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Problems with energy distribution & its multi-scale impact in the ICM

Presentation #100.50 in the session AGN.

Published onJul 01, 2023
Problems with energy distribution & its multi-scale impact in the ICM

Energy transport across a wide range of dynamical scales in the intracluster medium is one of the most interesting topics in current research and future interest. Hot baryons, visible in the X-rays, need to be stably sustained against radiative cooling over a large inner fraction of the cluster virial radius. A historical motivation has been the lack of sufficient observed cold gas and star-formation in the cluster cores that is expected in the absence of efficient heating. Quantitatively, there is enough energy from active galactic nuclei (AGN) to solve the problem at the simplest level, but the complexity of how that energy flows around is not well understood. Multiple transport mechanisms are being actively discussed including long wavelength, nearly isotropic sound waves, anisotropic heat conduction along local magnetic fields (depending on the local temperature gradient), generation and dissipation of volume-filling turbulence, etc. I find that a combined contribution from waves propagating to cluster outskirts and trapped turbulence in the core can dissipate energy to counter cooling catastrophe. While sound waves and turbulence have been strong contenders, thermal conduction has been claimed to be further suppressed by gyro-scale whistlers that scatter thermal electrons efficiently in the weakly magnetised ICM. In the latter scenario, sound wave propagation happens unhindered and thermal instability domain may be enhanced leading to excess and/or smaller scale cold gas. This further implies that observations may need to account for excess cold/mixed phase gas. In my talk, I will discuss my results related to energy transport in the ICM and such consequences.

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