Accurate fitting functions for peculiar velocity spectra in standard and massive-neutrino cosmologies

TL;DR

This paper develops accurate fitting functions for the nonlinear velocity spectra in cosmologies with and without massive neutrinos, based on extensive N-body simulations, to improve modeling of cosmic velocity fields.

Contribution

It introduces a new fitting formula for nonlinear velocity power spectra that accounts for different neutrino masses and redshifts, based on simulation data.

Findings

Nonlinear correction depends on the degree of nonlinear evolution, not neutrino mass.

Fitting formula achieves 3% accuracy below k=0.7 h/Mpc.

Velocity spectra are well modeled across various cosmological scenarios.

Abstract

We estimate the velocity field in a large set of $N$-body simulations including massive neutrino particles, and measure the auto-power spectrum of the velocity divergence field as well as the cross-power spectrum between the cold dark matter density and the velocity divergence. We perform these measurements at four different redshifts and within four different cosmological scenarios, covering a wide range in neutrino masses. We find that the nonlinear correction to the velocity power spectra largely depend on the degree of nonlinear evolution with no specific dependence on the value of neutrino mass. We provide a fitting formula, based on the value of the r.m.s. of the matter fluctuations in spheres of $8h^{-1}$Mpc, describing the nonlinear corrections with 3\% accuracy on scales below $k=0.7\; h$ Mpc$^{-1}$.