INTEGRAL Picture Of the Month
April 2007

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INTEGRAL probes large scale structure of the local Universe

From optical and infrared galaxy surveys we know that the distribution of visible mass in the local Universe is far from uniform. Over the characteristic distance of 100 Mpc the number density of galaxies in galaxy superclusters and voids may vary by an order of magnitude. Some huge mass agglomerations (M>1015 Msun) in the local Universe are the nearby Virgo cluster, more distant Great Attractor and Perseus-Pisces supercluster.

It is now widely accepted that practically every galaxy in the local Universe has a supermassive black hole and some of these black holes are AGNs with different luminosities. Therefore, it is quite natural to assume that the volume number density of X-ray emitting AGNs is proportional to the volume number density of galaxies.

The recent hard X-ray all sky survey performed with the INTEGRAL observatory (Krivonos et al., 2007; astro-ph/0701836) made it possible to obtain a census of AGNs covering the whole sky. The effective depth of the survey allows one to effectively probe the nearby Universe up to distances of 100 Mpc. The image above shows the AGN volume density in different directions of the sky. The value in each pixel of the map represents the number density of sources in a solid angle confined by cone with a half-opening angle of 45 degrees.

The image demonstrates the strong anisotropy in the distribution of nearby AGNs. The large-scale feature in the north-east direction is consistent with the projected position of the Virgo cluster and Great Attractor while the southern-west structure is consistent with the Perseus-Pisces supercluster. The green contour represents another indicator of mass agglomerations for comparison: the surface density of IRAS PCSz galaxies at distances <70 Mpc.

(Credit: R.Krivonos and INTEGRAL team, IKI,Moscow/MPA, Garching)

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