The splashback radius as a physical halo boundary and the growth of halo mass

Understand

The boundaries of cold dark matter halos are commonly defined to enclose a density contrast $\Delta$ relative to a reference (mean or critical) density.

• We argue that a more physical boundary of halos is the radius at which accreted matter reaches its first orbital apocenter after turnaround.
• This splashback radius, $R_{sp}$, manifests itself as a sharp density drop in the halo outskirts, at a location that depends upon the mass accretion rate.
• We present calibrations of $R_{sp}$ and the enclosed mass, $M_{sp}$, as a function of the accretion rate and alternatively peak height.