The dust content of damped Lyman α systems in the Sloan Digital Sky Survey
Abstract
The dust content of damped Lyman α systems (DLAs) is an important observable for understanding their origin and the neutral gas reservoirs of galaxies. While the average colour excess of DLAs, E(B - V), is known to be ≲ 15 millimagnitude (mmag), both detections and non-detections with ∼2 mmag precision have been reported. Here we find 3.2σ 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 ± 1.0 mmag, assuming a Small Magellanic Cloud (SMC) dust extinction law, and it correlates strongly (3.5σ) with the metal content, characterized by the Si II λ1526 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 <2.5 mmag per unit redshift (1σ), consistent with the known, mild DLA metallicity evolution. There is also no apparent relationship with neutral hydrogen column density, N_{H I}, though the data are consistent with a mean E(B-V)/N_{H I}=(3.5± 1.0)× 10^{-24} mag cm2, approximately the ratio expected from the SMC scaled to the lower metallicities typical of DLAs. We implement the SDSS selection algorithm in a portable code to assess the potential for systematic, redshift-dependent biases stemming from its magnitude and colour-selection criteria. The effect on the mean E(B - V) is negligible (<5 per cent) over the entire redshift range of interest. Given the broad potential usefulness of this implementation, we make it publicly available.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- January 2016
- DOI:
- 10.1093/mnras/stv2420
- arXiv:
- arXiv:1510.05667
- Bibcode:
- 2016MNRAS.455.1043M
- Keywords:
-
- dust;
- extinction;
- galaxies: high redshift;
- intergalactic medium;
- galaxies: ISM;
- quasars: absorption lines;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- Accepted to MNRAS. 18 pages, 17 figures, 5 tables. Tables 1-4 available in the published electronic version or from http://astronomy.swin.edu.au/~mmurphy/publications . Code emulating the SDSS colour-selection algorithm is available at doi:10.5281/zenodo.31470 (http://dx.doi.org/10.5281/zenodo.31470) and hosted on GitHub (https://github.com/mbernet79/SDSS_QSOsel_Bernet)