Abstract
We study optical profiles and the physical conditions of the narrow line region (NLR) of narrow-line Seyfert 1 galaxies (NLS1s). Our results show that the flux carried out by the narrow component of Hβ can be up to 10 times higher than the value usually adopted in the literature. As a result, the O IIIλ5007/Hβ ratio emitted in the NLR varies from 1 to 5, instead of the universally adopted value of 10. We test photoionization models that consider a NLR composed of a combination of matter-bounded and ionization-bounded clouds and show that this scenario reproduces with very good agreement the observed emission lines ratios of NLS1s. We propose that the peculiar properties of the NLR of NLS1s can be explained by a steep continuum of power-law form in the EUV-soft X-ray region, with spectral index α ~ -2.2, consistent with ROSAT observations of this class of objects.
