CARS: the CFHTLS-Archive-Research Survey; I. Five-band multi-colour data from 37 sq. deg. CFHTLS-Wide observations

TL;DR

The paper introduces the CARS survey, providing five-band multi-colour catalogues from CFHTLS-Wide data, with accurate photometric redshifts for galaxy studies, including cluster detection and gravitational lensing.

Contribution

It presents a comprehensive multi-colour catalogue and a novel method to assess photometric redshift reliability from CFHTLS-Wide data.

Findings

High-confidence photo-z accuracy of σ≈0.04-0.05 up to i'<24

Catalogue covers 37 sq. degrees with well-calibrated multi-band data

Reliable object colour estimates enable advanced galaxy studies

Abstract

We present the CFHTLS-Archive-Research Survey (CARS). It is a virtual multi-colour survey based on public archive images from the CFHT-Legacy-Survey. Our main scientific interests in CARS are optical searches for galaxy clusters from low to high redshift and their subsequent study with photometric and weak-gravitational lensing techniques. As a first step of the project we present multi-colour catalogues from 37 sq. degrees of the CFHTLS-Wide component. Our aims are to create astrometrically and photometrically well calibrated co-added images. Second goal are five-band (u*, g', r', i', z') multi-band catalogues with an emphasis on reliable estimates for object colours. These are subsequently used for photometric redshift estimates. The article explains in detail data processing, multi-colour catalogue creation and photometric redshift estimation. Furthermore we apply a novel technique, based on studies of the angular galaxy cross-correlation function, to quantify the reliability of photo-z's. The accuracy of our high-confidence photo-z sample (10-15 galaxies per sq. arcmin) is estimated to $\sigma_{\Delta_z/(1+z)}\approx 0.04-0.05$ up to i'<24 with typically only 1-3% outliers. Interested users can obtain access to our data by request to the authors.