Dynamical mass estimates for two luminous young stellar clusters in Messier 83

Free access article

Issue		A&A Volume 427, Number 2, November IV 2004


Page(s)		495 - 504
Section		Galactic structure, stellar clusters and populations
DOI		http://dx.doi.org/10.1051/0004-6361:20040547

A&A 427, 495-504 (2004)
DOI: 10.1051/0004-6361:20040547

Dynamical mass estimates for two luminous young stellar clusters in Messier 83

S. S. Larsen¹ and T. Richtler²

¹ European Southern Observatory (ESO), ST-ECF, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany
e-mail: slarsen@eso.org
² Universidad de Concepción, Departamento de Física, Casilla 160, Concepción, Chile

(Received 29 March 2004 / Accepted 23 July 2004)

Abstract
Using new data from the UVES spectrograph on the ESO Very Large Telescope and archive images from the Hubble Space Telescope, we have measured projected velocity dispersions and structural parameters for two bright young star clusters in the nearby spiral galaxy NGC 5236 . One cluster is located near the nuclear starburst of NGC 5236, at a projected distance of 440 pc from the centre, while the other is located in the disk of the galaxy at a projected galactocentric distance of 2.3 kpc. We estimate virial masses for the two clusters of $(4.2\pm0.7)\times10^5~\mbox{$M_{\odot}$ }$ and $(5.2\pm0.8)\times10^5~\mbox{$M_{\odot}$ }$ and ages (from broad-band photometry) of $10^{7.1\pm0.2}$ years and $10^{8.0\pm0.1}$ years, respectively. Comparing the observed mass-to-light (M/L) ratios with simple stellar population models, we find that the data for both clusters are consistent with a Kroupa-type stellar mass function (MF). In particular, we rule out any MF with a significantly lower M/L ratio than the Kroupa MF, such as a Salpeter-like MF truncated at a mass of 1 $~\mbox{$M_{\odot}$ }$ or higher. These clusters provide a good illustration of the fact that massive, globular cluster-like objects ("super star clusters") can form at the present epoch even in the disks of seemingly normal, undisturbed spiral galaxies.

Key words: galaxies: star clusters -- galaxies: spiral -- galaxies: individual: NGC 5236

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