The Luminosity Function of Young Star Clusters in “the Antennae” Galaxies (NGC 4038/4039)

The WFPC2 of the HST has been used to obtain high-resolution images of NGC4038/4039 that go roughly 3 magnitudes deeper in V than previous observationsmade during Cycle 2 (-14 < M_V < -6). To first order the luminosity function(LF) is a power law, with exponent \alpha = -2.12 +/- 0.04. However, afterdecoupling the cluster and stellar LFs, which overlap in the range -9 < M_V <-6, we find an apparent bend in the young cluster LF at approximately M_V =-10.4. The LF has a power law exponent -2.6 +/- 0.2 in the brightward and -1.7+/- 0.2 in the faintward. The bend corresponds to a mass ~ 10^5 M_{\odot}, onlyslightly lower than the characteristic mass of globular clusters in the MilkyWay (~2x10^5 M_{\odot}). The star clusters of the Antennae appear slightlyresolved, with median effective radii of 4 +/- 1 pc, similar to or perhapsslightly larger than those of globular clusters in our Galaxy. However, theradial extents of some of the very young clusters (ages < 10 Myr) are muchlarger than those of old globular clusters. A combination of the UBVI colors,\Halpha morphology, and GHRS spectra enables us to age-date the clusters indifferent regions of The Antennae. We find two groups of young star clusterswith ages <~ 20Myr and ~100Myr, as well as an intermediate-age group (~500 Myr)and a handful of old globular clusters from the progenitor galaxies. Ageestimates derived from GHRS spectroscopy yield 3 +/- 1 Myr for Knot K (justsouth of the nucleus of NGC 4038) and 7 +/- 1 Myr for Knot S in the WesternLoop, in good agreement with ages derived from the UBVI colors. Effectivegas-outflow velocities from Knots S and K are estimated to be about 25-30 km/s.However, the measured widths of the interstellar absorption lines suggestdispersion velocities of ~400 km/s along the lines of sight to Knots S and K.Comment: 56 pages, 4 tables and 23 figures, texts in AAS style, to be published in A