NGC 2403 and NGC 628 Halpha observation

Measurements of the electron density of populations of extragalactic HII regions in nearby galaxies remain limited, despite the relevance of this quantity for characterizing the...邻近星系中河外H II区（extragalactic HII regions）族群的电子密度测量数据仍较为有限，尽管该物理量对于表征（……）具有重要意义。