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