The soft X-ray cluster-AGN spatial cross-correlation function in the ROSAT-NEP survey

N. Cappelluti, H. Böhringer, P. Schuecker, E. Pierpaoli, C. R. Mullis, I. M. Gioia, J. P. Henry

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


Context. X-ray surveys facilitate investigations of the environment of AGNs. Deep Chandra observations have revealed that the AGN source surface density rises near clusters of galaxies. The natural extension of this finding is the measurement of spatial clustering of AGNs around clusters and the investigation of relative biasing between active galactic nuclei and galaxies near clusters. Aims. We aim to measure the correlation length of AGNs around clusters and the average clustering properties of a complete sample of AGNs in a dense environment. Methods. We present the first measurement of the soft X-ray cluster-AGN cross-correlation function in redshift space using the data of the ROSAT-NEP survey. The survey covers 9×9 deg2 around the North Ecliptic Pole where 442 X-ray sources were detected and almost completely spectroscopically identified. Results. We detected a >3σ significant clustering signal on scales s ≤ 50 h70-1 Mpc. We performed a classical maximum-likelihood power-law fit to the data and obtained a correlation length s0 = 8.70.3+1.2 h 70-1 Mpc and a slope γ = 1.70.7 +0.2, (1σ errors). Conclusions. This is strong evidence that AGNs are good tracers of the large scale structure of the Universe. Our data were compared to the results obtained by cross-correlating X-ray clusters and galaxies. We observe, with a large uncertainty, a similar behaviour of AGN clustering around clusters similar to the clustering of galaxies around clusters.

Original languageEnglish (US)
Pages (from-to)35-40
Number of pages6
JournalAstronomy and Astrophysics
Issue number1
StatePublished - Apr 2007
Externally publishedYes


  • Cosmology: dark matter
  • Cosmology: large-scale structure of universe
  • Galaxies: active
  • Galaxies: clusters: general
  • X-rays: galaxies: clusters

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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