A spectroscopic study of damped Lyman-alpha systems in the Las Campanas/Palomar survey

Abstract

view Abstract Citations (63) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Spectroscopic Study of Damped Lyman- alpha Systems in the Las Campanas/Palomar Survey Lu, Limin ; Wolfe, Arthur M. ; Turnshek, David A. ; Lanzetta, Kenneth M. Abstract Spectra of nine QSOs, containing 15 candidate damped Lyα absorption features, are obtained at intermediate resolution. The 15 candidates are part of a sample of candidate damped Lyα absorption lines given by Lanzetta and coworkers. Careful examination of the candidate features and their associated metal absorption lines shows that 10 of the 15 candidates are in fact damped Lyα absorption, including eight with neutral hydrogen column density N(H I) >= 2 x 10^20^ cm^-2^. Three others are not damped because the candidate Lyα lines break up into multiple components. The nature of the remaining two cannot he determined because of the complexity of the spectra around the candidate damped Lyα absorption and because of the insufficient signal-to-noise ratios of the spectra. We provide redshift, H I column density, and metal-line equivalent widths for each confirmed damped system in order to facilitate future studies. We have performed simple curve-of-growth analysis for seven of the 10 confirmed damped Lyα systems in order to gain some information on the kinematics of the absorbing gas. For most systems we deduce: effective velocity dispersion that is too large to be compatible with the simple velocity structure indicated by the 21 cm absorption data. We interpret this as evidence for a two-phase model, in which a damped Lyα absorber generally contains two phases of gas, a quiescent H I gas that is responsible for the damped Lyα absorption and the 21 cm absorption, and a turbulent gas that dominates the equivalent widths of the associated metal lines. Evidence relating the quiescent gas to the H I disk, and the turbulent gas to the extended halo of high- redshift galaxies, is briefly discussed. Element abundances of the quiescent gas, the phase comprising most of the mass, are difficult to infer from intermediate-resolution data, owing to blending between the few metal-line velocity components of the quiescent gas and the many velocity components of the turbulent gas. In that respect, the several systems which show relatively small effective velocity dispersions according to this study deserve special attention. Publication: The Astrophysical Journal Supplement Series Pub Date: January 1993 DOI: 10.1086/191743 Bibcode: 1993ApJS...84....1L Keywords: Astronomical Spectroscopy; Lyman Alpha Radiation; Quasars; Sky Surveys (Astronomy); Absorption Spectra; Abundance; Interstellar Gas; Velocity Distribution; Astrophysics; COSMOLOGY: OBSERVATIONS; GALAXIES: DISTANCES AND REDSHIFTS; GALAXIES: QUASARS: ABSORPTION LINES full text sources ADS | data products NED (21) SIMBAD (9)