The extended nebulosity in the radio galaxy 3C 227.

Abstract

3C 227 (z = 0.085) exhibits one of the more spectacular extended nebulosities to be found among active galaxies at moderate redshifts. The gas can be traced to radial distances of about 100 kpc (H_0_ = 50 km s^-1^ Mpc^-1^). The total [O III] 5007-A luminosity is 2.7 X 10^42^ erg s^-1^, of which at least 50 per cent is radiated from the extended region rather than from the immediate nuclear environment. Photoionization by continuum radiation from an active galactic nucleus (AGN) is indicated by both the emission line ratios and the variation of the ionization parameter with radial distance from the nucleus. Extrapolation into the EUV of the observed nuclear continuum does not explain the ionization state of the gas, and so it is necessary to hypothesize an anisotropic nuclear radiation field. The kinematic behaviour of the gas is reasonably well ordered with a general apparent rotation, but there is evidence for local distortions associated with variations in surface brightness and with the radio axis. We have modelled the velocity field with a filled biconical structure having an axis tilted 40^deg^ from the plane of the sky. We conclude that 3C 227 could be a radio-loud, lobe-dominated quasar viewed in a direction close to the edge of this radiation cone.