The obscured BLR in the radio galaxy 3C 234

Abstract

We present spectropolarimetric observations of the radio galaxy 3C 234 at optical and, for the first time, near-IR wavelengths. In agreement with previous observations we detect broad Hα in total and polarized flux, consistent with the scenario in which the central active nucleus is hidden from view and observed via scattered radiation. We model the flux and polarization properties at optical and near-IR wavelengths, which result in a point-source, cone-based scattering geometry in the optical, and an extended source scattering in the near-IR, with a dichroic view to the emission regions, which becomes important only at the longer wavelengths. From this model we calculate an intrinsic Hα luminosity of 4.9×1044 erg s−1, and an extinction to the near-IR emission region of 60 mag for AV. The scattered radiation also undergoes extinction, this time by 1 mag for AV, assuming a source function of a typical stellar-subtracted Seyfert 1 galaxy. Our modelling does not require the presence of a second featureless continuum (FC2). Additionally, we require that the scatterers are in bulk radial outflow at approximately 600 km s−1 to explain an observed increase in the intrinsic polarization of the scattered broad Hα line in the red wing, and blueshifted narrow-line components in polarized flux.