How to identify and weigh virialized clusters of galaxies in a complete redshift catalog

Journal Article · Sun Aug 15 04:00:00 EDT 1982 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/160183· OSTI ID:6708172

Press, W H; Davis, M

Groups or clusters of galaxies whose crossing time is small compared to the Hubble time can be ''weighed'' by the virial theorem. This paper develops a statistical procedure for identifying such subsystems within a magnitude-limited redshift catalog that is complete in some solid angle of sky. The procedure makes no a priori assumptions about the expected size of clusters, or their expected surface overdensity on the sky. The procedure is tested on simulated catalogs derived from N-body simulations; it is found to yield stable mass estimates over a large range of values of ..cap omega..*, with only a small statistical estimator bias (which is, by these simulations, calibrated out). When the procedure is applied to the Center for Astrophysics Redshift Survey data, the most striking result is a strong, approximately linear, relation between the virial mass per galaxy in a cluster and the radius of that cluster. This trend is uniform from scales as small as tens of kiloparsecs to scales as large as several megaparsecs. (A trend is not seen in the simulated catalogs.) Different values of ..cap omega..*, the clustered component mass density of the universe, are obtained corresponding to different interpretations of the Mapprox.R trend. As a lower limit, the mass actually measured in weighable clusters corresponds to ..cap omega..* = 0.07; however, only about half of the galaxies are in weighable clusters. If unweighable galaxies have the same average mass as weighable ones, then ..cap omega..*approx.0.15. If all galaxies have (or once had) the same mass as is measured by extending the trend line to the scale of the largest clusters, then a value as large as 0.6 is implied.

• Research Organization: Harvard-Smithsonian Center for Astrophysics
• OSTI ID: 6708172
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 259:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CATALOGS
DOCUMENT TYPES
GALAXY CLUSTERS
MANY-BODY PROBLEM
MASS
MATHEMATICS
PROBABILITY
RED SHIFT
STATISTICS
VIRIAL THEOREM