The properties of satellite galaxies in simulations of galaxy formation

TL;DR

This study uses cosmological simulations to explore how feedback processes, especially supernova-driven winds with velocity proportional to local dark matter velocity dispersion, influence satellite galaxy properties, luminosity functions, and metallicity relations.

Contribution

It demonstrates that variable wind models proportional to local velocity dispersion better reproduce observed satellite galaxy properties than constant wind models.

Findings

Wind models with v_w proportional to sigma match observed satellite luminosity functions.

Variable wind models reproduce the luminosity-metallicity relation.

Constant wind models overproduce faint satellites and misrepresent metallicity relations.

Abstract

We investigate the properties of satellite galaxies in cosmological N-body/SPH simulations of galaxy formation in Milky Way-sized haloes. Because of their shallow potential wells, satellite galaxies are very sensitive to heating processes which affect their gas content. Their properties can therefore be used to constrain the nature of feedback processes that regulate galaxy formation. In our simulations, we assume that all the energy produced by supernovae is used as kinetic energy to drive galactic winds. Several of our simulations produce bright, disc-dominated galaxies. We find that wind models in which the wind speed, v_w, is proportional to local velocity dispersion of dark matter, sigma, (and thus the wind mass-loading, eta_w \propto sigma^{-2}) have episodic star formation histories, reproduce the observed satellite luminosity function reasonably well (down to M_v=-7) and match the luminosity-metallicity relation observed in the Local Group satellites. By contrast, models that assume a constant wind speed overproduce faint satellites and predict an incorrect luminosity-metallicity relation. Our simulations therefore suggest that the feedback processes that operate on the scale of satellite galaxies should generate galactic outflows whose intensity varies inversely with the depth of the potential.