The DECADE cosmic shear project II: photometric redshift calibration of the source galaxy sample

TL;DR

This paper details the calibration of photometric redshifts for a large galaxy dataset used in weak lensing, employing innovative methods to estimate and validate redshift distributions with high precision.

Contribution

It introduces a novel photometric redshift calibration approach combining deep and wide-field data, and validates it against clustering redshift methods for a large galaxy sample.

Findings

Redshift uncertainties are approximately 0.01 for mean redshifts.

The SOMPZ method provides consistent estimates with clustering redshift techniques.

The calibration enables accurate tomographic binning for weak lensing analyses.

Abstract

We present the photometric redshift characterization and calibration for the Dark Energy Camera All Data Everywhere (DECADE) weak lensing dataset: a catalog of 107 million galaxies observed by the Dark Energy Camera (DECam) in the northern Galactic cap. The redshifts are estimated from a combination of wide-field photometry, deep-field photometry with associated redshift estimates, and a transfer function between the wide field and deep field that is estimated using a source injection catalog. We construct four tomographic bins for the galaxy catalog, and estimate the redshift distribution, $n(z)$, within each one using the Self-organizing Map Photo-Z (SOMPZ) methodology. Our estimates include the contributions from sample variance, zeropoint calibration uncertainties, and redshift biases, as quantified for the deep-field dataset. The total uncertainties on the mean redshifts are $\sigma_{\langle z \rangle} \approx 0.01$. The SOMPZ estimates are then compared to those from the clustering redshift method, obtained by cross-correlating our source galaxies with galaxies in spectroscopic surveys, and are shown to be consistent with each other.