SEARCH FOR COLD GAS IN CLUSTERS WITH AND WITHOUT COOLING FLOWS

The dominant galaxy in each of ∼40 clusters has been studied using co-added IRAS survey data, and 11 of these galaxies have been observed for CO (J = 1→0) emission with the NRAO 12 m telescope at Kitt Peak. Half of the galaxies in our sample are in clusters reported to have cooling flows, while the other half are not. Six of the galaxies appear to have been detected by IRAS with varying degrees of reliability, in addition to one previously known strong detection; all seven are reported to have cooling flows. None of the 11 galaxies observed was detected in CO emission. There is a possible, although weak, correlation between reported cooling flow rates and infrared luminosities, but no correlation between flow rates and derived ISM masses. No significant differences in the CO or IR properties are inferred between dominant galaxies in clusters with or without flows. Assuming that cluster cooling flows with Ṁ ∼ 100 M⊙ yr-1 exist and are feeding star formation in the central, dominant galaxies, then the star formation rates and efficiencies in these galaxies must be quite high in order to render the CO undetectable. At the same time, the infrared luminosities of these galaxies are unremarkable, suggesting that the correlation between star formation efficiency and infrared luminosity found for spirals does not apply to star formation in cooling flows. Alternatively, if cooling flows do not exist, or if the mass-flow rates have been overestimated, cluster-dominant galaxies could sit at the low end of the LCO-LIR relation found for spirals. A brief comparison with elliptical galaxies indicates that cluster-dominant galaxies and ellipticals have similar FIR properties.