ImpZ: a new photometric redshift code for galaxies and quasars

Abstract

We present a combined galaxy–quasar approach to template-fitting photometric redshift techniques and show the method to be a powerful one. The code (ImpZ) is presented, developed and applied to two spectroscopic redshift catalogues, namely the Isaac Newton Telescope Wide-Angle Survey ELAIS N1 and N2 fields and the Chandra Deep Field North. In particular, optical size information is used to improve the redshift determination. The success of the code is shown to be very good, with Δz/(1 +z) constrained to within 0.1 for 92 per cent of the galaxies in our sample. The extension of template fitting to quasars is found to be reasonable, with Δz/(1 +z) constrained to within 0.25 for 68 per cent of the quasars in our sample. Various template extensions into the far-ultraviolet are also tested.