H2 molecular gas absorption-selected systems trace CO molecular gas-rich galaxy overdensities

ABSTRACT Absorption-selected galaxies offer an effective way to study low-mass at high redshift. However, the physical properties of underlying galaxy population remain uncertain. In particular, multiphase circumgalactic medium is thought hold key information on gas flows into and out that are vital for evolution models. Here, we present ALMA observations CO molecular in host H2-bearing absorbers. our sample six absorbers, detect gas-rich five absorber fields, although did not target high-metallicity (>50 per cent solar) systems which previous studies reported highest detection rate. Surprisingly, find majority absorbers associated with multiple rather than single haloes. Together large impact parameters, these results suggest seen absorption part extended disc, but resides dense pockets intragroup medium.