Discovery of a Possible Splashback Feature in the Intracluster Light of
  MACS J1149.5+2223
  We present an analysis of the intracluster light in the Frontier Field
Cluster MACS J1149.5+2223 (z=0.544), which combines new and archival Hubble
WFC3/IR imaging to provide continuous radial coverage out to 2.8 Mpc from the
brightest cluster galaxy. Employing careful treatment of potential systematic
biases and using data at the largest radii to determine the background sky
level, we reconstruct the surface brightness profile out to a radius of 2 Mpc.
This radius is the largest to which the intracluster light (ICL) has been
measured for an individual cluster. Within this radius, we measure a total
luminosity of 1.5e13 Lsun for the brightest cluster galaxy plus ICL light. From
the profile and its logarithmic slope, we identify the transition from the
brightest cluster galaxy to ICL at r~70 kpc. Remarkably, we also detect an
inflection in the profile centered in the 1.2-1.7 Mpc (0.37-0.52 r200m) radial
bin, a signature of an infall caustic in the stellar distribution. Based upon
the shape and strength of the feature, we interpret it as potentially being at
the splashback radius, although the radius is smaller than theoretical
predictions. If this is the splashback radius, then it is the first such
detection in the ICL and the first detection of the splashback radius for an
individual cluster. Similar analyses should be possible with the other Frontier
Field clusters, and eventually with clusters from the Euclid and Roman
missions.
