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Abstract

Deriving the energetics of remnant and restarted active galactic nuclei (AGNs) is much more challenging than for active sources due to the complexity in accurately determining the time since the nucleus switched-off. I resolve this problem using a new approach that combines spectral ageing and dynamical models to tightly constrain the energetics and duty-cycles of dying sources. Fitting the shape of the integrated radio spectrum yields the fraction of the source age the nucleus is active; this, in addition to the flux density, source size, axis ratio, and properties of the host environment, provides a constraint on dynamical models describing the remnant radio source. This technique is used to derive the intrinsic properties of the well-studied remnant radio source B2 0924+30. This object is found to spend 50+14-12 Myr in the active phase and a further 28+6-5 Myr in the quiescent phase, have a jet kinetic power of 3.6+3.0-1.7 ×1037W⁠, and a lobe magnetic field strength below equipartition at the 8σ level. The integrated spectra of restarted and intermittent radio sources are found to yield a ‘steep-shallow’ shape when the previous outburst occurred within 100Myr⁠. The duty-cycle of B2 0924+30 is hence constrained to be δ < 0.15 by fitting the shortest time to the previous comparable outburst that does not appreciably modify the remnant spectrum. The time-averaged feedback energy imparted by AGNs into their host galaxy environments can in this manner be quantified.

Item Type:	Article
Authors/Creators:	Turner, RJ
Keywords:	galaxies: active – galaxies: jets – radio continuum: galaxies
Journal or Publication Title:	Monthly Notices of the Royal Astronomical Society
Publisher:	Blackwell Publishing Ltd
ISSN:	0035-8711
DOI / ID Number:	https://doi.org/10.1093/mnras/sty433
Copyright Information:	Copyright 2018 The Author. This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©2018 The Author. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Related URLs:	UTAS Profile: Turner, RJ
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