A&A 484, 303-309 (2008)
The candidate filament close to the 3C 295 galaxy cluster: optical and X-ray spectroscopyV. D'Elia1, F. Fiore1, S. Mathur2, and F. Cocchia1
1 INAF - Osservatorio Astronomico di Roma via Frascati 33, Monteporzio-Catone (RM) I00040, Italy
2 The Ohio State University Columbus, OH 43210, USA
Received 28 December 2007 / Accepted 29 February 2008
We present a detailed analysis of the overdensity of X-ray sources close to the 3C 295 galaxy cluster (z=0.46) to assess whether it is associated with a filament of the large-scale structure of the Universe. We obtained optical spectra of the optical counterparts of eleven sources associated with the filament, finding that one is at z=0.474. This is a type 1 AGN at 1.5 arcmin from the cluster center. We found three more sources with a redshift in the range . We extracted the stacked X-ray spectrum of 47 X-ray sources belonging to the putative filament. We found a significant narrow (at the resolution of the Chandra ACIS-I) line at keV, the energy of the iron K line at the redshift of the cluster. The detection of this line is confirmed at a confidence level of better than and its energy is constrained to be in the range 6.2-6.47 (at a 90% confidence level), excluding an identification with the 6.7 helium-like iron line from the hot cluster ICM at better than 4. We conclude that the detection of the redshifted line is a strong indication that at least several of the excess sources lie at and that AGNs are efficient tracers of the "filament" connected with the central cluster of galaxies.
Key words: X-rays: galaxies -- galaxies: clusters: individual: 3C 295 -- X-rays: diffuse background -- cosmology: large-scale structure of Universe
© ESO 2008