We present an overview of a 90-orbit Hubble Space Telescope treasury program
to obtain near ultraviolet imaging of the Hubble Ultra Deep Field using the
Wide Field Camera 3 UVIS detector with the F225W, F275W, and F336W filters.
This survey is designed to: (i) Investigate the episode of peak star formation
activity in galaxies at 1<z<2.5; (ii) Probe the evolution of massive galaxies
by resolving sub-galactic units (clumps); (iii) Examine the escape fraction of
ionizing radiation from galaxies at z~2-3; (iv) Greatly improve the reliability
of photometric redshift estimates; and (v) Measure the star formation rate
efficiency of neutral atomic-dominated hydrogen gas at z~1-3. In this overview
paper, we describe the survey details and data reduction challenges, including
both the necessity of specialized calibrations and the effects of charge
transfer inefficiency. We provide a stark demonstration of the effects of
charge transfer inefficiency on resultant data products, which when
uncorrected, result in uncertain photometry, elongation of morphology in the
readout direction, and loss of faint sources far from the readout. We agree
with the STScI recommendation that future UVIS observations that require very
sensitive measurements use the instrument's capability to add background light
through a "post-flash". Preliminary results on number counts of UV-selected
galaxies and morphology of galaxies at z~1 are presented. We find that the
number density of UV dropouts at redshifts 1.7, 2.1, and 2.7 is largely
consistent with the number predicted by published luminosity functions. We also
confirm that the image mosaics have sufficient sensitivity and resolution to
support the analysis of the evolution of star-forming clumps, reaching 28-29th
magnitude depth at 5 sigma in a 0.2 arcsecond radius aperture depending on
filter and observing epoch.
05/2013;
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ABSTRACT: Using a sample of 100 H I - selected damped Lyman alpha (DLA) systems,
observed with the High Resolution Echelle Spectrometer on the Keck I telescope,
we present evidence that the scatter in the well-studied correlation between
the redshift and metallicity of a DLA is largely due to the existence of a
mass-metallicity relationship at each redshift. To describe the fundamental
relations that exist between redshift, metallicity and mass, we use a
fundamental plane description, which is described by the following equation:
[M/H]=(-1.9+-0.5)+(0.74+-0.21)logdv_90-(0.32+-0.06)z. Here, we assert that the
velocity width, dv_90, which is defined as the velocity interval containing 90%
of the integrated optical depth, traces the mass of the underlying dark matter
halo. This description provides two significant improvements over the
individual descriptions of the mass-metallicity correlation and
metallicity-redshift correlation. Firstly, the fundamental equation reduces the
scatter around both relationships by about 20%, providing a more stringent
constraint on numerical simulations modeling DLAs. Secondly, it confirms that
the dark matter halos that host DLAs satisfy a mass-metallicity relationship at
each redshift between redshifts 2 through 5.
03/2013;
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ABSTRACT: We present chemical abundance measurements for 47 damped Lyman-alpha systems
(DLAs), 30 at z>4, observed with the Echellette Spectrograph and Imager and the
High Resolution Echelle Spectrometer on the Keck telescopes. HI column
densities of the DLAs are measured with Voigt profile fits to the Lyman-alpha
profiles, and we find an increased number of false DLA identifications with
SDSS at z>4 due to the increased density of the Lyman-alpha forest. Ionic
column densities are determined using the apparent optical depth method, and we
combine our new metallicity measurements with 195 from previous surveys to
determine the evolution of the cosmic metallicity of neutral gas. We find the
metallicity of DLAs decreases with increasing redshift, improving the
significance of the trend and extending it to higher redshifts, with a linear
fit of -0.22+-0.03 dex per unit redshift from z=0.09-5.06. The metallicity
'floor' of ~1/600 solar continues out to z~5, despite our sensitivity for
finding DLAs with much lower metallicities. However, this floor is not
statistically different from a steep tail to the distribution. We also find
that the intrinsic scatter of metallicity among DLAs of ~0.5 dex continues out
to z~5. In addition, the metallicity distribution and the alpha/Fe ratios of
z>2 DLAs are consistent with being drawn from the same parent population with
those of halo stars. It is therefore possible that the halo stars in the Milky
Way formed out of gas that commonly exhibits DLA absorption at z>2.
05/2012;
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ABSTRACT: We present evidence for spatially extended low surface brightness emission
around Lyman break galaxies (LBGs) in the V band image of the Hubble Ultra Deep
Field, corresponding to the z~3 rest-frame FUV light, which is a sensitive
measure of star formation rates (SFRs). We find that the covering fraction of
molecular gas at z~3 is not adequate to explain the emission in the outskirts
of LBGs, while the covering fraction of neutral atomic-dominated hydrogen gas
at high redshift is sufficient. We develop a theoretical framework to connect
this emission around LBGs to the expected emission from neutral H I gas i.e.,
damped Lyman alpha systems (DLAs), using the Kennicutt-Schmidt (KS) relation.
Working under the hypothesis that the observed FUV emission in the outskirts of
LBGs is from in situ star formation in atomic-dominated hydrogen gas, the
results suggest that the SFR efficiency in such gas at z~3 is between factors
of 10 and 50 lower than predictions based on the local KS relation. The total
SFR density in atomic-dominated gas at z~3 is constrained to be ~10% of that
observed from the inner regions of LBGs. In addition, the metals produced by in
situ star formation in the outskirts of LBGs yield metallicities comparable to
those of DLAs, which is a possible solution to the "Missing Metals" problem for
DLAs. Finally, the atomic-dominated gas in the outskirts of galaxies at both
high and low redshifts has similar reduced SFR efficiencies and is consistent
with the same power law.
11/2010;
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ABSTRACT: We present a sample of 407 z~3 Lyman break galaxies (LBGs) to a limiting isophotal u-band magnitude of 27.6 mag in the Hubble Ultra Deep Field (UDF). The LBGs are selected using a combination of photometric redshifts and the u-band drop-out technique enabled by the introduction of an extremely deep u-band image obtained with the Keck I telescope and the blue channel of the LRIS spectrometer. The Keck u-band image, totaling 9 hours of integration time, has a one sigma depth of 30.7 mag arcsec^-2, making it one of the most sensitive u-band images ever obtained. The u-band image also substantially improves the accuracy of photometric redshift measurements of ~50% of the z~3 Lyman break galaxies, significantly reducing the traditional degeneracy of colors between z~3 and z~0.2 galaxies. This sample provides the most sensitive, high-resolution multi-filter imaging of reliably identified z~3 LBGs for morphological studies of galaxy formation and evolution and the star formation efficiency of gas at high redshift. Comment: 18 pages, 13 figures, proof corrections included
08/2009;
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ABSTRACT: We report evidence for a bimodality in damped Ly systems (DLAs). Using [C II] 158 mu cooling rates, lc, we find a distribution with peaks at lc=10^-27.4 and 10^-26.6 ergs s^-1 H^-1 separated by a trough at lc^crit ~= lc < 10^-27.0 ergs s^-1 H^-1. We divide the sample into low cool DLAs with lc < lc^crit and high cool DLAs with lc > lc^crit and find the Kolmogorv-Smirnov probabilities that velocity width, metallicity, dust-to-gas ratio, and Si II equivalent width in the two subsamples are drawn from the same parent population are small. All these quantities are significantly larger in the high cool population, while the H I column densities are indistinguishable in the two populations. We find that heating by X-ray and FUV background radiation is insufficient to balance the cooling rates of either population. Rather, the DLA gas is heated by local radiation fields. The rare appearance of faint, extended objects in the Hubble Ultra Deep Field rules out in situ star formation as the dominant star-formation mode for the high cool population, but is compatible with in situ star formation as the dominant mode for the low cool population. Star formation in the high cool DLAs likely arises in Lyman Break galaxies. We investigate whether these properties of DLAs are analogous to the bimodal properties of nearby galaxies. Using Si II equivalent width as a mass indicator, we construct bivariate distributions of metallicity, lc, and areal SFR versus the mass indicators. Tentative evidence is found for correlations and parallel sequences, which suggest similarities between DLAs and nearby galaxies. We suggest that the transition-mass model provides a plausible scenario for the bimodality we have found. As a result, the bimodality in current galaxies may have originated in DLAs. Comment: Accepted for publication in the Astrophysical Journal 18 pages 14 figures
02/2008;
