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23 April 2024 |
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Article overview
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Galactic Structure from Late-Type Giants at Mid-Latitudes I: Identifying Contributions to the Stellar Halo from Accreted and In Situ Populations | | Allyson A. Sheffield
; Steven R. Majewski
; Kathryn V. Johnston
; Katia Cunha
; Verne V. Smith
; Andrew M. Cheung
; Christina M. Hampton
; Trevor J. David
; Rachel Wagner-Kaiser
; Marshall C. Johnson
; Evan Kaplan
; Jacob Miller
; Richard J. Patterson
; | | Date: |
23 Feb 2012 | | Abstract: | [Abridged] We present a medium-resolution spectroscopic survey of 1799 M
giant stars at mid-Galactic latitudes designed to probe the properties of this
population to distances of $sim$9 kpc. The distribution of radial velocity
(RV) as a function of $l$ for these stars shows (1) the expected thick disk
population and (2) local metal-rich halo stars moving at high speeds relative
to the disk, that in some cases form distinct sequences in $l$-RV.
High-resolution echelle spectra taken for 34 of these "RV outliers" reveal the
following patterns across the [Ti/Fe] and [Fe/H] plane: sixteen of the stars
have abundances reminiscent of the populations present in dwarf satellites of
the Milky Way; eight have abundances coincident with those of the Galactic disk
and metal-rich halo; and ten of the stars fall on the locus defined by the
majority of stars in the halo. The chemical abundance trends of the RV outliers
suggest that our sample consists predominantly of stars accreted from infalling
dwarf galaxies, with a more moderate fraction ($sim$20%) of stars potentially
formed in the Galactic disk and subsequently kicked to higher eccentricity
orbits. These results support scenarios where the stellar halo arises from
multiple formation mechanisms. We conclude that M giants with large RVs can
provide particularly fruitful samples to mine for accreted structures and that
some of the putative velocity sequences may indeed correspond to real physical
associations resulting from recent accretion events. | | Source: | arXiv, 1202.5310 | | Services: | Forum | Review | PDF | Favorites | |
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