Characterizing the circum-galactic medium of damped Lyman-α absorbing galaxies

Abstract

Gas flows in and out of galaxies through their circum-galactic medium (CGM) are poorly constrained and direct observations of this faint, diffuse medium remain challenging. We use a sample of five z ∼ 1-2 galaxy counterparts to damped Lyman-α absorbers (DLAs) to combine data on cold gas, metals and stellar content of the same galaxies. We present new Hubble Space Telescope (HST)/WFC3 imaging of these fields in three to five broad-band filters and characterize the stellar properties of the host galaxies. By fitting the spectral energy distribution, we measure their stellar masses to be in the range of log(M_*/M_⊙) ∼ 9.1-10.7. Combining these with IFU observations, we find a large spread of baryon fractions inside the host galaxies, between 7 and 100 per cent. Similarly, we find gas fractions between 3 and 56 per cent. Given their star formation rates, these objects lie on the expected main sequence of galaxies. Emission line metallicities indicate they are consistent with the mass-metallicity relation for DLAs. We also report an apparent anti-correlation between the stellar masses and N(H I), which could be due to a dust bias effect or lower column density systems tracing more massive galaxies. We present new ALMA observations of one of the targets leading to a molecular gas mass of log(M_mol/M_⊙) < 9.89. We also investigate the morphology of the DLA counterparts and find that most of the galaxies show a clumpy structure and suggest ongoing tidal interaction. Thanks to our high spatial resolution HST data, we gain new insights into the structural complexity of the CGM.