Dynamical friction - The Hubble diagram as a cosmological test

It has been reported that the frictional accretion of smaller cluster galaxies by their larger and brighter neighbors may have drastic effects on the Hubble diagram by making the observed value of the deceleration parameter smaller than its true value. Some schematic estimates of possibly observable consequences of such dynamical evolution are presented in this paper. Effects of accretion on the luminosities and colors of central galaxies in clusters of the same type are considered, and it is suggested that changes in color due to the capture of bluer galaxies seem to provide the most promising direct test of whether significant accretion has occurred. An investigation of the degree to which accretion changes the light within a finite photometric aperture indicates that accretion either has no effect on observed luminosity or makes it decrease, that the sign of the accretion effect depends on the structures of the galaxies involved, and that the magnitude of the effect is amplified when allowance is made for the relatively recent collapse times of the clusters. Several important questions raised by the present calculations are discussed.