Near-infrared spectroscopy of nearby Seyfert galaxies: Is there evidence
  for the shock excitation in narrow-line regions?
  One of the unsettled, important problems in active galactic nuclei (AGNs) is
the major ionization mechanism of gas clouds in their narrow-line regions
(NLRs). In order to investigate this issue, we present our $J$-band
spectroscopic observations for a sample of 26 nearby Seyfert galaxies. In our
study, we use the flux ratio of the following two forbidden emission lines, [Fe
II]1.257$\mu$m and [P II]1.188$\mu$m because it is known that this ratio is
sensitive to the ionization mechanism. We obtain the [Fe II]/[P II] flux ratio
or its lower limit for 19 objects. In addition to our data, we compile this
flux ratio (or its lower limit) of 23 nearby Seyfert galaxies from the
literature. Based on the collected data, we find that three Seyfert galaxies
show very large lower limits of [Fe II]/[P II] flux ratios ($\gtrsim$10); NGC
2782, 5005, and Mrk 463. It is thus suggested that the contribution of the fast
shock in the gas excitation is significantly large for them. However, more than
half of Seyfert galaxies in our sample show moderate [Fe II]/[P II] flux ratios
($\sim$2), that is consistent to the pure photoionization by power-law ionizing
continuum emission. We also find that the [Fe II]/[P II] flux ratio shows no
clear correlation with the radio loudness, suggesting that the radio jet is not
the primary origin of shocks in NLRs of Seyfert galaxies.
