Feedback from reorienting AGN jets

I. Jet–ICM coupling, cavity properties and global energetics^⋆

¹ Sorbonne Universités, UPMC Univ. Paris 6 et CNRS, UMR 7095, IAP, Paris, 98 bis bd Arago, 75014 Paris, France
e-mail: cielo@iap.fr; silk@iap.fr; volonteri@iap.fr
² University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 5C2, Canada
³ Institute of Computational Science, Centre for Theoretical Astrophysics and Cosmology, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
⁴ Institut d’Astrophysique de Paris, 98 bis bd Arago, 75014 Paris, France
⁵ INAF/Istituto Nazionale di Astrofisica-Catania Astrophysical Observatory, Via S. Sofia 78, 95126 Catania, Italy
⁶ AIM – Paris-Saclay, CEA/DSM/IRFU, CNRS, Univ Paris 7, 91191 Gif-sur-Yvette, France
⁷ Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218, USA
⁸ BIPAC, University of Oxford, 1 Keble Road, Oxford OX1 3RH, UK

Received: 3 January 2018
Accepted: 7 June 2018

Abstract

Aims. We test the effects of re-orienting jets from an active galactic nucleus (AGN) on the intracluster medium in a galaxy cluster environment with short central cooling time. We investigate both the appearance and the properties of the resulting cavities, and the efficiency of the jets in providing near-isotropic heating to the cooling cluster core.

Methods. We use numerical simulations to explore four models of AGN jets over several active/inactive cycles. We keep the jet power and duration fixed across the models, varying only the jet re-orientation angle prescription. We track the total energy of the intracluster medium (ICM) in the cluster core over time, and the fraction of the jet energy transferred to the ICM. We pay particular attention to where the energy is deposited. We also generate synthetic X-ray images of the simulated cluster and compare them qualitatively to actual observations.

Results. Jets whose re-orientation is minimal (≲20°) typically produce conical structures of interconnected cavities, with the opening angle of the cones being ~15–20°, extending to ~300 kpc from the cluster centre. Such jets transfer about 60% of their energy to the ICM, yet they are not very efficient at heating the cluster core, and even less efficient at heating it isotropically, because the jet energy is deposited further out. Jets that re-orientate by ≳20° generally produce multiple pairs of detached cavities. Although smaller, these cavities are inflated within the central 50 kpc and are more isotropically distributed, resulting in more effective heating of the core. Such jets, over hundreds of millions of years, can deposit up to 80% of their energy precisely where it is required. Consequently, these models come the closest in terms of approaching a heating/cooling balance and mitigating runaway cooling of the cluster core even though all models have identical jet power/duration profiles. Additionally, the corresponding synthetic X-ray images exhibit structures and features closely resembling those seen in real cool-core clusters.