Hybrid bias and displacement emulators for field-level modelling of galaxy clustering in real and redshift space

Abstract

Recently, hybrid bias expansions have emerged as a powerful approach to modelling the way in which galaxies are distributed in the Uni verse. Similarly, field-le vel emulators have recently become possible, thanks to advances in machine learning and N -body simulations. In this paper, we explore whether both techniques can be combined to provide a field-level model for the clustering of galaxies in real and redshift space. Specifically, here we will demonstrate that field-level emulators are able to accurately predict all the operators of a second-order hybrid bias expansion. The precision achieved in real and redshift space is similar to that obtained for the non-linear matter power spectrum. This translates to roughly 1-2 per cent precision for the power spectrum of a BOSS (Baryon Oscillation Spectroscopic Surv e y) and a Euclid-like galaxy sample up to k ∼0 . 6 h Mpc -1 . Remarkably, this combined approach also delivers precise predictions for field-level galaxy statistics. Despite all these promising results, we detect several areas where further improvements are required. Therefore, this work serves as a road map for the developments required for a more complete exploitation of upcoming large-scale structure surveys.