TY - JOUR
T1 - FR II radio galaxies at low frequencies I
T2 - morphology, magnetic field strength and energetics
AU - Harwood, Jeremy J.
AU - Croston, Judith H.
AU - Intema, Huib T.
AU - Stewart, Adam J.
AU - Ineson, Judith
AU - Hardcastle, Martin
AU - Godfrey, Leith
AU - Best, Philip
AU - Brienza, Marisa
AU - Heesen, Volker
AU - Mahony, Elizabeth K.
AU - Morganti, Raffaella
AU - Murgia, Matteo
AU - Orrú, Emanuela
AU - Röttgering, Huub
AU - Shulevski, Aleksandar
AU - Wise, Michael W.
N1 - This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2016 The Authors.
Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
PY - 2016/6/1
Y1 - 2016/6/1
N2 - Due to their steep spectra, low-frequency observations of FR II radio galaxies potentially provide key insights in to the morphology, energetics and spectrum of these powerful radio sources. However, limitations imposed by the previous generation of radio interferometers at metre wavelengths has meant that this region of parameter space remains largely unexplored. In this paper, the first in a series examining FR IIs at low frequencies, we use LOFAR observations between 50 and 160 MHz, along with complementary archival radio and X-ray data, to explore the properties of two FR II sources, 3C452 and 3C223. We find that the morphology of 3C452 is that of a standard FR II rather than of a double-double radio galaxy as had previously been suggested, with no remnant emission being observed beyond the active lobes. We find that the low-frequency integrated spectra of both sources are much steeper than expected based on traditional assumptions and, using synchrotron/inverse-Compton model fitting, show that the total energy content of the lobes is greater than previous estimates by a factor of around 5 for 3C452 and 2 for 3C223. We go on to discuss possible causes of these steeper than expected spectra and provide revised estimates of the internal pressures and magnetic field strengths for the intrinsically steep case. We find that the ratio between the equipartition magnetic field strengths and those derived through synchrotron/inverse-Compton model fitting remains consistent with previous findings and show that the observed departure from equipartition may in some cases provide a solution to the spectral versus dynamical age disparity.
AB - Due to their steep spectra, low-frequency observations of FR II radio galaxies potentially provide key insights in to the morphology, energetics and spectrum of these powerful radio sources. However, limitations imposed by the previous generation of radio interferometers at metre wavelengths has meant that this region of parameter space remains largely unexplored. In this paper, the first in a series examining FR IIs at low frequencies, we use LOFAR observations between 50 and 160 MHz, along with complementary archival radio and X-ray data, to explore the properties of two FR II sources, 3C452 and 3C223. We find that the morphology of 3C452 is that of a standard FR II rather than of a double-double radio galaxy as had previously been suggested, with no remnant emission being observed beyond the active lobes. We find that the low-frequency integrated spectra of both sources are much steeper than expected based on traditional assumptions and, using synchrotron/inverse-Compton model fitting, show that the total energy content of the lobes is greater than previous estimates by a factor of around 5 for 3C452 and 2 for 3C223. We go on to discuss possible causes of these steeper than expected spectra and provide revised estimates of the internal pressures and magnetic field strengths for the intrinsically steep case. We find that the ratio between the equipartition magnetic field strengths and those derived through synchrotron/inverse-Compton model fitting remains consistent with previous findings and show that the observed departure from equipartition may in some cases provide a solution to the spectral versus dynamical age disparity.
KW - acceleration of partciles
KW - radiation mechanisms: non-thermal
KW - galaxies: active
KW - galaxies: jets
KW - radio continuum: galaxies
KW - X-rays: galaxies
U2 - 10.1093/mnras/stw638
DO - 10.1093/mnras/stw638
M3 - Article
SN - 0035-8711
VL - 458
SP - 4443
EP - 4455
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
ER -