Microlensing towards the Large Magellanic Cloud: a study of the LMC halo contribution

¹ Institute for Theoretical Physics, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland e-mail: novati@physik.unizh.ch
² Dipartimento di Fisica “E. R. Caianiello”, Università di Salerno, Via S. Allende, 84081 Baronissi (SA), Italy
³ Istituto Nazionale di Fisica Nucleare, sez. Napoli, Italy
⁴ International Institute for Advanced Scientific Studies, Vietri sul Mare (SA), Italy

Received: 7 March 2006
Accepted: 10 July 2006

Abstract

We carry out a new analysis of the sample of MACHO microlensing candidates towards the LMC. Our main purpose is to determine the lens population to which the events may belong. We give particular emphasis to the possibility of characterising the Milky Way dark matter halo population with respect to the LMC one. Indeed, we show that only a fraction of the events have characteristics that match those expected for lenses belonging to the MACHO population of the Galactic halo. This suggests that this component cannot explain all the candidates. Accordingly, we challenge the view that the dark matter halo fraction of both the Galaxy and the LMC halos are equal, and indeed we show that, for a MACHO mass in the range 0.1–0.3 , the LMC halo fraction can be significantly larger than the Milky Way's. In this perspective, our main conclusion is that up to about half of the observed events could be attributed to the LMC MACHO dark matter halo.