Observing the Cold Molecular Gas in Cooling Flow Clusters

Abstract

During the last decades, many attempts have been carried out to detect a cold gas reservoir in galaxy cluster centers [9, 12, 13, 2]. But the cold residual of the hot cooling Intra-cluster medium, expected at larger wavelength, was not found apart from the single case of the Perseus cluster core [11]. More recently, thanks to the improved performance of heterodyne receivers, this very cold gas has been detected through CO(1-0), CO(2-1) and CO(3-2) emission lines, in a total of 23 cluster cores [8, 15] with the IRAM 30m telescope, the JCMT and the CSO. These results have shown the existence of large amount of cold gas inside a ∼50 kpc region around several central cluster cD galaxies. The molecular gas mass deduced with standard conversion factor is Mgas= 108−11.5 M . The CO line ratios are typical of an optically thick cold and dense molecular gas.