MUSE-ALMA Halos V: Physical properties and environment of z < 1.4 HI quasar absorbers

TL;DR

This study investigates the properties and environments of low-redshift HI quasar absorbers, revealing that most are linked to galaxy groups and that the CGM properties depend on galaxy group dynamics and metallicity.

Contribution

It provides new insights into the CGM of low-redshift galaxies, highlighting the prevalence of galaxy groups and the relationship between absorber properties and galaxy environments.

Findings

High detection rate of associated galaxies within 250 kpc.

Most absorbers are linked to galaxy groups or pairs.

Galaxies with smallest impact parameters are not always closest in velocity.

Abstract

We present results of the MUSE-ALMA Halos, an ongoing study of the Circum-Galactic Medium (CGM) of low redshift galaxies (z < 1.4), currently comprising 14 strong HI absorbers in five quasar fields. We detect 43 galaxies associated with absorbers down to star formation rate (SFR) limits of 0.01-0.1 solar masses/yr, found within impact parameters (b) of 250 kpc from the quasar sightline. Excluding the targeted absorbers, we report a high detection rate of 89 per cent and find that most absorption systems are associated with pairs or groups of galaxies (three to eleven members). We note that galaxies with the smallest impact parameters are not necessarily the closest to the absorbing gas in velocity space. Using a multi-wavelength dataset (UVES/HIRES, HST, MUSE), we combine metal and HI column densities, allowing for derivation of the lower limits of neutral gas metallicity as well as emission line diagnostics (SFR, metallicities) of the ionised gas in the galaxies. We find that groups of associated galaxies follow the canonical relations of N(HI) -- b and W_r(2796) -- b, defining a region in parameter space below which no absorbers are detected. The metallicity of the ISM of associated galaxies, when measured, is higher than the metallicity limits of the absorber. In summary, our findings suggest that the physical properties of the CGM of complex group environments would benefit from associating the kinematics of individual absorbing components with each galaxy member.