Another evolutionary correction to the luminosity of giant galaxies

Isolated giant galaxies may accrete their dwarf companions, and those in clusters their neighbors, by the process of dynamical friction. The computed effect is of the opposite sign and similar magnitude to the luminosity change caused by normal stellar evolution. The process, which would cause an increase in ΔM12 (the magnitude difference between first and second brightest cluster galaxies) with time, may be visible in the tabulated data of Sandage and Hardy (1973). Cosmological investigations could compensate for the postulated effect, if fainter galaxies were used as well as first brightest cluster galaxies in the magnitude-redshift test