The extended narrow line region in Mkn79. I.Observations

We present deep long slit spectra of Mkn79 in position angles PA=12$^{o}$ and PA=50$^{o}$ obtained with the WHT. These data prove the existence of an extended narrow line region in PA=12$^{o}$, which coincides with the triplet radio structure (Ulvestad \& Wilson 1984) and the observed outflow of material from the nucleus at PA=10$^{o}$ (Whittle et al. 1988). The ratios of the high to low ionization lines indicate a higher level of gas excitation in PA=12$^{o}$ compared to PA=50$^{o}$. The [NII]$\lambda$6583/H$\alpha$ and [SII]$\lambda$6717,31/H$\alpha$ versus [OIII]$\lambda$5007/H$\beta$ line ratios are consistent with excitation by an AGN continuum rather than a HII region.