The Heated Core of the Radio-Quiet Galaxy Cluster A644
  We present an analysis of a Chandra ACIS-I observation of the massive galaxy cluster A644. This cluster was previously classified as a cooling flow, but no radio emission has been detected from its cD galaxy. Outside the core (R ~75 kpc ~0.03R_vir) the hot ICM has properties consistent with a (relaxed) cool-core cluster out to the largest radii investigated (R ~415 kpc ~0.14 R_vir). Over this region the gravitating mass profile is described well by a Navarro-Frenk-White profile with concentration parameter, c = 6.1 +/- 1.2, and virial radius, R_vir = 2.9 +/- 0.4 Mpc. However, inside the core the temperature and entropy profiles reverse their inward radial decline and rise at the center; the inner temperature profile is inconsistent with a constant at the 2.3 sigma level. Although the core region does not display X-ray cavities or filamentary structures characteristic of radio-loud, cool-core clusters, the peak of the X-ray emission is offset from that of the centroid of the global X-ray halo by ~60 kpc. The position of the cD galaxy lies approximately between the X-ray peak and centroid, further testifying to a merger origin for the properties of the X-ray emission in the core. We discuss the implications of A644 and the small number of radio-quiet, cool-core clusters for the AGN feedback paradigm to suppress cooling flows in clusters. 
David A. Buote (1), Philip J. Humphrey (1), and John T. Stocke (2)   ((1) University of California, Irvine, (2) University o...