A new component of the Galaxy as the origin of the LMC microlensing events

Abstract

We suggest a new component of the Milky Way that can account for both the optical depth and event durations implied by microlensing searches targeting the Large Magellanic Cloud. This component, which represents less than 4% of the total dark matter halo mass, consists of mainly old white dwarf stars in a distribution that extends beyond the disk of the galaxy, but lies well within the dark matter halo. It is consistent with recent evidence for a significant population of white dwarfs detected in proper motion studies of the Hubble Deep Field that cannot be accounted for by stars in the disk or spheroid. Further, it evades all of the current observational constraints that restrict a halo population of white dwarfs.