The Optical Colors of Giant Elliptical Galaxies and their Metal-Rich
  Globular Clusters Indicate a Bottom-Heavy Initial Mass Function
  We report a systematic and statistically significant offset between the
optical (g-z or B-I) colors of seven massive elliptical galaxies and the mean
colors of their associated massive metal-rich globular clusters (GCs) in the
sense that the parent galaxies are redder by 0.12-0.20 mag at a given
galactocentric distance. However, spectroscopic indices in the blue indicate
that the luminosity-weighted ages and metallicities of such galaxies are equal
to that of their averaged massive metal-rich GCs at a given galactocentric
distance, to within small uncertainties. The observed color differences between
the red GC systems and their parent galaxies cannot be explained by the
presence of multiple stellar generations in massive metal-rich GCs, as the
impact of the latter to the populations' integrated g-z or B-I colors is found
to be negligible. However, we show that this paradox can be explained if the
stellar initial mass function (IMF) in these massive elliptical galaxies was
significantly steeper at subsolar masses than canonical IMFs derived from star
counts in the solar neighborhood, with the GC colors having become bluer due to
dynamical evolution, causing a significant flattening of the stellar MF of the
average surviving GC.
