Euclid preparation
Abstract
Accurate modelling of redshift-space distortions (RSDs) is essential for maximising the cosmological information extracted from large galaxy redshift surveys. In preparation for the forthcoming analysis of the Euclid spectroscopic data, we investigated three approaches to modelling RSD effects on the power spectrum multipoles of mock H α emission line galaxies. We focused on two one-loop perturbation theory models – the effective field theory (EFT) and velocity difference generator (VDG ∞ ) – that differ in their treatment of the real-to-redshift space mapping on small scales and a third approach, the BACCO emulator, that adopts a hybrid strategy combining perturbation theory with high-resolution N -body simulations. We assessed the ability of these models to recover key cosmological parameters, including the expansion rate h , the cold dark matter density parameter ω c , and the scalar amplitude A s across four redshift bins spanning 0.9 ≤ z ≤ 1.8. In each bin, we found that VDG ∞ and BACCO outperform the EFT model across all scales up to k max ≲ 0.35 h Mpc −1 . While BACCO saturates in constraining power at intermediate scales and higher redshift, the VDG ∞ model continues to improve parameter constraints beyond k max ≳ 0.30 h Mpc −1 . The EFT model, although robust on large scales, exhibits significant parameter biases for k max ≳ 0.25 h Mpc −1 , limiting its applicability to Euclid -like H α samples. Among the full perturbation theory-based models, the enhanced treatment of small-scale effects of RSDs in VDG ∞ improves cosmological parameter constraints by up to a factor of two.