The Hubble Space Telescope Quasar Absorption Line Key Project. XIII. A census of absorption-line systems at low redshift

We present a catalog of absorption lines obtained from the analysis of the ultraviolet spectra of 66 quasars. The data were acquired with the Faint Object Spectrograph of the Hubble Space Telescope (HST) as part of the Quasar Absorption Line Survey, a Key Project for the first four cycles of HST observations. This is the third of a series of catalogs of absorption lines produced from the survey and increases the number of quasars whose higher resolution (R = 1300) spectra we have published from 17 to 83. The general properties and execution of the survey are reviewed, including descriptions of the final sample of observed objects and the algorithmic processes used to construct the catalog. This database is suitable for a wide variety of studies of gaseous systems in the nearby universe. This third catalog includes 2594 absorption lines and brings the total number of absorption lines in the combined catalog to 3238. The third catalog has 878 identified Ly alpha lines, 27 extensive metal line systems (detected absorption lines from four or more metal ions), 88 C IV systems, and 34 O VI systems. The combined catalog contains the following numbers of extragalactic absorption lines: 1129 Ly alpha lines, 107 C IV systems, 41 O VI systems, 16 Lyman limit systems, and one damped Ly alpha system (in the spectrum of PG 0935 + 416). In addition, there are 25 pairs of identified Ly alpha lines that are candidate C IV doublets. Of the 122 identified C IV and candidate C IV systems in the completely identified sample of absorption lines, 24 +/- 5 are expected to be chance coincidences of other lines (based upon Monte Carlo simulations). The detection of a single damped Ly alpha system in a path length of Delta z = 49 yields an observed number of damped systems per unit redshift of (dN/dz)(damp)(z = 0.58) = 0.020 with 95% confidence boundaries of 0.001-0.096 systems per unit redshift. We include notes on our analysis of each of the observed quasars and the absorption systems detected in each spectrum. Some especially interesting systems include low-redshift Ly alpha absorbers suitable for extensive follow-up observations (e.g., in the spectra of TON 28 and PG 1216 + 069), possibly physically associated pairs of extensive metal line absorption systems (e.g., in the spectrum of PG 0117 + 213), and systems known to be associated with galaxies (e.g., in the spectrum of 3C 232). The spectra of five broad absorption line (BAL) quasars (UM 425, PG 1254 + 047, PG 1411 + 442, PG 1700 + 518, and PG 2112 + 059) can be found in this third catalog, bringing the total number of BAL quasars in the combined catalog to six (including PG 0043 + 039).