Evidence from the H3 Survey That the Stellar Halo Is Entirely Comprised of Substructure
AuthorNaidu, Rohan P.
Johnson, Benjamin D.
Cargile, Phillip A.
AffiliationUniv Arizona, Steward Observ
KeywordsGalaxy stellar halos
Milky Way evolution
Milky Way formation
Milky Way Galaxy
Milky Way stellar halo
MetadataShow full item record
PublisherIOP PUBLISHING LTD
CitationNaidu, R. P., Conroy, C., Bonaca, A., Johnson, B. D., Ting, Y. S., Caldwell, N., ... & Cargile, P. A. (2020). Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure. The Astrophysical Journal, 901(1), 48.
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AbstractIn the ΛCDM paradigm, the Galactic stellar halo is predicted to harbor the accreted debris of smaller systems. To identify these systems, the H3 Spectroscopic Survey, combined with Gaia, is gathering 6D phase-space and chemical information in the distant Galaxy. Here we present a comprehensive inventory of structure within 50 kpc from the Galactic center using a sample of 5684 giants at alpha disk, the in situ halo (disk stars heated to eccentric orbits), Sagittarius (Sgr), Gaia-Sausage-Enceladus (GSE), the Helmi Streams, Sequoia, and Thamnos. Additionally, we identify the following new structures: (i) Aleph ([Fe/H] = -0.5), a low-eccentricity structure that rises a surprising 10 kpc off the plane, (ii) and (iii) Arjuna ([Fe/H] = -1.2) and I'itoi ([Fe/H] < -2), which comprise the high-energy retrograde halo along with Sequoia, and (iv) Wukong ([Fe/H] = -1.6), a prograde phase-space overdensity chemically distinct from GSE. For each structure, we provide [Fe/H], [alpha/Fe], and orbital parameters. Stars born within the Galaxy are a major component at<CDATA<i(60%), but their relative fraction declines sharply to less than or similar to 5% past 15 kpc. Beyond 15 kpc, >80% of the halo is built by two massive (M similar to 10(8)-10(9)M) accreted dwarfs: GSE ([Fe/H] = -1.2) within 25 kpc and Sgr ([Fe/H] = -1.0) beyond 25 kpc. This explains the relatively high overall metallicity of the halo ([Fe/H] -1.2). We attribute greater than or similar to 95% of the sample to one of the listed structures, pointing to a halo built entirely from accreted dwarfs and heating of the disk.
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