The intracluster medium (ICM) in the centers of galaxy clusters is heavily influenced by the “feedback” from supermassive black holes (SMBHs). Feedback can drive turbulence in the ICM and turbulent dissipation can potentially be an important source of heating. Due to the limited spatial and spectral resolutions of X-ray telescopes, direct observations of turbulence in the hot ICM have been challenging. Recently, we developed a new method to measure turbulence in the ICM using multiphase filaments as tracers. These filaments are ubiquitous in cluster centers and can be observed at very high resolution using optical and radio telescopes. We study the kinematics of the filaments by measuring their velocity structure functions (VSFs) over a wide range of scales in the centers of ∼ 10 galaxy clusters. We find features of the VSFs that correlate with the SMBHs activities, suggesting that SMBHs are the main driver of gas motions in the centers of galaxy clusters. In all systems, the VSF is steeper than the classical Kolmogorov expectation and the slopes vary from system to system. One theoretical explanation is that the VSFs we have measured so far mostly reflect the motion of the driver (jets and bubbles) rather than the cascade of turbulence. We show that in Abell 1795, the VSF of the outer filaments far from the SMBH flattens on small scales to a Kolmogorov slope, suggesting that the cascade is only detectable farther out with the current telescope resolution. The level of turbulent heating computed at small scales is typically an order of magnitude lower than that estimated at the driving scale. Even though SMBH feedback heavily influences the kinematics of the ICM in cluster centers, the level of turbulence it drives is rather low, and turbulent heating can only offset ≲ 10% of the cooling loss, consistent with the findings of numerical simulations.
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Non-Kolmogorov turbulence in multiphase intracluster medium driven by cold gas precipitation and AGN jets
ABSTRACT Active galactic nuclei (AGNs) feedback is responsible for maintaining plasma in global thermal balance in extended haloes of elliptical galaxies and galaxy clusters. Local thermal instability in the hot gas leads to the formation of precipitating cold gas clouds that feed the central supermassive black holes, thus heating the hot gas and maintaining global thermal equilibrium. We perform 3D magnetohydrodynamical (MHD) simulations of self-regulated AGNs feedback in a Perseus-like galaxy cluster with the aim of understanding the impact of the feedback physics on the turbulence properties of the hot and cold phases of the intracluster medium (ICM). We find that, in general, the cold phase velocity structure function (VSF) is steeper than the prediction from Kolmogorov’s theory. We attribute the physical origin of the steeper slope of the cold phase VSF to the driving of turbulent motions primarily by the gravitational acceleration acting on the ballistic clouds. We demonstrate that, in the pure hydrodynamical case, the precipitating cold filaments may be the dominant agent driving turbulence in the hot ICM. The arguments in favour of this hypothesis are that: (i) the cold phase mass dominates over hot gas mass in the inner cool core; (ii) hot and cold gas velocities are spatially correlated; (iii) both the cold and hot phase velocity distributions are radially biased. We show that, in the MHD case, the turbulence in the ambient hot medium (excluding the jet cone regions) can also be driven by the AGN jets. The driving is then facilitated by enhanced coupling due to magnetic fields of the ambient gas and the AGN jets. In the MHD case, turbulence may thus be driven by a combination of AGN jet stirring and filament motions. We conclude that future observations, including those from high spatial and spectral resolution X-ray missions, may help to constrain self-regulated AGN feedback by quantifying the multitemperature VSF in the ICM.
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- Award ID(s):
- 2009227
- NSF-PAR ID:
- 10295443
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 504
- Issue:
- 1
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- 898 to 909
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/mnras/stab966
