The structure of nearby groups of galaxies: quantitative membership probabilities.
Abstract
An impersonal threedimensional method of classifying groups of galaxies is presented. A general statistical model for the distribution of galaxies is assumed. This leads to a probability density function (pdf) which is fitted to the observed distribution using the principle of maximum likelihood. The fitted pdf yields the main properties of the groups as well as numerical membership probabilities and a measure of the statistical significance of the groups. For illustrational purposes only, a Gaussian distribution on the sky and in projected velocities is assumed. The method is applied to the sample of all known galaxies having redshifts less than 500 km/s, from which an unbiased sample is drawn. The five nearby groups, Sculptor, M81, NGC 5128, CVn I, and M101, are detected and described. The membership assignment differs slightly from traditional analyses.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 April 1979
 Bibcode:
 1979A&A....74..235M
 Keywords:

 Galactic Clusters;
 Galactic Structure;
 Maximum Likelihood Estimates;
 Probability Density Functions;
 Astronomical Catalogs;
 Classifications;
 Normal Density Functions;
 Quantitative Analysis;
 Statistical Distributions;
 Astronomy;
 Groups of Galaxies:Membership;
 Groups of Galaxies:Statistics