The giant nebulae associated with 3C 227: emission-line profiles and kinematic modelling

Detailed line profiles from the nebular gas surrounding the radio galaxy 3C 227 are presented. High-resolution spectroscopy around [O III] 4959- and 5007-Angstrom emission lines, with an unprecedentedly high signal-to-noise ratio, reveals broad and asymmetric line profiles all across the nebulae. The average width of the line complex is of the order of 100 km s(-1), with the mean peak position shifting from red to blue according to a general rotation pattern. The line profiles were first compared with the popular bicone models. However, even when extended to include the effect of radial inflow or outflow, the bicone models fail to match the observed gas profiles. Instead, a ring model is proposed, in which gas particles move in several nonintersecting circular orbits in force balance with the halo potential. The multiple-peaked line complexes seen at various positions in the nebula are then interpreted as the contribution of different rings projected in the same line of sight.