Two-Dimensional Hydrodynamic Models of Super Star Clusters with a Positive Star Formation Feedback

Abstract

Using the hydrodynamic code ZEUS, we perform 2D simulations to determine the fate of the gas ejected by massive stars within super star clusters. It turns out that the outcome depends mainly on the mass and radius of the cluster. In the case of less massive clusters, a hot high velocity ($\sim 1000$ km s$^{-1}$) stationary wind develops and the metals injected by supernovae are dispersed to large distances from the cluster. On the other hand, the density of the thermalized ejecta within massive and compact clusters is sufficiently large as to immediately provoke the onset of thermal instabilities. These deplete, particularly in the central densest regions, the pressure and the pressure gradient required to establish a stationary wind, and instead the thermally unstable parcels of gas are rapidly compressed, by a plethora of re-pressurizing shocks, into compact high density condensations. Most of these are unable to leave the cluster volume and thus accumulate to eventually feed further generations of star formation. The simulations cover an important fraction of the parameter-space, which allows us to estimate the fraction of the reinserted gas which accumulates within the cluster and the fraction that leaves the cluster as a function of the cluster mechanical luminosity, the cluster size and heating efficiency.