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

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 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 $\approx 8\%$ relative to matter, even on gigaparsec scales. This is a consequence of star formation depleting gas in the densest and most clustered regions of the universe. On smaller scales, $k>0.1 \, h / \rm Mpc$, the power suppression for both gas densities and velocities is more significant and correlates 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 reaches scales as large as $10$ 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 using, for example, the kinetic Sunyaev-Zeldovich effect.