Phase-space distributions of chemical abundances in Milky Way-type Galaxy halos

Andreea S. Font, Kathryn V. Johnston, James S. Bullock, Brant E. Robertson

Research output: Contribution to journalArticle

78 Scopus citations

Abstract

Motivated by upcoming data from astrometric and spectroscopic surveys of the Galaxy, we explore the chemical abundance properties and phase-space distributions in hierarchically formed stellar halo simulations set in a ACDM universe. Our stellar halo metallicities increase with stellar halo mass. The slope of the [Fe/H]-M* trend mimics that of the satellite galaxies that were destroyed to build the halos, implying that the relation propagates hierarchically. All simulated halos contain a significant fraction of old stellar populations accreted more than 10 Gyr ago, and in a few cases some intermediate-age populations exist. In contrast with the Milky Way, many of our simulated stellar halos contain old stellar populations that are metal-rich, originating in the early accretion of massive satellites (M* ∼ 10 9 M). We suggest that the (metal-rich) stellar halo of M31 falls into this category, while the more metal-poor halo of the Milky Way is lacking in early massive accretion events. Interestingly, our hierarchically formed stellar halos often have nonnegligible metallicity gradients in both [Fe/H] and [α/Fe]. These gradients extend a few tens of kiloparsecs, and can be as large as 0.5 dex in [Fe/H] and 0.2 dex in [α/Fe], with the most metal-poor halo stars typically buried within the central ∼5 kpc of the galaxy. Finally, we find that chemical abundances can act as a rough substitute for time of accretion of satellite galaxies, and, based on this finding, we propose a criterion for identifying tidal streams spatially by selecting stars with [α/Fe] ratios below solar.

Original languageEnglish (US)
Pages (from-to)886-898
Number of pages13
JournalAstrophysical Journal
Volume646
Issue number2 I
DOIs
StatePublished - Aug 1 2006

Keywords

  • Cosmology: theory
  • Galaxies: abundances
  • Galaxies: evolution

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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