The Formation and Evolution of Young Globular Clusters in NGC 3256

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Abstract
We present images of the recent galaxy merger NGC 3256 obtained with the WFPC2 of the Hubble Space Telescope in B and I filters. We show that there is a large population of more than 1,000 compact, bright blue objects in this galaxy within the 7 kpc x 7 kpc region studied. These objects have sizes, colors and luminosities like those expected for young Galactic globular clusters with ages ranging from a few to several hundred Myr. On this basis, we identify at least some fraction of the compact, bright blue objects in NGC 3256 as young globular clusters. The young cluster system comprises 15-20% of the luminosity of the galaxy in B and half that in I within the region studied, indicating a high efficiency of cluster formation on a galaxy-wide scale. We find that the intrinsic color distribution is broad, and there is no significant trend of color with magnitude. The combination of the broad range of observed colors and the lack of a trend of redder colors at fainter magnitudes can not be fit solely by a broad age distribution and/or differential reddening, although the latter is clearly present. The observations can be accounted for by either the preferential depletion/destruction of lower mass clusters as they age, or a very young age (<= 20 Myr) for the cluster population, comparable to or less than the dynamical time of the region in which the clusters are observed. We also find that the luminosity function of the young cluster system can be roughly fit by a power-law with an exponent of -1.8, with tentative evidence that it flattens at faint magnitudes. The clusters are compact in size, with typical estimated half-light radii of 5-10 parsecs, but there is no obvious cut-off for larger radii, and only a shallow trend of size with luminosity. (slightly abridged).

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