The hidden circumgalactic medium
  The cycling of baryons in and out of galaxies is what ultimately drives
galaxy formation and evolution. The circumgalactic medium (CGM) represents the
interface between the interstellar medium and the cosmic web, hence its
properties are directly shaped by the baryon cycle. Although traditionally the
CGM is thought to consist of warm and hot gas, recent breakthroughs are
presenting a new scenario according to which an important fraction of its mass
may reside in the cold atomic and molecular phase. This would represent fuel
that is readily available for star formation, with crucial implications for
feeding and feedback processes in galaxies. However, such cold CGM, especially
in local galaxies where its projected size on sky is expected to be of several
arcminutes, cannot be imaged by ALMA due to interferometric spatial scale
filtering of large-scale structures. We show that the only way to probe the
multiphase CGM including its coldest component is through a large (e.g. 50-m)
single dish (sub-)mm telescope.
