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Issue A&A
Volume 383, Number 1, February III 2002
Page(s) 137 - 152
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20011704



A&A 383, 137-152 (2002)
DOI: 10.1051/0004-6361:20011704

Dynamical masses of young star clusters in NGC 4038/4039

S. Mengel, M. D. Lehnert, N. Thatte and R. Genzel

Max-Planck-Institut für extraterrestrische Physik Giessenbachstraße, 85748 Garching, Germany
    e-mail: mlehnert, thatte, genzel@mpe.mpg.de

(Received 11 September 2001 / Accepted 26 November 2001)

Abstract
In order to estimate the masses of the compact, young star clusters in the merging galaxy pair, NGC 4038/4039 ("the Antennae"), we have obtained medium and high resolution spectroscopy using ISAAC on VLT-UT1 and UVES on VLT-UT2 of five such clusters. The velocity dispersions were estimated using the stellar absorption features of CO at 2.29 $\mu$m and metal absorption lines at around 8500 Å, including lines of the Calcium Triplet. The size scales and light profiles were measured from HST images. From these data and assuming Virial equilibrium, we estimated the masses of five clusters. The resulting masses range from 6.5 $\times$ 10 5 to 4.7 $\times$ 10 6 $M_{\odot}$. These masses are large, a factor of a few to more than 10 larger than the typical mass of a globular cluster in the Milky Way. The mass-to-light ratios for these clusters in the V- and K-bands in comparison with stellar synthesis models suggest that to first order the IMF slopes are approximately consistent with Salpeter for a mass range of 0.1 to 100 $M_{\odot}$. However, the clusters show a significant range of possible IMF slopes or lower mass cut-offs and that these variations may correlate with the interstellar environment of the cluster. Comparison with the results of Fokker-Planck simulations of compact clusters with properties similar to the clusters studied here suggest that they are likely to be long-lived and may lose a substantial fraction of their total mass. This mass loss would make the star clusters obtain masses which are comparable to the typical mass of a globular cluster.


Key words: galaxies: star clusters -- galaxies: individual: NGC 4038/4039 -- IMF -- galaxies: clusters: general -- stars: fondamental parameters

Offprint request: S. Mengel, mengel@strw.leidenuniv.nl

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