WISE x SuperCOSMOS photometric redshift catalog: 20 million galaxies over 3pi steradians

TL;DR

This paper presents a new all-sky galaxy catalog of nearly 20 million galaxies with photometric redshifts, derived from cross-matching WISE and SuperCOSMOS data, enabling advanced 3D cosmology and survey pre-selection.

Contribution

The creation of a deep, wide-area galaxy catalog with accurate photometric redshifts over 3pi steradians, utilizing multiwavelength data and external spectroscopic training.

Findings

Catalog contains ~20 million galaxies with 95% purity and 90% completeness.

Photometric redshifts have a mean bias of ~10^{-3} and scatter of 0.033.

No significant variation in photo-z quality across the sky.

Abstract

We cross-match the two currently largest all-sky photometric catalogs, mid-infrared WISE and SuperCOSMOS scans of UKST/POSS-II photographic plates, to obtain a new galaxy sample that covers 3pi steradians. In order to characterize and purify the extragalactic dataset, we use external GAMA and SDSS spectroscopic information to define quasar and star loci in multicolor space, aiding the removal of contamination from our extended-source catalog. After appropriate data cleaning we obtain a deep wide-angle galaxy sample that is approximately 95% pure and 90% complete at high Galactic latitudes. The catalog contains close to 20 million galaxies over almost 70% of the sky, outside the Zone of Avoidance and other confused regions, with a mean surface density of over 650 sources per square degree. Using multiwavelength information from two optical and two mid-IR photometric bands, we derive photometric redshifts for all the galaxies in the catalog, using the ANNz framework trained on the final GAMA-II spectroscopic data. Our sample has a median redshift of z_{med} = 0.2 but with a broad dN/dz reaching up to z>0.4. The photometric redshifts have a mean bias of |delta_z|~10^{-3}, normalized scatter of sigma_z = 0.033 and less than 3% outliers beyond 3sigma_z. Comparison with external datasets shows no significant variation of photo-z quality with sky position. Together with the overall statistics, we also provide a more detailed analysis of photometric redshift accuracy as a function of magnitudes and colors. The final catalog is appropriate for `all-sky' 3D cosmology to unprecedented depths, in particular through cross-correlations with other large-area surveys. It should also be useful for source pre-selection and identification in forthcoming surveys such as TAIPAN or WALLABY.