Infrared High-Resolution Integrated Light Spectral Analyses of M31 Globular Clusters from APOGEE

TL;DR

This study presents infrared high-resolution spectral analysis of 25 M31 globular clusters, deriving chemical abundances that complement optical data, revealing insights into their compositions and multiple stellar populations.

Contribution

It provides the first integrated infrared K abundances for GCs and compares IR and optical abundances, enhancing understanding of extragalactic GC properties.

Findings

Infrared spectra yield new element lines and higher excitation potential data.

CNO abundances are consistent with red giant branch stars but offset from optical results.

First integrated K abundances show K tracks alpha-elements.

Abstract

Chemical abundances are presented for 25 M31 globular clusters (GCs), based on moderately high resolution (R = 22, 500) H-band integrated light spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE). Infrared spectra offer lines from new elements, of different strengths, and at higher excitation potentials compared to the optical. Integrated abundances of C, N, and O are derived from CO, CN, and OH molecular features, while Fe, Na, Mg, Al, Si, K, Ca, and Ti abundances are derived from atomic features. These abundances are compared to previous results from the optical, demonstrating the validity and value of infrared integrated light analyses. The CNO abundances are consistent with typical tip of the red giant branch stellar abundances, but are systematically offset from optical, Lick index abundances. With a few exceptions, the other abundances agree between the optical and the infrared within the 1{\sigma} uncertainties. The first integrated K abundances are also presented, and demonstrate that K tracks the alpha-elements. The combination of infrared and optical abundances allows better determinations of GC properties, and enables probes of the multiple populations in extragalactic GCs. In particular, the integrated effects of the Na/O anticorrelation can be directly examined for the first time.