Estimating the Luminosity Function of M51-Type Galaxies

A new sample of M51-type galaxies consisting of 46 systems is used to estimate the B-band luminosity function. The luminosity function for the primary components of the systems can be described by a Schechter function with the parameters _* = (1.4±0.3)×10^-5 Mpc^-3, = -1.3^+0.4 _-0.3, and M _* = -20.3^+0.2 _-0.1. The values of the latter two parameters are comparable to those for isolated galactic pairs. The resulting estimate of the average density of M51-type galaxies is (4±3)% of the average density of isolated pairs for luminosities in the range -22^m.0<M<-16^m.0