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A Kinematically Selected, Metal-poor Stellar Halo in the Outskirts of M31

Chapman, S. C. and Ibata, R. and Lewis, G. F. and Ferguson, A. M. N. and Irwin, M. and McConnachie, A. and Tanvir, N. (2006) A Kinematically Selected, Metal-poor Stellar Halo in the Outskirts of M31. Astrophysical Journal, 653 (1). pp. 255-266. ISSN 0004-637X. doi:10.1086/508599.

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We present evidence for a metal-poor, [Fe/H] ~- 1:4,σ = 0.2 dex, stellar halo component detectable at radii from 10 to 70 kpc, in our nearest giant spiral neighbor, the Andromeda galaxy. This metal-poor sample underlies the recently discovered extended rotating component and has no detected metallicity gradient. This discovery uses a large sample of 9861 radial velocities of red giant branch (RGB) stars obtained with the Keck II Telescope and DEIMOS spectrograph, with 827 stars with robust radial velocity measurements isolated kinematically to lie in the halo component primarily by windowing out the extended rotating component, which dominates the photometric profile of Andromeda out to<50 kpc (deprojected). The stars lie in 54 spectroscopic fields spread over an 8 deg^2 region, and are expected to fairly sample the halo to a radius of 70 kpc. The halo sample shows no significant evidence for rotation. Fitting a simple model in which the velocity dispersion of the component decreases with radius, we find a central velocity dispersion of 152 km s^(-1) decreasing by 0.90 km s^(-1) kpc^(-1). By fitting a cosmologically motivated NFW halo model to the halo stars we constrain the virial mass of M31 to be greater than 9.0 x 10^(11) M_☉ with 99% confidence. The properties of this halo component are very similar to that found in our Milky Way, revealing that these roughly equal mass galaxies may have led similar accretion and evolutionary paths in the early universe.

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Additional Information:© 2006 The American Astronomical Society. Received 2006 February 26; accepted 2006 August 15. S. C. C. acknowledges support from NASA. G. F. L. acknowledges support through ARC DP0343508 and thanks the Australian Academy of Science for financial support in visiting the Institute of Astronomy, Cambridge. A. M. would like to thank J. Navarro and S. Ellison for financial support. Data presented herein were obtained using the W.M. Keck Observatory, which is operated as a scientific partnership among Caltech, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
Funding AgencyGrant Number
Ames Research Center (ARC)DP0343508
Australian Academy of ScienceUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:galaxies: evolution; galaxies: individual (Andromeda); galaxies: spiral; Local Group
Issue or Number:1
Record Number:CaltechAUTHORS:20110222-092747500
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Official Citation:A Kinematically Selected, Metal-poor Stellar Halo in the Outskirts of M31 S. C. Chapman, R. Ibata, G. F. Lewis, A. M. N. Ferguson, M. Irwin, A. McConnachie, and N. Tanvir doi: 10.1086/508599
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:22402
Deposited By: Ruth Sustaita
Deposited On:22 Feb 2011 19:00
Last Modified:09 Nov 2021 16:04

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