Microlensing Maps for the Milky Way Galaxy

At any instant, there are ∼ 1000 microlensing events to sources brighter than 20th magnitude in the Milky Way Galaxy. Large-scale maps of the microlensing optical depth and the mean timescale are constructed for a number of models of the Galactic bar and disk, incorporating the effects of streaming and spiral structure. Freudenreich’s model can reproduce the high optical depths towards the Bulge. It is also in good agreement with the data towards the spiral arms (except for the field γ Norma). Spiral structure tends to increase the optical depth by ∼ < 20 % and the mean timescale by ∼ < 100%. Different bar morphologies give characteristically different shaped contours, especially at low Galactic latitudes (|b | < 2 ◦). These could be traced out with a K band microlensing survey, consuming ∼ 100 minutes per night on a telescope like VISTA. Subject headings: Galaxy: structure – Galaxy: kinematics and dynamics – gravitational lensing