Gas Metallicity of Narrow‐Line Regions in Narrow‐Line Seyfert 1 Galaxies and Broad‐Line Seyfert 1 Galaxies

We investigate gas metallicity of narrow-line regions in narrow-line Seyfert1 galaxies (NLS1s) and broad-line ones (BLS1s) in order to examine whether ornot there is a difference in the gas metallicity between the two populations ofSeyfert 1 galaxies. We apply two methods to study this issue. One is to use theemission-line flux ratio of [N II]6583/H_alpha in combination with some otheroptical emission-line flux ratios. This method, which has been often applied toSeyfert 2 galaxies, suggests that the gas metallicity of narrow-line regions isindistinguishable or possibly higher in BLS1s than in NLS1s. On the contrary,the other method in which only forbidden emission-line fluxes are used resultsin that NLS1s tend to possess metal-richer gas in the narrow-line regions thanBLS1s. We point out that this inconsistency may be owing to the contaminationof the broad component of permitted lines into the narrow component of ones inthe first method. Since the results derived by using only forbiddenemission-line fluxes do not suffer from any uncertainty of the fitting functionfor the broad component of Balmer lines, the results from this method are morereliable than those derived by using permitted lines. We thus conclude that thegas metallicity of narrow-line regions tends to be higher in NLS1s than inBLS1s.Comment: 12 pages including 10 figures, to appear in The Astrophysical Journa