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 MACSJ1149.5+2223 (z=0.544), which combines new and archival Hubble WFC3/IR imagingto provide continuous radial coverage out to 2.8 Mpc from the brightest cluster galaxy. Employingcareful treatment of potential systematic biases and using data at the largest radii todetermine the background sky level, we reconstruct the surface brightness profile out to a radiusof 2 Mpc. This radius is the largest to which the intracluster light (ICL) has been measuredfor an individual cluster. Within this radius, we measure a total luminosity of 1.5E13 L_Sunfor the brightest cluster galaxy plus ICL light. From the profile and its logarithmic slope, weidentify the transition from the brightest cluster galaxy to ICL at r~70 kpc. Remarkably, wealso detect an inflection in the profile centered in the 1.2-1.7 Mpc (0.37-0.52 r200m) radialbin, a signature of an infall caustic in the stellar distribution. Based upon the shape and strengthof the feature, we interpret it as potentially being at the splashback radius, although the radiusis smaller than theoretical predictions. If this is the splashback radius, then it is the first suchdetection 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 withclusters from the Euclid and Roman missions.