Binary galaxies and groups of galaxies

Citation

Turner, Edwin Lewis (1976) Binary galaxies and groups of galaxies. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/C4RG-BW87. https://resolver.caltech.edu/CaltechETD:etd-09092008-135416

Abstract

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Using precisely defined identification criteria, a sample of 156 binary galaxy systems is selected from the Zwicky Catalog of Galaxies and Clusters of Galaxies. Data on their magnitudes, morphological types, radial velocities, angular separations, et cetera are presented. Accurate, new radial velocities for both components of 66 of the pairs have been measured. Substantial effort is directed towards establishing a sample of binary galaxies in which all sources of systematic bias and statistical error are well understood.

With particular attention to the removal of selection effects, extensive statistical and dynamical analyses of these data lead to several conclusions: The ratio of the mass-to-light ratio in early-type galaxies to that in late-types is 2.0[...]0.5. The distribution of spatial separations r between binary galaxies has an approximately r[...] dependence. A variety of dynamical models for binary galaxy systems are viable; however, they all require total mass-to-light ratios for spirals far larger than conventional (rotation curve) values. The most plausible interpretation of the binary galaxy data requires that spiral galaxies possess halos containing [...]10 times the disk mass and have total mass-to-light ratios [...]. It is shown that previous studies of binary galaxies have probably underestimated masses by a factor [...]10 primarily because selection biases (particularly those toward small projected separations) were ignored. There is some evidence against halos containing significant mass on scales very large compared to 100 kpc. Orbits of moderate eccentricity are more consistent with the present data than either purely circular or purely radial (probably excluded) ones.

A catalog of small groups of galaxies is generated by identifying regions of the sky in which the surface number-density of galaxies is enhanced. The determinations of both group existence and membership are accomplished by well-defined procedures and are based entirely on the distribution of galaxies in the sky. A variety of data on the groups, their component galaxies, and those galaxies not assigned to groups (i.e. field galaxies) is presented. The generally small velocity dispersions of the groups validate the group identification algorithm.

Using the available data, statistical analyses of the galaxy luminosity function in groups, the group dynamics, and the multiplicity function are described. The luminosity function is shown to be similar to that in rich clusters, well fit by a Schechter function with [...] and [...], and useful for estimating group distances. The dynamical analysis indicated that the groups are bound and relaxed, and gives typical mass-to-light ratios of [...]. A crude estimate of the group multiplicity function (distribution of total group luminosities) suggests a power-law [...] for groups brighter than [...].

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