Spectroscopy of the nuclear emission-line regions of the two newly detected Seyfert 1 galaxies F10.01 and A08.12

Abstract

Long-slit medium-resolution spectra are used to study the continuum and ionization properties of the gas in the Seyfert 1 galaxies F10.01 and A08.12. We Ðnd that the nuclear underlying continuum can be described by a power law. In addition to this component, Balmer continuum (Bac) and high-order Balmer lines can Ðt the apparent excess of emission extending from 3900 Å to the blue end of the spectra. The observed Bac flux in A08.12 is about 9 times as strong as Hβ, stronger than that predicted by most photoionization models. From the analysis of the Fe II emission, we found Fe II λ4570/Hβ~1 in F10.01, leading us to consider this object as a strong Fe II emitter. Broad and symmetrical Balmer lines are observed in A08.12, while strongly asymmetrical ones are observed in F10.01, with the full width at zero intensity (FWZI) around 15,000 km s-ˡ. We interpret the above results as evidence for broad-line region (BLR) gas exposed to the anisotropic UV radiation emitted by a thin disk combined with an isotropic X-ray source. Such a model could explain observational differences like strong Fe II and weak Bac and He I λ5875 emission in F10.01, and strong Bac and He I λ5875 and weak Fe II in A08.12, as due to an angular dependence of emission-line intensities. The narrow-line region (NLR) of both objects shows strong high-ionization lines and T[OIII] temperatures that cannot be reproduced simultaneously using single-component ionization-bounded photoionization models. We explore here the possibility of a NLR composed of a combination of matter-bounded (MB) and ionization-bounded (IB) clouds. In this scheme, the MB component is responsible for most of the high-excitation lines, including the [O III] emission, while the IB clouds, photoionized by the radiation leaking the MB component, are located 140 times more distant from the central source than the MB clouds and show a much lower excitation. Using this scheme, we can successfully solve the "temperature problem" and obtain much stronger excitation lines, in accordance with our observations.