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

TL;DR

The study analyzes six void-dwelling galaxies in two triplets using integral-field unit spectroscopy from the CAVITY survey and full spectral fitting with FADO to derive spatially resolved stellar ages, metallicities, and star formation rates. Spatial reconstruction with INLA, combined with morphometric and emission-line diagnostics, reveals diverse evolutionary paths: a massive, AGN-host CAVITY52731 and five star-forming dwarfs with recent mass assembly and disturbed morphologies. Mass-assembly histories show early mass buildup in the massive system and recent, accelerated growth in the others, while the VGS31 triplet exhibits significant deviations from the void mass-metallicity relation, likely due to filamentary accretion and interactions. Overall, the results demonstrate that local interactions and substructures can drive substantial galaxy evolution even in the most underdense regions of the cosmic web, challenging the notion of voids as passive environments.

Abstract

Context. Cosmic voids are underdense regions of the Universe that provide a unique environment to study galaxy evolution in relative isolation. Galaxy triplets in voids are rare systems where local interactions may strongly influence galaxy properties. Aims. We study the stellar populations, morphologies, mass assembly histories, and dynamical properties of six galaxies belonging to two void triplets from the Calar Alto Void Integral-field Treasury surveY (CAVITY): CAVITY5273X and VGS31. Methods. We used integral-field unit spectroscopy and performed full spectral fitting with the FADO code, which models stellar and nebular emission simultaneously. Spatially resolved maps of stellar age, metallicity, and star formation rate were reconstructed using the integrated nested Laplace approximation. Morphological properties were derived using morfometryka, emission-line diagnostics were applied, and mass assembly functions were computed. Stellar masses and metallicities were compared to the mass-metallicity relation for void galaxies. Results. The two triplets show different evolutionary behaviours. CAVITY52731 is a massive quenched galaxy hosting an active galactic nucleus, while its companions and all galaxies in VGS31 are dominated by young stellar populations and recent star formation. Five galaxies experienced rapid stellar mass growth in the last 2 Gyr. Disturbed morphologies, including asymmetries and tidal features, indicate ongoing interactions. Galaxies in CAVITY5273X follow the expected void mass-metallicity relation, while VGS31 members show significant deviations. Conclusions. Our results show that local interactions can drive significant galaxy evolution even in the most underdense cosmic environments.

Figures (14)

• Figure 1: RGB images of the two triplets taken from DESI Legacy Survey. The left panel shows the VGS31 triplet, with VGS31a in the center, VGS31b to its southeast, and VGS31c to its west. The right panel shows CAVITY5273X, with CAVITY52731 to the east, CAVITY52732 to its west, and CAVITY52733 to its southwest.
• Figure 2: Comparison of the $<\log t>_L$ map for the galaxy CAVITY52731 before (left) and after (right) applying INLA.
• Figure 3: Maps of luminosities of the galaxies, with the colored lines indicating different contours of S/N. The red contour is for S/N$\geq10$, the green for 5, and the blue for 3. The S/Ns were computed in the wavelength interval of 4000 - 4060 Å.
• Figure 4: 2D maps of luminosities, SFR surface densities, mean stellar ages and metallicities, for all six galaxies in our sample.
• Figure 5: Maps of BPT classification for the galaxies. Blue is for star-forming spectra, green for composite, yellow for LINER-like emission, and red for Seyfert.