Metallicity relations in LMC and SMC from the slope of Red Giant Branch stars in globular clusters

TL;DR

This study uses near-IR photometry of 23 LMC and SMC globular clusters to analyze the RGB slope as a function of age and metallicity, revealing that RGB slope correlates with metallicity but not significantly with age.

Contribution

It provides new calibrations of RGB slope relations with age and metallicity for a diverse sample of globular clusters in the LMC and SMC.

Findings

RGB slope correlates with metallicity across clusters.

No significant age dependence of RGB slope found.

Younger clusters have a negative RGB slope, older clusters have a positive slope.

Abstract

Red giants are an excellent tool for probing the history of star formation and subsequent metallicity evolution in the galaxies. The well-defined red giant branch (RGB) stars of the globular clusters can be used to determine their slopes and to calibrate the RGB slope parameters, age, and metallicity relations. We obtained deep near-IR $JHK$ stellar photometry of 23 LMC/SMC globular clusters. The cluster sample covers a wide range in metallicities $(-1.76<{\rm [Fe/H]}<-0.32)$ and ages $(0.6\,{\rm Gyr}<t<14\,{\rm Gyr})$. The slope of the RGBs of each cluster was calculated and used to derive the relations between slope-age-metallicity. We have found that the RGB slope do not shows any statistically significant age dependence. The young and old clusters are found to be distributed differently in RGB slope-metallicity space, and the younger populations show a slightly less steep RGB slope dependence than the whole cluster sample. The population of the younger clusters shows a negative slope, whereas the older clusters show a positive slope.