FLAMINGO: Galaxy formation and feedback effects on the gas density and velocity fields

¹ Donostia International Physics Center, Manuel Lardizabal Ibilbidea, 4, 20018 Donostia, Gipuzkoa, Spain
² Department of Theoretical Physics, University of the Basque Country UPV/EHU, Bilbao E-48080, Spain
³ IKERBASQUE, Basque Foundation for Science, 48013 Bilbao, Spain
⁴ Institut für Astrophysik (DAP), Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland
⁵ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁶ Astrophysics Research Institute, Liverpool John Moores University, Liverpool L3 5RF, UK
⁷ Lorentz Institute for Theoretical Physics, Leiden University, PO Box 9506, 2300 RA Leiden, The Netherlands

^⋆ Corresponding author: lurdes.ondaro@dipc.org

Received: 17 December 2024
Accepted: 10 March 2025

Abstract

Most of the visible matter in the Universe is in a gaseous state, subject to hydrodynamic forces and galaxy formation processes that are much more complex to model than gravity. These baryonic effects can potentially bias the analyses of several cosmological probes, such as weak gravitational lensing. In this work, we study the gas density and velocity fields of the FLAMINGO simulations and compare them with their gravity-only predictions. We focus on the effect sourced by relatively high-mass halos, M>10¹³ h⁻¹ M_⊙. We find that while the gas velocities do not differ from those of dark matter on large scales, the gas mass power spectrum is suppressed by up to ≈8% relative to matter, even on gigaparsec scales. This is a consequence of star formation depleting the gas in the densest and most clustered regions of the Universe. On smaller scales, k>0.1 h/Mpc, the power suppression for both gas densities and velocities is more significant and correlated with the strength of the active galactic nucleus (AGN) feedback. The impact of feedback can be understood in terms of outflows, identified as gas bubbles with positive radial velocities ejected from the central galaxy. With increasing feedback strength, the outflowing gas has higher velocities and it can reach scales as large as ten times the virial radius of the halo, redistributing the gas and slowing its average infall velocity. Interestingly, different implementations of AGN feedback leave distinct features in these outflows in terms of their radial and angular profiles and their dependence on halo mass. In the future, such differences could be measured in observations that employ, for example, the kinetic Sunyaev-Zeldovich effect.