The Narrow-Line Region of Seyfert Galaxies: Narrow-Line Seyfert 1 Galaxies versus Broad-Line Seyfert 1 Galaxies

Abstract

It is known that the spectral energy distribution (SED) of the nuclear radiation of narrow-line Seyfert 1 galaxies (NLS1s) has different shapes with respect to that of ordinary broad-line Seyfert 1 galaxies (BLS1s), particularly in wavelengths of X-ray. This may cause some differences in the ionization degree and the temperature of gas in narrow-line regions (NLRs) between NLS1s and BLS1s. 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 NLS1s and 83 BLS1s from the literature. Comparing these two samples, we have found that the line ratios of [O {\sc i}]$λ$6300/[O {\sc iii}]$λ$5007 and [O {\sc iii}]$λ$4363/[O {\sc iii}]$λ$5007, which represent the ionization degree and the gas temperature respectively, are statistically indistinguishable between NLS1s and BLS1s. 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.