Jets, bubbles, and heat pumps in galaxy clusters

Abstract

Feedback from AGN jets has been proposed to counteract the catastrophic cooling in many galaxy clusters. However, it is still unclear which physical processes are acting to couple the energy from the bi-directional jets to the ICM. We study the long-term evolution of rising bubbles that were inflated by AGN jets using MHD simulations. In the wake of the rising bubbles, a significant amount of low-entropy gas is brought into contact with the hot cluster gas. We assess the energy budget of the uplifted gas and find it comparable to the total energy injected by the jets. Although our simulation does not include explicit thermal conduction, we find that, for reasonable assumptions about the conduction coefficient, the rate is fast enough that much of the uplifted gas may be thermalized before it sinks back to the core. Thus, we propose that the AGN can act like a geothermal heat pump to move low-entropy gas from the cluster core to the heat reservoir and will be able to heat the inner cluster more efficiently than would be possible by direct energy transfer from jets alone. We show that the maximum efficiency of this mechanism, i.e. the ratio between the conductive thermal energy and the work needed to lift the gas, ξ max can exceed 100 per cent. While ξ < ξ max in realistic scenarios, AGN-induced thermal conduction has the potential to significantly increase the efficiency with which AGN can heat cool-core clusters and transform the bursty AGN activities into a smoother and enduring heating process.

Constraining simulated black hole feedback in the Perseus Cluster

“…We use the FLASH code (Dubey et al, 2009) to model and AGN jet firing for 10 Myr at the center of a spherically symmetric atmosphere. The cluster atmosphere is set with density and temperature tuned to match the parameters found for the Perseus cluster according to the widely used β-model that describes relaxed clusters (Chen et al, 2019). The jet itself is modelled as a nozzle through which mass, momentum, energy, and magnetic flux are fired into the atmosphere in both the positive and negative z-directions.…”

Constraining black hole feedback in galaxy clusters from X-ray power spectra

“…We use magnetohydrodynamic simulations with an adaptive mesh refinement (AMR) grid. A more in-depth discussion of the numerical set up is included in Chen et al (2019), where the simulations used in this paper were first described.…”

“…The base of the jet is modeled as a nozzle at the center of the cluster (Heinz et al 2006;Chen et al 2019) which injects energy, mass, momentum, and magnetic flux into the atmosphere in both directions along the z-axis, with a small wobble added to account for the precession of the spin axis of the black hole and dynamical instabilities in the jet below the resolution scale, as an effective implementation of the "dentist drill" effect first postulated by Scheuer (1982). The simulation models the magnetic field in the jet, injecting magnetic field in equipartition with the particle pressure and a helicity of 𝐵 𝜙 /𝐵 z = 1, however, the ICM is nonmagnetized.…”

“…The jet fires for 10 Myr at a power of 𝑃 jet = 10 45 ergs/s before being shut off and allowed to propagate through the cluster for an additional 500 Myr. The AMR resolution of the cluster gas changes throughout the simulation, based on the propagation of the jet, increasing refinement where the most activity occurs and decreasing resolution in low-activity areas to maximize computational efficiency (Chen et al 2019). The original simulation was designed to study the magnetic properties of the jets and as such required a high resolution of 30 pc to fully resolve the jets.…”

“…Motl et al 2004;Rossetti & Molendi 2010;Parrish et al 2010; Su ★ E-mail: amheinrich@wisc.edu et al 2016, 2017), thermal conduction (e.g. Narayan & Medvedev 2001;Yang & Reynolds 2016;Chen et al 2019), and cosmic ray streaming (e.g. Sharma et al 2010;Ruszkowski et al 2017;Ehlert et al 2018).…”