EDP Sciences
Free Access
Volume 443, Number 3, December I 2005
Page(s) 911 - 928
Section Extragalactic astronomy
DOI https://doi.org/10.1051/0004-6361:20053135

A&A 443, 911-928 (2005)
DOI: 10.1051/0004-6361:20053135

POINT-AGAPE pixel lensing survey of M 31

Evidence for a MACHO contribution to galactic halos
S. Calchi Novati1, S. Paulin-Henriksson2, J. An3, P. Baillon4, V. Belokurov3, B. J. Carr5, M. Crézé2, 6, N. W. Evans3, Y. Giraud-Héraud2, A. Gould7, P. Hewett3, Ph. Jetzer1, J. Kaplan2, E. Kerins8, S. J. Smartt3, 9, C. S. Stalin2, Y. Tsapras5 and M. J. Weston5

1  Institute for Theoretical Physics, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland
2  APC, 11 Place Marcelin Berthelot, 75231 Paris, France
3  Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
4  CERN, 1211 Genève, Switzerland
5  Astronomy Unit, School of Mathematical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK
6  Université Bretagne-Sud, campus de Tohannic, BP 573, 56017 Vannes Cedex, France
7  Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
8  Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD, UK
9  Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast BT7 1NN, UK

(Received 26 March 2005 / Accepted 8 August 2005 )

The POINT-AGAPE collaboration is carrying out a search for gravitational microlensing toward M 31 to reveal galactic dark matter in the form of MACHOs (Massive Astrophysical Compact Halo Objects) in the halos of the Milky Way and M 31. A high-threshold analysis of 3 years of data yields 6 bright, short-duration microlensing events, which are confronted to a simulation of the observations and the analysis. The observed signal is much larger than expected from self lensing alone and we conclude, at the 95% confidence level, that at least 20% of the halo mass in the direction of M 31 must be in the form of MACHOs if their average mass lies in the range 0.5-1 $M_\odot$. This lower bound drops to 8% for MACHOs with masses ~0.01 $M_\odot$. In addition, we discuss a likely binary microlensing candidate with caustic crossing. Its location, some 32' away from the centre of M 31, supports our conclusion that we are detecting a MACHO signal in the direction of M 31.

Key words: galaxies: halos -- gravitational lensing -- dark matter -- galaxies: individual: M 31

SIMBAD Objects

© ESO 2005