Testing Narrow-Line-Seyfert-1 scenarios with photoionization models

Details Testing Narrow-Line-Seyfert-1 scenarios with photoionization models Testing Narrow-Line-Seyfert-1 scenarios with photoionization models

Aug 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995agm....11p.217k&link_type=abstract

AG Abstract Services, vol. 11, Abstracts of Contributed Talks and Posters presented at the Annual Scientific Meeting of the Astr

Astronomy and Astrophysics

Astronomy

Narrow-Line Seyfert 1 Galaxies, Emission Lines: Nlr And Blr, Photoionization Modelling

Scientific paper

Using 3 recently discovered ultrasoft AGN, which have been optically identified as Narrow Line Seyfert 1 galaxies (NLSy1) (Greiner et al. 1995), we investigate some scenarios to explain the main characteristics of NLSy1, i.e. steep X-ray spectra, narrow Balmer lines and weak forbidden lines. In particular, we address the following issues (always assuming the absorption and emission line regions to be photoionized by the central continuum source): Production of steep X-ray spectra via warm absorption: Warm absorbers are usually invoked to explain the absorption edges that have recently been seen in the X-ray spectra of several Seyfert 1 galaxies. Ultrasoft AGN might be the ``missing link" between these objects and those completely absorbed, with only the down-turning part of the oxygen absorption-edge being visible in the ROSAT spectral region. Calculating phototionization models for the warm gas with the spectral energy distribution (SED) incident on the clouds fixed to a mean Seyfert continuum with Gammax=-1.9, we can successfully reproduce the observed X-ray spectra of our 3 objects. The best-fit parameters, ionization parameter U and warm hydrogen column density NH, are in the range log U = 0.2-0.4 and log NH = 22.7-23.2. Stability of broad line clouds and narrowness of broad lines: One explanation for the small FWHM (< 2000 km/s) of the broad lines in NLSy1 could be the removal of multiphase cloud-equilibrium within the BLR caused by the steep X-ray spectrum. To test this idea, we calculated equilibrium curves for the BLR gas for intrinsically steep X-ray continua. We also checked the influence of pre-absorbed X-ray spectra with warm column densities of the range derived from the warm absorber fits to our objects. Additionally, the metal abundances were varied, which affect the cooling of the gas. We find that intrinsically steep X-ray spectra (Gammax < -3.0) remove the two-phase equilibrium completely; overabundant metals delay this trend and pre-absorbed spectra narrow down the range of stability. Weakness of forbidden lines: We consider several scenarios based solely on photoionization to account for the weaker forbidden lines (like [OIII]lambda5007) in NLSy1 as compared to `normal' Sy1. We find that neither a modified SED illuminating the NLR nor overabundant metals provide a sufficient explanation.

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