SOAR Imaging of sub-Damped Lyman-Alpha Systems at z<1

TL;DR

This study uses deep imaging to identify and analyze galaxies associated with sub-Damped Lyman-alpha systems at redshifts below 1, revealing that these systems are often linked to luminous, massive galaxies and their environments.

Contribution

First detailed imaging survey of sub-DLA environments at z<1 showing these systems are typically associated with luminous, massive galaxies, and providing spectroscopic confirmation of galaxy-absorber associations.

Findings

Detected a surplus of galaxies near QSOs with sub-DLAs.

Most identified galaxies are luminous (L>L*) and within 10" of the QSOs.

Sub-DLAs may be more representative of massive galaxies than DLA systems.

Abstract

We present deep ground based imaging of the environments of five QSOs that contain sub-Damped Lyman-alpha systems at z<1 with the SOAR telescope and 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* galaxies for four of the five fields within 10" 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*). In the case of the absorber towards Q1009-0026 at z=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* < 8 depending on the magnitude of the K-correction. These observations are in concordance with the view that sub-DLAs may be more representative of massive galaxies than DLA systems. The environments of the absorbers span a range of types, from the inner disk 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(HI) and the impact parameter at the 2 sigma 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.