Charles C. Steidel

The Hubble Space Telescope quasar absorption line key project. v. redshift evolution of lyman limit absorption in the spectra of a large sample of quasars

Using a sample of 119 QSOs, containing objects we have selected having previously available high quality ground-based and IUE spectral observations, together with Hubble Space Telescope (HST) observations of 26 QSOs from Bahcall et al. (1993, 1995) and Impey et al. (1995) and new optical observations of 41 objects by Steidel & Sargent (1995), we study the redshift evolution of Lyman limit absorption systems (LLSs; tau greater than 1.0) over the reshift range 0.32 less than or equal to z(sub LLS) less than or equal to 4.11. The HST observations significantly improve the determination of the low redshift (0.4 less than or equal to z(sub LLS) less than or equal to 1.4) distribution. We find the effect which may have been responsible for the apparent strong evolution at a(sub LLS) greater than or equal to 2.5 found by Lanzetta (1991), which led him to consider a broken, not single power law as a better description of the redshift distribution of LLSs. After removing objects which may bias our sample, leaving a total of 169 QSOs, we find the distribution is well described by a single power law, and obtain for the number density as a function of redshift the form N(z) = N(sub 0)(1 + z)(exp gamma) with gamma = 1.50 =/- 0.39 and N(sub 0) = 0.25(sup -0.10)(sub +0.17), consistent with a constant comoving density of absorbers in a Firedmann universe with q(sub 0) = 0 but indicating evolution if q(sub 0) = 1/2.

The Nature and Evolution of Absorption­ Selected Galaxies

We present results of surveys for high redshift galaxies selected by their having produced detectable Mg II and Lyman limit absorption in the spectra of background QSOs. We discuss the properties of the absorbing galaxies, the connection between galaxy properties and absorption line signatures, and how a combination of QSO absorption line and conventional faint galaxy techniques can be used to study field galaxy evolution to very large redshifts.

A critical analysis of interstellar Zn and Cr as galactic abundance benchmarks for quasar absorbers

We present interstellar gas-phase abundances of zinc and chromium in the Milky Way for comparison with the abundances of these elements in damped Ly-alpha systems at redshifts near z approximately 2. We make use of both IUE (International Ultraviolet Explorer) and GHRS (Goddard High Resolution Spectrograph) archival information in deriving the Milky Way values and find that the average difference in (Zn/H) and (Cr/Zn) between the Milky Way and damped Ly-alpha systems at large N(H1) is about 0.9 dex. The Zn/H values we find for the Milky Way are approximately -0.2 to -0.7 dex below solar and are due in large part to depletion of Zn onto dust grains. The amount of this gas-phase depletion is variable and depends upon the H1 column density and molecular fraction of the gas. Milky Way sight lines having low molecular fractions have values of (Zn/H) within approximately 0.2 dex of the solar value. Combined with larger values of (Cr/Zn) found for the damped Ly-alpha systems, this result confirms that measures of (Zn/H) should accurately reflect the lower gas-phase abundances of Zn found in these systems.

From Metal—Line Absorption Profiles to Halo Kinematics?

We present work in progress of a detailed study of the kinematic, chemical, and ionization conditions of the halos of intermediate redshift (0.3 < z < 1.1) Mg II absorbing galaxies. We aim to incorporate detailed imaging information about the absorbing galaxies themselves with studies of high resolution QSO absorption profiles. We address the questions: “what physical processes are consistent with observed absorption signatures?” and “what parts of galactic halos give rise to what types of characteristic absorption profiles?” Answers to these questions promise to provide a foundation upon which we can interpret both high redshift QSO absorption and Galactic absorption within theories of galactic formation and evolution.

Galaxy Evolution from QSO Absorption-Line Selected Samples

We present results of surveys for high redshift field galaxies selected by their having produced detectable absorption in the spectra of background QSOs. Such surveys, in essence selected by gas cross-section rather than by flux density, are almost completely independent of the conventional magnitude--limited redshift survey, and allow one to follow objects of normal luminosity well beyond

8C1435+635: a radio galaxy at z = 4.25

z\sim 1

Ionizing Radiation From Galaxies And The IGM At Z 2-3

, the redshift at which many of the standard techniques break down. We summarize the principal results for our completed survey at

Understanding substructure in the SSA22 protocluster region using cosmological simulations

z \le 1

Rest-frame Optical Imaging Of z 2-3 Galaxies With HST/WFC3

, and give the preliminary results of a second survey designed to extend the sample to

Resolved Images of Escaping Lyman Continuum Emission from z=3 Galaxies

z=1.6