No Need for MACHOS in the Halo

One interpretation of the more than dozen microlensing events seen in the direction of the LMC is a halo population of 0.5 M☉ MACHOs that accounts for about half of the mass of the Galaxy. Such an interpretation is not without its problems, and we show that LMC microlensing can be explained by a combination of dark components of the thick disk and spheroid in a viable and detailed model of the Galaxy. In our models, the total mass within 50 kpc is ~1011 M☉, about 60% of the value based on halo MACHO models, and the estimate for the lens mass is lower, 0.3 M☉ versus 0.5 M☉. The chemical evolution problems associated with the MACHO progenitors are not resolved. However, since the MACHO distribution does not trace the 1/r2 dark halo, which extends significantly beyond 50 kpc, the total baryon mass fraction of the Galaxy is reduced considerably, which lessens the problem.