Halo bias in mixed dark matter cosmologies

TL;DR

This paper develops a method to calculate how massive neutrinos affect the distribution of dark matter halos, revealing a scale-dependent bias feature that impacts cosmological measurements and offers a new signature of neutrino mass.

Contribution

It introduces a novel approach to compute halo bias in mixed dark matter cosmologies, highlighting a neutrino-induced feature in the bias near the free-streaming scale.

Findings

Neutrino presence causes a small step in halo bias near the free-streaming scale.

The bias feature increases with halo and neutrino mass density.

The bias feature can serve as an independent signature of massive neutrinos.

Abstract

The large-scale distribution of cold dark matter halos is generally assumed to trace the large-scale distribution of matter. In a universe with multiple types of matter fluctuations, as is the case with massive neutrinos, the relation between the halo field and the matter fluctuations may be more complicated. We develop a method for calculating the bias factor relating fluctuations in the halo number density to fluctuations in the mass density in the presence of multiple fluctuating components of the energy density. In the presence of massive neutrinos we find a small but pronounced feature in the halo bias near the neutrino free-streaming scale. The neutrino feature is a small step with amplitude that increases with halo mass and neutrino mass density. The scale-dependent halo bias lessens the suppression of the small-scale halo power spectrum and should therefore weaken constraints on neutrino mass from the galaxy auto-power spectrum and correlation function. On the other hand, the feature in the bias is itself a novel signature of massive neutrinos that can be studied independently.