CaII Absorbers in the Sloan Digital Sky Survey: Element Abundances and Dust

Abstract

We present measurements of element abundance ratios and dust in CaII~absorbers identified in SDSS 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 $W_0^{\lambda 3934} = 0.7$ \AA, they are then representative of two physically different populations. Comparisons of abundance ratios between the two CaII absorber populations indicate that the weaker $W_0^{\lambda 3934}$ absorbers have properties consistent with halo-type gas, while the stronger absorbers have properties intermediate between halo- and disk-type gas. We also show that, on average, the dust extinction properties of the overall sample is consistent with a LMC or SMC dust law, and the stronger absorbers are nearly 6 times more reddened than their weaker counterparts. The absorbed-to-unabsorbed composite flux ratio at $\lambda_{rest} = 2200$ \AA\ is $\mathcal{R} \approx 0.73$ and $E(B-V) \approx 0.046$ for the stronger CaII absorbers ($W_0^{\lambda 3934} \ge 0.7$ \AA), and $\mathcal{R} \approx 0.95$ and $E(B-V) \approx 0.011$ for the weaker CaII absorbers ($W_0^{\lambda 3934} < 0.7$ \AA).