Photometric redshift calibration in DES Y3

Abstract

Biased redshift calibration is one of the limiting factors of wide-field imaging surveys. Cosmological constraints from weak gravitational lensing suffer particularly from this misestimation, relying on the redshift distributions of both the lens and source galaxies. In this thesis we present the redshift calibration methodology developed for the analysis of the first three years of data of the Dark Energy Survey (DES Y3). It consists of a combination of constraints from photometry and galaxy positions, respectively from a Self-Organising Maps scheme (SOMPZ) and clustering redshifts (WZ). We present the estimated redshift distributions and inherent uncertainties of the WZ method and its combination with SOMPZ for the DES Y3 weak lensing source galaxy sample, while for the fiducial lens sample MagLim we present the whole methodology, which has proven to be more accurate than the original DES Y3 redshift calibration. We study the impact of using the newly calibrated redshift distribution of the MagLim lens sample on cosmological constraints from galaxy clustering and galaxy-galaxy lensing. Assuming a ΛCDM cosmology, we obtain a ~0.4σ shift in the matter density and clustering amplitude plane compared to the fiducial DES Y3 results, highlighting the importance of the redshift calibration of the lens sample in multi-probe cosmological analyses.

Date of Award	23 Sept 2022
Original language	English
Supervisor	Juste Rozas, Aurelio (Director), Maria del Pilar Casado Lechuga (Tutor), Grinstein , Sebastian (Director) & Miquel Pascual, Ramon (Director)