Diffuse Ionized Gas in the Dwarf Irregular Galaxy DDO 53

Abstract

The spectral characteristics throughout the dwarf irregular galaxy DDO 53 are studied. The results are very similar to those for other irregular galaxies: high excitation and low values of the [SII]/Halpha ratio. The most likely ionization source is photon leakage from the classical HII regions, without any other source, although the interstellar medium of the galaxy is quite perturbed. Moreover, the physical conditions throughout the galaxy do not change very much because both the photon leakage percentage and the ionization temperature are very similar. In addition, the determined metal content for two HII regions indicates that DDO 53 is a low-metallicity galaxy.Comment: 32 pages, 9 figures, 7 tables. AJ, in pres