SDSS-FIRST-selected interacting galaxies: Optical long-slit spectroscopy study using MODS at the LBT

Journal article, 2023

Context. In the hierarchical model of evolution of the Universe, galaxy mergers play an important role, especially at high redshifts. Interactions among galaxies appear to be associated with incidences of radio-loudness in quasars and it is of interest to study the galaxies that are in the process of interacting with each other, where there is at least one nucleus that is active in the radio regime. Aims. In order to understand the various processes taking place within colliding galaxies, it is important to study the radio and optical properties of these sources, as well as any possible correlations that might exist. Methods. To this end, we present optical long-slit spectroscopy data for ten pairs of interacting galaxies selected from SDSS-FIRST at redshifts of ~0.05, observed using the multi-object double spectrographs at the Large Binocular Telescope. Results. We used line fluxes extracted from the spectra of the nuclear regions of galaxies to plot optical diagnostic diagrams and estimate the masses of the central supermassive black holes, as well as their Eddington ratios. Additionally, we used previously published Effelsberg radio telescope data at 4.85 GHz and FIRST survey data at 1.4 GHz to estimate radio spectral slopes and the radio-loudness parameters for all of the radio-detected sources. We also used WISE data to plot a mid-infrared colour-colour diagram. Conclusions. We see that while the sample of galaxies covers all of the classes on the optical diagnostic diagrams, the sources that are radio-detected fall in the composite or transition region of the diagram. Additionally, we notice a trend of the highest radio-loudness parameter in a pair of interacting galaxies being associated with the galaxy that hosts the more massive central supermassive black hole. We do not see any obvious trends with respect to the radio spectral slope, radio-loudness parameter, and Eddington ratio. With respect to the mid-infrared data of the galaxies detected by WISE, we see that most of them have some type of contribution from star formation, however, two of them seem to have a significant contribution from an AGN as well.