VEGAS-SSS: An intra-group component in the globular cluster system of the NGC 5018 galaxy group using VST data

¹ INAF-Osservatorio Astronomico d’Abruzzo, Via Maggini, 64100 Teramo, Italy
² University of Rome Tor Vergata, Via della Ricerca Scientifica 1, I-00133 Rome, Italy
³ Gran Sasso Science Institute (GSSI), Viale Francesco Crispi 7, 67100 L’Aquila, Italy
⁴ INFN Laboratori Nazionale del Gran Sasso, Via Giovanni Acitelli 22, 67100 L’Aquila, Italy
⁵ INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, I-80131 Naples, Italy
⁶ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany

^⋆ Corresponding author; pratik.lonare@inaf.it

Received: 11 September 2024
Accepted: 21 December 2024

Abstract

Context. Globular clusters (GCs) offer a valuable tool as a fossil tracer of the formation and evolution of galaxies and their environment. Studying the properties of these stellar systems provides crucial insights into the past formation and interaction events of the galaxies, especially in galaxy group and cluster environments.

Aims. We study the properties of globular cluster (GC) candidates in an area of 1.25 × 1.03 sq. degrees centred on the NGC 5018 galaxy group. We use the deep, wide field, and multi-passband (ugr) observations obtained with the VLT Survey Telescope (VST) as part of the VST Elliptical GAlaxy Survey (VEGAS). With a focus on studying small stellar systems (SSS) associated with bright galaxies, this paper constitutes an extension of the VEGAS-SSS series investigating GCs in the NGC 5018 group.

Methods. We derived photometric catalogues of compact and extended sources in the area and identified GC candidates using a set of photometric and morphometric selection parameters. A GC candidate catalogue has been provided and inspected using a statistical background decontamination technique, benefiting from the wide area coverage of the data.

Results. The 2D distribution map of GC candidates reveals an over-density of sources on the brightest member of the NGC 5018 group. No significant GC over-densities are observed in the other bright galaxies of the group. We report the discovery of a candidate local nucleated low-surface-brightness (LSB) dwarf galaxy that may possibly be engaged in a tidal interaction with NGC 5018. The 2D map also reveals an intra-group GC population aligning with the bright galaxies and along the intra-group light (IGL) component of the group. The radial density profile of GC candidates in NGC 5018 follows the galaxy surface brightness profile. The (g − r) colour profile of GC candidates centred on this galaxy shows no evidence of the well-known colour bimodality; however, it is observed instead in the intra-group population. From the GC luminosity function (GCLF) analysis, we find a low specific frequency, S​_N = 0.59 ± 0.27 for NGC 5018, which is consistent with previous results based on less deep optical data over a smaller area. This relatively low S​_N value, coupled with the lack of colour bimodality, might be due to a combination of observational data limitations as well as the post-merger status of NGC 5018, which might host a population of relatively young GCs. For the intra-group GC population, we obtained a lower limit of S​_N, gr ∼ 0.6. Using the GCLF as a distance indicator, we estimate that NGC 5018 is located 38.0 ± 7.9 Mpc away, which is consistent with values reported in the literature.