0 Assigned ID: 7875 ----- Attempting Submission 1 (Mon Sep 21 21:19:13 GMT 2026) ----- In the local universe, there is a strong correspondence between a cluster's central entropy and the radio loudness of its central brightest cluster galaxy (BCG), with the vast majority of radio-loud BCGs found in low-entropy cores. Recent work at high redshift has found that this relationship does not hold above z>0.75. Here we propose deep observations of a sample of 3 high-entropy cores at <z>=0.93, with the goal of understanding the (apparently!) evolving relationship between feedback and cooling in cluster cores. Specifically, we seek to understand whether feedback is over-heating cluster cores at early time, or if low-entropy cores are more elusive (e.g., more compact) in the early universe. McDonald is an expert in OIR, X-ray, and radio observations of galaxy cluster cores and low and high redshift. He has published data of similar quality to these numerous times. Galaxies 6 false false false false false false false true SECONDARY CHANDRA 28800215 false SUPPORTED J2000 J2000 J2000 J2000 WFC3/IR Imaging No No F110W WFC3/UVIS Imaging No No F200LP WFC3/UVIS Imaging No No F200LP WFC3/IR Imaging No No F110W