103 research outputs found
The Ultraviolet Luminosity Density of the Universe from Photometric Redshifts of Galaxies in the Hubble Deep Field
Studies of the Hubble Deep Field (HDF) and other deep surveys have revealed
an apparent peak in the ultraviolet (UV) luminosity density, and therefore the
star-formation rate density, of the Universe at redshifts 1<z<2. We use
photometric redshifts of galaxies in the HDF to determine the comoving UV
luminosity density and find that, when errors (in particular, sampling error)
are properly accounted for, a flat distribution is statistically
indistinguishable from a distribution peaked at z~1.5. Furthermore, we examine
the effects of cosmological surface brightness (SB) dimming on these
measurements by applying a uniform SB cut to all galaxy fluxes after correcting
them to redshift z=5. We find that, comparing all galaxies at the same
intrinsic surface brightness sensitivity, the UV luminosity density contributed
by high intrinsic SB regions increases by almost two orders of magnitude from
z~0 to z~5. This suggests that there exists a population of objects with very
high star formation rates at high redshifts that apparently do not exist at low
redshifts. The peak of star formation, then, may occur somewhere beyond a
redshift z~>5.Comment: 4 pages total, including 3 embedded figures, to appear in the
proceedings of the Xth Rencontres de Blois, "The Birth of Galaxies." LaTeX
style file include
The Star Formation Rate Intensity Distribution Function--Implications for the Cosmic Star Formation Rate History of the Universe
We address the effects of cosmological surface brightness dimming on
observations of faint galaxies by examining the distribution of "unobscured"
star formation rate intensities versus redshift. We use the star formation rate
intensity distribution function to assess the ultraviolet luminosity density
versus redshift, based on our photometry and photometric redshift measurements
of faint galaxies in the HDF and the HDF--S WFPC2 and NICMOS fields. We find
that (1) previous measurements have missed a dominant fraction of the
ultraviolet luminosity density of the universe at high redshifts by neglecting
cosmological surface brightness dimming effects, which are important at
redshifts larger than z = 2, (2) the incidence of the highest intensity star
forming regions increases monotonically with redshift, and (3) the ultraviolet
luminosity density plausibly increases monotonically with redshift through the
highest redshifts observed. By measuring the spectrum of the luminosity density
versus redshift, we also find that (4) previous measurements of the ultraviolet
luminosity density at redshifts z < 2 must be reduced by a factor 2 to allow
for the spectrum of the luminosity density between rest-frame wavelengths 1500
and 2800 A. And by comparing with observations of high-redshift damped
Lyman-alpha absorption systems detected toward background QSOs, we further find
that (5) the distribution of star formation rate intensities matches the
distribution of neutral hydrogen column densities at redshifts z = 2 through 5,
which establishes a quantitative connection between high-redshift galaxies and
high column density gas and suggests that high-redshift damped Lyman-alpha
absorption systems trace lower star formation rate intensity regions of the
same galaxies detected in star light in the HDF and HDF--S.Comment: 28 pages, 9 figures; accepted for publication in the Astrophysical
Journa
Photometry and Photometric Redshifts of Faint Galaxies in the Hubble Deep Field South NICMOS Field
We present a catalog of photometry and photometric redshifts of 335 faint
objects in the HDF-S NICMOS field. The analysis is based on (1) infrared images
obtained with the Hubble Space Telescope (HST) using the Near Infrared Camera
and Multi-Object Spectrograph (NICMOS) with the F110W, F160W, and F222M
filters, (2) an optical image obtained with HST using the Space Telescope
Imaging Spectrograph (STIS) with no filter, and (3) optical images obtained
with the European Southern Observatory (ESO) Very Large Telescope (VLT) with U,
B, V, R, and I filters. The primary utility of the catalog of photometric
redshifts is as a survey of faint galaxies detected in the NICMOS F160W and
F222M images. The sensitivity of the survey varies significantly with position,
reaching a limiting depth of AB(16,000) ~ 28.7 and covering 1.01 arcmin^2 to
AB(16,000) = 27 and 1.05 arcmin^2 to AB(16,000) = 26.5. The catalog of
photometric redshifts identifies 21 galaxies (or 6% of the total) of redshift z
> 5, 8 galaxies (or 2% of the total) of redshift z > 10, and 11 galaxies (or 3%
of the total) of best-fit spectral type E/S0, of which 5 galaxies (or 1% of the
total) are of redshift z > 1.Comment: 33 pages, 10 figures, accepted for publication in the Astrophysical
Journal, August 1, 2000 issu
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