Energy distributions of radio galaxies

Far-infrared observations of 140 radio galaxies from the 3CR and B2 catalogs are presented. The galaxies span a range of over four orders of magnitude in radio power, from weak nuclear sources in nearby galaxies, to powerful FR II doubled-lobed sources at moderate redshift. Scanned or pointed observations with IRAS detect 38 of the radio galaxies in at least one waveband; 21 are detected at both 60 and 100 μm. The strength of the far-infrared emission is more closely correlated with core radio emission than with total radio emission, and it is independent of the absolute visual magnitude of the host galaxy. The more luminous 3CR galaxies have warmer far infrared emission than the less luminous B2 galaxies. The relationship between radio and far-infrared luminosity is determined in a way that is insensitive to the large number of infrared nondetections. Radio galaxies have far-infrared emission with similar color temperatures to normal ellipticals; however the inferred amounts of cold interstellar material are typical of gas-rich galaxies. Infrared luminous radio galaxies are rare. Only one in 10 ellipticals with M_v< -17 has a strong enough radio source to have 10¹¹ L_⊙ of far-infrared emission. Indirect arguments indicate that far-infrared emission in radio galaxies represents star formation that is more closely tied to the active nucleus than to the global properties of the galaxy. The far-infrared luminosity function shows good continuity between radio galaxies and radio loud quasars.