Where are H II regions found in the Milky Way Galaxy?

In the Milky Way Galaxy, H II regions are primarily located within the galactic plane, where they are found intermixed with young stars, stellar associations, and the youngest open clusters.1

These regions are concentrated within the spiral arms of the Galaxy, though some are also situated between the arms. They are frequently associated with areas of ongoing star formation, often appearing alongside molecular clouds on their borders. While they are distributed throughout the Galaxy, the highest concentration of H II regions is found at an intermediate distance of approximately 10,000 light-years from the galactic center. Because these regions are often obscured by dust, astronomers map their distribution across the Galaxy by detecting their characteristic thermal radio emissions.12