Fourier analysis of small-scale plasma instabilities within the ICM

It is known that roughly 99.9% of the matter in the Universe is in the plasma state. The intracluster medium (ICM) is primarily composed of plasma and is continuously heated over time. This heating can arise due to large-scale phenomena such as active galactic nuclei, in addition to small-scale plasma instabilities such as the mirror and firehose instabilities. It is known that these instabilities persist under the production of pressure anisotropy. In this research, two particle-in-cell simulations with different magnetization values are constructed in order to analyze the effects of these instabilities for a particular, sheared magnetic field configuration. A detailed Fourier analysis is conducted for each simulation in order to document relevant plasma wave characteristics in the ICM. The resulting power spectra suggest that the radiated power is dominated by low frequency waves. Furthermore, the results display ion-cyclotron resonances for both instabilities and additional peaks that require a deeper analysis. These plots are compared with the average magnetic field energy fluctuations in order to match the phases of the sheared magnetic field over time with the corresponding plasma instabilities. A discussion regarding the implications for plasma heating is also provided. A proper understanding of these small-scale plasma instabilities can then be directly extended to the context of galaxy clusters and their properties. The ICM plasma has important connections to events such as galaxy mergers, galactic outflows, and relativistic jets.