Probing galaxies through Quasar absorption lines: Magnesium(II)-selected systems at 0.5 less than or equal to Z less than or equal to 1.5.

摘要

Quasar absorption lines are a powerful means of probing kinematics, chemical content, and ionization conditions of the gas in intervening galaxies and the intergalactic medium over a large redshift epoch. At intermediate redshift, 0.5 ≤ z ≤ 1.5, however, metal-line absorption systems (e.g. MgII systems identified in high-resolution optical spectra) have only been studied at relatively low resolution in the ultraviolet (e.g. Bergeron et al. (1994); Churchill et al. (1999); Churchill & Charlton (1999)). Now with the advent of high-resolution UV spectroscopy, we have gained access to many fine details in the absorption features and hence grasped a more comprehensive view of the formation and evolution of various gaseous structures in the universe.;In this thesis, I combine modeling work over the past four years, using a combination of high-resolution HST/STIS and Keck/HIRES data. The results of modeling nearly twenty MgII-selected systems over the redshift range 0.5 ≤ z ≤ 1.5 are presented and their implications for the formation and evolution of galaxies over this intermediate redshift epoch are discussed.;At z ∼ 1, luminous galaxies (>0.05L* galaxies, where L* is the Schechter luminosity) are traced by strong MgII absorbers (those with rest-frame equivalent width Wr(2796) > 0.3 A). We find that many of these galaxies have large spatial variations of density in their disk ISM. In a few cases, small, dense pockets, representing cooler ISM regions, are also intersected along the lines of sight. A variety of kinematic structures are displayed in the corona/halo gas of these galaxies, indicating different morphologies, evolutionary stages, and/or ionizing mechanisms. Satellite clouds, sometimes found around strong absorbers, could represent an analog to the Milky Way high-velocity clouds at higher redshifts.;Weak MgII absorbers, constituting the majority (>65%) of the MgII absorber population at 0.5 ≤ z ≤ 1, make up much of the high column density end of the Lyalpha forest (log N(HI) ≥ 15). Single-cloud, weak absorbers usually have high metallicities and could be potential tracers of self-enriched fragments or clusters in missing galaxies in cold dark matter haloes that are predicted by theoretical simulations. Multiple-cloud, weak MgII absorbers have an indicated origin in either dwarf/low-surface-brightness galaxies or in the outskirts of giant galaxies.