1708.06181
Haloes at the ragged edge: the importance of the splash back radius
Snaith, et al
Explored the outskirts of DM haloes out to 2.5 times the viral radius using a large sample of haloes drawn from Illustris, along with a set of zoom simulations (MUGS). Using these, make a systematic exploration of the shape profile beyond R_vir. In the mean sphericity profile of Illustris haloes, identify a dip close to the viral radius, which is robust across a broad range of masses and infall rates. The inner edge of this feature may be related to the viral radius and the outer edge with the splash back radius. Due to the high halo-to-halo variation this result is visible only on average. However, in 4 individual haloes in the MUGS sample, a decrease in the sphericity and a subsequent recovery is evident close to the splashback radius. Find that this feature persists for several Gyr, growing with the halo. This feature appears at the interface between the spherical halo density distribution and the filamentary structure in the environment. The shape feature is strongest when there is a high rate of infall, implying that the effect is due to the mixing of accreting and virtualizing material. The filamentary velocity field becomes rapidly mixed in the halo region inside the viral radius, with the area between this and the splash back radius serving as the transition region. Also identify a long-lasting and smoothly evolving splash back region in the radial density gradient in many of the MUGS halos.
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