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FR II radio galaxies at low frequencies – II. Spectral ageing and source dynamics

Harwood, Jeremy J.; Hardcastle, Martin J.; Morganti, Raffaella; Croston, Judith H.; Brüggen, Marcus; Brunetti, Gianfranco; Röttgering, Huub J. A.; Shulevski, Aleksander and White, Glenn J. (2017). FR II radio galaxies at low frequencies – II. Spectral ageing and source dynamics. Monthly Notices of the Royal Astronomical Society, 469(1) pp. 639–655.

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DOI (Digital Object Identifier) Link: https://doi.org/10.1093/mnras/stx820
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Abstract

In this paper, the second in a series investigating FR II radio galaxies at low frequencies, we use LOFAR and VLA observations between 117 and 456 MHz in addition to archival data to determine the dynamics and energetics of two radio galaxies, 3C452 and 3C223, through fitting of spectral ageing models on small spatial scales. We provide improved measurements for the physical extent of the two sources, including a previously unknown low surface brightness extension to the northern lobe of 3C223, and revised energetics based on these values. We find spectral ages of $77.05^{+9.22}_{-8.74}$ and $84.96^{+15.02}_{-13.83}$ Myr for 3C452 and 3C223 respectively suggesting a characteristic advance speed for the lobes of around one per cent the speed of light. For 3C452 we show that, even for a magnetic field strength not assumed to be in equipartition, a disparity of factor of approximately 2 exists between the spectral age and that determined from a dynamical standpoint. We confirm that the injection index of both sources (as derived from the lobe emission) remains steeper than classically assumed values even when considered on well resolved scales at low frequencies, but find an unexpected sharp discontinuity between the spectrum of the hotspots and the surrounding lobe emission. We suggest that this discrepancy is due to the absorption of hotspot emission and/or non-homogeneous and additional acceleration mechanisms and, as such, hotspots should not be used in the determination of the underlying initial electron energy distribution.

Item Type: Journal Item
Copyright Holders: 2017 The Authors
ISSN: 1365-2966
Keywords: acceleration of particles; radiation mechanisms: non-thermal; galaxies: active; galaxies: jets; radio continuum: galaxies; X-rays: galaxies
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Interdisciplinary Research Centre: Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
Item ID: 49245
Depositing User: G. J. White
Date Deposited: 07 Jun 2017 15:05
Last Modified: 24 Jul 2017 09:54
URI: http://oro.open.ac.uk/id/eprint/49245
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