The narrow-line region of Seyfert galaxies: Narrow-line Seyfert 1 galaxies versus broad-line Seyfert 1 galaxies

It is known that the spectral energy distribution (SED) of the nuclear radiation of narrow-line Seyfert 1 galaxies (NLS1's) has different shapes with respect to that of ordinary broad-line Seyfert 1 galaxies (BLS1's) particularly in X-ray wavelengths. This may cause some differences in the ionization degree and the temperature of gas in narrow-line regions (NLRs) between NLS1's and BLS1's This paper aims to examine whether or not there are such differences in the physical conditions of NLR gas between them. For this purpose, we have compiled the emission-line ratios of 36 NLS1's and 83 BLS1's from the literature. Comparing these two samples, we have found that the line ratios of [O I] λ6300/[O III] λ5007 and [O III] λ4363/[O III] λ5007, which represent the ionization degree and the gas temperature respectively, are statistically indistinguishable between NLS1's and BLS1's. Based on new photoionization model calculations, we show that these results are not inconsistent with the difference of the SED between them. The influence of the difference of SEDs on the highly ionized emission lines is also briefly discussed.