The galaxy counterpart and environment of the dusty damped Lyman-αabsorber atz= 2.226 towards Q 1218+0832

Abstract

We report on further observations of the field of the quasar Q 1218+0832. Geier et al. (2019, A&A, 625, L9) presented the discovery of the quasar resulting from a search for quasars reddened and dimmed by dust in foreground damped Lyman-αabsorbers (DLAs). The DLA is remarkable by having a very large H Icolumn density close to 1022cm−2. Its dust extinction curve shows the 2175 Å bump known from the Local Group. It also shows absorption from cold gas exemplified by C Iand CO molecules. For this paper, we present narrow-band observations of the field of Q 1218+0832 and also use an archivalHubbleSpace Telescope (HST) image to search for the galaxy counterpart of the DLA. No emission from the DLA galaxy is found in either the narrow-band imaging or in the HST image. In the HST image, we could probe down to an impact parameter of 0.3 arcsec and a 3-σdetection limit of 26.8 mag per arcsec2. In the narrow-band image, we probed down to a 0 arcsec impact parameter and detected nothing down to a 3-σdetection limit of about 3 × 10−17erg s−1cm−2. We did detect a bright Lyman-αemitter 59 arcsec south of Q 1218+0832 with a flux of 3 × 10−16erg s−1cm−2. We conclude that the DLA galaxy must be located at a very small impact parameter (< 0.3 arcsec, 2.5 kpc) or it is optically dark. Also, the DLA galaxy most likely is part of a galaxy group.