Extragalactic Globular Clusters in the Near Infrared: IV. Quantifying the Age Structure using Monte-Carlo Simulations

Abstract

In previous papers of the series we used a combination of optical and near-infrared colours to derive constraints 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 $\chi$${}^2$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.

arXiv comment14 pages, 20 figures, accepted for publication in A&A

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• A Database of 2MASS Near-Infrared Colors of Magellanic Cloud Star Clusters
• Globular Clusters in NGC 4365: New K-band Imaging and a Reassessment of the Case for Intermediate-age Clusters
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• The Role of Dust in Models of Population Synthesis
• Intermediate-age Globular Clusters in Four Galaxy Merger Remnants
• Extragalactic Globular Clusters in the Near-Infrared: V. IC 4051 and NGC 3311
• Colour-colour diagrams and extragalactic globular cluster ages. Systematic uncertainties using the (V-K)-(V-I) diagram