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Session 39 - AGNs, QSOs, Active Galaxies.
Display session, Wednesday, June 11
South Main Hall,

[39.01] The `q problem' in Seyfert NLRs

S. K. Metz, D. J. Axon (STScI), A. Robinson (U. Hertfordshire), C. N. Tadhunter (U. Sheffield)

We present the results of a critical test for the central source photoionization model, applied to four nearby Seyferts (NGC 4151, NGC 2110, Mrk 3 and NGC 2992) with resolved Narrow Line Regions (NLRs) and extended radio structures. Inferring the ionizing photon flux, q, from the common definition of the ionization parameter (U=q/ncr^2), gives the surpising result that q is not the constant value expected for a central source model.

The implications for the models of the ionization mechanisms in Seyfert NLRs (ionization-bounded photoionization; matter-bounded/ionization-bounded cloud mix models; and shock ionization) are discussed, as are the questions this result raises about the assumptions involved in the use of [OIII](5007)/[OII](3727) to determine U, and [SII](6717/6731) to estimate the density.

Program listing for Wednesday