Gas distribution from clusters to filaments in IllustrisTNG
  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. 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 (~ R200) and fast infalling motions
outside clusters (> 1.5 R200). 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 found that WHIM gas follows the azimuthal distribution
of DM by tracing cosmic filament patterns. Azimuthal symmetries of hot and warm
gas distribution is finally shown to be imprints of cluster mass assembly
history, by strongly correlating 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.
