The M / L * Ratio of Young Star Clusters in Galactic Mergers

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Abstract
We point out a strong time evolution of the mass-to-light conversion factor h commonly used to estimate masses of dense star clusters from observed cluster radii and stellar velocity dispersions. We use a gasdynamical 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 initial mass function in the range of 0.15-17 M,. We find that h, and hence the estimated cluster mass, increases by factors as large as 3 over timescales of 20 million years. Increasing the upper mass limit to leads to a sharp rise of similar 50 M, amplitude but in as little as 10 million years. Fitting truncated isothermal (Michie-King) models to the projected light profile leads to overestimates of the concentration parameter c of compared to the same functional dc ≈ 0.3 fit applied to the projected mass density. Subject headings: galaxies: star clusters — methods: numerical — stars: luminosity function, mass function Online material: color figure
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