A radio galaxy (RG) is a galaxy emitting a lot of radio electromagnetic radiation (i.e., radio-loud; The phrase radio-quiet is sometimes used to distinguish radio-loud objects from others in discussion). They have been found with as much as 1039 watts of power in the radio spectrum. Distant radio galaxies are useful as they are relatively easily observed.
Some emit most of their radio emission from regions away from the center, which are termed lobes.
The spectral energy distribution and polarization often suggests synchrotron radiation as the source.
An SFRG (star forming radio galaxy) has rest-frame ultraviolet spectral features consistent with a starburst galaxy.
The term GRG (giant radio galaxy), naturally is used to indicate a large one, 2 Mpc being a commonly-used threshold.
A radio galaxy is generally an active galaxy. Quasars and blazars with a similar radio spectrum are called radio-loud quasars and radio-loud blazars and are assumed to be more distant radio-loud radio galaxies.