Numerical modelling of the lobes of radio galaxies in cluster environments – III. Powerful relativistic and non-relativistic jets

Abstract

We present results from two suites of simulations of powerful radio galaxies in poor cluster environments, with a focus on the formation and evolution of the radio lobes. One suite of models uses relativistic hydrodynamics and the other relativistic magnetohydrodynamics; both are set up to cover a range of jet powers and velocities. The dynamics of the lobes are shown to be in good agreement with analytical models and with previous numerical models, confirming in the relativistic regime that the observed widths of radio lobes may be explained if they are driven by very light jets. The ratio of energy stored in the radio lobes to that put into the intracluster gas is seen to be the same regardless of jet power, jet velocity or simulation type, suggesting that we have a robust understanding of the work done on the ambient gas by this type of radio source. For the most powerful jets we at times find magnetic field amplification by up to a factor of two in energy, but mostly the magnetic energy in the lobes is consistent with the magnetic energy injected. We confirm our earlier result that for jets with a toroidally injected magnetic field, the field in the lobes is predominantly aligned with the jet axis once the lobes are well developed, and that this leads to radio flux anisotropies of up to a factor of about two for mature sources. We reproduce the relationship between 151-MHz luminosity and jet power determined analytically in the literature.

AGN jet feedback on a moving mesh: cocoon inflation, gas flows and turbulence

“…This rises to ∼ 40 per cent if we include gas with fJ > 0.001 and is consistent with other simulations of jet lobe inflation that find, depending on jet parameters, ∼ 40-60 per cent of the energy is retained in the jet lobes (e.g. Hardcastle & Krause 2013;English et al 2016;Weinberger et al 2017). In Fig.…”

“…English et al 2016;Weinberger et al 2017). However, we find that it is both instructive and important to understand the hydrodynamic evolution of the jets prior to adding further physics, while also presenting a model that can be readily implemented into hydrodynamic cosmological simulations.…”

“…Other work, however, has specifically included the inflation and evolution of the jet cavities themselves and their subsequent impact on cluster haloes (e.g. Churazov et al 2001;Reynolds et al 2001;Basson & Alexander 2003;Omma et al 2004;Gaibler et al 2009;Dubois et al 2011;Hardcastle & Krause 2013English et al 2016;Weinberger et al 2017), focusing mostly on isolated halo models. Further, simulations including self-consistent feedback, in which the jet properties are linked to estimated SMBH accretion rates (e.g.…”

The Cocoon Shocks of Cygnus A: Pressures and Their Implications for the Jets and Lobes

“…This is minimized in a single explosive outburst, which is clearly ruled out for the lobes and cavities of Cyg A. If the energy were deposited at a constant rate instead, approximately twice as much energy would be required to obtain the same shock strength (Hardcastle & Krause 2013;English et al 2016). In the absence of a more detailed model, we assume that the outburst power has been roughly constant, so that the total energy estimate needs to be boosted by a further factor of ≃ 2 over the value from the explosive hydrodynamic model.…”

The morphological classification of distant radio galaxies explored with three-dimensional simulations

“…Radio images have also been presented more rigorously by Tingay et al (2008) and Hardcastle & Krause (2014) where three dimensional simulations with a magnetic field were analysed. These simulations explored the dependence on the ambient density profile and demon-strated that the total radio flux will essentially level off (English et al 2016). This is due to the emission being dominated by high pressure warm regions of constant volume through which jet material is advected at a constant rate.…”