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20 August 2010

A relationship between AGN jet power and radio power

Authors: Cavagnolo, McNamara, Nulsen, Carilli, Jones & Birzan
Link to article: arxiv:1006.5699

The powerlaw scaling relation between jet power (derived from X-ray cavities) and radio power by Birzan et al. (2008) for clusters is extended to giant ellipticals. A powerlaw scaling is found over 6 orders of magnitude in jet power and it is found consistent with the relations of Willott et al. (1999) if the energy in non-radiating particles is about 100 times larger than in synchrotron-emitting electrons (ranging between tens to thousands). The scatter for the relation still is considerable - more than 1 dex wide for 68% confidence. The authors furthermore discuss the behaviour of poorly confined sources, which are not included in the fits.


  1. The really nice thing about this cavity method is that it's independent of any poorly understood radio evolution. What I would find very interesting is how the "evolutionary phase" of the source changes these fits. An active FR II source would start fading slowly and become more diffuse once the jet is switched off, in particular the hotspots, but also the lobes. This would move the source towards the left in Fig. 1. It will cause a strong scatter, which is also heavily dependent on radio and X-ray sensitivity (once they are too far left, sources simply become undetectable). Would it then not make sense to try fitting the most active sources only (the ones on lower-right edge)? In B08, the active sources (non-ghosts) are all there and show a much different slope. What FR type are the sources in the study?

  2. Looking at Fig.1, the error bars are much smaller than the scatter in P_cav. Does this mean that basically all the scatter is intrinsic? The scatter actually looks quite large, by eye more than a dex (though the authors say it is 0.7 dex). I am not sure if the error bars include the possible uncertainties in modelling P_cav, i.e. volume, t_cavity etc..

  3. @Volker: The FR source type in this study is a mix of I/II. We did not discriminate on morphology as our primary concern was including all sources for which we have reliably measured P_cav and P_radio. Your comment is spot-on: the radio source age and jet composition will have an impact on the scatter in the P_jet-P_rad relation. This was considered in detail in B08, but not in our study as the new gE sources have sparse radio data to execute a similar analysis. However, a student at UWaterloo has been working on this, and the project is likely to produce a paper. So keep an eye on our publications as this topic should be addressed in the near future.

    @Sadegh: "Does this mean that basically all the scatter is intrinsic?" I won't say 'all,' but the intrinsic scatter dominates (see my comment above about age/composition). We did not calculate the intrinsic scatter (the parameter space is large), only the scatter about the best-fit relation.