The angular correlation function of the ROSAT All Sky Survey Bright Source Catalogue
Abstract
We have investigated the clustering properties of a sample of 2096 sources detected in the ROSAT All Sky Survey Bright Source Catalogue. Our sample is constructed by rejecting all known stars, as well as extended X-ray sources. Areas with |b|<30 degrees and declination <-30 are also rejected due to the high or uncertain neutral hydrogen absorption. Cross-correlation of our sample with the Hamburg/RASS optical identification catalogue, suggests that the vast majority of our sources are indeed AGN. A 4.3 sigma correlation signal between 2 and 8 degrees was detected with w(<8 degs)=2.5 +- 0.6 X 10^{-2}. Assuming a 2-point correlation function of the form w(\theta)=(\theta/\theta_0)^{-0.8}, we find \theta_0=0.062 degrees. Deprojection on 3 dimensions, using the Limber's equation, yields a spatial correlation length of r_0 ~ 6.0 +- 1.6 h^{-1} Mpc. This is consistent with results derived at higher redshifts in optical surveys and suggests a comoving model for the clustering evolution.Keywords
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