# Accurate mass and velocity functions of dark matter halos

## TL;DR

This paper provides highly accurate models of dark matter halo mass and velocity functions using large-scale N-body simulations, improving understanding of galaxy distribution in the universe.

## Contribution

It introduces precise models for halo mass and velocity functions based on extensive simulations, linking covariance, bias, and mass functions within the Planck cosmology.

## Key findings

- Achieved less than 2% accuracy in halo mass function modeling
- Provided analytical fits for the maximum velocity function up to redshift 2.3
- Developed a comprehensive framework connecting covariance, bias, and mass functions

## Abstract

$N$-body cosmological simulations are an essential tool to understand the observed distribution of galaxies. We use the MultiDark simulation suite, run with the Planck cosmological parameters, to revisit the mass and velocity functions. At redshift $z=0$, the simulations cover four orders of magnitude in halo mass from $\sim10^{11}M_\odot$ with 8,783,874 distinct halos and 532,533 subhalos. The total volume used is $\sim$515 Gpc$^3$, more than 8 times larger than in previous studies. We measure and model the halo mass function, its covariance matrix w.r.t halo mass and the large scale halo bias. With the formalism of the excursion-set mass function, we explicit the tight interconnection between the covariance matrix, bias and halo mass function. We obtain a very accurate ($<2\%$ level) model of the distinct halo mass function. We also model the subhalo mass function and its relation to the distinct halo mass function. The set of models obtained provides a complete and precise framework for the description of halos in the concordance Planck cosmology. Finally, we provide precise analytical fits of the $V_{max}$ maximum velocity function up to redshift $z<2.3$ to push for the development of halo occupation distribution using $V_{max}$. The data and the analysis code are made publicly available in the \textit{Skies and Universes} database.