extragalactic H II region

extragalactic H II region

(eks-tră-gă-lak -tik) A cloud of hot ionized gas that is isolated in extragalactic space and is believed to consist of intergalactic gas that has begun to condense into stars and will probably become a dwarf irregular galaxy. Extragalactic H II regions were identified in 1970. They have no old stars, and a low metallicity indicates that some (like the compact galaxy IZw18) are less than 10⁸ years old. These are the only ‘galaxies' significantly different in age from our Galaxy.