H-ATLAS: estimating redshifts of Herschel sources from sub-mm fluxes

TL;DR

This paper develops a method to estimate redshifts of Herschel sources using sub-mm fluxes and a derived average SED template, enabling redshift estimation for large samples without spectroscopic data.

Contribution

It introduces a new average SED template for high-redshift Herschel sources and demonstrates its effectiveness in estimating redshifts from fluxes.

Findings

Achieved a redshift estimation accuracy of Δz/(1+z)=0.26 overall.

Improved accuracy to Δz/(1+z)=0.12 for sources with prior high-redshift information.

Estimated bimodal redshift distribution for H-ATLAS sources with mean redshifts of 1.2, 1.9, and 2.5.

Abstract

Upon its completion the Herschel ATLAS (H-ATLAS) will be the largest submillimetre survey to date, detecting close to half-a-million sources. It will only be possible to measure spectroscopic redshifts for a small fraction of these sources. However, if the rest-frame spectral energy distribution (SED) of a typical H-ATLAS source is known, this SED and the observed Herschel fluxes can be used to estimate the redshifts of the H-ATLAS sources without spectroscopic redshifts. In this paper, we use a subset of 40 H-ATLAS sources with previously measured redshifts in the range 0.5<z<4.2 to derive a suitable average template for high redshift H-ATLAS sources. We find that a template with two dust components T_c = 23.9 K, T_h = 46.9 K and ratio of mass of cold dust to mass of warm dust of 30.1) provides a good fit to the rest-frame fluxes of the sources in our calibration sample. We use a jackknife technique to estimate the accuracy of the redshifts estimated with this template, finding a root mean square of Delta z/(1+z) = 0.26. For sources for which there is prior information that they lie at z > 1 we estimate that the rms of Delta z/(1+z) = 0.12. We have used this template to estimate the redshift distribution for the sources detected in the H-ATLAS equatorial fields, finding a bimodal distribution with a mean redshift of 1.2, 1.9 and 2.5 for 250, 350 and 500 um selected sources respectively. \end{abstract}