The circumnuclear region in the Seyfert 1 galaxy NGC 3227

This article presents Hoc and [O iii] narrow-band images and long-slit optical and near-infrared spectroscopy at position angles 65.5° and 25° through the circumnuclear region in the Seyfert 1 galaxy NGC 3227. After subtraction of a bulge + disc model, the continuum image at λ5900 Å shows an excess of emission aligned with the companion galaxy NGC 3226. We attribute this emission to a stellar bar induced by the interaction. Along the leading parts of the bar, we find dust lanes and 70 per cent of the H ii regions detected in the disc. The Hα and [O iii] images show extended emission in the circumnuclear region with very different morphologies. [O iii] is elongated to the north and nearly aligned with the bar. This emission is formed by two kinematical components, a broad component blueshifted with respect to a narrower component. The blue component could be photoionized by radiation from the active nucleus, but the red component might be associated with the starburst detected to the west. The Hα image is aligned along PA = 65°, and shows a bright knot at 4 arcsec south-west of the nucleus and a shell-like structure; there the line ratios can be fitted by photoionization by a stellar source. To the north-east, the spectrum shows characteristics of a high-excitation low-ionization nuclear emission region (LINER), and the line ratios can be explained as photoionization by a blackbody with a temperature of 140 000 K, ionization parameter 0.001, and solar chemical composition with an overabundance of N and S. Even though Hα and [O iii] present different morphologies, both are extended 500 pc from the nucleus, inside the inner Lindblad resonance; this suggests that gravitational torques, associated with the non-axisymmetric potential produced by the bar and by interaction with the companion galaxy, transport the gas to the inner Lindblad resonance (ILR), from where it fuels the circumnuclear region in NGC 3227.