NOAO >   Observing Info >   Approved Programs >   2005B-0517

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Proposal Information for 2005B-0517


PI: Steven Majewski, University of Virginia, srm4n@virginia.edu
Address: Department of Astronomy, P.O. Box 3818, Charlottesville, VA 22903-0818, USA

CoI: Richard J. Patterson, University of Virginia
CoI: James Ostheimer, Information Extraction and Transport
CoI: Puragra Guhathakurta, UC-Santa Cruz
CoI: R. Michael Rich, UC-Los Angeles

Title: Exploring the Newly Discovered Halo Of M31

Abstract: Understanding the formation of galaxies and their structural components is a goal of modern cosmology. Cold dark matter (CDM) models make specific predictions about the shape and smoothness of halos, but few halos outside the Milky Way's (MW) have been explored for even the most basic, global properties, while even the MW halo presents some difficulties for study from inside. But the neighboring Andromeda spiral (M31) offers a global external perspective and yet is close enough for us to resolve individual stars. Recently, using Mayall 4-m + Mosaic photometry in the Washington M, T_2 + DDO51 filters and follow- up spectroscopy of identified M31 giant candidates, we made the first direct and unambiguous detection of the M31 halo, and traced its projected r^-2 density profile to 150 kpc along the M31 minor axis. We propose to expand on this discovery with the first systematic photometric and spectroscopic study of the extent, shape, smoothness, and chemodynamics of this newly found M31 component. Latest observations suggest that the MW halo potential is both more smooth and spherical than predicted by CDM models. Our photometric study will test these same fundamental properties of the M31 halo, and whether the MW is simply unusual or whether CDM models need further fine-tuning. Spectroscopic study of a subsample of our existing outer M31 giant sample will provide the first measure of the velocity dispersion, kinematic substructure and metallicity gradient of M31 halo to provide direct constraints on hierarchical formation models.


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