The Power of DESI for Photometric Redshift Calibration: A Case Study with KiDS-1000

arXiv:2512.15964 · astro-ph.CO · Submitted 2025-12-17 · Read on arXiv

D. Blanco, A. Leauthaud, J. U. Lange, A. H. Wright, H de_l_o_u_d_e_r _i _n _g _e r s - s a m p l e s

Department of Astronomy and Astrophysics, University of California Santa Cruz · Department of Physics, American University · Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute (AIRUB), German Centre for Cosmological Lensing · Department of Physics and Astronomy, The University of Utah · Department of Astrophysical Sciences, Princeton University · Department of Astronomy & Astrophysics, University of Toronto · Lawrence Berkeley National Laboratory · Department of Physics, Boston University · Dipartimento di Fisica “Aldo Pontremoli”, Università degli Studi di Milano, Italy · Università degli Studi di Milano, Italy · INAF-Osservatorio Astronomico di Brera, INAF-Oss0ervatorio Astronomico di Brera, INAFL-INAFL-INAFL-INAFL-INAFL-INAFL... (long string of repetitions) long string of repetitions

astro-ph.CO

Submitted: 2025-12-17

Updated: 2026-09-10

Comments: 21 pages, 14 figures. Published in OJAp

License: http://creativecommons.org/licenses/by/4.0/

Importance score: 50/100

The gist: Accurate redshift estimates are a critical requirement for weak lensing surveys and one of the main uncertainties in constraints on dark energy and large-scale cosmic structure.

Terminology

Abstract

Accurate redshift estimates are a critical requirement for weak lensing surveys and one of the main uncertainties in constraints on dark energy and large-scale cosmic structure. In this paper, we study the potential to calibrate photometric redshift (photo-z) distributions for gravitational lensing using the Dark Energy Spectroscopic Instrument (DESI). Since beginning its science operations in 2021, DESI has collected more than 50 million redshifts, adding about one million monthly. In addition to its large-scale structure samples, DESI has also acquired over 256k high-quality spectroscopic redshifts (spec-zs) in the COSMOS and XMM and VVDS fields. This is already a factor of 3 larger than previous spec-z calibration compilations in these two regions. Here, we explore calibrating photo-zs for the subset of KiDS-1000 galaxies that fall into joint self-organizing map (SOM) cells overlapping the DESI COSMOS footprint using the DESI COSMOS observations. Estimating the redshift distribution in KiDS-1000 with the new DESI data, we find broad consistency with previously published results while also detecting differences in the mean redshift in some tomographic bins with an average shifts of Delta Mean(z) = -0.028 in the mean and Delta Median(z) = +0.011 in the median across tomographic bins. However, we also find that incompleteness per SOM cell, i.e., groups of galaxies with similar colors and magnitudes, can modify n(z) distributions. Finally, we comment on the fact that larger photometric catalogs, aligned with the DESI COSMOS and DESI XMM and VVDS footprints, would be needed to fully exploit the DESI dataset and would extend the coverage to nearly eight times the area of existing 9-band photometry.

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