4.3 Physical Basis So far, the motivation for the GCLF as a
standard candle is almost totally empirical rather than
theoretical. The astrophysical basis for its similarity from one
galaxy to another is a challenging problem, and is probably less
well understood than for any other standard candle currently in
use. Because globular clusters are old-halo objects that
probably predate the formation of most of the other stellar
populations in galaxies (e.g. Harris 1986, 1988b, 1991; Fall and
Rees 1988), to first order it is not surprising that they look
far more similar from place to place than their parent galaxies
do. Methods for allowing clusters to form with average masses
that are nearly independent of galaxy size or type have been put
forward by Fall and Rees (1985, 1988), Larson (1988, 1990),
Rosenblatt et al. (1988), and Ashman and Zepf (1992) under
various initial assumptions. Other constraints arising from
cluster metallicity distributions and the early chemical
evolution of the galaxies are discussed by