The faint X-ray source population near 3C 295
1
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
Corresponding author: V. D'Elia, delia@mporzio.astro.it
Received:
10
June
2003
Accepted:
31
March
2004
We present a statistical analysis of the Chandra
observation of the source field around the 3C 295 galaxy cluster
(
) 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
© ESO, 2004