The evolution of the baryon fraction in halos as a cause of scatter in the galaxy stellar mass in the EAGLE simulation

TL;DR

This paper investigates the origins of scatter in galaxy stellar mass within the EAGLE simulation, linking it to baryonic mass variation driven by feedback and gas accretion differences, and how this affects galaxy evolution.

Contribution

It identifies the baryonic mass variation at progenitor stages as the main source of scatter in galaxy stellar mass at fixed halo properties, highlighting the role of feedback and gas accretion.

Findings

Scatter in stellar mass correlates with galaxy age.

Progenitor baryonic mass explains 75% of variance.

Feedback and gas accretion drive baryonic mass differences.

Abstract

The EAGLE simulation suite has previously been used to investigate the relationship between the stellar mass of galaxies, $M_{*}$, and the properties of dark matter halos, using the hydrodynamical reference simulation combined with a dark matter only (DMO) simulation having identical initial conditions. The stellar masses of central galaxies in halos with $M_{\mathrm{200c}} > 10^{11} \mathrm{M_{\odot}}$ were shown to correlate with the DMO halo maximum circular velocity, with $\approx 0.2$ dex of scatter that is uncorrelated with other DMO halo properties. Here we revisit the origin of the scatter in the $M_{*}-V_{\mathrm{max, DMO}}$ relation in EAGLE at $z = 0.1$. We find that the scatter in $M_{*}$ correlates with the mean age of the galaxy stellar population such that more massive galaxies at fixed $V_{\mathrm{max, DMO}}$ are younger. The scatter in the stellar mass and mean stellar population age results from variation in the baryonic mass, $M_{\mathrm{bary}} = M_{\mathrm{gas}} + M_{*}$, of the galaxies' progenitors at fixed halo mass and concentration. At the redshift of peak correlation ($z \approx 1$), the progenitor baryonic mass accounts for $75\%$ of the variance in the $z=0.1$ $M_{*}-V_{\mathrm{max, DMO}}$ relation. The scatter in the baryonic mass, in turn, is primarily set by differences in feedback strength and gas accretion over the course of the evolution of each halo.