The importance of the diffuse ionized gas for interpreting galaxy
  spectra
  Diffuse ionized gas (DIG) in galaxies can be found in early-type galaxies, in
bulges of late-type galaxies, in the interarm regions of galaxy disks, and
outside the plane of such disks. The emission-line spectrum of the DIG can be
confused with that of a weakly active galactic nucleus. It can also bias the
inference of chemical abundances and star formation rates in star forming
galaxies. We discuss how one can detect and feasibly correct for the DIG
contribution in galaxy spectra.
