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The Dual Origin of Stellar Halos

Zolotov, Adi and Willman, Beth and Brooks, Alyson M. and Governato, Fabio and Brook, Chris B. and Hogg, David W. and Quinn, Tom and Stinson, Greg (2009) The Dual Origin of Stellar Halos. Astrophysical Journal, 702 (2). pp. 1058-1067. ISSN 0004-637X.

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We investigate the formation of the stellar halos of four simulated disk galaxies using high-resolution, cosmological SPH + N-body simulations. These simulations include a self-consistent treatment of all the major physical processes involved in galaxy formation. The simulated galaxies presented here each have a total mass of ~1012 M , but span a range of merger histories. These simulations allow us to study the competing importance of in situ star formation (stars formed in the primary galaxy) and accretion of stars from subhalos in the building of stellar halos in a ΛCDM universe. All four simulated galaxies are surrounded by a stellar halo, whose inner regions (r < 20 kpc) contain both accreted stars, and an in situ stellar population. The outer regions of the galaxies' halos were assembled through pure accretion and disruption of satellites. Most of the in situ halo stars formed at high redshift out of smoothly accreted cold gas in the inner 1 kpc of the galaxies' potential wells, possibly as part of their primordial disks. These stars were displaced from their central locations into the halos through a succession of major mergers. We find that the two galaxies with recently quiescent merger histories have a higher fraction of in situ stars (~20%-50%) in their inner halos than the two galaxies with many recent mergers (~5%-10% in situ fraction). Observational studies concentrating on stellar populations in the inner halo of the Milky Way will be the most affected by the presence of in situ stars with halo kinematics, as we find that their existence in the inner few tens of kpc is a generic feature of galaxy formation.

Item Type:Article
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URLURL TypeDescription
Willman, Beth0000-0003-2892-9906
Hogg, David W.0000-0003-2866-9403
Additional Information:© 2009 American Astronomical Society. Print publication: Issue 2 (2009 September 10); received 2009 April 23; accepted for publication 2009 July 16; published 2009 August 18. We thank the anonymous referee for suggestions which helped to extensively clarify the paper. A.Z. thanks the Institute of Theory & Computation at Harvard-Smithsonian’s Center for Astrophysics for its hospitality during part of this work. B.W. and A.Z. thank the Smithsonian Astrophysical Observatory and the Clay Fellowship for partial financial support. We thank Joe Cammisa at Haverford for computing support. A.Z. was partially supported by New York University’s Horizon Fellowship. A.B. acknowledges support from the Sherman Fairchild Postdoctoral Program in Theoretical Astrophysics. D.W.H. was partially supported by NASA grant NNX08AJ48G. Simulations were run at ARSC, NASA AMES. and Texas Supercomputing Center. F.G. acknowledges support from a Theodore Dunham grant, HST GO-1125, NSF ITR grant PHY- 0205413 (also supporting T.Q.), NSF grant AST-0607819 and NASA ATP NNX08AG84G. C.B.B. acknowledges the support of the UK’s Science & Technology Facilities Council (ST/F002432/1).
Funding AgencyGrant Number
Smithsonian Astrophysical ObservatoryUNSPECIFIED
Clay FellowshipUNSPECIFIED
New York University (NYU)UNSPECIFIED
Sherman Fairchild FoundationUNSPECIFIED
Theodore Dunham grantUNSPECIFIED
Science and Technology Facilities Council (STFC)ST/F002432/1
Subject Keywords:Galaxy: formation; Galaxy: halo; galaxies: formation; galaxies: halos; methods: N-body simulations
Issue or Number:2
Record Number:CaltechAUTHORS:20090915-121230831
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Official Citation:The Dual Origin of Stellar Halos Adi Zolotov, Beth Willman, Alyson M. Brooks, Fabio Governato, Chris B. Brook, David W. Hogg, Tom Quinn, and Greg Stinson 2009 ApJ 702 1058-1067 doi: 10.1088/0004-637X/702/2/1058
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15857
Deposited By: Jason Perez
Deposited On:16 Sep 2009 19:53
Last Modified:09 Mar 2020 13:18

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