SDSS-IV MaNGA: Ionization Sources of the Extra-planar Diffuse Ionized Gas

Abstract

We investigate the ionization sources of the diffuse gas at various galactic heights in galaxies with various stellar masses, H\(\alpha\) luminosities, and specific star formation rates. For this purpose, we use the SDSS-IV MaNGA DR16 data and the theoretical models of photoionization and shock ionization from the Mexican Million Models database (3MdB). Our final sample contains 239 edge-on galaxies, which makes the results statistically significant and allows even great galactic heights to be investigated using the spectra stacking procedure. Using diagnostic diagrams, we show that for galaxies of all the types being investigated the behavior of the diffuse ionized gas is adequately described by the models of photoionization by young OB stars and hot low-mass evolved stars. However, in galaxies with high stellar masses or passive star formation shocks can also contribute to the ionization. For galaxies of all the types being investigated we find that the flux from OB stars and the ionization parameter decrease with height, while the relative contribution of hot low-mass evolved stars to the ionization increases. The greatest difference of the contributions from these sources to the gas ionization is observed between galaxies with different specific star formation rates and different stellar masses: hot low-mass evolved stars are the main source of gas ionization in galaxies with passive star formation (and with high stellar masses), whereas in galaxies with active star formation (and with lower stellar masses) OB stars are a decisive factor of the diffuse gas ionization.