On star formation and the nonexistence of dark galaxies

Abstract

We investigate whether a baryonic dark galaxy or "galaxy without stars" could persist indefinitely in the local universe, while remaining stable against star formation. To this end, a simple model has been constructed to determine the equilibrium distribution and composition of a gaseous protogalactic disk. Specifically, we determine the amount of gas that will transit to a Toomre unstable cold phase via the H2 cooling channel in the presence of a UV-X-ray cosmic background radiation field. All but one of the models are predicted to become unstable to star formation: we find that, in the absence of an internal radiation field, the majority of gas will become Toomre unstable in all putative d..