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A&A 422, 11-21 (2004)
DOI: 10.1051/0004-6361:20040149
The faint X-ray source population near 3C 295
V. D'Elia1, F. Fiore1, M. Elvis2, M. Cappi3, S. Mathur4, P. Mazzotta5, E. Falco6 and F. Cocchia11 INAF - Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio-Catone (RM), Italy
2 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
3 IASF - CNR, Bologna, Italy
4 The Ohio State University, Columbus, OH 43210, USA
5 University of Durham, South Road, Durham DH1 3LE, UK
6 Smithsonian Institution Whipple Observatory, AZ 85645, USA
(Received 10 June 2003 / Accepted 31 March 2004)
Abstract
We present a statistical analysis of the Chandra
observation of the source field around the 3C 295 galaxy cluster
(
z=0.46) to search for clustering of X-ray sources.
We applied three different methods of analysis, all suggesting a
strong clustering in the field on scales of a few arcmin. In
particular 1) the
computed separately for the four ACIS-I chips reveals that there is a significant (
in the
0.5-2 keV,
in the 2-10 keV and
in
the 0.5-10 keV band) excess of sources to the North-North East and a
void to the South of the central cluster; 2) the two point,
two-dimensional Kolmogorov-Smirnov (KS) test, shows the probability
that the sources are uniformly distributed is only a few percent; 3) a
strong spatial correlation emerges from the study of the angular
correlation function of the field: the angular correlation function
(ACF) shows a clear signal on scales of
arcmin,
correlation angle in the 0.5-7 keV band
,
90% confidence limit
(assuming a power law ACF with
slope
). This correlation angle is
2 times higher than that
of a sample of
8 ACIS-I field at the
confidence level.
The above scales translate to 0.2
2
Mpc at the cluster redshift, higher than the typical cluster core
radius, and more similar to the size of a "filament" of the large
scale structure.
Key words: X-rays: galaxies -- galaxies: clusters: individual: 3C 295 -- X-rays: diffuse background -- cosmology: large-scale structure of Universe
Offprint request: V. D'Elia, delia@mporzio.astro.it
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