ar X iv : a st ro - p h / 03 10 71 2 v 1 2 4 O ct 2 00 3 CO emission associated with a cooling flow

1 Abstract The existence of cooling flows in the center of galaxy clusters has always been a puzzle, and in particular the fate of the cooling gas, since the presence of cold gas has never been proven directly. X-ray data from the satellites Chandra and XMM-Newton have constrained the amount of cooling, and it was realized that feedback and heating from a central AGN and its jets could reduce the amount of cold gas. Recently, a few central galaxies of cooling flow clusters have been detected in the CO lines. For the first time, we show IRAM interferometer maps of CO(1-0) and CO(2-1) emission in a cooling flow, showing a clear association of the cold gas (at about 20K) with the cooling flow. This shows that although the AGN provides a feedback heating, the cooling phenomenon does occur, with about the expected rate. Cooling flows are suspected to occur in the center of rich galaxy clusters, since the cooling time of the hot gas is shorter than Hubble time. Until recently, large flow rates were expected, of the order of 100 to 1000 M ⊙ /yr. But the fate of the cooled gas has always been a mystery, the gas or the stars formed out of it could not be seen. Attempts to observe this cold gas either in HI have always obtained upper limits. Only in NGC1275 (Perseus A) has molecular gas been detected (Lazareff et al 1989), but being associated to merging galaxies, its origin was ambiguous. Recently, CO emission has been detected in 3C31 (RXJ0107+32) and 3C264 (A1367) at the center of cooling flows (Lim et al 2001), and towards 16 central galaxies of clusters (Edge 2001). One of the main results of the X-ray satellites Chandra and XMM-Newton was to change considerably our view on cooling flows: the deduced cooling rates have been reduced by at least one order of magnitude; the old view of quiet and regular, quasi-spherical cooling has given place to partial and intermittent cooling, perturbed by reheating processes, feedback due to the