A MaNGA view of isolated galaxy mergers in the star-forming main sequence

Abstract

Context. There are still many open questions in the complex process of galaxy evolution during interactions, as each stage is characterized by different periods of star formation. Aims. We aim to better understand the processes triggered in galaxies by interactions. We consider low-density environments in which in-situ interaction between the members is the main process that drives evolution. Methods. In this work we carried out an analysis of star-formation and nuclear activity at different stages during a galaxy merger identified in isolated systems (isolated galaxies, isolated pairs, and isolated triplets) using integral field spectroscopy from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) project. We classified galaxies into close pairs, pre-mergers, mergers, and post-mergers (including galaxies with post-starburst spectroscopic features) for a total sample of 137 galaxies. We constrained their star formation history from spectro-photometric SED fitting with Code Investigating GALaxy Emission (CIGALE), and used spatially resolved WHAN diagrams, with other MaNGA data products to explore whether there is any connection between their physical properties and their merging stage. Results. In general, galaxies show characteristic properties intrinsically related to each stage of the merger process. Galaxies in the merger and post-merger stages present higher star-formation activity (measured by their integrated sSFR). In the merger stage, the fraction of strong AGN spaxels is comparable to the fraction of spaxels with pure star-formation emission, with no difference between the AGN activity in close pairs and strongly interacting galaxies with the same stellar mass. Conclusions. Our results support the scenario where galaxy interactions trigger star formation and nuclear activity on galaxies. Nonetheless, the AGN has a minor role in quenching galaxies following a merger, as AGN feedback might not have had sufficient time to inhibit star formation. In addition, we found that the quenching process in post-merger galaxies with post-starburst emission happens outside-in, which is an observational proof of the effect of interactions on the quenching process. The transforming processes after a recent major galaxy interaction may happen slowly in isolated environments, where the system evolves in a common dark matter halo with no perturbation from external galaxies.