The scale-dependence of halo assembly bias

The two-point clustering of dark matter haloes is influenced by halo properties besides mass, a phenomenon referred to as halo assembly bias. Using the depth of the gravitational potential well, V max , as our secondary halo property, in this paper, we present the first study of the scale-dependence of assembly bias. In the large-scale linear regime, r 10 h -1 Mpc, our findings are in keeping with previous results. In particular, at the low-mass end (<M coll 10 12.5 M h -1 ), haloes with high V max show stronger large-scale clustering relative to haloes with low V max of the same mass; this trend weakens and reverses for M vir M coll . In the non-linear regime, assembly bias in low-mass haloes exhibits a pronounced scale-dependent 'bump' at 500 kpc h -1 -5 Mpc h -1 . This feature weakens and eventually vanishes for haloes of higher mass. We show that this scale-dependent signature can primarily be attributed to a special subpopulation of ejected haloes, defined as present-day host haloes that were previously members of a higher mass halo at some point in their past history. A corollary of our results is that galaxy clustering on scales of r 1-2 Mpc h -1 can be impacted by up to 15 per cent by the choice of the halo property used in the halo model, even for stellar mass-limited samples.