Identifying Contributions To The Stellar Halo From Accreted, Kicked-Out, And In Situ Populations

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dc.contributor.utaustinauthorJohnson, Marshall C.en_US
dc.creatorSheffield, Allyson A.en_US
dc.creatorMajewski, Steven R.en_US
dc.creatorJohnston, Kathryn V.en_US
dc.creatorCunha, Katiaen_US
dc.creatorSmith, Verne V.en_US
dc.creatorCheung, Andrew M.en_US
dc.creatorHampton, Christina M.en_US
dc.creatorDavid, T. J.en_US
dc.creatorWagner-Kaiser, Rachel.en_US
dc.creatorJohnson, Marshall C.en_US
dc.creatorKaplan, Evanen_US
dc.creatorMiller, Jacoben_US
dc.creatorPatterson, Richard J.en_US
dc.date.accessioned2016-04-28T19:37:06Z
dc.date.available2016-04-28T19:37:06Z
dc.date.issued2012-12en
dc.description.abstractWe present a medium-resolution spectroscopic survey of late-type giant stars at mid-Galactic latitudes of (30 degrees < | b| < 60 degrees), designed to probe the properties of this population to distances of similar to 9 kpc. Because M giants are generally metal-rich and we have limited contamination from thin disk stars by the latitude selection, most of the stars in the survey are expected to be members of the thick disk (<[Fe/H]> similar to -0.6) with some contribution from the metal-rich component of the nearby halo. Here we report first results for 1799 stars. 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, which in some cases form distinct sequences in RV-l space. High-resolution echelle spectra taken for 34 of these "RV outliers" reveal the following patterns across the [Ti/Fe]-[Fe/H] plane: 17 of the stars have abundances reminiscent of the populations present in dwarf satellites of the Milky Way, 8 have abundances coincident with those of the Galactic disk and a more metal-rich halo, and 9 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 this sample consists predominantly of stars accreted from infalling dwarf galaxies. A smaller fraction of stars in the RV outlier sample may have been formed in the inner Galaxy and subsequently kicked to higher eccentricity orbits, but the sample is not large enough to distinguish conclusively between this interpretation and the alternative that these stars represent the tail of the velocity distribution of the thick disk. Our data do not rule out the possibility that a minority of the sample could have formed from gas in situ on their current orbits. These results are consistent with scenarios where the stellar halo, at least as probed by M giants, arises from multiple formation mechanisms; however, when taken at face value, our results for metal-rich halo giants suggest a much higher proportion to be accreted than found by Carollo et al. and more like the fraction suggested in the analysis by Nissen & Schuster and Schuster et al. We conclude that M giants with large RVs can provide particularly fruitful samples to mine for accreted structures and that some of the velocity sequences may indeed correspond to real physical associations resulting from recent accretion events.en_US
dc.description.departmentAstronomyen_US
dc.description.sponsorshipVassar College Committee on Researchen_US
dc.description.sponsorshipColumbia Science Fellows Programen_US
dc.description.sponsorshipNSF AST-0806558, AST-1107373, AST-0807945en_US
dc.description.sponsorshipNASA/JPL 1228235en_US
dc.identifierdoi:10.15781/T2NV5G
dc.identifier.Filename2012_12_stellarhalo.pdfen_US
dc.identifier.citationSheffield, Allyson A., Steven R. Majewski, Kathryn V. Johnston, Katia Cunha, Verne V. Smith, Andrew M. Cheung, Christina M. Hampton et al. "Identifying Contributions to the Stellar Halo from Accreted, Kicked-out, and In Situ Populations." The Astrophysical Journal, Vol. 761, No. 2 (Dec., 2012): 161.en_US
dc.identifier.doi10.1088/0004-637x/761/2/161en_US
dc.identifier.issn0004-637Xen_US
dc.identifier.urihttp://hdl.handle.net/2152/34922
dc.language.isoEnglishen_US
dc.relation.ispartofen_US
dc.relation.ispartofserialAstrophysical Journalen_US
dc.rightsAdministrative deposit of works to Texas ScholarWorks: This works author(s) is or was a University faculty member, student or staff member; this article is already available through open access or the publisher allows a PDF version of the article to be freely posted online. The library makes the deposit as a matter of fair use (for scholarly, educational, and research purposes), and to preserve the work and further secure public access to the works of the University.en_US
dc.rights.restrictionOpenen_US
dc.subjectgalaxy: disken_US
dc.subjectgalaxy: evolutionen_US
dc.subjectgalaxy: formationen_US
dc.subjectgalaxy: haloen_US
dc.subjectgalaxy: kinematics and dynamicsen_US
dc.subjectsolar neighborhooden_US
dc.subjectstars: abundancesen_US
dc.subjectall-sky surveyen_US
dc.subjectsagittarius dwarf galaxyen_US
dc.subjectabsolute proper motionsen_US
dc.subjectmilky-way tomographyen_US
dc.subjectgiant branch starsen_US
dc.subjectgalactic haloen_US
dc.subjectchemicalen_US
dc.subjectabundancesen_US
dc.subjectthick disken_US
dc.subjectsolar neighborhooden_US
dc.subjectred giantsen_US
dc.subjectastronomy & astrophysicsen_US
dc.titleIdentifying Contributions To The Stellar Halo From Accreted, Kicked-Out, And In Situ Populationsen_US
dc.typeArticleen_US

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