Validation of semi-analytical, semi-empirical covariance matrices for two-point correlation function for Early DESI data

Abstract

We present an extended validation of semi-analytical, semi-empirical covariance matrices for the two-point correlation function (2PCF) on simulated catalogs representative of Luminous Red Galaxies (LRG) data collected during the initial two months of operations of the Stage-IV ground-based Dark Energy Spectroscopic Instrument (DESI). We run the pipeline on multiple effective Zel'dovich (EZ) mock galaxy catalogs with the corresponding cuts applied and compare the results with the mock sample covariance to assess the accuracy and its fluctuations. We propose an extension of the previously developed formalism for catalogs processed with standard reconstruction algorithms. We consider methods for comparing covariance matrices in detail, highlighting their interpretation and statistical properties caused by sample variance, in particular, nontrivial expectation values of certain metrics even when the external covariance estimate is perfect. With improved mocks and validation techniques, we confirm a good agreement between our predictions and sample covariance. This allows one to generate covariance matrices for comparable datasets without the need to create numerous mock galaxy catalogs with matching clustering, only requiring 2PCF measurements from the data itself. The code used in this paper is publicly available at https://github.com/oliverphilcox/RascalC.

arXiv comment19 pages, 1 figure. Published in MNRAS. Code available at https://github.com/oliverphilcox/RascalC, table and figure data available at https://dx.doi.org/10.5281/zenodo.7750637

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• DESI 2024 III: Baryon Acoustic Oscillations from Galaxies and Quasars
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• Optimal Reconstruction of Baryon Acoustic Oscillations for DESI 2024
• Analytical and EZmock covariance validation for the DESI 2024 results
• Fiducial-Cosmology-dependent systematics for the DESI 2024 BAO Analysis
• HOD-Dependent Systematics in Emission Line Galaxies for the DESI 2024 BAO analysis
• Generating mock galaxy catalogues for flux-limited samples like the DESI Bright Galaxy Survey
• ELG Spectroscopic Systematics Analysis of the DESI Data Release 1
• HOD-Dependent Systematics for Luminous Red Galaxies in the DESI 2024 BAO Analysis
• Modelling the covariance matrix for the power spectra before and after the BAO reconstruction