The ionization mechanism in low level emission galaxy nuclei: Shocks

We analyze the emission component of galaxy nuclei at very low intensity levels (W(Ha)=2Å). This emission level is considerably lower than that of classical LINERS like NGC 1052. We have access to weaker emission lines by averaging spectra with similar line ratios for Ha [NII], and [SII]. From the resulting spectrum for very low level emission nuclei, the [SII] ??6717, 6731/[SIII] ??9069, 9532 line ratio criterion (Diazet al., 1985a) unambiguously shows that shock-wave heating is the mechanism responsible for the ionization in such objects.