Studying Quasar Absorber Host Galaxy Properties Using Image Stacking
  Technique
  Studying the stellar mass, age, luminosity, star-formation rate, and impact
parameter of quasar absorber host galaxies can aid in the understanding of
galaxy formation and evolution as well as in testing their models. We derive
the Spectral Energy Distribution (SED) and impact parameter limits of low
redshift ($z_{abs} = 0.37 - 0.55$) Mg II absorbers and of higher redshift
($z_{abs} = 1.0 - 2.5$) 2175 \AA\ dust absorbers (2DAs). We use an imaging
stacking technique to statistically boost the signal-to-noise ratio (SNR) to
increase detection of the absorber host galaxies. The point spread function of
the background quasar is modeled with Principal Component Analysis (PCA). This
method efficiently reduces the uncertainty of traditional PSF modeling. Our SED
for Mg II absorbers indicates that low redshift Mg II absorber host galaxies
are likely star-forming galaxies transitioning into red quiescent galaxies,
with a low star formation rate of 2.2 $M_\odot$ $yr^{-1}$. From the stacked
images and simulations, we show that the average impact parameter of 2DAs is >
5 times smaller than that of Mg II absorbers, at < 7 kpc instead of Mg II
absorbers' 48 kpc, indicating that 2DAs are likely associated with disk
components of high redshift galaxies. This means that 2DAs are likely good
probes to study precursors to the Milky Way.
