Dark Energy Survey Year 3 Results: Calibration of Lens Sample Redshift Distributions using Clustering Redshifts with BOSS/eBOSS

TL;DR

This paper introduces a clustering redshift method using BOSS/eBOSS data to calibrate the redshift distributions of DES Year 3 lens galaxies, achieving high accuracy and validating the approach with simulations.

Contribution

The study develops and validates a new clustering redshift calibration technique for DES lens samples, improving redshift accuracy for cosmological analyses.

Findings

Redshift mean differences below |Δz|=0.01 in most bins

Uncertainties on mean redshift ranged from 0.003 to 0.008

Redshift width uncertainties ranged from 4% to 9%

Abstract

We present clustering redshift measurements for Dark Energy Survey (DES) lens sample galaxies to be used in weak gravitational lensing and galaxy clustering studies. To perform this measurement, we cross-correlate with spectroscopic galaxies from the Baryon Acoustic Oscillation Survey (BOSS) and its extension, eBOSS. We validate our methodology in simulations, including a new technique to calibrate systematic errors due to the galaxy clustering bias, finding our method to be generally unbiased in calibrating the mean redshift. We apply our method to the data, and estimate the redshift distribution for eleven different photometrically-selected bins. We find general agreement between clustering redshift and photometric redshift estimates, with differences on the inferred mean redshift to be below $|\Delta z|=0.01$ in most of the bins. We also test a method to calibrate a width parameter for redshift distributions, which we found necessary to use for some of our samples. Our typical uncertainties on the mean redshift ranged from 0.003 to 0.008, while our uncertainties on the width ranged from 4 to 9\%. We discuss how these results calibrate the photometric redshift distributions used in companion DES Year 3 Results papers.