Near-infrared imaging polarimetry of Cygnus A

We present a 2.2-μm polarization image of the nuclear regions of Cygnus A. The degree of polarization in the central 1 arcsec is (4.1±0.50) per cent, at a position angle of (23.6±3.6)°, approximately perpendicular to the axis of the radio jet. Modelling of the results suggests that at this wavelength the polarization along the line of sight to the central source is most likely produced by dichroism, through an Av∼40 mag, with the polarization in surrounding regions produced by scattering. For this model, the K-band luminosity of the central source is calculated to be ∼2×1044 erg s−1.