Three Ultraluminous X-ray Sources Hosted by Globular Clusters in NGC 1316

TL;DR

This study reports the discovery of three new ultraluminous X-ray sources in globular clusters of NGC 1316, expanding the known population and analyzing their spectral and optical properties to understand their formation.

Contribution

It presents the identification of three new GC ULXs in NGC 1316 and compares their properties to other GCs, providing insights into their formation mechanisms.

Findings

The three new ULXs have spectral behaviour consistent with known GC ULXs.

Clusters hosting ULXs differ in properties from typical GCs.

No strong correlation between metal-rich clusters and ULX hosting.

Abstract

We have identified three ultraluminous X-ray sources (ULXs) hosted by globular clusters (GCs) within NGC 1316's stellar system. These discoveries bring the total number of known ULXs in GCs up to 20. We find that the X-ray spectra of the three new sources do not deviate from the established pattern of spectral behaviour of the other known GC ULXs. The consistency of the X-ray spectral behaviour for these sources points to multiple paths of formation and evolution mechanisms for these rare and unique sources. Using the now larger sample of GC ULXs, we compare the optical properties of the entire known population of GC ULXs to other GCs across five galaxies and find that the properties of clusters that host ULXs are quite different from the typical clusters. Lastly, any trend of GC ULXs being preferentially hosted by metal-rich clusters is not strongly significant in this sample.