The detection of molecular gas in the central galaxies of cooling flow clusters

We present the detections of CO line emission in the central galaxy of 16 extreme cooling flow clusters using the IRAM 30-m and the JCMT 15-m telescopes. These detections of CO(1-0), CO(2-1), CO(3-2) and CO(4-3) are consistent with the presence of a substantial mass of warm molecular gas (10(9-11.5) M.) within 50-kpc radius of the central galaxy. We present limits on 13 other galaxies in similarly extreme cooling flow clusters. These results are consistent with the presence of a massive starburst in the central galaxy, which warms a population of cold gas clouds producing both optical and near-infrared emission lines and significant CO line emission. Curiously, our CO detections are restricted to the lower radio power central galaxies. These are the first detections of molecular gas in a cooling flow other than NGC 1275 in the Perseus cluster. As four of our targets have firm limits on their dust mass from SCUBA and the rest have crude limits from IRAS, we can calculate gas-to-dust ratios. Simple analysis indicates that the best secondary indicator of molecular gas is optical line luminosity. We review the implications of these results and the prospects for observations in the near future.