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Extended X-ray emission around FR II radio galaxies: hotspots, lobes and galaxy clusters

Jimenez-Gallardo, Ana and Massaro, Francesco and Paggi, Alessandro and D'Abrusco, Raffaele and Prieto, M. Almudena and Peña-Herazo, Harold A. and Berta, Vittoria and Ricci, Federica and Stuardi, Chiara and Wilkes, Belinda J. and O'Dea, Christopher P. and Baum, Stefi A. and Kraft, Ralph P. and Froman, William R. and Jones, Christine and Mingo, Beatriz and Liuzzo, Elisabetta and Balmaverde, Barbara and Capetti, Alessandro and Missaglia, Valentina and Hardcastle, Martin J. and Baldi, Ranieri D. and Morabito, Leah K. (2021) 'Extended X-ray emission around FR II radio galaxies: hotspots, lobes and galaxy clusters.', The Astrophysical Journal Supplement, 252 (2). p. 31.


We present a systematic analysis of the extended X-ray emission discovered around 35 FR II radio galaxies from the revised Third Cambridge catalog (3CR) Chandra Snapshot Survey with redshifts between 0.05 to 0.9. We aimed to (i) test for the presence of extended X-ray emission around FR II radio galaxies, (ii) investigate if the extended emission origin is due to Inverse Compton scattering of seed photons arising from the Cosmic Microwave Background (IC/CMB) or to thermal emission from an intracluster medium (ICM) and (iii) test the impact of this extended emission on hotspot detection. We investigated the nature of the extended X-ray emission by studying its morphology and compared our results with low-frequency radio observations (i.e., ∼150 MHz), in the TGSS and LOFAR archives, as well as with optical images from Pan-STARRS. In addition, we optimized a search for X-ray counterparts of hotspots in 3CR FR II radio galaxies. We found statistically significant extended emission (>3σ confidence level) along the radio axis for ∼90%, and in the perpendicular direction for ∼60% of our sample. We confirmed the detection of 7 hotspots in the 0.5 - 3 keV. In the cases where the emission in the direction perpendicular to the radio axis is comparable to that along the radio axis, we suggest that the underlying radiative process is thermal emission from ICM. Otherwise, the dominant radiative process is likely non-thermal IC/CMB emission from lobes. We found that non-thermal IC/CMB is the dominant process in ∼70% of the sources in our sample, while thermal emission from the ICM dominates in ∼15% of them.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Publisher statement:This is the Accepted Manuscript version of an article accepted for publication in The Astrophysical Journal Supplement Series. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at
Date accepted:30 October 2020
Date deposited:13 January 2021
Date of first online publication:05 February 2021
Date first made open access:05 February 2022

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