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The Stellar Halo and Outer Disk of M33

McConnachie, Alan W. and Chapman, Scott C. and Ibata, Rodrigo A. and Ferguson, Annette M. N. and Irwin, Mike J. and Lewis, Geraint F. and Tanvir, Nial R. and Martin, Nicholas (2006) The Stellar Halo and Outer Disk of M33. Astrophysical Journal Letters, 647 (1). L25-L28. ISSN 2041-8205.

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We present first results from a Keck DEIMOS spectroscopic survey of red giant branch (RGB) stars in M33. The radial velocity distributions of the stars in our fields are well described by three Gaussian components, corresponding to a candidate halo component with an uncorrected radial velocity dispersion of σ ≃ 50 km s^(-1), a candidate disk component with a dispersion σ ≃ 16 km s^(-1), and a third component offset from the disk by ~50 km s^(-1), but for which the dispersion is not well constrained. By comparing our data to a model of M33 based on its H I rotation curve, we find that the stellar disk is offset in velocity by ~25 km s^(-1) from the H I disk, consistent with the warping that exists between these components. The spectroscopic metallicity of the halo component is [Fe/H] ≃ -1.5, significantly more metal-poor than the implied metallicity of the disk population ([Fe/H] ≃ -0.9), which also has a broader color dispersion than the halo population. These data represent the first detections of individual stars in the halo of M33 and, despite being ~10 times less massive than M31 or the Milky Way, all three of these disk galaxies have stellar halo components with a similar metallicity. The color distribution of the third component is different from the disk and the halo but is similar to that expected for a single, coeval, stellar population, and could represent a stellar stream. More observations are required to determine the true nature of this intriguing third kinematic component in M33.

Item Type:Article
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URLURL TypeDescription
Martin, Nicholas0000-0002-1349-202X
Additional Information:© 2006 American Astronomical Society. Received 2006 May 9; accepted 2006 June 29; published 2006 July 31. 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 E. Corbelli for supplying us with her data for the H i rotation curve of M33 and the anonymous referee for constructive comments. A. W. M. would like to thank J. Navarro and S. Ellison for financial support. A. M. N. F. is supported by a Marie Curie Excellence grant from the European Commission under contract MCEXT-CT-2005-025869. G. F. L. acknowledges support through ARC DP0343508.
Funding AgencyGrant Number
Marie Curie FellowshipMCEXT-CT-2005-025869
Australian Research CouncilDP0343508
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:galaxies: individual (M33); galaxies: stellar content; galaxies: structure; Local Group
Issue or Number:1
Record Number:CaltechAUTHORS:20110616-111757296
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Official Citation:The Stellar Halo and Outer Disk of M33 Alan W. McConnachie et al 2006 ApJ 647 L25
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:24027
Deposited By: Jason Perez
Deposited On:20 Jun 2011 20:55
Last Modified:03 Oct 2019 02:52

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