First supernovae in Galactic globular clusters

• Published in: Monthly notices of the Royal Astronomical Society Vol. 319; no. 4; pp. 1047 - 1055
• Main Authors: Shustov, Boris M., Wiebe, Dmitri S.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 21.12.2000
• Subjects: Galaxy: abundances; Galaxy: evolution; globular clusters: general; supernovae: general
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1046/j.1365-8711.2000.03852.x

We address the question of whether globular clusters (GC) in a protogalaxy could evolve chemically for some time as isolated systems, enriching themselves with heavy elements produced in the first supernova events that follow initial star formation. We determine both the critical mass of a protoglobular cluster (proto-GC) that is needed to retain the ejecta of the very first supernova, and the critical energy (i.e. number of supernovae) that is needed to expel the residual gas from a cluster of a given mass. We show that the critical mass of a proto-GC for a wide range of parameters (size, degree of fragmentation, degree of central concentration) does not exceed 8 × 105 to 106 M⊙. The critical star formation efficiency (resulting in a certain number of supernova events) that is needed to expel the residual gas is about 1–3 per cent. Assuming that all the star-forming activity in the cluster stops after the critical number of supernovae have exploded, we reproduce the basic parameters of the present-day globular clusters, i.e. their final masses and oxygen abundances. A typical globular cluster in our model originates from a cloud with a mass of 5 × 107 to 108 M⊙. When all the remaining gas is lost from the cluster, its mass is about a few times 105 M⊙. A significant fraction (∼97 per cent) of an initial protocluster cloud is then available for galactic disc formation. We check our results with the method that is usually applied to elliptical galaxy modelling. The assumption that a protocluster cloud evolves and accumulates metals until the gas thermal energy (increased due to supernova explosions) exceeds its binding energy leads to the same conclusions. We also comment on the observed homogeneity of the iron distribution in globular clusters, which is often considered as a primary argument against self-enrichment. According to the current paradigm, iron originates mainly in Type Ia supernovae with long-lived progenitors. If one states that iron has existed in globular clusters prior to their formation, it should have had a pre-Galactic origin. We argue that it is hard to reconcile this with the observed correlation of average iron abundances in extragalactic GC systems with the luminosities of parent galaxies.