Host Galaxy Properties of CaII and NaI Quasar Absorption-Line Systems

摘要

Many questions remain within the areas of galaxy formation and evolution. Understanding the origin of gas in galaxy environments, whether as tidal debris, infalling High Velocity Clouds, galaxy outflows, or as gaseous material residing in galaxy disks, is an important step in answering those questions. Quasar absorption-lines can often be used to probe the environments of intervening galaxies. Traditionally, quasar absorption-lines are studied independently of the host galaxy but this method denies us the exploration of the connection between galaxy and environment. Instead, one can select pairs of known galaxies and quasars. This gives much more information regarding the host galaxy and allows us to better connect galaxy properties with associated absorbers.ud udWe use the seventh data release of the Sloan Digital Sky Survey to generate a sample of spectroscopic galaxy-quasar pairs. We cross-correlated a sample of 105,000 quasars and ~800,000 galaxies to produce ~98,000 galaxy-quasar pairs, with the quasar projected within 100 kpc of the galaxy. Adopting an automated line-finding algorithm and using the galaxy redshift as a prior, we search through all quasar spectra and identify CaII and NaI absorption due to the intervening galaxy. This procedure produced 1745 Ca~II absorbers and 4500 NaI absorbers detected at or above 2-sigma. Stacking analysis of a subset of absorbers at z>0.01, with significances at or above 3-sigma, showed strong CaII and NaI features around external galaxies. ud udUsing the same subset of absorbers at z>0.01, we looked for correlations between absorber and galaxy properties and examined differences in galaxy properties between the absorbers and non-absorbers. We found no correlations with absorber strength or differences between many galaxy properties at the 3-sigma level. The lack of correlations and differences between absorbers and non-absorbers suggest a ubiquitous nature for CaII and NaI around all types of galaxies, with the absorbers showing no geometric preference within galaxy halos. This suggests a possible origin as leftover debris from past mergers that has been redistributed within the halo over time. ududThe main results are presented in Chapters 3 and 4, with complimentary work presented in Chapter 5.