We report the X-ray analysis of a sample of candidate high-redshift (1<z<2)
FRI sources from the sample of Chiaberge et al. (2009), 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 FRI sources from the diffuse X-ray emission by the
associated hot plasma. Among 19 FRI candidates, 6 have an X-ray unresolved
counterpart in the C-COSMOS catalog. Two additional sources are not present in
the C-COSMOS catalog 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, suggest that some of them have significant
intrinsic absorption (N_H~10^22 cm^-2), and high X-ray luminosities with
respect to local FRIs. 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 FRI candidates.
From the analysis of the stacked images of all 19 FRI 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.Comment: 11 pages, 5 figures, MNRAS accepted; added co-author affiliatio
