The XMM-Newton wide-field survey in the COSMOS field. II. X-ray data and the log N-log S relations

N. Cappelluti, G. Hasinger, M. Brusa, A. Comastri, G. Zamorani, H. Böhringer, H. Brunner, F. Civano, A. Finoguenov, F. Fiore, R. Gilli, R. E. Griffiths, V. Mainieri, I. Matute, T. Miyaji, J. Silverman

Research output: Contribution to journalArticlepeer-review

104 Scopus citations


We present data analysis and X-ray source counts for the first season of XMM-Newton observations in the COSMOS field. The survey covers ∼2 deg 2 within the region of sky bounded by 09 h57 m30 s < R.A. < 10 h03 m30 s, 01°27′30″ < decl. < 02°57′ 30″ with a total net integration time of 504 ks. A maximum likelihood source detection was performed in the 0.5-2, 2-4.5, and 4.5-10 keV energy bands, and 1390 pointlike sources were detected in at least one band. Detailed Monte Carlo simulations were performed to fully test the source-detection method and to derive the sky coverage to be used in the computation of the log N-log S relations. These relations were then derived in the 0.5-2, 2-10, and 5-10 keV energy bands, down to flux limits of 7.2 × 10 -16 ergs cm -2 s -1,4.0 × 10 -15 ergs cm -2 s -1, and 9.7 × 10 -15 ergs cm -2 s -1, respectively. Thanks to the large number of sources detected in the COSMOS survey, the log N-log S curves are tightly constrained over a range of fluxes which were poorly covered by previous surveys, especially in the 2-10 and 5-10 keV bands. The 0.5-2 and 2-10 keV differential log N-log S relations were fitted with a broken power-law model which revealed a Euclidean slope at the bright end and a flatter slope (α ∼ 1.5) at faint fluxes. In the 5-10 keV energy band a single power law provides an acceptable fit to the observed source counts with a slope α ∼ 2.4. A comparison with the results of previous surveys shows good agreement in all the energy bands under investigation in the overlapping flux range. We also notice a remarkable agreement between our log N-log S relations and the most recent model of the X-ray background.

Original languageEnglish (US)
Pages (from-to)341-352
Number of pages12
JournalAstrophysical Journal, Supplement Series
Issue number1
StatePublished - 2007
Externally publishedYes


  • Cosmology: observations
  • Dark matter
  • Galaxies: evolution
  • Galaxies: formation
  • Large-scale structure of universe
  • Surveys

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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