Testing three derivative methods of stellar population synthesis models

TL;DR

This study compares three publicly available stellar population synthesis methods to determine their accuracy in estimating ages and metallicities of Galactic globular clusters, revealing strengths and limitations in each technique.

Contribution

It provides a systematic comparison of colour, Lick-index, and spectrum-fitting methods using Bruzual & Charlot models, assessing their reliability against CMD and stellar spectra data.

Findings

Lick-index method is suitable for -1.5<=[Fe/H]<=-0.7 metallicity range.

Spectrum-fitting method works well for -2.3<=[Fe/H]<=-1.5.

All three methods tend to underestimate ages by about 2 Gyr.

Abstract

The number of methods used to study the properties of galaxies is increased, and testing these methods is very important. Galactic globular clusters (GCs) provide an excellent medium for such test, because they can be considered as simple stellar populations. We present ages and metallicities for 40 Galactic GCs as determined from three publicly available techniques, including colour, Lick-index and spectrum-fitting methods, based on Bruzual & Charlot evolutionary population synthesis (EPS) models. By comparing with the ages obtained from colour-magnitude diagrams (CMDs) and metallicities obtained from spectra of stars, we are able to estimate the ability of 'these methods on determination of GCs parameters, which is absolutely necessary. As a result, we find that: (i) for the metallicity, our derived metallicities agree with those derived from the spectra of stars, Lick-index method is suitable to study metallicity for the stellar population systems in the range of -1.5=<[Fe/H]=<-0.7 and spectrum- fitting method is suitable to study metallicity for the stellar population systems in the range of -2.3=<[Fe/H]=<-1.5; (ii) for the age, these three methods have difficulties in age determination, our derived ages are smaller (about 2.0 Gyr, on average) than the results of CMDs for all these three methods. We use Vazdekis and Maraston models to analyze whether our results are dependent on EPS models, and find that the tendency of these two models is the same as that of Bruzual & Charlot models. Our results are independent of the EPS models. In addition, our test is based on the old GCs and our conclusions may hold for old stellar population systems. The whole abstract can be found in my PDF version.