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Gaia reveals a metal-rich in-situ component of the local stellar halo

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arxiv 1704.05463 v1 pith:4FYQDKBD submitted 2017-04-18 astro-ph.GA

Gaia reveals a metal-rich in-situ component of the local stellar halo

classification astro-ph.GA
keywords starshalometal-richdiskformedgaiain-situlatte
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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We use the first Gaia data release, combined with 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 with a relative speed of at least 220 km/s with respect to the local standard of rest. These stars are in general more metal-poor 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 isotropic orbital distribution of the more 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, while 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 in fact 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.

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Cited by 5 Pith papers

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