Anisotropic radio and optical emission in the Seyfert nucleus of NGC 3227

Abstract

We present a high-sensitivity study of the photoionized and relativistic plasma associated with the Seyfert nucleus of NGC 3227. [O III] 5007-Å images of the high-excitation ionized gas show an asymmetric distribution extending ~ 7 arcsec to the north-east (NE) of the optical continuum nucleus. The axis of symmetry of the [O III] 5007-Å structure is along PA ~ 30°, and could be consistent with photoionization by a cone of UV continuum from the nucleus. Long-slit spectroscopy shows that the [O III] 5007-Å emitting gas has relatively broad lines ( ~ 250 km s^–1) typical of a ‘narrow-line region’ rather than an ‘extended narrow-line region’.<br/><br/>MERLIN images at wavelengths of 6 and 18 cm reveal a 0.4-arcsec double radio source. The PA of the double is ~ –10° and hence does not align with the symmetry axis of the [O III] 5007-A structure. We consider a number of mechanisms to account for this misalignment, ranging from the effect of ‘density bounding’ of collimated UV emission, to the possibility that the ionized gas is flowing out from the nucleus, along a density gradient, in a different direction from the radio collimation. We tentatively conclude that NGC 3227 may represent a case in which the radio structure and [O III] 5007-Å gas are physically misaligned.