Which part of the interstellar medium is primarily photoionized?

Question

Quizplus · Accepted Answer

The warm interstellar medium is primarily photoionized due to its high temperature and low density, which make it easier for photons to ionize atoms and molecules. Molecular clouds and H I clouds are less likely to be photoionized, as they contain denser and cooler gas, which requires higher-energy photons to ionize. Coronary gas refers to the outer atmosphere of a star, which is not part of the interstellar medium.

Which Part of the Interstellar Medium Is Primarily Photoionized