Astro Seminar: "The Scale-Dependence of Halo Assembly Bias"

Wed, 12/02/2015 - 14:00 - 16:00
Tomomi Sunayama (Yale University)

The clustering of dark matter halos is influenced by halo
properties besides mass, a phenomenon referred to as halo assembly
bias. It is because halos of the same mass in different environments
have different assembly histories and cluster differently. There have
been several studies showing such environmental effects on the linear
bias of halos. The halo bias on small scales, however, is
scale-dependent. I will present the first study of the
scale-dependence of halo assembly bias using the depth of the
gravitational potential well, Vmax, as our secondary halo property.
We find that assembly bias in low-mass halos exhibits a pronounced
scale-dependent "bump" at 500 kpc/h - 5 Mpc/h. This feature weakens
and eventually vanishes for halos of higher mass. We show that this
scale-dependent signature can primarily be attributed to a special
subpopulation of ejected halos, defined as present-day host halos
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 can be impacted by up to ~15% by
the choice of the halo property used in the halo model, even for
stellar mass-limited samples. 

David Rittenhouse Laboratoy, A6