A MaNGA view of isolated galaxy mergers in the star-forming Main Sequence

In this work we carry out an analysis of star-formation and nuclear activity in the different stages during a galaxy merger identified in isolated systems (isolated galaxies, isolated pairs, and isolated triplets) using integral field spectroscopy from the SDSS-IV/MaNGA project. We classify 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 spectrophotometric SED fitting with CIGALE, and used spatially resolved WHAN diagrams, with other MaNGA data products to explore if there is any connection of their physical properties with their merging stage. 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 AGN activity in close pairs and strongly interacting galaxies with the same stellar mass. Our results support the scenario where galaxy interactions trigger star-formation and nuclear activity on galaxies. Nonetheless, 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-mergers galaxies with post-starburst emission is happening outside-in, being an observational proof of the effect of interactions on the quenching process. The transforming processes after a recent major galaxy interaction may happen slowly on isolated environments, where the system evolves in a common dark matter halo without any perturbation of external galaxies.
Comment: Accepted for publication in A&A, 30 pages, 24 figures, and 6 tables