2014MNRAS.444.1747S

We present the results of a survey for Caii λλ3934, 3969 absorption-line systems culled from ∼ 95000 Sloan Digital Sky Survey (SDSS) Data Release 7 and Data Release 9 quasar spectra. With 435 doublets identified in the catalogue, this list is the largest Caii catalogue compiled to date, spanning redshifts z < 1.34, which corresponds to the most recent ∼ 8.9 Gyr of the history of the Universe. We derive statistics on the Caii rest equivalent width distribution and incidence. We find that the λ3934 rest equivalent width (W_0^λ3934) distribution cannot be described by a single exponential function. A double exponential function is required to produce a satisfactory description. The function can be written as a sum of weak and strong components: ∂ n/∂ W_0^λ3934= (N_wk^*/W_wk^*) exp( -W_0^λ3934/W_wk^*) + (N_str^*/W_str^*) exp( -W_0^λ3934/W_str^*). A maximum likelihood fit to the unbinned data indicates N_wk^*=0.140±0.029, W_wk^*=0.165±0.020 Å, N_str^*=0.024±0.020, and W_str^*=0.427±0.101 Å. This suggests that the Caii absorbers are composed of at least two distinct populations. The incidence of the overall Caii absorber population does not show evidence for evolution in the standard cosmology. The normalization of the no-evolution curve, i.e. the value of the Caii incidence extrapolated to redshift z = 0, for W_0^λ3934 ≥0.3 Å, is n0 = 0.017±0.001. In comparison to Mgii surveys, we found that only 3 percent of Mgii systems in the SDSS have Caii, confirming that Caii systems are rare. We also report on some preliminary investigations of the nature of the two populations of Caii absorbers, and show that they can likely be distinguished using their Mgii properties.