Der CFA Galaxien Katalog

Der 1985 begonnene CfA survey von John Huchra und Margot Geller hat Mauern ähnliche Filamente (engl. "Sheets", Struktur 100 Mpc) gefunden. Neben Massenverdichtungen lieferte diese (erstmals dreidimensionale) Untersuchung auch riesige Leerräume. Die größte Struktur, die Große Mauer, ("Great Wall") hat eine Abmessung von 80´ 225´ 6 Mpc und eine Masse von 2× 1016M. Voids Daneben gibt es riesige Leerräume (engl. "Voids" genannt) vergleichbarer Größe. Der SDSS schließlich hat (2003) 200 Mpc als größte zusammenhängende Struktur gefunden.

Data from the survey of galaxies show the universe to be clumpy and uneven. The voids and "walls" that form the large-scale structure are mapped here by 11,000 galaxies. Our galaxy, the Milky Way, is at the center of the figure. The outer radius is at a distance of approximately 450 million light-years. Obscuration by the plane of the Milky Way is responsible for the missing pie-shaped sectors. North is at the top. (Original image courtesy Smithsonian Astrophysical Observatory, 1993.)

Sheets and Voids

Maps of the galaxy distribution in the nearby universe reveal large coherent structures. The extent of the largest features is limited only by the size of the survey. Voids are present in every survey large enough to contain them. Many galaxies lie in thin sheet-like structures. The largest sheet detected so far is the Great Wall. The frequent occurrence of these structures is one of several serious challenges to our current understanding of the origin and evolution of the large-scale distribution of matter in the universe.

Margaret Geller & John Huchra (Harvard-Smithsonian Center for Astrophysics, Cambridge Ma).

Geller and Huchra discovered the Great Wall on the first three sections of the CfA (Center for Astrophysics) redshift survey, which covered the region from eight to 16 hours of right ascension and from 26.5 to 42.5 degrees of (north) declination. Although the Leo and Hercules Clusters lie slightly south of this region, the authors make it clear that the same structure extends south of the survey boundaries. The wall of galaxies is skewed to our line of sight, with a mean redshift distance that varies from Z = 0.023 (~350 million light years) in Leo to Z = 0.033 (~500 million light years) in Hercules.

NAME	OTHER	CON	GAL1	MAG	Z	RA	DEC
AGC1367	Leo Cluster	LEO	NGC 3842	13.5	.022	1145	+19.8
AGC 1656	Coma Cluster	COM	NGC 4874	13.5	.023	1300	+28.0
AGC 2147	na	HER	IC 1165	13.8	.038	1602	+15.9
AGC 2151	Hercules Cluster	HER	NGC 6040	13.8	.036	1605	+17.8
AGC 2197	na	HER	NGC 6146	13.9	.030	1628	+40.9
AGC 2199	na	HER	NGC 6166	13.9	.031	1629	+39.5

THE GREAT WALL

It measures 200 million by 600 million light years in area with a thickness of only 20 million light years. At 10¹⁶ solar masses the Coma-Hercules superclusters make up the bulk this wall. In the schematic below only part of the great wall--the Coma supercluster--is visible. The Hercules cluster (composed of Abell clusters A2147, A2151 and A2152) is not pictured in the schematic but it would be up above and adjacent to the coma supercluster.

Stellar maps, published in 1986, were a great surprise to the astrophysicists. They had expected to find relative uniformity above the scale of the already-familiar galaxy clusters. Instead, the first surveys showed--and subsequent surveys have confirmed--that great clusters of galaxies are arranged in thin sheets or long filaments. The longest sheet detected, called the "Great Wall," extends hundreds of millions of light years across the maps.

North and South, Sheets and Voids
(Courtesy: Margaret J. Geller and Emilio E. Falco,
Harvard-Smithsonian Center for Astrophysics.
Credits: Geller, da Costa, Huchra, and Falco.)

Large-scale structure in the universe in the northern and southern galactic hemispheres. Each of the 9,325 points in this image represents a galaxy. The Earth lies at the center; unmapped regions to the top and bottom are inaccessible because the plane of the Milky Way obscures them. Note the large-scale patterns in both hemispheres, like the Great Wall stretching across the northern hemisphere.  

This 3D presentation of the CFA Galaxy Catalogue shows where the main concentration of galaxy clusters are in our observable universe.

H. Heintzmann

( Eintrag vom 21. 11. 2006)

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