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The M/L ratio of massive young clusters

C. M. Boily·A. Lacon·S. Deiters·D. C. Heggie
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Abstract

We point out a strong time-evolution of the mass-to-light conversion factor ηcommonly 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 M_\sun]. We find that $η$, 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 $50 M_\sun$ 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 par ameter c of $δc\approx 0.3$ compared to the same functional fit applied to the proj ected mass density.

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C. M. Boily, A. Lacon, S. Deiters, D. C. Heggie. 2005-02-25. The M/L ratio of massive young clusters. https://doi.org/10.1086/428398

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