On the degeneracy between baryon feedback and massive neutrinos as probed by matter clustering and weak lensing

TL;DR

This paper investigates the potential degeneracy between baryon feedback and massive neutrinos in matter clustering and weak lensing measurements, finding it unlikely to hinder future neutrino mass constraints.

Contribution

It demonstrates that baryon feedback and neutrino effects can be distinguished in future surveys, using mock data and MCMC analysis, with minimal impact on neutrino mass measurement.

Findings

Neutrino mass can be recovered within 0.25σ accuracy.

Degeneracy between feedback parameters and neutrino mass is limited.

Intrinsic alignments introduce some degeneracy but do not prevent accurate parameter recovery.

Abstract

Massive neutrinos, due to their free streaming, produce a suppression in the matter power spectrum at intermediate and small scales which could be probed by galaxy clustering and/or weak lensing observables. This effect happens at scales that are also influenced by baryon feedback, i.e. galactic winds or Active Galactic Nuclei (AGN) feedback, which in realistic hydrodynamic simulations has also been shown to produce a suppression of power. Leaving aside, for the moment, the complex issue of galaxy bias, we focus here on matter clustering and tomographic weak lensing, we investigate the possible degeneracy between baryon feedback and neutrinos showing that it is not likely to degrade significantly the measurement of neutrino mass in future surveys. To do so, we generate mock data sets and fit them using the Markov Chain Monte Carlo (MCMC) technique and explore degeneracies between feedback parameters and neutrino mass. We model baryon feedback through fitting functions, while massive neutrinos are accounted for, also in the non-linear regime, using Halofit calibrated against accurate N-body neutrino simulations. In the error budget, we include the uncertainty in the modelling of non-linearities. For both matter clustering and weak lensing, we always recover the input neutrino mass within $\sim 0.25\sigma$ confidence level. Finally, we also take into account the intrinsic alignment effect in the weak lensing mock data. Even in this case, we are able to recover the right parameters: in particular, we find a significant degeneracy pattern between $M_\nu$ and the intrinsic alignment parameter $A_\mathrm{IA}$ .