2011MNRAS.410.2516M

We present deep ground based imaging of the environments of five quasi-stellar objects (QSOs) that contain sub-damped Lyman α (sub-DLA) systems at z < 1 with the Southern Observatories Astrophysics Research (SOAR) telescope and SOAR Optical Imager (SOI) camera. We detect a clear surplus of galaxies in these small fields, supporting the assumption that we are detecting the galaxies responsible for the absorption systems. Assuming these galaxies are at the redshift of the absorption line systems, we detect luminous L > L^{Ux2605} galaxies for four of the five fields within 10 arcsec of the QSO. In contrast to previous imaging surveys of DLA systems at these redshifts, which indicate a range of morphological types and luminosities for the host galaxies of the systems, the galaxies we detect in these sub-DLA fields appear to be luminous (L ≳ L_{Ux2605}). In the case of the absorber towards Q1009-0026 at z_abs= 0.8866 we have spectroscopic confirmation that the candidate galaxy is at the redshift of the absorber, at an impact parameter of ∼ 35 kpc with a luminosity of 3 ≲ L/L^{Ux2605} ≲ 8 depending on the magnitude of the K-correction. These observations are in concordance with the view that sub-DLA systems may be more representative of massive galaxies than DLA systems. The environments of the absorbers span a range of types, from the inner disc of a galaxy, the periphery of a luminous galaxy and the outskirts of interacting galaxies. The large impact parameters to some of the candidate galaxies suggest that galactic outflows or tidal tails are likely responsible for the material seen in absorption. We find a weak correlation between N_ H I_ and the impact parameter at the 2σ level, which may be expected from the heterogeneous population of galaxies hosting the absorption line systems and random orientation angles. In addition, we detect a possible gravitationally lensed image of the BL-Lac object Q0826-2230.