Ei. Gates et G. Gyuk, A new (old) component of the galaxy as the origin of the observed Large Magellanic Cloud microlensing events, ASTROPHYS J, 547(2), 2001, pp. 786-791
We suggest a new component of the Milky Way galaxy that can account for bot
h the optical depth and the event durations obtained by the MACHO microlens
ing survey toward the Large Magellanic Cloud. This component is consistent
with recent evidence for a significant population of faint white dwarf star
s, detected in a proper-motion study of the Hubble Deep Field, which cannot
be accounted for by stars in the disk or spheroid. This new component, whi
ch represents less than 4% of the total dark halo mass, consists of (mostly
) old white dwarf stars distributed in a highly extended (very thick) disk
configuration. It extends beyond the traditional thin and thick disks, but
well within the dark, roughly spherical cold dark matter (CDM) halo. We exp
lore the distribution of proper motions expected for white dwarfs in this m
odel and the ability of future surveys to differentiate between models. Fin
ally, we argue that such a component is reasonable, natural, and consistent
with a variety of observations, and many of the problems associated with a
significant halo population of white dwarfs are ameliorated.