AAS 199th meeting, Washington, DC, January 2002
Session 138. AGN - Surveys
Display, Thursday, January 10, 2002, 9:20am-4:00pm, Exhibit Hall

## [138.19] The Spatial Correlation Function of X-ray Selected AGN

C.R. Mullis (ESO), J.P. Henry (IfA), I.M. Gioia (IRA-CNR), H. Boehringer, U.G. Briel, W. Voges (MPE), J.P. Huchra (CfA)

In the {\em ROSAT\/} All-Sky Survey, an 80.7 deg2 region around the north ecliptic pole (NEP) constitutes the deepest observation of the X-ray sky ever achieved with such a large, contiguous solid angle. Here 445 unique sources are detected with fluxes measured at greater than 4\sigma significance. We have identified the physical nature of 443 (99.6%) of the {\em ROSAT\/} NEP X-ray sources through a comprehensive program of imaging and spectroscopy. Active galactic nuclei (AGN) are the dominant constituents comprising nearly half (49.0%) of the sample.

The {\em ROSAT\/} NEP sample of 217 AGN is particularly well suited for a clustering analysis. The AGN are drawn from a contiguous, wide-angle region in the sky sampled to a relatively deep X-ray flux limit (~3 \times 10-14 erg s-1 cm-2, 0.5 -- 2.0 keV). The AGN sample is essentially complete and we have spectroscopically measured redshifts for the entire sample. Furthermore, the survey selection function is well determined and only a function of X-ray flux. Finally, our low-redshift determination of the AGN correlation function complements the high-redshift results obtained for optically selected AGN.

We have measured the degree of clustering in the {\em ROSAT\/} NEP AGN data by calculating the two-point spatial correlation function. The significance of the clustering signal (>3.5\sigma) suggests these results are likely the best constraints reported so far for X-ray selected AGN. Our results indicate that X-ray luminous AGN are spatially clustered in a manner similar to that of normal galaxies and optically selected AGN (i.e., r0 ~6\,h-1 Mpc). Furthermore, the NEP determination is a measure of the local behavior (z~.4) of AGN clustering and thus argues that the correlation strength has not evolved strongly since z ~1.4, the redshift typically probed by optical AGN correlation studies.