Journal Article

Extended X-ray emission from non-thermal sources in the COSMOS field: a detailed study of a large radio galaxy at <i>z</i>= 1.168

Vibor Jelić, Vernesa Smolčić, Alexis Finoguenov, Masayuki Tanaka, Francesca Civano, Eva Schinnerer, Nico Cappelluti and Anton Koekemoer

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 423, issue 3, pages 2753-2763
Published in print July 2012 | ISSN: 0035-8711
Published online June 2012 | e-ISSN: 1365-2966 | DOI:
Extended X-ray emission from non-thermal sources in the COSMOS field: a detailed study of a large radio galaxy at z= 1.168

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X-ray selected galaxy group samples are usually generated by searching for extended X-ray sources that reflect the thermal radiation of the intragroup medium. On the other hand, large radio galaxies that regularly occupy galaxy groups also emit in the X-ray window, and their contribution to X-ray selected group samples is still not well understood. In order to investigate their relative importance, we have carried out a systematic search for non-thermal extended X-ray sources in the Cosmic Evolution Survey (COSMOS) field. Based on the morphological coincidence of X-ray and radio extensions, out of 60 radio galaxies, and ∼300 extended X-ray sources, we find only one candidate where the observed extended X-ray emission arises from non-thermal processes related to radio galaxies. We present a detailed analysis of this source, and its environment. Our results yield that external inverse Compton emission of the lobes is the dominant process that generates the observed X-ray emission of our extended X-ray candidate, with a minor contribution from the gas of the galaxy group hosting the radio galaxy. Finally, we show that finding only one potential candidate in the COSMOS field (in a redshift range 0 < z < 6 and with radio luminosity between 1025 and 1030 W Hz−1) is consistent with expected X-ray counts arising from synchrotron lobes. This implies that these sources are not a prominent source of contamination in samples of X-ray selected clusters/groups, but they could potentially dominate the z > 1 cluster counts at the bright end (SX > 7 × 10−15 erg s−1 cm2).

Keywords: radiation mechanisms: non-thermal; radiation mechanisms: thermal; surveys; galaxies: active; radio continuum: galaxies; X-rays: galaxies: clusters

Journal Article.  7925 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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