Annu. Rev. Astron. Astrophys. 1997. 35: 101-136
Copyright © 1997 by . All rights reserved

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In this section I gather together some of the most recent results and ideas concerning the Malmquist biases of the first and second kind.

8.1. Sosies Galaxies and Partial Incompleteness

Witasse & Paturel (1997) have discussed the effect of partial incompleteness on the derivation of the Hubble constant, when Kapteyn's Equation 1 is used to make the bias (of the second kind) correction at each redshift. They inspected the completeness of their sample of sosies galaxies ["look-alike"; the distance indicator introduced by Paturel (1984)] and concluded that there is partial incompleteness starting at B = 12.0 mag, relative to the assumed 100.6m law. (Another possibility, which Witasse & Paturel (1997) mention for the first time in this kind of work, is that the apparent incompleteness may actually reflect a fractal distribution of galaxies.) Inserting the empirical selection probability into Kapteyn's formula, they could reduce the Hubble constant by about 15%, as compared with the assumption of a complete sample and obtained Ho approx 60 from 181 sosies galaxies. In comparison, Sandage (1996b) applied Paturel's look-alike idea to the sosies galaxies of M31 and M101 and derived by the Spaenhauer method Ho approx 50.