  We present simulation results addressing the dynamics of a colloidal system
with attractive interactions close to gelation. Our interaction also has a
soft, long range repulsive barrier which suppresses liquid-gas type phase
separation at long wavelengths. The new results presented here lend further
weight to an intriguing picture emerging from our previous simulation work on
the same system. Whereas mode coupling theory (MCT) offers quantitatively good
results for the decay of correlators, closer inspection of the dynamics reveals
a bimodal population of fast and slow particles with a very long exchange
timescale. This population split represents a particular form of dynamic
heterogeneity (DH). Although DH is usually associated with activated hopping
and/or facilitated dynamics in glasses, the form of DH observed here may be
more collective in character and associated with static (i.e., structural)
heterogeneity.
