2007ApJ...664..284T

We present Gemini optical spectroscopy of 23 young star clusters in NGC 3256. We find that the cluster ages range from few to ∼150 Myr. All these clusters are relatively massive [(2-40)x10⁵ M_☉] and appear to be of roughly 1.5 Z_☉metallicity. The majority of the clusters in our sample follow the same rotation curve as the gas and hence were presumably formed in the molecular-gas disk. However, a western subsample of five clusters has velocities that deviate significantly from the gas rotation curve. These clusters may either belong to the second spiral galaxy of the merger or may have formed in tidal-tail gas falling back into the system. We discuss our observations in light of other known cluster populations in merging galaxies, and suggest that NGC 3256 is similar to Arp 220, and hence may become an ultraluminous infrared galaxy as the merger progresses and the star formation rate increases. Some of the clusters that appeared as isolated in our ground-based images are clearly resolved into multiple subcomponents in the HST ACS images. The same effect has been observed in the Antennae galaxies, showing that clusters are often not formed in isolation, but instead tend to form in larger groups or cluster complexes.