Determine the spatial distribution of isolated black holes

Determine the spatial distribution of isolated black holes across the Milky Way and Magellanic Clouds, including its dependence on observing direction and distance, rather than assuming that it follows the distribution of the total stellar and dark-matter populations scaled by the isolated-black-hole mass fraction.

Background

The microlensing optical depth and event rate toward the Magellanic Clouds depend directly on the spatial density of IBHs along each line of sight. The paper notes that this distribution is not uniquely established, which affects predictions for the relative contributions of Galactic halo lensing and self-lensing within the Magellanic Clouds.

For its simulations, the paper assumes that IBHs in the 3–5000 solar-mass range share the directional and distance dependence of the known total stellar and dark-matter density, with an overall normalization given by the fraction of the total Galactic mass contained in IBHs. A directly constrained spatial distribution would improve the robustness of predicted event numbers and exclusion limits.