AAS 201st Meeting, January, 2003
Session 109. Fine Structure in Galaxies
Oral, Wednesday, January 8, 2003, 2:00-3:30pm, 613-614

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[109.04D] Evidence for Halo Microlensing in M31

R. Uglesich, A.P.S. Crotts, E. Baltz (Columbia University), J. deJong (Kapteyn Institute), A. Tomaney (University of Washington), R. Boyle, C. Corbally (Vatican Observatory), A. Gould (Ohio State University)

We present results from the VATT/Columbia survey of microlensing and variability of stars in M31, with particular emphasis on events from 3 days to two month timescales that are potentially caused by microlensing by masses in M31. These observations were conducted intensively from 1997-1999, with less intensive monitoring from 1995-present, at the Vatican Advanced Technology Telescope and the 1.3-meter telescope at MDM Observatory, including about 200 epochs total. The fields monitored cover about 560 square arcminutes total, positioned along the minor axis on either side of M31. A total of 4 bona fide and 14 probable microlensing events, when compared to carefully computed event rate and efficiency models, indicate a significant amount of microlensing activity above that expected for the stars alone in M31 acting as lenses. A maximum likelihood analysis of the distribution of events in timescale and across the face of M31 indicate a microlensing dark matter halo fraction consistent with that seen in our Galaxy towards the Large Magellanic Cloud (Alcock et al. 2000, ApJ, 542, 281), but significantly different from the no-halo expectation. The masses of these lensing objects are also consistent with the Alcock et al. result, and indicate that stellar-mass halo objects are important in spiral galaxies beyond the LMC sightline through our Galaxy's halo.

The author(s) of this abstract have provided an email address for comments about the abstract: rru@astro.columbia.edu

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.