Probing Low-Redshift Galaxies Using Quasar Absorption Lines with an Emphasis on CaII Absorption

We searched for intervening CaII absorption in nearly 95,000 quasar spectra with i$\leq$20 from the Sloan Digital Sky Survey(SDSS) data releases DR7+DR9. Our identification of $>$400 CaII systems is the largest compilation of CaII absorbers in a blind search. Unlike other absorption line species with similar strengths, a single exponential profile is insufficient to describe the sensitivity-corrected CaII$\lambda$3934 rest equivalent width distribution. Instead, two distributions are needed to describe the CaII absorbers, suggesting that there are at least two distinct absorber populations. The two populations can roughly be separated to lie above and below $W_0^{\lambda 3934}=\mathrm{0.7\AA}$. Using this $\mathrm{0.7\AA}$ value to separate absorbers, we find from composite spectra that the mean dust content of the strong absorbers makes them nearly six times more reddened than the weak absorbers. Also, the mean element abundance ratios of the strong absorbers are intermediate to that of disk- and halo-type gas, while the abundance patterns of the weak absorbers are consistent with Milky Way halo-type gas. For absorbers with $z_{abs}\lesssim0.4$ we identified associated galaxies in four cases using rare overlapping SDSS data. The four galaxies have impact parameters between 5-25kpc and luminosities between $\sim$0.1-1$L_r^{\star}$. The most reliable brightness profiles derived from stacked composite images reveal a more concentrated and steeper light profile for the stronger absorbers. The average luminosity-weighted impact parameter is $\approx$26kpc for strong absorbers, and $\approx$48kpc for weak absorbers. We also conducted the first Hubble Space Telescope quasar absorption line study to search for absorbing gas in M31. While galaxies in the distant universe can normally be probed with only one quasar sightline, this study of M31 utilized ten sightlines with impact parameters between 13-112kpc. Low- and high-ionization metal-line absorption systems arising in M31 were associated with its high velocity clouds and its disk and halo gas. However, contrary to the standard picture that metal-line absorption systems in quasar spectra arise in extended halos of galaxies, the four outermost sightlines showed no metal-line absorption to within our observational limits. Along sightlines where M31 MgII$\lambda\lambda$2796,2803 absorption was detected, the absorption was significantly weaker than that attributed to high-redshift galaxies at similar impact parameters