Seeing Galaxy Formation in a Cold Light


The submillimeter-selected galaxies span an extremely wide range of optical properties and colors and appear to have little relation to optically-selected objects undergoing intensive star formation. This can be seen from the color thumbnails of the optical images --- here ground based BV (blue),RI (green) and HK (red) data obtained with Keck and the CFHT --- at the position of the three brightest submillimeter sources seen in the HDF by Hughes et al: at least some of the sources are nearly invisible in the optical while some correspond to relatively bright galaxies. A similar result is found by Smail et al. who find a wide range of optical properties in their sources, again including some optically invisible sources.
A full image of the HDF in HK, RI and BV, with the position of all the known radio and 15µ sources marked, also shows little correlation, except for the single brightest source, which may be associated with a known radio source. Thus the submillimeter population appears to be a separate set of objects which could not easily be picked out from other information.