Diffuse Ionized Gas in Irregular Galaxies. I. GR 8 and ESO 245-G05

We have studied the spectral characteristics of the Diffuse Ionized Gas intwo irregular galaxies with low metallicities and intermediate Star FormationRates: ESO 245-G05 and Gr 8. The [OIII]/Hbeta in these galaxies is higher thanin the DIG of spiral galaxies but not as high as in other irregular galaxiespreviously studied, such as IC 10 and NGC 6822. The [NII]/Halpha and[SII]/Halpha ratios have very small values, indicating the absence of shocks asthe ionization source for this gas. This ionization can be explained in bothgalaxies with photon leakage from the HII regions as the only source. Thepercentage of photons escaped from the HII regions is small in ESO 245-G05, ofonly 35%, but varies from 35% up to 60% in Gr 8. We also investigated if thedifferences found between spiral and irregular galaxies in the [OIII]/Hbeta andthe [NII]/Halpha ratio are due to differences in the metal content betweenthese types of galaxies. Although the number of galaxies studied is not verylarge, it can be concluded that the [OIII]/Hbeta is not related with the oxygencontent, while the situation is more ambiguous for the [NII]/Halpha ratio.