Limits on the microlens mass function of Q2237 0305

Abstract

Gravitational microlensing at cosmological distances is potentially a powerful tool for probing the mass functions of stars and compact objects in other galaxies. In the case of multiply imaged quasars, microlensing data have been used to determine the average microlens mass. However, the measurements have relied on an assumed transverse velocity for the lensing galaxy. Since the measured mass scales with the square of the transverse velocity, published mass limits are quite uncertain. In the case of Q2237+0305 we have properly constrained this uncertainty. The distribution of light-curve derivatives allows a quantitative treatment of the relative rates of microlensing arising from proper mo..