Submillimetre observations of galaxy clusters with the BLAST: the star formation activity in Abell 3112

We present observations at 250, 350 and 500 mu m of the nearby galaxy cluster Abell 3112 (z = 0.075) carried out with the Balloon-borne Large Aperture Submillimeter Telescope. Five cluster members are individually detected as bright submillimetre (submm) sources. Their far-infrared spectral energy distributions and optical colours identify them as normal star-forming galaxies of high mass, with globally evolved stellar populations. They all have (B - R) colours of 1.38 +/- 0.08, transitional between the blue, active population and the red, evolved galaxies that dominate the cluster core. We stack to estimate the mean submm emission from all cluster members, which is determined to be 16.6 +/- 2.5, 6.1 +/- 1.9 and 1.5 +/- 1.3 mJy at 250, 350 and 500 mu m, respectively. Stacking analyses of the submm emission of cluster members reveal trends in the mean far-infrared luminosity with respect to clustercentric radius and K-S-band magnitude. We find that a large fraction of submm emission comes from the boundary of the inner, virialized region of the cluster, at clustercentric distances around R-500. Stacking also shows that the bulk of the submm emission arises in intermediate-mass galaxies with K-S magnitude similar to 1 mag fainter than the giant ellipticals. The results and constraints obtained in this work will provide a useful reference for the forthcoming surveys to be conducted on galaxy clusters by Herschel.