Chemical composition and ages of four globular clusters in M31 from the analysis of their integrated-light spectra

TL;DR

This study analyzes the chemical composition and ages of four globular clusters in M31 using integrated-light spectra, revealing higher alpha-element abundances and suggesting complex star formation history involving gas inflow and supernova activity.

Contribution

It provides new detailed chemical abundance measurements of four M31 globular clusters and compares them with Galactic counterparts, highlighting differences in metallicity and star formation history.

Findings

Higher Mg, Ca, and C abundances than literature estimates.

No complete analogues in the Galaxy for the studied clusters.

Indications of complex star formation with gas inflow and supernova activity.

Abstract

We compare the results on the chemical composition of four globular clusters (GCs) in M31 (Bol 6, Bol 20, Bol 45, and Bol 50) (Maricheva M. 2021). Study of integrated spectra of four globular clusters in M31. Astrophys. Bull. 76:389-404. doi: https://doi.org/10.1134/S199034132104009X) to the available literature data on integrated-light spectroscopy of GCs with similar ages and chemical abundances in our Galaxy and M31 and on the chemical abundances of stars in two galaxies. The clusters and their literature analogues are of moderate metallicity -1.1<[Fe/H]<-0.75 dex and old (10 Gyr). Mg, Ca, and C abundances of four GCs are higher than literature estimates for the GCs in M31 with [Fe/H]~-1 dex obtained using high-resolution integrated-light spectroscopy methods. Using literature data, we did not find complete analogues for the studied clusters in our Galaxy and M31 in terms of age, helium mass fraction (Y), and chemical composition. The alpha-element abundances in four clusters are about 0.2 dex higher than the average for stars in the Galactic field at [Fe/H]~-1 dex. We suggest that these and M. Maricheva's (Maricheva M. 2021) findings about lower metallicities of the studied objects than the average metallicity of red giants in the M31 halo and about the abundances of alpha-process elements in them corresponding to the average value for stars in the M31 inner halo likely indicate that the star formation process in the vicinity of M31 at the time of our sample cluster formation was complex with the inflow of fresh gas from the intergalactic medium and violent star forming events associated with SNe II bursts.