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Microlensing Events: End of the Dark Halo?

Andrew Gould
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Abstract

I obtain an upper limit for the optical depth to microlensing toward Baade's Window of $3\times 10^{-6}$ by assuming that all of the mass of the Galaxy interior to the Sun (and not in the bulge) is in a disk. The exponential scale height of the disk is left as a completely arbitrary function of radius and is varied to maximize the optical depth. I take account of the relatively small corrections induced by the fact that the bulge is not axisymmetric. If initial estimates by the OGLE collaboration of an observed optical depth $τ\sim 3.3\times 10^{-6}$ are confirmed, then essentially all of the dark matter interior to the Sun must be in a disk with a scale height of a few hundred parsecs.

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Andrew Gould. 1994-08-17. Microlensing Events: End of the Dark Halo?. https://arxiv.org/abs/astro-ph/9408060

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