DES Y3 cosmic shear down to small scales: Constraints on cosmology and baryons

¹ Institute for Computational Science, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
e-mail: giovanni.arico@uzh.ch
² Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián, Guipuzkoa, Spain
e-mail: reangulo@dipc.org
³ IKERBASQUE, Basque Foundation for Science, 48013 Bilbao, Spain
⁴ Department of Physics (Astrophysics), University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
⁵ Kavli Institute for the Physics and Mathematics of the Universe (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
⁶ Department of Astrophysics Research, Instituto de Astrofísica de Canarias, C.Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁷ Departamento de Astrofísica, Universidad de La Laguna, Avenida Francisco Sánchez s/n, 38205 La Laguna, Tenerife, Spain

Received: 30 March 2023
Accepted: 2 August 2023

Abstract

We present the first analysis of cosmic shear measured in DES Y3 that employs the entire range of angular scales in the data. To achieve this, we built upon recent advances in the theoretical modelling of weak lensing provided by a combination of N-body simulations, physical models of baryonic processes, and neural networks. Specifically, we used BACCOemu to model the linear and non-linear matter power spectrum including baryonic physics, allowing us to robustly exploit scales smaller than those used by the DES Collaboration. We show that the additional data produce cosmological parameters that are tighter but consistent with those obtained from larger scales, while also constraining the distribution of baryons. In particular, we measured the mass scale at which haloes have lost half of their gas, log M_c = 14.38_−0.56^+0.60 log(h⁻¹ M_⊙), and a parameter that quantifies the weighted amplitudes of the present-day matter inhomogeneities, S₈ = 0.799_−0.015^+0.023. Our constraint on S₈ is statistically compatible with that inferred from the Planck satellite data at the 0.9σ level. We find instead a 1.4σ shift in comparison to that from the official DES Y3 cosmic shear, because of different choices in the modelling of intrinsic alignment, non-linearities, baryons, and lensing shear ratios. We conclude that small scales in cosmic shear data contain valuable astrophysical and cosmological information and thus should be included in standard analyses.