Uncovering mass segregation with galaxy analogues in dark-matter simulations

We investigate mass segregation in group and cluster environments by identifying galaxy analogues in high-resolution dark-matter simulations. Subhaloes identified by the Amiga's Halo Finder (ahf) and rockstar halo finders have similar mass functions, independent of resolution, but different radial distributions due to significantly different subhalo hierarchies. We propose a simple way to classify subhaloes as galaxy analogues. The radial distributions of galaxy analogues agree well at large halocentric radii for both ahf and rockstar but disagree near parent halo centres where the phase-space information used by rockstar is essential. We see clear mass segregation at small radii (within 0.5 rvir) with average galaxy analogue mass decreasing with radius. Beyond the virial radius, we find a mild trend where the average galaxy analogue mass increases with radius. These mass segregation trends are strongest in small groups and dominated by the segregation of low-mass analogues. The lack of mass segregation in massive galaxy analogues suggests that the observed trends are driven by the complex accretion histories of the parent haloes rather than dynamical friction.