Searching for globular clusters in the inner halo of the Circinus galaxy

Abstract

ABSTRACT In this study, we search for globular clusters (GCs) in the inner halo of the Circinus galaxy using a combination of observational data. Our data set includes observations from the VISTA Variables in the Vía Láctea Extended Survey (VVVX), optical data from Gaia Release 3 (DR3), and observations from the Dark Energy Camera (DECam). These multiple data sources provide a comprehensive basis for our analysis. Our search was concentrated within a 50 kpc radius from the centre, leading to the identification of 93 sources that met our established criteria. To ensure the reliability of our findings, we conducted multiple examinations for sample contamination. These examinations incorporated tests based on Gaia Astrometric Excess Noise (AEN), the blue photometer/red photometer (BRexcess) excess factor, as well as comparisons with stellar population models. This analysis confidently classified 41 sources as genuine GCs, as they successfully passed both the 3σ Gaia AEN and BRexcess tests. We used the ISHAPE program to determine the structural parameters (half-light radii) of the GC candidates, with a peak effective radius of 4 ± 0.5 pc. The catalogue mainly consists of bright GCs. Relationships between colour, size, and distance were found in the GC candidates, alongside confirmation of bi-modality in colour distributions.