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One of the unsettled, important problems in active galactic nuclei (AGNs) isthe major ionization mechanism of gas clouds in their narrow-line regions(NLRs). In order to investigate this issue, we present our $J$-bandspectroscopic observations for a sample of 26 nearby Seyfert galaxies. In ourstudy, we use the flux ratio of the following two forbidden emission lines, [FeII]1.257$\mu$m and [P II]1.188$\mu$m because it is known that this ratio issensitive to the ionization mechanism. We obtain the [Fe II]/[P II] flux ratioor its lower limit for 19 objects. In addition to our data, we compile thisflux ratio (or its lower limit) of 23 nearby Seyfert galaxies from theliterature. Based on the collected data, we find that three Seyfert galaxiesshow very large lower limits of [Fe II]/[P II] flux ratios ($\gtrsim$10); NGC2782, 5005, and Mrk 463. It is thus suggested that the contribution of the fastshock in the gas excitation is significantly large for them. However, more thanhalf of Seyfert galaxies in our sample show moderate [Fe II]/[P II] flux ratios($\sim$2), that is consistent to the pure photoionization by power-law ionizingcontinuum emission. We also find that the [Fe II]/[P II] flux ratio shows noclear correlation with the radio loudness, suggesting that the radio jet is notthe primary origin of shocks in NLRs of Seyfert galaxies.

Near-infrared spectroscopy of nearby Seyfert galaxies: Is there evidence for the shock excitation in narrow-line regions?