The S4G perspective on circumstellar dust extinction of AGB stars in
  M100
  We examine the effect of circumstellar dust extinction on the near-IR
contribution of asymptotic giant branch (AGB) stars in intermediate-age
clusters throughout the disk of M100. For our sample of 17 AGB-dominated
clusters we extract optical-to-mid-IR SEDs and find that NIR brightness is
coupled to the mid-IR dust emission in such a way that a significant reduction
of AGB light, of up to 1 mag in K-band, follows from extinction by the dust
shell formed during this stage. Since the dust optical depth varies with AGB
chemistry (C-rich or O-rich), our results suggest that the contribution of AGB
stars to the flux from their host clusters will be closely linked to the
metallicity and the progenitor mass of the AGB star, to which dust chemistry
and mass-loss rate are sensitive. Our sample of clusters--each the analogue of
a ~1 Gyr old post-starburst galaxy--has implications within the context of mass
and age estimation via SED modelling at high z: we find that the average ~0.5
mag extinction estimated here may be sufficient to reduce the AGB contribution
in (rest-frame) K-band from ~70%, as predicted in the latest generation of
synthesis models, to ~35%. Our technique for selecting AGB-dominated clusters
in nearby galaxies promises to be effective for discriminating the
uncertainties associated with AGB stars in intermediate-age populations that
plague age and mass estimation in high-z galaxies.
