Investigating the electron density stratification in the low-metallicity dwarf galaxy IC10

The study of the electron density distribution helps to infer the structure of the interstellar medium (ISM) and quantify the ionizing radiation escaping the ISM. While it is not possible to study in detail the electron density distribution of the high-z galaxies, the ionizing sources of the early universe, the "chemically-young' environment that characterizes those galaxies can be found in the nearby low-metallicity dwarf galaxies. These galaxies are characterized by a prominent [OIII] 88 mm emission, which indicates a presence of an extended ionized gas. To investigate the suggested porosity of the ISM of the low-metallicity galaxies, we studied the electron density distribution of the nearby dwarf galaxy IC10, which has a metallicity of 12+log(O/H) = 8.26.

The electron density can be estimated using the line ratios of the same ion but different transitions. In this study, we used several infrared diagnostics, which are less affected by temperature fluctuations than other electron density tracers. There are several infrared density tracers, each of them covering a different and complementary range of electron densities. Together, these line ratios cover a density range from 1 cm^-3 up to 10⁵ cm^-3. Combining data from SOFIA/FIFI-LS, Herschel/PACS, and Spitzer/IRS, we estimated the electron density for various star-forming regions of IC10 with several density diagnostics. Our study shows that each line ratio traces a different gas component of the ionized gas, and the denser clouds are found in a more energetic environment.