SDSS DLA and absorber quasar samples

While the average colour excess of DLAs, E(B-V), is known to be <~15-millimagnitude (mmag), both detections and non-detections with ~2mmag precision have been reported. Here we find 3.2{sigma} statistical evidence for DLA dust-reddening of 774 Sloan Digital Sky Survey (SDSS) quasars by comparing their fitted spectral slopes to those of ~7000 control quasars.

The corresponding E(B-V) is 3.0+/-1.0mmag, assuming a Small Magellanic Cloud (SMC) dust extinction law, and it correlates strongly (3.5{sigma}) with the metal content, characterized by the SiII {lambda}1526 absorption-line equivalent width, providing additional confidence that the detection is due to dust in the DLAs. Evolution of E(B-V) over the redshift range 2.1<z<4.0 is limited to <2.5mmag per unit redshift (1{sigma}), consistent with the known, mild DLA metallicity evolution.