Ionized Gas in irregular galaxies : I - Gr 8 and ESO 245 - G 05

We have studied the spectral characteristics of the Diffuse Ionized Gas in two irregular galaxies with low metallicities and intermediate Star Formation Rates: ESO 245-G05 and Gr 8. The [OIII]/Hβ in these galaxies is higher than in the DIG of spiral galaxies but not as high as in other irregular galaxies previously studied, such as IC 10 and NGC 6822. The [NII]/Hα and [SII]/Hα ratios have very small values, indicating the absence of shocks as the ion-ization source for this gas. This ionization can be explained in both galaxies with photon leakage from the H ii regions as the only source. The percentage of photons escaped from the H ii regions is small in ESO 245-G05, of only 35%, but varies from 35% up to 60% in Gr 8. We also investigated if the differences found between spiral and irregular galaxies in the [OIII]/Hβ and the [NII]/Hα ratio are due to differences in the metal content between these types of galaxies. Although the number of galaxies studied is not very large, it can be concluded that the [OIII]/Hβ is not related with the oxygen content, while the situation is more ambiguous for the [NII]/Hα ratio. keywords galaxies: irregular – galaxies: – inter-stellar medium: H ii regions: general – galaxies: individual: Gr 8 – galaxies: individual: ESO 245-G05