2018MNRAS.481.1469Z

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 Å dust absorbers (2DAs). We use an imaging stacking technique to statistically boost the signal-to-noise ratio to increase detection of the absorber host galaxies. The point spread function (PSF) of the background quasar is modelled with principal component analysis. This method efficiently reduces the uncertainty of traditional PSF modelling. 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_☉ 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 disc components of high-redshift galaxies. This means that 2DAs are likely good probes to study precursors to the Milky Way.