Mon. Not. R. Astron. Soc., 436, 2852-2863 (2013/December-2)
Constraining globular cluster formation through studies of young massive clusters - I. A lack of ongoing star formation within young clusters.
BASTIAN N., CABRERA-ZIRI I., DAVIES B. and LARSEN S.S.
Abstract (from CDS):
We present a survey of 130 Galactic and extragalactic young massive clusters (YMCs, 104 < M/M☉ < 108, 10 < t/Myr < 1000) with integrated spectroscopy or resolved stellar photometry (40 presented here and 90 from the literature) and use the sample to search for evidence of ongoing star formation within the clusters. Such episodes of secondary (or continuous) star formation are predicted by models that attempt to explain the observed chemical and photometric anomalies observed in globular clusters as being due to the formation of a second stellar population within an existing first population. Additionally, studies that have claimed extended star formation histories within Large/Small Magellanic Cloud intermediate-age clusters (1-2Gyr), also imply that many YMCs should show ongoing star formation. Based on visual inspection of the spectra and/or the colour-magnitude diagrams, we do not find evidence for ongoing star formation within any of the clusters, and use this to place constraints on the above models. Models of continuous star formation within clusters, lasting for hundreds of Myr, are ruled out at high significance (unless stellar initial mass function variations are invoked). Models for the (nearly instantaneous) formation of a secondary population within an existing first generation are not favoured, but are not formally discounted due to the finite sampling of age/mass-space.