Press Release

Research by an international team of scientists has revealed a "stealth merger" of dwarf galaxies, where an in-falling satellite galaxy is nearly undetectable by conventional means yet has a substantial influence on its host galaxy. The Subaru Telescope captured high-resolution images of individual stars in a dense stream of stars in the outer regions of a nearby dwarf galaxy (NGC 4449); these outlying stars are the remains of an even smaller companion galaxy in the process of merging with its host.

An international research group led by Masamune Oguri, an assistant professor at IPMU, has made a precise measurement of dark matter distribution in galaxy clusters by analyzing both 'strong' and 'weak' gravitational lensing phenomena observed in images of 28 galaxy clusters taken at the Subaru 8.2-meter telescope. The result settles a long-standing controversy about the central concentration of dark matter distribution.