Optical and near infra-red colours as a discriminant of the age and
  metallicity of stellar populations
  We present a comprehensive analysis of the ability of current stellar
population models to reproduce the optical (ugriz) and near infra-red (JHK)
colours of a small sample of well-studied nearby elliptical and S0 galaxies. We
find broad agreement between the ages and metallicities derived using different
population models, although different models show different systematic
deviations from the measured broad-band fluxes. Although it is possible to
constrain Simple Stellar Population models to a well defined area in
age-metallicity space, there is a clear degeneracy between these parameters
even with such a full range of precise colours. The precision to which age and
metallicity can be determined independently, using only broad band photometry
with realistic errors, is Delta{[Fe/H]} ~ 0.18 and Delta{log(Age)} ~ 0.25. To
constrain the populations and therefore the star formation history further it
will be necessary to combine broad-band optical-IR photometry with either
spectral line indices, or else photometry at wavelengths outside of this range.
