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Astron. Astrophys. 320, 705-716 (1997)

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The large scale structure of the soft X-ray background

II. Galaxies

Andrzej M. Sol tan 1, 2, Günther Hasinger 3, Roland Egger 2, Steve Snowden 2, 4, 5 and Joachim Trümper 2

1 Copernicus Astronomical Center, Bartycka 18, PL-00716 Warsaw, Poland
2 Max Planck Institut für extraterrestrische Physik, D-85748 Garching, Germany
3 Astrophysikalisches Institut, D-14482 Potsdam, Germany
4 NASA/GSFC, LHEA Code 666, Greenbelt, MD 20771, USA
5 Universities Space Research Association

Received 11 June 1996 / Accepted 12 September 1996


The intensity of the soft X-ray background is correlated with the distribution of galaxies. To demonstrate this, magnitude limited galaxy samples extracted from bright galaxy catalogues and the Lick counts are utilized. Significant correlations are detected for all magnitude ranges, i.e. [FORMULA]. The local X-ray volume emissivity between 0.5 and 2.0 keV correlated spatially with the galaxy population falls in the range ([FORMULA] - [FORMULA]) erg s-1 Mpc-3 ([FORMULA] km s-1 Mpc-1). Without evolution, this could account for 30 % - 40 % of the total X-ray background, an amount consistent with analogous estimates based on X-ray experiments at higher energies. The comparison of correlation amplitudes of the X-ray background with galaxies at different apparent magnitudes indicates that roughly half of the emission correlated with galaxies can be produced in extended regions substantially larger than optical extent of a typical galaxy. A crude estimate for the average size of these sources is [FORMULA] Mpc. This extended signal in various correlation functions is possibly produced by X-ray emission of hot gas in clusters or groups of galaxies, although a contribution from individual galaxies cannot be ruled out.

Key words: cosmology: observations, diffuse radiation – X-rays: galaxies – X-rays: general

Send offprint requests to: A. M. Sol tan, Copernicus Center address


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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998