A study of the circumgalactic medium at z ∼ 0.6 using damped Lyman α galaxies

Abstract

We present the study of a sample of nine QSO fields, with damped-Ly-alpha\n(DLA) or sub-DLA systems at z~0.6, observed with the X-Shooter spectrograph at\nthe Very Large Telescope. By suitably positioning the X-Shooter slit based on\nhigh spatial resolution images of HST/ACS we are able to detect absorbing\ngalaxies in 7 out of 9 fields (~ 78\\% success rate) at impact parameters from\n10 to 30 kpc. In 5 out of 7 fields the absorbing galaxies are confirmed via\ndetection of multiple emission lines at the redshift of DLAs where only 1 out\nof 5 also emits a faint continuum. In 2 out of these 5 fields we detect a\nsecond galaxy at the DLA redshift. Extinction corrected star formation rates\n(SFR) of these DLA-galaxies, estimated using their H-alpha fluxes, are in the\nrange 0.3-6.7 M_sun yr^-1. The emission metallicities of these five\nDLA-galaxies are estimated to be from 0.2 to 0.9 Z_sun. Based on the Voigt\nprofile fits to absorption lines we find the metallicity of the absorbing\nneutral gas to be in a range of 0.05--0.6 Z_sun. The two remaining DLA-galaxies\nare quiescent galaxies with SFR < 0.4 M_sun yr^-1 (3-sigma) presenting\ncontinuum emission but weak or no emission lines. Using X-Shooter spectrum we\nestimate i-band absolute magnitude of -19.5+/-0.2 for both these DLA-galaxies\nthat indicates they are sub-L* galaxies. Comparing our results with that of\nother surveys in the literature we find a possible redshift evolution of the\nSFR of DLA-galaxies.\n