Gas distribution from clusters to filaments in IllustrisTNG

TL;DR

This study analyzes the distribution and dynamics of gas around galaxy clusters in the IllustrisTNG simulation, revealing how gas phases trace cluster structure and formation history, and proposing azimuthal mode decomposition as a diagnostic tool.

Contribution

It provides a detailed analysis of gas distribution and dynamics in galaxy clusters and filaments, linking gas properties to cluster assembly history and introducing azimuthal mode decomposition as a new probe.

Findings

Hot plasma is virialized inside clusters.

Warm hot inter-galactic medium (WHIM) shows distinct infall regimes.

Azimuthal symmetries trace cluster structure and assembly history.

Abstract

Matter distribution in the environment of galaxy clusters, from their cores to their connected cosmic filaments, must be in principle related to the underlying cluster physics and it evolutionary state. We aim to investigate how radial and azimuthal distribution of gas is affected by cluster environments, and how it can be related to cluster mass assembly history. Radial physical properties of gas (velocity, temperature, and density) is first analysed around 415 galaxy cluster environments from IllustrisTNG simulation at z = 0 (TNG300-1). Whereas hot plasma is virialised inside clusters (< R200), the dynamics of warm hot inter-galactic medium (WHIM) can be separated in two regimes: accumulating and slowly infalling gas at cluster peripheries and fast infalling motions outside clusters (> 1.5R200). The azimuthal distribution of dark matter (DM), hot and warm gas phases is secondly statistically probed by decomposing their 2-D distribution in harmonic space. Inside clusters, the azimuthal symmetries of DM and hot gas are well tracing cluster structural properties, such as their center offsets, substructure fractions and elliptical shapes. Beyond cluster virialised regions, we find that WHIM gas follows the azimuthal distribution of DM thus tracing cosmic filament patterns. Azimuthal symmetries of hot and warm gas distribution are finally shown to be imprints of cluster mass assembly history, strongly correlated with the formation time, mass accretion rate, and dynamical state of clusters. Azimuthal mode decomposition of 2-D gas distribution is a promising probe to assess the 3-D physical and dynamical cluster properties up to their connected cosmic filaments.