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

I use recent photometric and stellar velocity dispersion measurements of thesuper-star-clusters (SSCs) NGC 1569A and NGC 1705-1 to determine theirpresent-day luminosity/mass (L_V/M) ratios. I then use the inferred L_V/Mratios, together with population synthesis models of evolving star-clusters, toconstrain the initial-mass-functions (IMFs) in these objects. I find that (L_V/M)_solar=28.9 in 1569A, and (L_V/M)_solar=126 in 1705-1. Itfollows that in 1569A the IMF is steep with alpha~2.5 for m**(-alpha)dm IMFswhich extend to 0.1 M_sun. This implies that most of the stellar mass in 1569Ais contained in low-mass (< 1 M_sun) stars. However, in 1705-1 the IMF iseither flat, with alpha<2$, or it is truncated at a lower mass-limit between 1and 3 M_sun. I compare the inferred IMFs with the mass functions (MFs) of Galacticglobular clusters. It appears that 1569A has a sufficient reservoir of low-massstars for it to plausibly evolve into an object similar to Galactic globularclusters. However, the apparent deficiency of low-mass stars in 1705-1 may makeit difficult for this SSC to become a globular cluster. If low-mass stars dodominate the cluster mass in 1705-1, the large L_V/M ratio in this SSC may beevidence that the most massive stars have formed close to the cluster cores.Comment: ApJ, in press. 19 Pages, Latex; amiel@astro.berkeley.ed