A representative survey of the dynamics and energetics of FRII radio galaxies

Judith Ineson, Judith H. Croston, Martin Hardcastle, Beatriz Mingo

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We report the first large, systematic study of the dynamics and energetics of a representative sample of FRII radio galaxies with well-characterized group/cluster environments. We used X-ray inverse-Compton and radio synchrotron measurements to determine the internal radio-lobe conditions, and these were compared with external pressures acting on the lobes, determined from measurements of the thermal X-ray emission of the group/cluster. Consistent with previous work, we found that FRII radio lobes are typically electron-dominated by a small factor relative to equipartition, and are over-pressured relative to the external medium in their outer parts. These results suggest that there is typically no energetically significant proton population in the lobes of FRII radio galaxies (unlike for FRIs), and so for this population, inverse-Compton modelling provides an accurate way of measuring total energy content and estimating jet power. We estimated the distribution of Mach numbers for the population of expanding radio lobes, finding that at least half of the radio galaxies are currently driving strong shocks into their group/cluster environments. Finally, we determined a jet power--radio luminosity relation for FRII radio galaxies based on our estimates of lobe internal energy and Mach number. The slope and normalisation of this relation are consistent with theoretical expectations, given the departure from equipartition and environmental distribution for our sample.
Original languageEnglish
Pages (from-to)1586-1607
Number of pages22
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date22 Jan 2017
Publication statusPublished - 1 May 2017


  • galaxies: active
  • gaalxies: clusters: intracluster medium
  • galaxies: jets


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