  We present surface brightness fluctuations (SBFs) in the near--IR for 191
Magellanic star clusters available in the Second Incremental and All Sky Data
releases of the Two Micron All Sky Survey (2MASS), and compare them with SBFs
of Fornax Cluster galaxies and with predictions from stellar population models.
Our goals are twofold. First, to provide an empirical calibration of near--IR
SBFs, given that existing stellar population synthesis models are particularly
discrepant in the near--IR. Second, whereas most previous SBF studies have
focused on old, metal rich populations, this is the first application to a
system with such a wide range of ages (~ 10^6 to more than 10^10 yr, i.e., 4
orders of magnitude), at the same time that the clusters have a very narrow
range of metallicities (Z ~ 0.0006 -- 0.01, ie., 1 order of magnitude only).
Since stellar population synthesis models predict a more complex sensitivity of
SBFs to metallicity and age in the near--IR than in the optical, this analysis
offers a unique way of disentangling the effects of age and metallicity. We
find a satisfactory agreement between models and data. We also confirm that
near--IR fluctuations and fluctuation colors are mostly driven by age in the
Magellanic cluster populations, and that in this respect they constitute a
sequence in which the Fornax Cluster galaxies fit adequately. Moreover,
fluctuation colors display a tendency to redden with age that can be fit by a
straight line. Finally, we use for the first time a Poissonian approach to
establish the error bars of the fluctuation measurements, instead of the
customary Monte Carlo simulations.
