Stellar splashback: the edge of the intracluster light
  We examine the outskirts of galaxy clusters in the C-EAGLE simulations to
quantify the `edges' of the stellar and dark matter distribution. The radius of
the steepest slope in the dark matter, commonly used as a proxy for the
splashback radius, is located at ~r_200m; the strength and location of this
feature depends on the recent mass accretion rate, in good agreement with
previous work. Interestingly, the stellar distribution (or intracluster light,
ICL) also has a well-defined edge, which is directly related to the splashback
radius of the halo. Thus, detecting the edge of the ICL can provide an
independent measure of the physical boundary of the halo, and the recent mass
accretion rate. We show that these caustics can also be seen in the projected
density profiles, but care must be taken to account for the influence of
substructures and other non-diffuse material, which can bias and/or weaken the
signal of the steepest slope. This is particularly important for the stellar
material, which has a higher fraction bound in subhaloes than the dark matter.
Finally, we show that the `stellar splashback' feature is located beyond
current observational constraints on the ICL, but these large projected
distances (>> 1 Mpc) and low surface brightnesses (mu >> 32 mag/arcsec^2) can
be reached with upcoming observational facilities such as the Vera C. Rubin
Observatory, the Nancy Grace Roman Space Telescope, and Euclid.
