Microlensing Maps for the Galactic Bulge

Abstract

Microlensing maps -- that is, contours of equal numbers of events per $10^6$ source stars -- are provided for the inner Galaxy under two alternative hypotheses : (1) the bulge is an oblate axisymmetric spheroid or (2) the bulge is a prolate bar. Oblate spheroids yield a total of $\sim 12$ events per year per $10^6$ stars at Baade's Window ($\sim 15$ events if the disk is maximal). The event rate is slightly lower for prolate bars viewed at $\sim 45^\circ$ and the maps have a characteristic asymmetry between positive and negative longitudes. Prolate bars can yield mild amplifications of the event rate if viewed almost down the long axis. The disk provides the dominant lensing population on the bulge major axis for $|\ell | \gta 6^\circ$. Measurements of the rate at major axis windows can test for disk dark matter or maximal disk models.