THE MICROLENSING RATE AND MASS FUNCTION VERSUS DYNAMICS OF THE GALACTIC BAR

With the steady increase of the sample size of observed microlenses to wards the central regions of the Galaxy, the main source of the uncert ainty in the lens mass will shift from the simple Poisson noise to the intrinsic non-uniqueness of our dynamical models of the inner Galaxy, particularly the Galactic bar. We use a set of simple self-consistent bar models to investigate how the microlensing event rate varies as a function of axis ratio, bar angle and velocity distribution. The non- uniqueness of the velocity distribution of the bar model adds a signif icant uncertainty (by about a factor of 1.5) to any prediction of the lens mass. Kinematic data and self-consistent models are critical to l ift the non-uniqueness. We discuss the implications of these results f or the interpretation of microlensing observations of the Galactic bul ge. In particular we show that Freeman bar models scaled to the mass o f the Galactic bulge/bar imply a typical lens mass of around 0.8 M., a factor of 3-5 times larger than the value from other models.