Nonlinear Color-Metallicity Relations of Globular Clusters. VIII.
  Reproducing Color Distributions of Individual Globular Cluster Systems in the
  Virgo and Fornax Galaxy Clusters
  The color distributions of globular clusters (GCs) in individual early-type
galaxies show great diversity in their morphology. Based on the conventional
"linear" relationship between the colors and metallicities of GCs, the GC
metallicity distributions inferred from colors and in turn their formation
histories, should be as diverse as they appear. In contrast, here we show that
an alternative scenario rooted in the "nonlinear" nature of the
metallicity-to-color transformation points to a simpler and more coherent
picture. Our simulations of the color distributions for $\sim$80 GC systems in
early-type galaxies from the ACS Virgo and Fornax Cluster Surveys suggest that
the majority ($\sim$70$\%$) of early-type galaxies have old ($\sim$13 Gyr) and
coeval GCs. Their variety in the color distribution morphology stems mainly
from one parameter, the mean metallicity of a GC system. Furthermore, the color
distributions of the remaining ($\sim$30$\%$) GC systems are also explained by
the nonlinearity scenario, assuming additional young or intermediate-age GCs
with a number fraction of $\sim$20$\%$ of underlying old GCs. Our results
reinforce the nonlinearity explanation for the GC color bimodality and provide
a new perspective on early-type galaxy formation in the cluster environment,
such as the Virgo and Fornax galaxy clusters.
