Galaxy interactions in void substructures: Morphology and stellar populations of two triplets from CAVITY

¹ Departamento de Física Teórica y del Cosmos, Universidad de Granada (UGR) Avenida de la Fuente Nueva s/n C.P. 18071 Granada, Spain
² Instituto de Física, Universidade Federal do Rio Grande do Sul (UFRGS) Av. Bento Goncalves 9500 Porto Alegre RS, Brazil
³ Instituto Universitario Carlos I de Física Teórica y Computacional, Universidad de Granada 18071 Granada, Spain
⁴ Instituto de Matemática Estatística e Física, Universidade Federal do Rio Grande (IMEF – FURG) Av Itália s/n Rio Grande RS, Brazil
⁵ Centre for Astrophysics Research, University of Hertfordshire College Lane Hatfield AL10 9AB, UK

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 7 July 2025
Accepted: 28 November 2025

Abstract

Context. Cosmic voids, vast, underdense regions of the Universe, serve as unique laboratories for studying galaxy evolution in isolation. Within these voids, galaxy triplets, rare systems of three close galaxies, provide crucial insights into how local interactions shape stellar populations and morphology in the absence of strong environmental perturbations.

Aims. We investigate the spatially resolved stellar populations, morphologies, mass assembly histories, and dynamical properties of six galaxies from the Calar Alto Void Integral-field Treasury surveY (CAVITY). These galaxies reside in two void triplet systems, CAVITY5273X and VGS31.

Methods. We employed integral field unit (IFU) spectroscopy combined with full spectral fitting using the FADO code, which simultaneously models stellar and nebular emission. We derived maps of stellar ages, metallicities, and star formation rates, applying the integrated nested Laplace approximation (inla) for spatial reconstruction. Morphological analysis was conducted using morfometryka, and emission-line diagnostics were employed to assess ionization mechanisms. Mass-assembly functions were computed to reveal the stellar mass evolution of the galaxies. We also compared stellar metallicities and stellar masses to the mass-metallicity relation (MMR) for void galaxies.

Results. The two triplets exhibit distinct evolutionary pathways. CAVITY52731 is a massive, quenched active galactic nucleus host, while young stellar populations and recent star formation dominate its companions and the three members of VGS31. The galaxies in both triplets show diverse mass assembly functions, with some building most of their stellar mass early and others exhibiting significant late-time star formation. All five star-forming galaxies present rapid mass growth in the last 2 Gyr (by a factor of ∼1.4 − 4). Morphological analysis in the g band of the DESI Legacy Survey and in the literature reveals widespread disturbances, including tidal tails, arcs, and asymmetries, indicating active dynamical evolution. Although galaxies in CAVITY5273X follow the expected MMR for voids, those in VGS31 deviate significantly, likely due to filamentary accretion and recent interactions.

Conclusions. Our results demonstrate that even in the most underdense regions of the cosmic web, galaxies can experience dynamic evolution driven by local interactions and minor mergers. Void triplets challenge the traditional view of voids as passive environments and highlight the importance of small-scale structures in shaping galaxy properties.