7 Discussion and conclusions

The analysis of five years of microlensing data towards the SMC yielded four candidates, and allowed us to put stringent limits on the amount of galactic dark matter made of compact objects. Objects with a mass between $2\times10^{-7}~M_\odot$ and 1 $M_\odot$ cannot account for more than 25% of the mass of a standard spherical, isothermal and isotropic Galactic halo of $4 \times 10^{11}~M_\odot$ out to 50 kpc.

The new method described in this paper to combine the results and use all the information available on the events has one drawback compared to methods used in previous works: it could be more sensitive to the halo model, adding an extra dependence on the velocity distribution. Previously, only the influence of the halo model on the number of expected events has been studied, as in  SM98. A change in the velocity distribution, however, would mainly shift the "dent'' in the EROS2 LMC limit. In addition, since the final exclusion limit is quite flat over a large range of masses, the final result should not be influenced by reasonable changes in the velocity distribution assumptions.

This limit excludes a sizeable fraction of the allowed domain shown in Fig. 12 of Alcock et al. (2000).

All the candidates that have been detected so far towards the SMC have long durations, and seem more compatible with unidentified variable stars or self-lensing within the cloud than with halo objects. These would need to have supersolar masses to account for such durations.

The statistics are still very low for a quantitative comparison of the SMC and LMC samples of microlensing candidates. They have, however, quite different characteristics which is poorly compatible with a unique population of lenses.

Acknowledgements

We thank J. Bouchez for very useful discussions. We are grateful to D. Lacroix and the technical staff at the Observatoire de Haute Provence and to A. Baranne for their help in refurbishing the MARLY telescope and remounting it in La Silla. We are also grateful for the support given to our project by the technical staff at ESO, La Silla. We thank J. F. Lecointe for assistance with the online computing. AG was supported by grant AST 02-01266 from the NSF.