SCYON Abstract

Received on May 2 2005

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

AuthorsC.M. Boily1, A. Lançon1, S. Deiters2, D.C. Heggie2
Affiliation1 Observatoire astronomique de Strasbourg
2 School of Mathematics, University of Edinburgh
Accepted byAstrophysical Journal


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.