Hunting CIB Galaxies where They Live: Breaking the Confusion Limit with Blind Line Surveys

Abstract

The galaxies responsible for the Cosmic Infrared Background (CIB) are key targets for the SPICA mission. CIB emission peaks at ∼150 μm. Direct observations of the continuum emission of individual galaxies making up the CIB at this wavelength will be hampered by confusion. For the 3.5 m SPICA primary we expect a confusion limit of ∼5 mJy at 150 μm. Unfortunately much of the CIB flux is produced by sources fainter than this. SPICA, however, is not limited to continuum observations. We have thus examined the possibility of using blank field line surveys using SPICA-SAFARI in spectrometer mode to detect CIB galaxies by their line emission rather than their continuum emission. We find that such observations can not only detect sources with continuum fluxes up to an order of magnitude below the confusion limit, but are also able to measure source spectroscopic redshifts for most objects and offer the potential for far-IR line diagnostics in some. The redshift distributions determined from these observations can be used to directly test galaxy evolution models. We conclude that blank field line surveys are a new and uniquely powerful observing mode for SPICASAFARI, with the potential of revealing much about the galaxies responsible for the CIB.