Spectral energy distribution of submillimeter sources

Abstract

The submillimeter universe has now been explored with the Submillimeter Common User Bolometer Array (SCUBA) camera on the James Clerk Maxwell Telescope, and claims have been made to the presence of a new population of optically unidentified starforming dusty galaxies at high redshifts. An alternative interpretation of the submillimeter (submm) emission from these sources, however, is that their far infrared emission is due to the presence of an active galactic nucleus (AGN) enshrouded by dust. Using examples of submm sources, selected primarily due to the availability of multiwavelength observations, we investigate whether the spectral energy distribution (SED) selected sources is consistent with either the dusty starforming or dusty AGN scenarios. Among these sources, we find that the SED of HDF850.4, one of the sources detected in the Hubble Deep Field (HDF), and CFRS14F, one of the sources in the Canada France Redshift Survey Fields, are fully consistent with the dusty starformation hypothesis, while the SED of APM 08279+5255 is consistent with a dusty AGN. For some submm sources, it is suggested that observations at rest wavelengths between ∼1 μm and 100 μm may be needed to differentiate between the dusty starformation and dusty AGN scenarios. We discuss implications of our results for the interpretation of submm sources and suggest that dusty AGNs can contribute up to ∼30% of the submm source counts. However, an exact observational determination on the ratio of dusty star-forming to dusty AGN contribution to submm counts require detailed followup observations of a flux limited source catalog, beyond what is currently available.