Abstract
ABSTRACT Vast cavities in the intergalactic medium are excavated by radio galaxies. The cavities appear as such in X-ray images because the external medium has been swept-up, leaving a hot but low-density bubble surrounding the radio lobes. We explore here the predicted thermal X-ray emission from a large set of high-resolution three-dimensional simulations of radio galaxies driven by supersonic jets. We assume adiabatic non-relativistic hydrodynamics with injected straight and precessing jets of supersonic gas emitted from nozzles. Images of X-ray bremsstrahlung emission tend to generate oval cavities in the soft keV bands and leading arcuate structures in hard X-rays. However, the cavity shape is sensitive to the jet-ambient density contrast, varying from concave-shaped at η = 0.1 to convex for η = 0.0001 where η is the jet/ambient density ratio. We find lateral ribs in the soft X-rays in certain cases and propose this as an explanation for those detected in the vicinity of Cygnus A. In bi-lobed or X-shaped sources and in curved or deflected jets, the strongest X-ray emission is not associated with the hotspot but with the relic lobe or deflection location. This is because the hot high-pressure and dense high-compression regions do not coincide. Directed towards the observer, the cavity becomes a deep round hole surrounded by circular ripples. With short radio-mode outbursts with a duty cycle of 10 per cent, the intracluster medium simmers with low Mach number shocks widely dissipating the jet energy in between active jet episodes.
Highlights
It is well established that powerful Active Galactic Nuclei are capable of inflating bubbles in the intergalactic and intracluster media
The cavities are observed as depressions in the surface brightness of X-ray emission which encompass the radio lobes
Such cavities are found in diverse cluster environments and surround a variety of radio galaxy types (Carilli et al 1994; Giacintucci et al 2011; Pandge et al 2012; Vagshette et al 2017; Pandge et al 2019); with evidence for low Mach number bow shocks being driven into, and capable of supporting, the environment (Wilson et al 2006; Stawarz et al 2014)
Summary
It is well established that powerful Active Galactic Nuclei are capable of inflating bubbles in the intergalactic and intracluster media. The cavities are observed as depressions in the surface brightness of X-ray emission which encompass the radio lobes Such cavities are found in diverse cluster environments and surround a variety of radio galaxy types (Carilli et al 1994; Giacintucci et al 2011; Pandge et al 2012; Vagshette et al 2017; Pandge et al 2019); with evidence for low Mach number bow shocks being driven into, and capable of supporting, the environment (Wilson et al 2006; Stawarz et al 2014).
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