MeerKAT radio continuum imaging of nearby star-forming spirals in the NGC 6221, NGC 3256/3263, and NGC 2434 galaxy groups

¹ Instituto Argentino de Radioastronomía, CONICET-CICPBA-UNLP, CC5 (1897) Villa Elisa, Prov. de Buenos Aires, Argentina
² Australia Telescope National Facility (ATNF), CSIRO, Space and Astronomy, P.O. Box 76 Epping, NSW 1710, Australia
³ School of Science, Western Sydney University, Locked Bag 1797, Penrith, NSW 2751, Australia
⁴ Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
⁵ Departamento de Astronomia, Instituto de Astronomia, Geofísica e Ciências Atmosféricas da USP, Cidade Universitária, 05508-090 São Paulo, SP, Brazil

^⋆ Corresponding author: jsaponara@iar-conicet.gov.ar

Received: 16 December 2024
Accepted: 14 July 2025

Abstract

Context. We present high-resolution MeerKAT 1.3 GHz radio continuum images of star-forming spirals in the nearby galaxy groups around NGC 6221, NGC 3256/3263, and NGC 2434. This sample spans the evolutionary timeline for galaxy groups, encompassing early, intermediate, and late stages, respectively. The NGC 6221 group contains an interacting galaxy pair with tidal debris, along with at least three dwarf galaxies. In contrast, the NGC 3256/3263 group represents a loose group consisting of several spiral as well as dwarf galaxies, while a massive elliptical galaxy dominates the NGC 2434 group.

Aims. We study the star formation activity in all detected galaxies as it is one of the dominant physical processes in their formation and evolution, seeking evidence of environmental impact.

Methods. We used MeerKAT radio continuum data and archival WISE infrared data to locate and measure the star formation rate in all group members. In particular, we used polycyclic aromatic hydrocarbons (PAHs) as tracers of gas heated due to star formation activity. Furthermore, we created in-band spectral index maps, providing insights into the underlying physical processes associated with the detected star-forming regions. For some galaxies, we also determined key stellar properties such as age and mass through SED fittings.

Results. We found that galaxies are distributed differently in the WISE colour-colour diagram depending on their evolutionary group stage, as was expected. Except for ESO 059-G012, the galaxies in our sample follow the radio-W3PAH correlation. A possible scenario that explains the ESO 059-G012 result is that the galaxy has already consumed the gas. We also found evidence that the interaction among the spiral galaxies NGC 3263, NGC 3256B, and NGC 3256C is causing the Vela Cloud complex and that the galaxies NGC 6221 and NGC 3256 might host a low-luminosity active galactic nucleus, as was previously proposed in the literature.