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where could be found hii emission nebula regions Sometimes several hundred light-years across, are often associated with giant molecular clouds what does this region mean? It is a region of interstellar atomic hydrogen that is ionized how did it get the name? The term H II is pronounced "H two" by astronomers. "H" is the chemical symbol for hydrogen, and "II" is the Roman numeral for 2. what are it's features? It vary greatly in their physical properties, their size is also known as the Stromgren radius and essentially depends on the intensity of the source of ionising photons and the density of the region, their densities range from over a million particles per cm³ in the ultra-compact H II regions to only a few particles per cm³ in the largest and most extended regions how is it distributed? The reason H II regions rarely appear in elliptical galaxies is that ellipticals are believed to form through galaxy mergers. In galaxy clusters, such mergers are frequent.
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H II region [SEP] Numbers and distribution
H II regions are found only in spiral galaxies like the Milky Way and irregular galaxies. They are not seen in elliptical galaxies. In irregular galaxies, they may be dispersed throughout the galaxy, but in spirals they are most abundant within the spiral arms. A large spiral galaxy may contain thousands of H II regions. The reason H II regions rarely appear in elliptical galaxies is that ellipticals are believed to form through galaxy mergers. In galaxy clusters, such mergers are frequent. When galaxies collide, individual stars almost never collide, but the GMCs and H II regions in the colliding galaxies are severely agitated.