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In the cores of galaxy clusters comma the hot intracluster medium should cool rapidly comma leading to d_commacooling flowsd_comma of order virgul100-1000 Msun-yr. Our current picture is that AGN feedback is responsible for preventing these runaway cooling events comma leading to more typical star formation rates of virgul1-10 Msun-yr in the centers of relaxed comma cool core clusters. However comma recent work suggests that feedback may saturate in the most massive clusters comma leading to a cooling imbalance in the most extreme systems. In this proposal comma we target one of the most star-forming central cluster galaxies in the Universe (with the other 5 having already been observed) comma which is forming stars at nearly the classical cooling flow prediction. We will obtain narrow-band CORCHETE_OPENO IICORCHETE_CLOSE imaging using the ACS ramp filter on this cluster comma allowing us to probe the development of thermal instabilities as gas condenses out of the hot phase and ultimately forms stars. Combining these data with the larger sample sample of six massive clusters provides an opportunity to test the limits of AGN feedback comma where cooling does not appear to be significantly suppressed. Three of these six clusters also harbor central QSOs comma allowing us to probe the different effects of mechanical (radio-mode) and radiative (quasar-mode) feedback in the inner regions of clusters. As the six most star-forming central cluster galaxies comma these will make stunning and inspiring images and have tremendous legacy value comma as recent Chandra+ALMA and future JWST targets. NOTEdoublePoint This is a reobservation of a failed visit for a larger approved program.