SNe and their impact during the early evolution of Type I Globular Clusters

TL;DR

This study investigates how supernova feedback influences gas retention and chemical enrichment in early globular clusters, explaining the observed uniformity in iron content despite multiple stellar populations.

Contribution

It introduces a semi-analytic and numerical framework to assess supernova ejecta retention and mixing during proto-globular cluster evolution, highlighting conditions for secondary star formation.

Findings

Supernova ejecta often escape due to blowout outside the superwind radius.

Complete gas expulsion prevents supernova ejecta from enriching subsequent stars.

Conditions for partial retention can produce observed metallicity spreads.

Abstract

The iron composition of globular clusters (GCs) is homogeneous in all but a few massive clusters, despite the presence of multiple stellar populations. Hence, most if not all the supernovae (SN) ejecta was not used to form stars. Here by means of semi-analytic and numerical studies we address this issue considering both stellar winds and supernovae feedback during the early evolution of proto-globular clusters. We calculate the ability of stellar winds to form a global wind that removes the gas left over from star formation. The innermost radius from which such a global wind can be formed, the superwind radius $R_{SW}$, is a function of the cloud parameters and the star formation efficiency. In the case of complete gas expulsion ($R_{\textrm{SW}}=0$), the SN ejecta merge with shock-heated winds and exit the cluster. On the other hand, when $R_{\textrm{SW}}>0$, supernova remnants (SNRs) become pressure-confined if evolving within a critical radius $R_{\textrm{blow}}$, and mix their products with the residual gas. However, outside of this central zone the SNRs experience blowout. In such cases, the thermalized ejecta escapes the cluster, making the SN products unavailable for the formation of new stars. We estimated the metallicity enhancement ($\Delta\textrm{[Fe/H]}$) of the leftover gas and discuss the conditions required to produce secondary stellar populations with $\Delta\textrm{[Fe/H]}$ in the range observed in the majority of GCs.