Volume 419, Number 3, June I 2004
|Page(s)||863 - 876|
|Published online||07 May 2004|
Extragalactic globular clusters in the near infrared
IV. Quantifying the age structure using Monte-Carlo simulations
European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany e-mail: [mhempel,mkissler]@eso.org
Corresponding author: M. Hempel, firstname.lastname@example.org
Accepted: 23 February 2004
In previous papers of the series, we used a combination of optical and near-infrared colours to derive constrains on the relative age structure in globular cluster systems. Here, we present the details, strength and limitations of our method based on Monte-Carlo simulations of colour–colour diagrams and cumulative age distributions. The simulations are based on general informations about the globular cluster systems (e.g. colour-ranges, the number ratios between sub-populations) and the different single stellar population models (SSP's) which are used to derive relative ages. For both the modeled systems and the observed globular cluster systems we derive the cumulative age distribution and introduce two parameters to define it, the so-called 50% age and the result of the reduced χ2 test of the comparison between models and observations. The method was tested successfully on several systems and allowed to reveal significant intermediate age populations in two of them.
Key words: galaxies: photometry / galaxies: star clusters
© ESO, 2004
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