Spectroscopic Analysis of H i Absorption-Line Systems in 40 HIRES Quasars

Abstract

We list and analyze H I absorption lines at redshifts 2 < z < 4 with column density 12 < 19 in 40 high-resolution (FWHM = 8.0 km s _1) quasar spectra obtained with the Keck HIRES. We deblend and fit all H I lines within 1000 km s _1 of 86 strong H I lines whose column densities are log N HI, ≥ 15 cm -2. Unlike most prior studies, we use not only Lyα but also all visible higher Lyman series lines to improve the fitting accuracy. This reveals components near higher column density systems that cannot be seen in Lyα. We list the Voigt profile fits to the 1339 H I components that we found. We examined the physical properties of the H I lines after separating them into several subsamples according to their velocity separation from the quasars, redshift, column density, and S/N ratio of the spectrum. We found two interesting trends for lines with 12 < 15 which are within 200-1000 km s -1 of systems with log (N HI/cm -2) > 15. First, their column density distribution becomes steeper, meaning relatively fewer high column density lines, at z < 2.9. Second, their column density distribution also becomes steeper and their line width becomes broader by about 2-3 km s -1 when they are within 5000 km s -1 of their quasar. © 2007. The American Astronomical Society. All rights reserved.