EDP Sciences
Free access
Volume 417, Number 2, April II 2004
Page(s) 461 - 477
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20031734

A&A 417, 461-477 (2004)
DOI: 10.1051/0004-6361:20031734

First microlensing candidates from the MEGA survey of M 31

J. T. A. de Jong1, K. Kuijken2, 1, A. P. S. Crotts3, P. D. Sackett4, W. J. Sutherland5, R. R. Uglesich3, E. A. Baltz3, P. Cseresnjes3, G. Gyuk6 and L. M. Widrow ()7

1  Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV, Groningen, The Netherlands
2  Sterrewacht Leiden, University of Leiden, PO Box 9513, 2300 RA, Leiden, The Netherlands
3  Columbia Astrophysics Laboratory, 550 W 120th St., Mail Code 5247, New York, NY 10027, USA
4  Research School of Astronomy and Astrophysics, Australian National University, Mt. Stromlo Observatory, Cotter Road, Weston ACT 2611, Australia
5  Institute of Astronomy, Madingley Rd, Cambridge CB3 0HA, UK
6  Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
7  Department of Physics, Queen's University, Kingston, ON K7L 3N6, Canada

(Received 5 June 2003 / Accepted 10 December 2003 )

We present the first M 31 candidate microlensing events from the Microlensing Exploration of the Galaxy and Andromeda (MEGA) survey. MEGA uses several telescopes to detect microlensing towards the nearby Andromeda galaxy, M 31, in order to establish whether massive compact objects are a significant contribution to the mass budget of the dark halo of M 31. The results presented here are based on observations with the Isaac Newton Telescope on La Palma, during the 1999/00 and 2000/01 observing seasons. In this data set, 14 variable sources consistent with microlensing have been detected, 12 of which are new and 2 have been reported previously by the POINT-AGAPE group. A preliminary analysis of the spatial and timescale distributions of the candidate events support their microlensing nature. We compare the spatial distributions of the candidate events and of long-period variable stars, assuming the chances of finding a long-period variable and a microlensing event are comparable. The spatial distribution of our candidate microlensing events is more far/near side asymmetric than expected from the detected long-period variable distribution. The current analysis is preliminary and the asymmetry not highly significant, but the spatial distribution of candidate microlenses is suggestive of the presence of a microlensing halo.

Key words: gravitational lensing -- M 31: halo -- dark matter

Offprint request: J. T. A. de Jong, jdejong@astro.rug.nl

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