Microlensing Results and Removing the Baryonic Degeneracy

Abstract

One of the biggest obstacles to our full understanding of the global dynamics in Milky Way and other spiral galaxies is uncertainty with respect to the form of baryonic dark matter in galactic haloes. Two basic forms discussed recently are MACHOs and various states of halo gas. We investigate constraints which could be obtained from the empirical microlensing optical depth on combined MACHO + gas models, and show that improved statistics will certainly be able to discriminate between various such models. This has profound consequences not only for galactic dynamics and baryonic budget, but for investigation of the low-redshift Ly$α$ absorption systems and general cosmological distribution of gas.