Resolving the Cooling Flow at the Center of the Phoenix Cluster

The centers of galaxy clusters represent an ideal laboratory to study black hole feeding and feedback. In nearly every cluster that has been observed, cooling of the intracluster medium (ICM) appears to be well-regulated by a mechanically-efficient, radio-loud AGN within the central giant elliptical galaxy. This mechanical power appears to offset cooling of the ICM over long (~10 Gyr) timescales, allowing only ~1% of the hot ICM to cool to low enough temperatures to form stars and fuel the AGN. This precise balance prevents the overcooling of the ICM, keeps central cluster galaxies red and dead, and keeps central AGN in a low (mechanically-efficient) accretion state. The Phoenix cluster (z=0.597) represents an exception to this paradigm, with a starburst (~800 Msun/yr) central galaxy and a rapidly-accreting central quasar. This system appears to be fulfilling many of the early “cooling flow” predictions, with evidence from X-ray spectroscopy that the hot (>10^7K) gas in the core is cooling at nearly the maximal rate. We propose MIRI IFU spectroscopy to image the core of this unique cluster. In particular, we will utilize the NeVI emission line, which probes gas at 300,000K, to map out the intermediate temperature gas both spatially and kinematically, and determine whether a cooling flow is indeed fueling the observed starburst. The full mid-IR spectrum will allow new insights into the cooling flow, ICM turbulence, the central QSO, and the cold gas reservoir.