Semi-Analytic Galaxy Formation in Massive Neutrino Cosmologies

TL;DR

This study investigates how massive neutrinos influence galaxy formation and distribution by combining N-body simulations with semi-analytic models, highlighting the importance of $\sigma_8$ estimates for interpreting cosmological data.

Contribution

It introduces a semi-analytic galaxy formation model within massive neutrino cosmologies, emphasizing the role of $\sigma_8$ in interpreting structure growth and galaxy properties.

Findings

Massive neutrinos slow down dark matter perturbation growth.

Galaxy properties are weak indicators of neutrino effects alone.

Neutrino effects oppose those of modified gravity, complicating detection.

Abstract

The constraints on neutrino masses led to the revision of their cosmological role, since the existence of a cosmological neutrino background is a clear prediction of the standard cosmological model. In this paper, we study the impact of such background on the spatial distribution of both Dark Matter (DM) and galaxies, by coupling $N$-body numerical simulations with semi-analytic models (SAMs) of galaxy formation. Cosmological simulations including massive neutrinos predict a slower evolution of DM perturbations with respect to the $\Lambda$CDM runs with the same initial conditions and a suppression on the matter power spectrum on small and intermediate scales, thus impacting on the predicted properties of galaxy populations. We explicitly show that most of these deviations are driven by the different $\sigma_8$ predicted for cosmologies including a massive neutrino background. We conclude that independent estimates of $\sigma_8$ are needed, in order to unambiguously characterise the effect of this background on the growth of structures. Galaxy properties alone are a weak tracer of deviations with respect to the $\Lambda$CDM run, but their combination with the overall matter distribution at all scales allows to disentangle between different cosmological models. Moreover, these deviations go on opposite direction with respect to competing models like modified gravity, thus weakening any detectable cosmological signal. Given the ubiquitous presence of a neutrino background, these effects have to be taken into account in future missions aimed at constraining the properties of the "Dark" components of the Universe.