Fourth Galaxy

Galaxy 4 was the location of the planet Drahva. (TV: Galaxy 4)

The Semestran Interlude were natives of Galaxy 4. (AUDIO: Voyage to the New World)

Behind the scenes
It is not stated whether Galaxy 4 was one of the Ten Galaxies ruled by the Dominators (TV: The Dominators) or the same galaxy as the Fourth Galaxy, which allied itself with the Daleks. (TV: The Daleks' Master Plan)