USING NEAR-INFRARED [FE-II] LINES TO IDENTIFY ACTIVE GALAXIES

The ([Fe II] 1.644 mu m)/Br gamma and ([Fe II] 1.2567 mu m)/Pa beta ra tios provide good separation of starburst and Seyfert galaxies; we sho w that ([Fe II] 1.644 mu m)/Br gamma is nearly as good a discriminant as the commonly used ([O I] lambda 6300)/H alpha ratio. The behavior o f both the ([O I] lambda 6300)/H alpha and the ([Fe II] 1.644 mu m)/Br gamma ratios is readily understood if there is a progression in the p roportion of shock excitation going from H II region through starburst and Seyfert galaxies to supernova remnants. We use the CLOUDY program to show that the behavior is also explained if the dominant excitatio n mechanism is photoionization. As a test of this technique for identi fying excitation mechanisms, we have obtained infrared spectra of two LINER galaxies. NGC 1052, which is thought to be excited by a nuclear power-law UV source, is the prototype of LINERs, and NGC 3504 is class ified as a weak-[O I] lambda 6300 LINER, better understood in terms of photoionization by O stars than by a nonstellar source. The placement of these galaxies on the ([Fe II] 1.644 mu m)/Br gamma versus ([O I] lambda 6300)/H alpha diagram is in agreement with these previously det ermined characteristics. The ([Fe II] 1.644 mu m)/Br gamma and ([Fe II ] 1.2567 mu m)/Pa beta ratios should be useful in classifying heavily obscured galaxies because the ratios (1) are constructed at wavelength s where extinction is relatively small and (2) involve lines over narr ow spectral ranges.