National Astronomical Observatory of Japan

Subaru Telescope Captures Images of the “Stealth Merger” of Dwarf Galaxies

| Science

Suprime-Cam captured this image of the nearby dwarf galaxy NGC 4449 (lower left) and its companion (upper right), a dwarf galaxy that has been gravitationally pulled apart into a stellar stream. It shows individual stars composing the galaxies. R. Jay GaBany (Blackbird Observatory) produced the composite: blue hues in the center of the larger galaxy are brought about by a burst of recent star formation, while the red in its periphery and in its satellite indicates the presence of older, red-giant stars.

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.