Submillimetre and near-infrared observations of galaxies selected at 170 μm

We present results from James Clerk Maxwell Telescope (JCMT) submillimetre (submm) observations of sources selected from the Infrared Space Observatory (ISO ) FIRBACK (Far-infrared Background) survey, along with United Kingdom Infrared Telescope (UKIRT) near-infrared imaging of a subsample. This gives valuable insight into the brightest similar to10 per cent of galaxies that contribute to the cosmic infrared background (CIB). We estimate the photometric redshifts and luminosities of these sources by fitting their spectral energy distributions (SEDs). The data appear to show a bimodal galaxy distribution, with normal star-forming galaxies at z similar or equal to 0, and a much more luminous population at z similar to 0.4-0.9. These are similar to the ultraluminous infrared galaxies which are found to evolve rapidly with redshift in other surveys. The detectability threshold of FIRBACK biases the sample away from much higher redshift (z similar or equal to 1.5) objects. Nevertheless, the handful of z similar to 0.5 sources that we identify are likely to be the low-z counterparts of the typically higher-z sources found in blank field submm observations. This subsample, being much more nearby than the average Submillimetre Common User Bolometer Array (SCUBA) galaxies, has the virtue of being relatively easy to study in the optical. Hence their detailed investigation could help elucidate the nature of the submm bright galaxies.