correlation function


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correlation function

A measure of the clustering on extragalactic scales obtained from redshift surveys. It is the probability for a galaxy to have another neighbor within a given distance of separation, in excess of the probability expected from a uniform random distribution of galaxies, expressed as a function of that distance. Galaxy positions are highly correlated, with the probability decreasing approximately as the inverse square of the galaxy separation. The correlation length for clusters of galaxies is the radius within which the chance of finding another galaxy is double the chance expected from a uniform random distribution of galaxies. Galaxies cluster into groups and clusters on a length-scale of around 30 megaparsecs, whereas superclusters have correlation lengths nearer 130 megaparsecs.
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