The Growth of Central and Satellite Galaxies in Cosmological Smoothed Particle Hydrodynamics Simulations

TL;DR

This study uses cosmological SPH simulations to analyze the growth, accretion, and merger histories of central and satellite galaxies, revealing ongoing gas accretion and gradual transformation processes.

Contribution

It provides new insights into the continuous accretion and merger activities of satellite galaxies, challenging simpler models of galaxy evolution.

Findings

Satellites continue gas accretion after merging with larger halos.

A significant fraction of galaxies have merged since z=1.

Satellite galaxies can remain 'central' within substructures.

Abstract

We examine the accretion and merger histories of central and satellite galaxies in a smoothed particle hydrodynamics (SPH) cosmological simulation that resolves galaxies down to 7e9 M[Sun]. Most friends-of-friends halos in the simulation have a distinct central galaxy, typically two to five times more massive than the most massive satellite. As expected, satellites have systematically higher assembly redshifts than central galaxies of the same baryonic mass, and satellites in more massive halos form earlier. However, contrary to the simplest expectations, satellite galaxies continue to accrete gas and convert it to stars; the gas accretion declines steadily over a period of 0.5-1 Gyr after the satellite halo merges with a larger parent halo. Satellites in a cluster mass halo eventually begin to lose baryonic mass. Since z=1, 27% of central galaxies (above 3e10 M[Sun]) and 22% of present-day satellite galaxies have merged with a smaller system above a 1:4 mass ratio; about half of the satellite mergers occurred after the galaxy became a satellite and half before. In effect, satellite galaxies can remain "central" objects of halo substructures, with continuing accretion and mergers, making the transition in assembly histories and physical properties a gradual one. Implementing such a gradual transformation in semi-analytic models would improve their agreement with the observed colour distributions of satellite galaxies in groups and with the observed colour dependence of galaxy clustering.