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    Resolving the Metallicity Distribution of the Stellar Halo with the H3 Survey

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    Conroy_2019_ApJ_887_237.pdf
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    Author
    Conroy, Charlie cc
    Naidu, Rohan P.
    Zaritsky, Dennis
    Bonaca, Ana
    Cargile, Phillip
    Johnson, Benjamin D. cc
    Caldwell, Nelson cc
    Affiliation
    Univ Arizona, Steward Observ
    Issue Date
    2019-12-23
    
    Metadata
    Show full item record
    Publisher
    IOP PUBLISHING LTD
    Citation
    Charlie Conroy et al 2019 ApJ 887 237
    Journal
    ASTROPHYSICAL JOURNAL
    Rights
    Copyright © 2019. The American Astronomical Society. All rights reserved.
    Collection Information
    This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.
    Abstract
    The Galactic stellar halo is predicted to have formed at least partially from the tidal disruption of accreted dwarf galaxies. This assembly history should be detectable in the orbital and chemical properties of stars. The H3 Survey is obtaining spectra for 200,000 stars and, when combined with Gaia data, is providing detailed orbital and chemical properties of Galactic halo stars. Unlike previous surveys of the halo, the H3 target selection is based solely on magnitude and Gaia parallax; the survey therefore provides a nearly unbiased view of the entire stellar halo at high latitudes. In this paper we present the distribution of stellar metallicities as a function of Galactocentric distance and orbital properties for a sample of 4232 kinematically selected halo giants to 100 kpc. The stellar halo is relatively metal-rich, <[Fe/H]> = -1.2, and there is no discernible metallicity gradient over the range 6 < R-gal < 100 kpc. However, the halo metallicity distribution is highly structured, including distinct metal-rich and metal-poor components at R-gal < 10 kpc and R-gal > 30 kpc, respectively. The Sagittarius stream dominates the metallicity distribution at 20-40 kpc for stars on prograde orbits. The Gaia-Enceladus merger remnant dominates the metallicity distribution for radial orbits to approximate to 30 kpc. Metal-poor stars with [Fe/H] < -2 are a small population of the halo at all distances and orbital categories. We associate the "in situ" stellar halo with stars displaying thick disk chemistry on halo-like orbits; such stars are confined to vertical bar z vertical bar < 10 kpc. The majority of the stellar halo is resolved into discrete features in chemical-orbital space, suggesting that the bulk of the stellar halo formed from the accretion and tidal disruption of dwarf galaxies. The relatively high metallicity of the halo derived in this work is a consequence of the unbiased selection function of halo stars and, in combination with the recent upward revision of the total stellar halo mass, implies a Galactic halo metallicity that is typical for its mass.
    ISSN
    0004-637X
    DOI
    10.3847/1538-4357/ab5710
    Version
    Final published version
    ae974a485f413a2113503eed53cd6c53
    10.3847/1538-4357/ab5710
    Scopus Count
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    UA Faculty Publications

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