INTEGRAL Picture Of the Month
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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
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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