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Astron. Astrophys. 349, 354-362 (1999)

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The large scale structure of the soft X-ray background

III. Cosmological implications

A.M. Sotan 1, M. Freyberg 2, G. Hasinger 3, T. Miyaji 2, M. Treyer 4 and J. Trümper 2

1 Nicolaus Copernicus Astronomical Center, Bartycka 18, PL-00-716 Warsaw, Poland
2 Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching, Germany
3 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany
4 Laboratoire d'Astronomie Spatiale, Marseille, France

Received 8 April 1999 / Accepted 13 July 1999


The auto-correlation function of the X-ray background in the range of angular scales [FORMULA] is determined using the ROSAT All-Sky Survey. In the power-law approximation, our best fit estimate is [FORMULA]. At the small separation end, this is substantially above previous estimates based on ROSAT pointings. The present upward revision of the correlation amplitude results from variations in the background intensity at angular scales larger than the field of view of the X-ray telescope.

Various assumptions for the local clustering amplitude, clustering evolution rate and luminosity/density evolution of the sources producing the background are explored, and the predicted auto-correlation functions compared with the measured fluctuations. We show that the large amplitude of the background angular auto-correlation function is incompatible with the weak clustering amplitude observed for normal galaxies, while it is marginally compatible with some measurements of the AGN clustering amplitude at moderate redshifts.

Key words: cosmology: observations – cosmology: large-scale structure of Universe – X-rays: general

Send offprint requests to: A.M. Sotan

Correspondence to: soltan@camk.edu.pl

© European Southern Observatory (ESO) 1999

Online publication: September 2, 1999