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Lookup NU author(s): Dr Markus RauORCiD, Dr Niko Šarčević, Dr Dani LeonardORCiD
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
© The Author(s) 2025. Published by Oxford University Press on behalf of Royal Astronomical Society. Photometric redshifts of the source galaxies are a key source of systematic uncertainty in the Rubin Observatory Legacy Survey of Space and Time (LSST)’s galaxy clustering and weak lensing analysis, i.e. the 3 × 2pt analysis. This paper introduces a Fisher forecast code fishera2z for the LSST Yr 10 (Y10) 3 × 2pt and cosmic shear analyses, utilizing a 15-parameter redshift distribution model, with one redshift bias, variance, and outlier rate per tomographic bin.fishera2z employs the Core Cosmology Library ccl to compute the large-scale structure power spectrum and incorporates a four-parameter non-linear alignment model for intrinsic alignments. We evaluate the impact of marginalizing over redshift distribution parameters on weak lensing, forecast biases in cosmological parameters due to redshift errors, and assess cosmological parameter sensitivity to redshift systematic parameters using decision trees. The sensitivity study reveals that for LSST 3 × 2pt analysis, S8 is most sensitive to the mean redshift of the fourth out of the five source tomographic bins, while other cosmological parameters possess different sensitivities. Additionally, we provide cosmological analysis forecasts based on different scenarios of spectroscopic training data sets. We find that the figures-of-merit for the cosmological results increase with the number of spectroscopic training galaxies, and with the completeness of the training set above z=1.6, assuming the redshift information comes solely from the training set galaxies without other external constraints.
Author(s): Zhang T, Almoubayyed H, Mandelbaum R, Rau MM, Sarcevic N, Leonard CD, Newman JA, Andrews BH, Liang S
Publication type: Article
Publication status: Published
Journal: Monthly Notices of the Royal Astronomical Society
Year: 2026
Volume: 545
Issue: 2
Print publication date: 01/01/2026
Online publication date: 03/12/2025
Acceptance date: 13/10/2025
Date deposited: 22/12/2025
ISSN (print): 0035-8711
ISSN (electronic): 1365-2966
Publisher: Oxford University Press
URL: https://doi.org/10.1093/mnras/staf1829
DOI: 10.1093/mnras/staf1829
Data Access Statement: The software and data to produce the results of this work are open source at github.com/LSSTDESC/fisherA2Z.
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