To be published in:
Astronomy and Astrophysics
The Old Halo metallicity gradient:
the trace of a self-enrichment process
A. Noels and
Institut d'Astrophysique et de Géophysique, Université de
Liège, 5, Avenue de Cointe, B-4000 Liège, Belgium
* Chercheur qualifié au Fonds National de la Recherche
Based on a model of globular cluster self-enrichment
published in a
previous paper, we present an explanation for the metallicity gradient
observed throughout the galactic Old Halo.
Our self-enrichment model is based on the ability of globular cluster
progenitor clouds to retain the ejecta of a first generation of Type II
Supernovae. The key point is that this ability depends on the pressure
exerted on the progenitor cloud by the surrounding protogalactic medium
and therefore on the location of the cloud in the protoGalaxy.
Since there is no significant (if any) metallicity gradient in the whole halo,
we also present a review in favour of a galactic halo partly build
via accretions and mergers of satellite systems. Some of them bear
their own globular clusters and therefore "contaminate"
the system of globular clusters formed "in situ", namely
within the original potential well of the Galaxy.
Therefore, the comparison between our
self-enrichment model and the observational data should be limited to
the genuine galactic globular clusters,
the so-called Old Halo group.
evolution -- Galaxy: formation --
globular clusters: general -- Galaxy: halo
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Halo stars" Page