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The narrow-line region (NLR) consists of gas clouds ionized by the strongradiation from the active galactic nucleus (AGN), distributed in the spatialscale of AGN host galaxies. The strong emission lines from the NLR are usefulto diagnose physical and chemical properties of the interstellar medium in AGNhost galaxies. However, the origin of the NLR is unclear; the gas clouds inNLRs may be originally in the host and photoionized by the AGN radiation, orthey may be transferred from the nucleus with AGN-driven outflows. For studyingthe origin of the NLR, we systematically investigate the gas density andvelocity dispersion of NLR gas clouds using a large spectroscopic data settaken from the Sloan Digital Sky Survey. The [S II] emission-line flux ratioand [O III] velocity width of 9,571 type-2 Seyfert galaxies and 110,041star-forming galaxies suggest that the gas density and velocity dispersion ofNLR clouds in Seyfert galaxies (ne ~ 194 cm-3 and sigma([O III]) ~ 147 km s-1)are systematically larger than those of clouds in H II regions of star-forminggalaxies (ne ~ 29 cm-3 and sigma([O III]) ~ 58 km s-1). Interestingly, theelectron density and velocity dispersion of NLR gas clouds are larger forSeyfert galaxies with a higher [O III]/Hbeta flux ratio, i.e., with a moreactive AGN. We also investigate the spatially-resolved kinematics of ionizedgas clouds using the Mapping Nearby Galaxies at the Apache Point Observatory(MaNGA) survey data for 90 Seyfert galaxies and 801 star-forming galaxies. Wefind that the velocity dispersion of NLR gas clouds in Seyfert galaxies islarger than that in star-forming galaxies at a fixed stellar mass, at bothcentral and off-central regions. These results suggest that gas clouds in NLRscome from the nucleus, probably through AGN outflows.

Do gas clouds in narrow-line regions of Seyfert galaxies come from their nuclei?