SDSS-IV MaNGA: Ionization sources of diffuse extra-planar galactic medium

Abstract: We explore sources of ionization of diffuse gas at different altitudes in galaxies in dependence of their stellar mass, \Ha\ luminosity, and specific star formation rate. We use the MaNGA data from SDSS-IV data release DR16 together with photoionization and shock ionization models provided by the 3MdB database. Our sample comprises 239 edge-on galaxies, which makes our results statistically valuable. We reach very high galactic altitudes with the help of spectra stacking. We demonstrate that models of the gas photoionization in a combination of young OB-stars and hot low-mass evolved stars (HOLMES) describes the gas ionization state in the galaxies of all types on diagnostic diagrams. Nevertheless, the shock waves may contribute to the gas ionization in massive galaxies with passive star formation. We observe a general trend of decreasing the fraction of the ionizing flux from OB-stars and the ionization parameter with the altitude, while the role of the ionization by the HOLMES increases. The biggest difference in the contribution from these types of ionizing sources correlates with the specific star formation rate and with stellar masses of galaxies. The HOLMES are the principal gas ionization sources in massive galaxies with passive star formation, while OB-stars dominate the gas ionization in low-mass galaxies with active star formation.