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

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(Mmol/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.