The detection of dust in the central galaxies of distant cooling-flow clusters

We present 850-mu m observations with the SCUBA submillimetre (sub-mm) came ra of the central galaxies in seven concentrated clusters of galaxies at re dshifts between 0.19 and 0.41, We detect sub-mm emission from the central g alaxies in the rich clusters A1835 and A2390, and present upper limits for the central galaxies in the remaining five clusters. The two galaxies that we detect both exhibit unusually blue UV-optical colours and lie in cluster s that contain massive cooling flows, greater than or equal to 1000 M-. yr( -1). Moreover, both galaxies host relatively strong radio sources. Focusing on these two systems, we present new and archival radio-optical observatio ns to provide a detailed view of their spectral energy distributions. Our a nalysis indicates that sub-mm emission from the central galaxy of A1835 can be best understood as arising from dust, heated by either vigorous star fo rmation or an obscured active galactic nucleus. For the central galaxy of A 2390, the sub-mm flux is marginally consistent with an extrapolation of the cm-mm emission from the luminous radio source that lies in its core, altho ugh we cannot rule out an excess flux density from dust emission comparable to that seen in A1835. We present details of our multiwavelength observati ons and discuss the implications of these data for the interpretation of st ar formation in cooling-flow galaxies.