The halo mass function in alternative dark matter models

TL;DR

This paper evaluates the halo mass function predictions in alternative dark matter models, highlighting discrepancies in existing fitting functions and emphasizing the need for detailed subhalo evolution studies.

Contribution

It compares different methods for predicting halo mass functions in alternative dark matter models and identifies underestimations in popular fitting functions.

Findings

Fitting functions underestimate low-mass halo counts by a factor of 2.

Extended Press-Schechter method aligns better with comprehensive models.

Small-scale power suppression affects halo abundance predictions.

Abstract

The claimed detection of large amounts of substructure in lensing flux anomalies, and in Milky Way stellar stream gaps statistics, has lead to a step change in constraints on simple warm dark matter models. In this study we compute predictions for the halo mass function both for these simple models and also for comprehensive particle physics models of sterile neutrinos and dark acoustic oscillations. We show that the mass function fit of Lovell et al. underestimates the number of haloes less massive than the half-mode mass, $M_\mathrm{hm}$ by a factor of 2, relative to the extended Press-Schechter (EPS) method. The alternative approach of applying EPS to the Viel et al. matter power spectrum fit instead suggests good agreement at $M_\mathrm{hm}$ relative to the comprehensive model matter power spectra results, although the number of haloes with mass $<M_\mathrm{hm}$ is still suppressed due to the absence of small scale power in the fitting function. Overall, we find that the number of dark matter haloes with masses $<10^{8}M_{\odot}$ predicted by competitive particle physics models is underestimated by a factor of $\sim2$ when applying popular fitting functions, although careful studies that follow the stripping and destruction of subhaloes will be required in order to draw robust conclusions.