1996A&A...315..335M

Infrared observations of [SiIX], [SIX] [SiVII], [SiVI], and [CaVIII] coronal line emission in NGC1068 are presented and discussed together with visible spectra covering [FeVII], [FeX], [FeXI] and [SVIII]. These lines are found to peak ≃50pc NE of the nucleus and appear to arise predominantly in outflowing gas within the prominent ionization cone aligned with the radio jet. The line ratios argue against collisional ionization but could be explained with photoionization by radiation from the active nucleus. The observed [SiIX](3.935µm)/[SiVI](1.96µm) ratio is ≃10³ larger than in NGC6302, one of the highest excitation planetary nebulae known, demonstrating both that photoionization by hot stars is excluded and the potential value of the [SiIX](3.935µm) line as a tracer of AGN activity in visually obscured galactic nuclei.