IR Integrated Light Colors For Galactic GCs and An Update on Young M31 Globular Clusters

Abstract

In our recent publication, Cohen, Matthews and Cameron [3], we presented observations made with the newly commissioned Keck laser-guide star adaptive optics system of 6 objects in M31 that are alleged in multiple recent studies to be young globular clusters (GCs); all are supposed to have ages ≤5 Gyr. The resulting FWHM of the PSF core in our images was ~70 mas. The four youngest of these objects are asterisms; they are with certainty not young GCs in M31. Based on their morphology, the two oldest are GCs in M31. While the M31 GCs with ages 5–8 Gyr appear to be mostly genuine, it appears that many of the alleged very young GCs in M31 are spurious identifications. This problem will be even more severe in studies of the GC systems of more distant spiral galaxies now underway, for which imaging at the spatial resolution of our observations in M31 may not be adequate to detect sample contamination by asterisms. Here we provide a brief update for this work.