Linking the Metallicity Distribution of Galactic Halo Stars to the Enrichment History of the Universe

Abstract

We compare the metallicity distribution of Galactic Halo stars with 3D realizations of hierarchical galaxy formation. Outflows from dwarf galaxies enrich the intergalactic medium inhomogeneously, at a rate depending on the local galaxy density. Consequently, the first stars created in small early-forming galaxies are less metal-rich that the first stars formed in more massive galaxies which typically form later. As most halo stars are likely to originate in accreted dwarfs, while disk stars formed out of outflow-enriched gas, this scenario naturally generates a ``metallicity floor'' for old disk stars, which we find to be roughly coincident with the higher end of our predicted metallicity distribution of halo stars, in agreement with observations. The broad and centrally peaked distribution of halo star metallicities is well reproduced in our models, with a natural dispersion depending on the exact accretion history. Our modeling includes the important ``baryonic stripping'' effect of early outflows, which brush away the tenuously held gas in neighboring pre-virialized density perturbations. This stripping process does not significantly modify the predicted shape of the halo star metal distribution but inhibits star-formation and hence the number of accreted stars, helping to reproduce the observed total Galactic halo luminosity and also the lack of low-luminosity local dwarf galaxies relative to N-body predictions.

5 pages, 1 figure, ApJ Letters, accepted

References in corpus (9)

• Dark Matter Substructure in Galactic Halos
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Cited by in corpus (6)

• Cosmological SPH simulations: A hybrid multi-phase model for star formation
• Spectral Evidence for Widespread Galaxy Outflows at z>4
• The Spatial Distribution of the Galactic First Stars I: High-Resolution N-body Approach
• The metallicity distribution of the halo and the satellites of the Milky way in the hierarchical merging paradigm
• Modelling the chemical evolution of the Galaxy halo
• On the chemical evolution of the Milky Way