Massive Neutrinos Promote the Size Growth of Early-Type Galaxies

TL;DR

Massive neutrinos significantly accelerate the size growth of early-type galaxies over cosmic time, potentially explaining their observed compactness at high redshift.

Contribution

This study demonstrates that including massive neutrinos in cosmological models enhances galaxy merger rates, leading to faster size evolution of early-type galaxies compared to standard models.

Findings

Size evolution is steeper with neutrinos, with $eta \\sim 1.5$ for $f_{\\nu}=0.05$.

Neutrinos increase the merger rate, accelerating galaxy growth.

Properly accounting for neutrinos can explain the compactness of high-$z$ ETGs.

Abstract

The effect of massive neutrinos on the evolution of the early type galaxies (ETGs) in size ($R_{e}$) and stellar mass ($M_{\star}$) is explored by tracing the merging history of galaxy progenitors with the help of the robust semi-analytic prescriptions. We show that as the presence of massive neutrinos plays a role of enhancing the mean merger rate per halo, the high-$z$ progenitors of a descendant galaxy with fixed mass evolves much more rapidly in size for a $\Lambda$MDM ($\Lambda$CDM + massive neutrinos) model than for the $\Lambda$CDM case. The mass-normalized size evolution of the progenitor galaxies, $R_{e}[M_{\star}/(10^{11}M_{\odot})]^{-0.57}\propto (1+z)^{-\beta}$, is found to be quite steep with the power-law index of $\beta\sim 1.5$ when the neutrino mass fraction is $f_{\nu}=0.05$, while it is $\beta\sim 1$ when $f_{\nu}=0$. It is concluded that if the presence and role of massive neutrinos are properly taken into account, it may explain away the anomalous compactness of the high-$z$ ETGs compared with the local ellipticals with similar stellar masses.