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

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

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


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 10 25 and 10 30WHz -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 (S X > 7 × 10 -15ergs -1cm 2).

Original languageEnglish (US)
Pages (from-to)2753-2763
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Jul 2012
Externally publishedYes


  • Galaxies: active
  • Radiation mechanisms: non-thermal
  • Radiation mechanisms: thermal
  • Radio continuum: galaxies
  • Surveys
  • X-rays: galaxies: clusters

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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