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Global Properties of M31's Stellar Halo from the SPLASH Survey. I. Surface Brightness Profile

Gilbert, Karoline M. and Guhathakurta, Puragra and Beaton, Rachael L. and Bullock, James and Geha, Marla C. and Kalirai, Jason S. and Kirby, Evan N. and Majewski, Steven R. and Ostheimer, James C. and Patterson, Richard J. and Tollerud, Erik J. and Tanaka, Mikito and Chiba, Masashi (2012) Global Properties of M31's Stellar Halo from the SPLASH Survey. I. Surface Brightness Profile. Astrophysical Journal, 760 (1). Art. No. 76. ISSN 0004-637X. doi:10.1088/0004-637X/760/1/76.

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We present the surface brightness profile of M31's stellar halo out to a projected radius of 175 kpc. The surface brightness estimates are based on confirmed samples of M31 red giant branch stars derived from Keck/DEIMOS spectroscopic observations. A set of empirical spectroscopic and photometric M31 membership diagnostics is used to identify and reject foreground and background contaminants. This enables us to trace the stellar halo of M31 to larger projected distances and fainter surface brightnesses than previous photometric studies. The surface brightness profile of M31's halo follows a power law with index –2.2 ± 0.2 and extends to a projected distance of at least ~175 kpc (~2/3 of M31's virial radius), with no evidence of a downward break at large radii. The best-fit elliptical isophotes have b/a = 0.94 with the major axis of the halo aligned along the minor axis of M31's disk, consistent with a prolate halo, although the data are also consistent with M31's halo having spherical symmetry. The fact that tidal debris features are kinematically cold is used to identify substructure in the spectroscopic fields out to projected radii of 90 kpc and investigate the effect of this substructure on the surface brightness profile. The scatter in the surface brightness profile is reduced when kinematically identified tidal debris features in M31 are statistically subtracted; the remaining profile indicates that a comparatively diffuse stellar component to M31's stellar halo exists to large distances. Beyond 90 kpc, kinematically cold tidal debris features cannot be identified due to small number statistics; nevertheless, the significant field-to-field variation in surface brightness beyond 90 kpc suggests that the outermost region of M31's halo is also comprised to a significant degree of stars stripped from accreted objects.

Item Type:Article
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URLURL TypeDescription Paper
Gilbert, Karoline M.0000-0003-0394-8377
Guhathakurta, Puragra0000-0001-8867-4234
Beaton, Rachael L.0000-0002-1691-8217
Bullock, James0000-0003-4298-5082
Geha, Marla C.0000-0002-7007-9725
Kalirai, Jason S.0000-0001-9690-4159
Kirby, Evan N.0000-0001-6196-5162
Majewski, Steven R.0000-0003-2025-3147
Tollerud, Erik J.0000-0002-9599-310X
Chiba, Masashi0000-0002-9053-860X
Additional Information:© 2012 American Astronomical Society. Received 2012 April 21; accepted 2012 September 25; published 2012 November 6. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We thank Teresa Krause of Castilleja School, a participant in the Science Internship Program (SIP) at UCSC, for her work on the separation of M31 RGB and MW dwarf star samples. Support for this work was provided by NASA through Hubble Fellowship grants 51273.01 and 51256.01 awarded to K.M.G. and E.N.K. by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. P.G., J.S.B., and S.R.M. acknowledge support from collaborative NSF grants AST-1010039, AST-1009973, AST-1009882, and AST-0607726. This project was also supported by NSF grants AST03-07842, AST03-07851, AST06-07726, AST08-07945, and AST10-09882, NASA grant HST-GO-12105.03 through STScI, NASA/JPL contract 1228235, the David and Lucile Packard Foundation, and the F. H. Levinson Fund of the Peninsula Community Foundation (S.R.M., R.J.P., and R.L.B.). E.J.T. acknowledges support from a Graduate Assistance in Areas of National Need (GAANN) fellowship. R.L.B. acknowledges receipt of the Mark C. Pirrung Family Graduate Fellowship from the Jefferson Scholars Foundation and a Fellowship Enhancement for Outstanding Doctoral Candidates from the Office of the Vice President of Research at the University of Virginia. The analysis pipeline used to reduce the DEIMOS data was developed at UC Berkeley with support from NSF grant AST-0071048. The authors recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
Funding AgencyGrant Number
NASA Hubble Fellowship51273.01
NASA Hubble Fellowship51256.01
NASANAS 5-26555
David and Lucile Packard FoundationUNSPECIFIED
Peninsula Community FoundationUNSPECIFIED
Graduate Assistance in Areas of National Need (GAANN) fellowshipUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:galaxies: halos; galaxies: individual (M31); galaxies: structure
Issue or Number:1
Record Number:CaltechAUTHORS:20121219-104906863
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Official Citation:Global Properties of M31's Stellar Halo from the SPLASH Survey. I. Surface Brightness Profile Karoline M. Gilbert, Puragra Guhathakurta, Rachael L. Beaton, James Bullock, Marla C. Geha, Jason S. Kalirai, Evan N. Kirby, Steven R. Majewski, James C. Ostheimer, Richard J. Patterson, Erik J. Tollerud, Mikito Tanaka, and Masashi Chiba doi:10.1088/0004-637X/760/1/76
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:36047
Deposited By: Ruth Sustaita
Deposited On:19 Dec 2012 19:31
Last Modified:09 Nov 2021 23:19

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