The Initial Mass Functions in the Super–Star Clusters NGC 1569A and NGC 1705‐1

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Abstract
I use recent photometric and stellar velocity dispersion measurements of the super-star clusters (SSCs) NGC 1569A and NGC 1705-1 to determine their present-day luminosity/mass ratios (LV/M). I then use the inferred LV/M, together with population synthesis models of evolving star clusters, to constrain the initial mass functions (IMFs) in these objects. I find that (LV/M)☉ = 28.9 in 1569A and (LV/M)☉ = 126 in 1705-1. It follows that in 1569A the IMF is steep with α ~ 2.5 for m-αdm IMFs that extend to 0.1 M☉. This implies that most of the stellar mass in 1569A is contained in low-mass (M☉) stars; however, in 1705-1 the IMF is either flat, with α 2, or it is truncated at a lower mass limit between 1 and 3 M☉. I compare the inferred IMFs with the mass functions (MFs) of Galactic globular clusters. It appears that 1569A has a sufficient reservoir of low-mass stars for it plausibly to evolve into an object similar to Galactic globular clusters; however, the apparent deficiency of low-mass stars in 1705-1 may make it difficult for this SSC to become a globular cluster. If low-mass stars do dominate the cluster mass in 1705-1, the large LV/M in this SSC may be evidence that the most massive stars have formed close to the cluster cores.
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