Spectropolarimetry of broad Hα lines in radio galaxies: constraints on the geometry of the broad-line and scattering regions

摘要: We present optical spectropolarimetric observations of three radio-loud broad-line active galactic nuclei: 3C 332, 3C 351 and 4C 73.18, together with new 3C 390.3, which we observed previously. Intrinsically polarized broad Hα emission was detected in 3C 332 3C 390.3 at levels ∼3 per cent ∼1 cent, respectively. Significant polarization not 3C 351, while the measured 4C 73.18 (∼1 per cent) is consistent foreground contamination by interstellar medium. Although both exhibit ‘double-peaked’ line profiles, their properties differ significantly. The has a similar profile to that seen total flux continuum 70° axis radio source. In however, double peaks are suppressed ∼5° emission. Comparison these data obtained 2 years previously reveals significant variations flux. The implications for relationship between geometry region scattering medium discussed. argue models arises relativistically rotating disc cannot easily explain and, particular, 3C 390.3. consider instead model originates bipolar outflow calculations showing can be broadly explained from inner wall an obscuring torus, those particles situated above poles torus. outline scheme either toroidal or polar dominates given object, depending on orientation its jet our sight.