Photometric redshift using the far-infrared SED

Abstract

A method for using the sub-millimeter band to determine photometric redshifts of luminous high-z dusty galaxies is presented. It is based on the observation that local ultra-luminous IR galaxies show an average spectral energy distribution which has a remarkably small dispersion for wavelengths >50 microns. The shape of the long wavelength part is independent on whether the local ULIRG possesses an AGN or not. A local template is derived from a sample of ULIRG data presented by Klaas et al. (2001). Using this template and the internal dispersion in its shape, it is shown that observations at two fixed submm wavelengths can be used to determine the photometric redshift of galaxies in the redshift range 1<z<5. The uncertainty in the redshift arising from the template SED amounts to Δz/z ~ 0.3.