Iras-allsky

Euclid: The linear-construction covariance and cosmology

October 2026 • 2026A&A...714A.440L

Authors • Lindholm, V. • Sihvola, E. • Valiviita, J. • Fumagalli, A. • Altieri, B. • Andreon, S. • Auricchio, N. • Baccigalupi, C. • Baldi, M. • Bardelli, S. • Battaglia, P. • Biviano, A. • Branchini, E. • Brescia, M. • Camera, S. • Capobianco, V. • Carbone, C. • Cardone, V. F. • Carretero, J. • Casas, S. • Castellano, M. • Castignani, G. • Cavuoti, S. • Chambers, K. C. • Cimatti, A. • Colodro-Conde, C. • Congedo, G. • Conversi, L. • Copin, Y. • Courbin, F. • Courtois, H. M. • Da Silva, A. • Degaudenzi, H. • De Lucia, G. • Dole, H. • Dubath, F. • Dupac, X. • Dusini, S. • Escoffier, S. • Farina, M. • Farinelli, R. • Ferriol, S. • Finelli, F. • Fosalba, P. • Fotopoulou, S. • Frailis, M. • Franceschi, E. • Fumana, M. • Galeotta, S. • George, K. • Gillis, B. • Giocoli, C. • Gracia-Carpio, J. • Grazian, A. • Grupp, F. • Haugan, S. V. H. • Holmes, W. • Hormuth, F. • Hornstrup, A. • Jahnke, K. • Jhabvala, M. • Kermiche, S. • Kiessling, A. • Kubik, B. • Kunz, M. • Kurki-Suonio, H. • Le Brun, A. M. C. • Ligori, S. • Lilje, P. B. • Lloro, I. • Mainetti, G. • Maiorano, E. • Mansutti, O. • Marcin, S. • Marggraf, O. • Martinelli, M. • Martinet, N. • Marulli, F. • Massey, R. J. • Medinaceli, E. • Mei, S. • Melchior, M. • Meneghetti, M. • Merlin, E. • Meylan, G. • Mora, A. • Moresco, M. • Moscardini, L. • Nakajima, R. • Neissner, C. • Niemi, S.-M. • Padilla, C. • Paltani, S. • Pasian, F. • Pedersen, K. • Pettorino, V. • Pires, S. • Polenta, G. • Poncet, M. • Popa, L. A. • Raison, F. • Renzi, A. • Rhodes, J. • Riccio, G. • Romelli, E. • Roncarelli, M. • Rosset, C. • Saglia, R. • Sakr, Z. • Sánchez, A. G. • Sapone, D. • Schneider, P. • Schrabback, T. • Secroun, A. • Seidel, G. • Simon, P. • Sirignano, C. • Sirri, G. • Stanco, L. • Tallada-Crespí, P. • Taylor, A. N. • Tereno, I. • Toft, S. • Toledo-Moreo, R. • Torradeflot, F. • Tutusaus, I. • Vassallo, T. • Verdoes Kleijn, G. • Wang, Y. • Weller, J. • Zamorani, G. • Zucca, E. • Castro, T. • Martín-Fleitas, J. • Monaco, P. • Pezzotta, A. • Scottez, V. • Sereno, M. • Viel, M. • Sciotti, D.

Abstract • We study the properties of galaxy cluster two-point correlation function covariance matrices estimated using the linear-construction (LC) method, which is computationally up to 20 times faster than the standard sample-covariance method. Our goal is to assess how well the LC method performs in cosmological parameter estimation compared to the sample covariance. We used a set of 1000 mock dark matter halo catalogues to compute both the LC-covariance and the sample-covariance estimates in four redshift shells. These numerical matrices were used to fit a theoretical four-parameter model for the covariance. We then used the two fitted covariance models in a likelihood function to estimate two cosmological parameters -- the matter density parameter Ωm and the amplitude of the matter density fluctuations σ8 -- from the simulated mock catalogues. The purpose of this was to validate the LC-covariance-based model against the sample-covariance model. The catalogues were simulated assuming the spatially flat ΛCDM cosmology, with Ωm = 0.30711 and σ8 = 0.8288. We find that the parameter posteriors obtained using the sample- and LC-covariance models agree well with each other and with the simulation cosmology. The two pairs of marginalised constraints are Ωm = 0.307 ± 0.003 and σ8 = 0.826 ± 0.009 (sample covariance), and Ωm = 0.308 ± 0.003 and σ8 = 0.825 ± 0.009 (LC covariance). The posterior widths are the same, and the difference in the median values is less than 0.16σ for both parameters. ★ This paper is published on behalf of the Euclid Consortium.

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Yun Wang

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