The Correlations between the Intrinsic Colors and Spectroscopic Metallicities of M31 Globular Clusters

TL;DR

This study explores the relationship between intrinsic colors and spectroscopic metallicities of M31 globular clusters, identifying highly correlated colors that can be used to estimate metallicity efficiently.

Contribution

It systematically analyzes correlations between multiple colors and metallicities, highlighting specific color indices with strong predictive power for metallicity estimation.

Findings

23 colors have correlation coefficients r>0.7 with metallicity.

Colors $(f-k)_0$, $(f-o)_0$, and $(h-k)_0$ have r>0.8.

$(u-K)_0$ is identified as the most metal-sensitive color.

Abstract

We present the correlations between the spectroscopic metallicities and ninety-three different intrinsic colors of M31 globular clusters, including seventy-eight BATC colors and fifteen SDSS and near infrared ugrizK colors. The BATC colors were derived from the archival images of thirteen filters (from c to p), which were taken by Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey with a 60/90 cm f/3 Schmidt telescope. The spectroscopic metallicities adopted in our work were from literature. We fitted the correlations of seventy-eight different BATC colors and the metallicities for 123 old confirmed globular clusters, and the result implies that correlation coefficients of twenty-three colors r>0.7. Especially, for the colors $(f-k)_0$, $(f-o)_0$, and $(h-k)_0$, the correlation coefficients are r>0.8. Meanwhile, we also note that the correlation coefficients (r) approach zero for $(g-h)_0$, $(k-m)_0$, $(k-n)_0$, and $(m-n)_0$, which are likely to be independent of metallicity. Similarity, we fitted the correlations of metallicity and ugrizK colors for 127 old confirmed GCs. The result indicates that all these colors are metal-sensitive (r>0.7), of which $(u-K)_0$ is the most metal-sensitive color. Our work provides an easy way to simply estimate the metallicity from colors.