Cosmic rays and thermal instability in self-regulating cooling flows of massive galaxy clusters

Ricarda Beckmann, Yohan Dubois, Alisson Pellissier, Valeria Olivares, Fiorella Polles, Oliver Hahn, Pierre Guillard, Matthew Lehnert

One of the key physical processes that helps prevent strong cooling flows in galaxy clusters is the continued energy input from the central active galactic nucleus (AGN) of the cluster. However, it remains unclear how this energy is thermalised so that it can effectively prevent global thermal instability. One possible option is that a fraction of the AGN energy is converted into cosmic rays (CRs), which provide non-thermal pressure support, and can retain energy even as thermal energy is radiated away. By means of magneto-hydrodynamical simulations, we investigate how CR injected by the AGN jet influence cooling flows of a massive galaxy cluster. We conclude that converting a fraction of the AGN luminosity as low as 10% into CR energy prevents cooling flows on timescales of billion years, without significant changes in the structure of the multi-phase intra-cluster medium. CR-dominated jets, by contrast, lead to the formation of an extended, warm central nebula that is supported by CR pressure. We report that the presence of CRs is not able to suppress the onset of thermal instability in massive galaxy clusters, but CR-dominated jets do significantly change the continued evolution of gas as it continues to cool from isobaric to isochoric. The CR redistribution in the cluster is dominated by advection rather than diffusion or streaming, but the heating by CR streaming helps maintain gas in the hot and warm phase. Observationally, self-regulating, CR-dominated jets produce a γ-ray flux in excess of current observational limits, but low CR fractions in the jet are not ruled out.

Department of Astrophysics, Department of Mathematics
External organisation(s)
Institut d'astrophysique de Paris (IAP), UMR7095 - CNRS, University of Cambridge, French Alternative Energies and Atomic Energy Commission (CEA), Laboratoire d’Études du Rayonnement et de la Matière en Astrophysique et Atmosphères (LERMA), CNRS UMR 8112, Université Paris IV - Paris-Sorbonne, Université de recherche Paris Sciences et Lettres
Astronomy & Astrophysics
No. of pages
Publication date
Peer reviewed
Austrian Fields of Science 2012
103004 Astrophysics, 103044 Cosmology, 103003 Astronomy
ASJC Scopus subject areas
Astronomy and Astrophysics, Space and Planetary Science
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