SPECTROSCOPY OF THE CIRCUMNUCLEAR EMISSION LINE REGIONS IN SEYFERT GALAXIES: I. NGC 1667

In this paper we investigate the physical properties in the circumnuclear and extranuclear regions of the Seyfert 2 galaxy NGC 1667. Long-slit, medium-resolution spectra are used to derive the ionization properties of the gas in nuclear and circumnuclear regions with the aid of a grid of photoionization models computed with the code CLOUDY 84. In the nuclear regions the high [NII] λ6583/Hα and [SII] λ6725/Hα ratios are best fitted assuming an overabundance of nitrogen and sulphur relative to the solar value in clouds photoionized by a 'hard' power-law continuum. The Seyfert nucleus is surrounded by extended HII regions the ionization of which is only weakly influenced by the central engine. The star formation rates (SFR) in these regions are evaluated from the measured Hα luminosities and compared with the values derived from infrared data. The equivalent stellar content in terms of O5 stars estimated in the extranuclear regions, N(O5)~700 - 3000, is a strong evidence that an intense star formation activity is occurring in the inner 10kpc. The observed velocity curve is well fitted by a model of spherical gravitational potential and purely circular motions. We derived a mass M~1.3E11 Solar Masses within a 30'' (~9kpc) radius.