The loss of the intracluster medium in globular clusters

Abstract

ABSTRACT Stars in globular clusters (GCs) lose a non-negligible amount of mass during their post-main-sequence evolution. This material is then expected to build up a substantial intracluster medium (ICM) within the GC. However, the observed gas content in GCs is a couple of orders of magnitude below these expectations. Here, we follow the evolution of this stellar wind material through hydrodynamical simulations to attempt to reconcile theoretical predictions with observations. We test different mechanisms proposed in the literature to clear out the gas such as ram-pressure stripping by the motion of the GC in the Galactic halo medium and ionization by UV sources. We use the code ramses to run 3D hydrodynamical simulations to study for the first time, the ICM evolution within discretized multimass GC models including stellar winds and full radiative transfer. We find that the inclusion of both ram pressure and ionization is mandatory to explain why only a very low amount of ionized gas is observed in the core of GCs. The same mechanisms operating in ancient GCs that clear the gas could also be efficient at younger ages, meaning that young GCs would not be able to retain gas and form multiple generations of stars as assumed in many models to explain ‘multiple populations’. However, this rapid clearing of gas is consistent with observations of young massive clusters.