2015MNRAS.452.3192S

We present measurements of element abundance ratios and dust in CaII absorbers identified in Sloan Digital Sky Survey DR7+DR9. In an earlier paper we formed a statistical sample of 435 CaII absorbers and postulated that their statistical properties might be representative of at least two populations of absorbers. Here, we show that if the absorbers are roughly divided into two subsamples with CaII rest equivalent widths larger and smaller than W_0^λ3934 = 0.7Å, they are then representative of two physically different populations. Comparisons of abundance ratios between the two CaII absorber populations indicate that the weaker W_0^λ3934 absorbers have properties consistent with halo-type gas, while the stronger absorbers have properties intermediate between halo- and disc-type gas. We also show that, on average, the dust-extinction properties of the overall sample is consistent with a Large Magellanic Cloud or Small Magellanic Cloud dust law, and the stronger absorbers are nearly six times more reddened than their weaker counterparts. The absorbed-to-unabsorbed composite flux ratio at λrest = 2200Å is R ~0.73 and E(B - V) ~ 0.046 for the stronger CaII absorbers (W_0^λ3934 ≥0.7Å), and R ~0.95 and E(B - V) ~ 0.011 for the weaker CaII absorbers (W_0^λ3934 < 0.7Å).