Chemical Abundances of Globular Clusters in NGC 5128 (Centaurus A)

TL;DR

This study analyzes the chemical composition of 20 globular clusters in NGC 5128 using integrated-light spectra, revealing slight alpha-enhancement in metal-poor clusters and intra-cluster Na variations, with first measurements of several Fe-peak elements.

Contribution

It provides the first detailed abundance measurements of multiple elements in NGC 5128 GCs, highlighting differences from the Milky Way and suggesting unique chemical enrichment history.

Findings

Slight alpha-enhancement in metal-poor GCs compared to MW

Detection of intra-cluster Na abundance variations

First measurements of Cr, Mn, Ni in NGC 5128 GCs

Abstract

We perform a detailed abundance analysis on integrated-light spectra of 20 globular clusters (GCs) in the early-type galaxy NGC 5128 (Centaurus A). The GCs were observed with X-Shooter on the VLT. The cluster sample spans a metallicity range of $-1.92 < $ [Fe/H] $< -0.13$ dex. Using theoretical isochrones we compute synthetic integrated-light spectra and iterate the individual abundances until the best fit to the observations is obtained. We measured abundances of Mg, Ca, and Ti, and find a slightly higher enhancement in NGC 5128 GCs with metallicities [Fe/H] < $-$0.75 dex, of the order of $\sim$0.1 dex, than in the average values observed in the MW for GCs of the same metallicity. If this $\alpha$-enhancement in the metal-poor GCs in NGC 5128 is genuine, it could hint at a chemical enrichment history different than that experienced by the MW. We also measure Na abundances in 9 out of 20 GCs. We find evidence for intra-cluster abundance variations in 6 of these clusters where we see enhanced [Na/Fe] > $+$0.25 dex. We obtain the first abundance measurements of Cr, Mn, and Ni for a sample of the GC population in NGC 5128 and find consistency with the overall trends observed in the MW, with a slight enhancement ($<$0.1 dex) in the Fe-peak abundances measured in the NGC 5128.