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The X-ray properties of high-z Fanaroff–Riley type I candidates in the COSMOS field

Authors

  • E. Tundo,

    Corresponding author
    1. INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, I-34143 Trieste, Italy
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  • P. Tozzi,

    Corresponding author
    1. INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, I-34143 Trieste, Italy
    2. INFN – Istituto Nazionale di Fisica Nucleare, Sezione di Trieste I-34127, Italy
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  • M. Chiaberge

    Corresponding author
    1. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
    2. INAF-IRA, Via P. Gobetti 101, Bologna I-40129, Italy
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E-mail: tundo@oats.inaf.it (ET); tozzi@oats.inaf.it (PT); marcoc@stsci.edu (MC)

ABSTRACT

We report the X-ray analysis of a sample of candidate high-redshift (1 < z < 2) Fanaroff–Riley type I (FR I) sources from the sample of Chiaberge et al., observed in the Chandra COSMOS field (C-COSMOS). Our main goals are to study their nuclear properties by means of unresolved X-ray emission, and to constrain the presence of clusters surrounding the FR I sources from the diffuse X-ray emission by the associated hot plasma. Among 19 FR I candidates, six have an X-ray-unresolved counterpart in the C-COSMOS catalogue. Two additional sources are not present in the C-COSMOS catalogue but are clearly detected in the Chandra images. X-ray spectral analysis, when possible, or hardness ratio of the stacked emission from X-ray-detected sources, suggests that some of them have significant intrinsic absorption (NH≳ 1022 cm−2), and high X-ray luminosities with respect to local FR Is. From the stacking analysis of the 11 non-detected sources, however, we find evidence for unresolved soft X-ray emission and no detected hard emission, suggesting an unabsorbed spectrum. Therefore, the X-ray properties vary significantly from source to source among these FR I candidates. From the analysis of the stacked images of all 19 FR I candidates we can rule out the presence of virialized haloes with temperatures larger than 2–3 keV; however, the upper limit on the average extended emission is still consistent with the presence of 1–2 keV hot gas.

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