Résumé
We present here experimental results obtained by time resolved x-ray correlation spectroscopy,revealing the heterogeneous nature of the dynamics down to the nanoscale in a dense dispersionof magnetic nanoparticles. The dynamical susceptibility, which quantifies the amplitude of thedynamical fluctuations, is investigated in a repulsive colloidal glass. Its value is an order ofmagnitude smaller than the ones found in gels and is length scale independent in theQ-range ofthe x-ray scattering experiment.