Gas Perturbations in the Cool Cores of Galaxy Clusters: Effective Equation of State, Velocity Power Spectra, and Turbulent Heating

Zhuravleva, Irina and Allen, Steven W. and Mantz, Adam and Werner, Norbert (2018) Gas Perturbations in the Cool Cores of Galaxy Clusters: Effective Equation of State, Velocity Power Spectra, and Turbulent Heating. ASTROPHYSICAL JOURNAL, 865 (1). ISSN 1538-4357

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Abstract

We present the statistical analysis of X-ray surface brightness and gas density fluctuations in the cool cores of 10 nearby, X-ray-bright galaxy clusters that have deep Chandra observations and show observational indications of radio-mechanical active galactic nucleus (AGN) feedback. Within the central parts of the cool cores, the total variance of fluctuations is dominated by isobaric and/or isothermal fluctuations on spatial scales similar to 10-60 kpc, which are likely associated with slow gas motions and bubbles of relativistic plasma. Adiabatic fluctuations, associated with weak shocks and/or sonic turbulence, constitute less than 10% of the total variance in all clusters. The typical amplitude of density fluctuations is small, similar to 10% or less on scales of similar to 10-15 kpc. The observed subdominant contribution of adiabatic fluctuations and the small amplitude of density fluctuations support a model of gentle AGN feedback. The measured one-component velocities of gas motions are typically below 100-150 km s(-1) on scales <50 kpc and can be up to similar to 300 km s(-1) on similar to 100 kpc scales. The nonthermal energy is <12% of the thermal energy. Regardless of the source that drives these motions, the dissipation of the energy in such motions provides heat that is sufficient to balance radiative cooling on average, albeit with significant uncertainties. The results presented here support previous conclusions based on the analysis of the Virgo and Perseus Clusters and agree with the Hitomi measurements. With next-generation observatories like Athena and Lynx, these techniques will be yet more powerful.

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