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A submillimeter galaxy (SMG, or submillimeter-selected galaxy or dusty star-forming galaxy, i.e., DSFG) is a galaxy showing mostly through submillimeter radiation, the term generally used for galaxies identified for being submillimeter sources. These include high redshift galaxies. Specifically, the 850 μm flux density is generally greater than 3-5 millijanskys. They are very luminous because of star formation rather than because they are active galaxies. The spectrum typically seen is black-body radiation from dust grains and emission lines from the gas in the interstellar medium. Some have been estimated to have huge amounts of dust.
An SMG is typically a massive high-redshifted elliptical starburst galaxy, and is essentially the same as a luminous infrared galaxy (LIRG). The phrase dusty galaxy is often used for them or to include them.