Friedrich, O;
Andrade-Oliveira, F;
Camacho, H;
Alves, O;
Rosenfeld, R;
Sanchez, J;
Fang, X;
... Wilkinson, RD; + view all
(2021)
Dark Energy Survey year 3 results: covariance modelling and its impact on parameter estimation and quality of fit.
Monthly Notices of the Royal Astronomical Society
, 508
(3)
pp. 3125-3165.
10.1093/mnras/stab2384.
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Abstract
We describe and test the fiducial covariance matrix model for the combined two-point function analysis of the Dark Energy Survey Year 3 (DES-Y3) data set. Using a variety of new ansatzes for covariance modelling and testing, we validate the assumptions and approximations of this model. These include the assumption of Gaussian likelihood, the trispectrum contribution to the covariance, the impact of evaluating the model at a wrong set of parameters, the impact of masking and survey geometry, deviations from Poissonian shot noise, galaxy weighting schemes, and other sub-dominant effects. We find that our covariance model is robust and that its approximations have little impact on goodness of fit and parameter estimation. The largest impact on best-fitting figure-of-merit arises from the so-called fsky approximation for dealing with finite survey area, which on average increases the χ2 between maximum posterior model and measurement by 3.7 per cent (Δχ2 ≈ 18.9). Standard methods to go beyond this approximation fail for DES-Y3, but we derive an approximate scheme to deal with these features. For parameter estimation, our ignorance of the exact parameters at which to evaluate our covariance model causes the dominant effect. We find that it increases the scatter of maximum posterior values for Ωm and σ8 by about 3 per cent and for the dark energy equation-of-state parameter by about 5 per cent.
| Type: | Article |
|---|---|
| Title: | Dark Energy Survey year 3 results: covariance modelling and its impact on parameter estimation and quality of fit |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1093/mnras/stab2384 |
| Publisher version: | https://doi.org/10.1093/mnras/stab2384 |
| Language: | English |
| Additional information: | C The Author(s) 2021. Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. |
| Keywords: | large-scale structure of Universe, cosmology: observations |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10140505 |
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