Assembly bias of dwarf-sized dark matter haloes

Abstract

Previous studies indicate that assembly bias effects are stronger for lower mass dark matter haloes. Here we make use of high resolution re-simulations of rich clusters and their surroundings from the Phoenix Project and a large volume cosmological simulation, the Millennium-II run, to quantify assembly bias effects on dwarf-sized dark matter haloes. We find that, in the regions around massive clusters, dwarf-sized haloes ($[10^9,10^{11}]\ms$) form earlier ($\Delta z \sim 2$ in redshift) and possess larger $V_{\rm max}$ ($\sim20%$) than the field galaxies. We find that this environmental dependence is largely caused by tidal interactions between the ejected haloes and their former hosts, while other large scale effects are less important. Finally we assess the effects of assembly bias on dwarf galaxy formation with a sophisticated semi-analytical galaxy formation model. We find that the dwarf galaxies near massive clusters tend to be redder ($\Delta(u-r) = 0.5$) and have three times as much stellar mass compared to the field galaxies with the same halo mass. These features should be seen with observational data.