The Mass Function of Unprocessed Dark Matter Halos and Merger Tree Branching Rates

Understand

A common approach in semi-analytic modeling of galaxy formation is to construct Monte Carlo realizations of merger histories of dark matter halos whose masses are sampled from a halo mass function.

• Both the mass function itself, and the merger rates used to construct merging histories are calibrated to N-body simulations.
• Typically, "backsplash" halos (those which were once subhalos within a larger halo, but which have since moved outside of the halo) are counted in both the halo mass function, and in the merger rates (or, equivalently, progenitor mass functions).
• This leads to a double-counting of mass in Monte Carlo merger histories which will bias results relative to N-body results.