Gaia Reveals a Metal-rich, in situ Component of the Local Stellar Halo

Journal Article · Sun Aug 20 04:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA7D0C· OSTI ID:22875908

Bonaca, Ana; Conroy, Charlie ^[1]; Wetzel, Andrew; Hopkins, Philip F. ^[2]; Kereš, Dušan ^[3]

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1. Department of Astronomy, Harvard University, Cambridge, MA 02138 (United States)
2. TAPIR, California Institute of Technology, Pasadena, CA (United States)
3. Department of Physics, Center for Astrophysics and Space Sciences, University of California, San Diego, La Jolla, CA (United States)

We use the first Gaia data release, combined with the RAVE and APOGEE spectroscopic surveys, to investigate the origin of halo stars within ≲3 kpc from the Sun. We identify halo stars kinematically as moving at a relative speed of at least 220 km s{sup −1} with respect to the local standard of rest. These stars are generally less metal-rich than the disk, but surprisingly, half of our halo sample is comprised of stars with [Fe/H]>−1. The orbital directions of these metal-rich halo stars are preferentially aligned with the disk rotation, in sharp contrast with the intrinsically isotropic orbital distribution of the metal-poor halo stars. We find similar properties in the Latte cosmological zoom-in simulation of a Milky Way-like galaxy from the FIRE project. In Latte, metal-rich halo stars formed primarily inside of the solar circle, whereas lower-metallicity halo stars preferentially formed at larger distances (extending beyond the virial radius). This suggests that metal-rich halo stars in the solar neighborhood actually formed in situ within the Galactic disk, rather than having been accreted from satellite systems. These stars, currently on halo-like orbits, therefore have likely undergone substantial radial migration/heating.

• OSTI ID: 22875908
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 845; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COMPUTERIZED SIMULATION
DISTANCE
DISTRIBUTION
GALACTIC EVOLUTION
METALLICITY
MILKY WAY
ORBITS
ROTATION
SATELLITES
VELOCITY