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

Abstract

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 0.22 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.