The virialization density of peaks with general density profiles under spherical collapse

Abstract

We calculate the non-linear virialization density, $Δ_c$, of halos under spherical collapse from peaks with an arbitrary initial and final density profile. This is in contrast to the standard calculation of $Δ_c$ which assumes top-hat profiles. Given our formalism, the non-linear halo density can be calculated once the shape of the initial peak's density profile and the shape of the virialized halo's profile are provided. We solve for $Δ_c$ for halos in an Einstein de-Sitter and $Λ$CDM universe. As examples, we consider power-law initial profiles as well as spherically averaged peak profiles calculated from the statistics of a Gaussian random field. We find that, depending on the profiles used, $Δ_c$ is smaller by a factor of a few to as much as a factor of 10 as compared to the density given by the standard calculation ($\approx 200$). Using our results, we show that, for halo finding algorithms that identify halos through an over-density threshold, the halo mass function measured from cosmological simulations can be enhanced at all halo masses by a factor of a few. This difference could be important when using numerical simulations to assess the validity of analytic models of the halo mass function.