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The IMF in the Galactic Disk and Bulge are Indistinguishable

  • Christopher Wegg (a1), Ortwin Gerhard (a1) and Matthieu Portail (a1)


We have measured the IMF of the inner Galaxy using ~3000 OGLE-III microlensing events. Each event’s timescale depends on both the lens mass, and the velocities and distances of the lens and source. New dynamical models were used provide the distribution of distances and velocities, and thereby measure the lens mass distribution. Using a power-law or log-normal parameterisation the resultant IMF is indistinguishable from local measurements by Kroupa or Chabrier respectively. The lenses lie in the inner Galaxy where the stars are mostly ~10 Gyr old and formed on a fast α-element enhanced timescale thereby constraining IMF variability with the properties of the collapsing gas cloud. Furthermore microlensing measures the stellar mass budget, including dark remnants, to low mass. Stars contribute most of the mass in the inner Galaxy with a low fraction remaining for dark matter. Reconciling this with local dark matter estimates requires a core or shallow cusp in its profile.



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