The edges of dark matter halos: in theory and observations
Surhud More
Kavli Institute, University of Tokyo

Dark matter halos are the basic building blocks that form the large scale structure in the Universe. However the boundaries of these halos have been arbitrarily defined, which make their inferred growth histories susceptible to misinterpretation. I will argue that a more physical boundary of halos is the radius at which accreted matter reaches its first orbital apocenter after turnaround. This splashback radius, Rsp, manifests itself as a sharp density drop in the halo outskirts, at a location that depends upon the mass accretion rate. I will discuss the simple physical model which explains the presence of the splashback radius as well as its dependence on the accretion rate. I will then discuss our efforts to observationally detect the splashback radius in galaxy clusters (both optically selected and selected in the SZ and the Xrays). By modelling the cross-correlation of galaxy clusters with galaxies from the Pan-STARRS survey, I will present of evidence for the presence of the splashback radius of galaxy clusters at a location consistent with expectations from cosmological simulations.