Preprint Logo P43 October

To be published in:
Astronomy & Astrophysics

The self-enrichment of galactic halo globular clusters: a clue to their formation ?

G. Parmentier1, E. Jehin1, P. Magain1,*, C. Neuforge1 , A. Noels1 and A. Thoul1,**

1 Institut d'Astrophysique et de Géophysique - Université de Liège, Avenue de Cointe 5, 4000 Liège, Belgium

* Maître de Recherches FNRS, Belgium
** Chercheur Qualifié FNRS, Belgium


     We present a model of globular cluster self-enrichment. In the protogalaxy, cold and dense clouds embedded in the hot protogalactic medium are assumed to be the progenitors of galactic halo globular clusters. The massive stars of a first generation of metal-free stars, born in the central areas of the proto-globular cluster clouds, explode as Type II supernovae. The associated blast waves trigger the expansion of a supershell, sweeping all the material of the cloud, and the heavy elements released by these massive stars enrich the supershell. A second generation of stars is born in these compressed and enriched layers of gas. These stars can recollapse and form a globular cluster. This work aims at revising the most often encountered argument against self-enrichment, namely the presumed ability of a small number of supernovae to disrupt a proto-globular cluster cloud. We describe a model of the dynamics of the supershell and of its progressive chemical enrichment. We show that the minimal mass of the primordial cluster cloud required to avoid disruption by several tens of Type II supernovae is compatible with the masses usually assumed for proto-globular cluster clouds. Furthermore, the corresponding self-enrichment level is in agreement with halo globular cluster metallicities.

Key Words
globular clusters: general - Galaxy: evolution - supernovæ: general - ISM: bubbles - population III

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