RAiSE II: resolved spectral evolution in radio AGN

Abstract

The active galactic nuclei (AGN) lobe radio luminosities modelled in hydrodynamical simulations and most analytical models do not address the redistribution of the electron energies due to adiabatic expansion, synchrotron radiation and inverse-Compton scattering of CMB photons. We present a synchrotron emissivity model for resolved sources which includes a full treatment of the loss mechanisms spatially across the lobe, and apply it to a dynamical radio source model with known pressure and volume expansion rates. The bulk flow and dispersion of discrete electron packets is represented by tracer fields in hydrodynamical simulations; we show that the mixing of different aged electrons strongly effects the spectrum at each point of the radio map in high-powered FR-II sources. The inclusion of this mixing leads to a factor of a few discrepancy between the spectral age measured using impulsive injection models (e.g. JP model) and the dynamical age. The observable properties of radio sources are predicted to be strongly frequency dependent: FR-II lobes are expected to appear more elongated at higher frequencies, while jetted FR-I sources appear less extended. The emerging FR0 class of radio sources, comprising gigahertz peaked and compact steep spectrum sources, can potentially be explained by a population of low-powered FR-Is. The extended emission from such sources is shown to be undetectable for objects within a few orders of magnitude of the survey detection limit and to not contribute to the curvature of the radio SED.

20 pages, 17 figures, 1 table; accepted in MNRAS

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Cited by in corpus (10)

• RAiSE III: 3C radio AGN energetics and composition
• The duty cycle of radio galaxies revealed by LOFAR: remnant and restarted radio source populations in the Lockman Hole
• The life cycle of radio galaxies in the LOFAR Lockman Hole field
• Radio spectral properties and jet duty cycle in the restarted radio galaxy 3C388
• Investigating the spectral age problem with powerful radio galaxies
• Making Faranoff-Riley I radio sources II. The effects of jet magnetization
• Remnant Radio Galaxies Discovered in a Multi-frequency Survey
• The best of both worlds: Combining LOFAR and Apertif to derive resolved radio spectral index images
• The XXL Survey: XXXVI. Evolution and black hole feedback of high-excitation and low-excitation radio galaxies in XXL-S
• RAiSERed: radio continuum redshifts for lobed AGNs