Turbulence, Thermal Pressure, and Their Dynamical Effects on Cosmic Baryonic Fluid

TL;DR

This study uses the IllustrisTNG simulation to analyze cosmic baryonic turbulence and thermal motions, revealing their evolution, environmental dependence, and impact on structure formation, challenging traditional views on turbulent support.

Contribution

It introduces a wavelet transform method to quantify turbulence and thermal motions in cosmic gas, providing new insights into their dynamical roles across different redshifts and environments.

Findings

Turbulent pressure grows from z=4 to 1, then stabilizes.

High-density regions have turbulent pressure up to six times thermal pressure.

Turbulent pressure counteracts thermal support, affecting structure formation.

Abstract

We employ the IllustrisTNG simulation data to investigate the turbulent and thermal motions of the cosmic baryonic fluid. With continuous wavelet transform techniques, we define the pressure spectra, or density-weighted velocity power spectra, as well as the spectral ratios, for both turbulent and thermal motions. We find that the magnitude of the turbulent pressure spectrum grows slightly from $z=4$ to $2$ and increases significantly from $z=2$ to $1$ at large scales, suggesting progressive turbulence injection into the cosmic fluid, whereas from $z=1$ to $0$, the spectrum remains nearly constant, indicating that turbulence may be balanced by energy transfer and dissipation. The magnitude of the turbulent pressure spectra also increases with environmental density, with the highest density regions showing a turbulent pressure up to six times that of thermal pressure. We also explore the dynamical effects of turbulence and thermal motions, discovering that while thermal pressure provides support against structure collapse, turbulent pressure almost counteracts this support, challenging the common belief that turbulent pressure supports gas against overcooling.