SCYON Abstract

Received on May 2 2005

The M/L ratio of young star clusters in galactic mergers

Authors	C.M. Boily¹, A. Lançon¹, S. Deiters², D.C. Heggie²
Affiliation	¹ Observatoire astronomique de Strasbourg ² School of Mathematics, University of Edinburgh
Accepted by	Astrophysical Journal
Contact	cmb@astro.u-strasbg.fr
URL	http://babbage.sissa.it/abs/astro-ph/0502530
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Abstract

We point out a strong time-evolution of the mass-to-light conversion factor eta commonly used to estimate masses of dense star clusters from observed cluster radii and stellar velocity dispersions. We use a gas-dynamical model coupled with the Cambridge stellar evolution tracks to compute line-of-sight velocity dispersions and half-light radii weighted by the luminosity. Stars at birth are assumed to follow the Salpeter mass function in the range [0.15--17 Mo]. We find that eta, and hence the estimated cluster mass, increases by factors as large as 3 over time-scales of $20$ million years. Increasing the upper mass limit to 50 Mo leads to a sharp rise of similar amplitude but in as little as 10 million years. Fitting truncated isothermal (Michie-King) models to the projected light profile leads to over-estimates of the concentration parameter c of delta c ~ 0.3 compared to the same functional fit applied to the projected mass density.