The Metal-poor non-Sagittarius (?) Globular Cluster NGC 5053: Orbit and Mg, Al and Si Abundances

TL;DR

This study investigates the orbit and detailed chemical abundances of NGC 5053, a metal-poor globular cluster, revealing significant Al and Si variations and arguing against its association with the Sagittarius dwarf galaxy.

Contribution

It provides the first detailed near-infrared spectral analysis of NGC 5053's Mg, Al, and Si abundances using multiple methods, and clarifies its orbital history and lack of connection to Sagittarius.

Findings

NGC 5053 shows large Al variation.

Substantial Si spread observed in NGC 5053.

NGC 5053 is the lowest mass cluster with observable Si spread.

Abstract

Metal-poor globular clusters (GCs) exhibit intriguing Al-Mg anti-correlations and possible Si-Al correlations, which are important clues to decipher the multiple-population phenomenon. NGC 5053 is one of the most metal-poor GCs in the nearby Universe, and has been suggested to be associated with the Sagittarius (Sgr) dwarf galaxy, due to its similarity in location and radial velocity with one of the Sgr arms. In this work, we simulate the orbit of NGC 5053, and argue against a physical connection between Sgr and NGC 5053. On the other hand, the Mg, Al, and Si spectral lines, which are difficult to detect in the optical spectra of NGC 5053 stars, have been detected in the near-infrared APOGEE spectra. We use three different sets of stellar parameters and codes to derive the Mg, Al, and Si abundances. Regardless of which method is adopted, we see a large Al variation, and a substantial Si spread. Along with NGC 5053, metal-poor GCs exhibit different Mg, Al, and Si variations. Moreover, NGC 5053 has the lowest cluster mass among the GCs that have been identified to exhibit an observable Si spread until now.