Computer Science
Scientific paper
Jul 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996hst..prop.6419w&link_type=abstract
HST Proposal ID #6419
Computer Science
Hst Proposal Id #6419 Agn
Scientific paper
We propose to investigate the currently favored model of Seyfert galaxies, in which a torus of gas and obscuring dust surrounds a Seyfert 1 nucleus. Seyfert 1 galaxies are considered to be viewed ``pole-on'' and Seyfert 2's ``edge- on'', so that our view of the broad line region is blocked in the latter objects. We have recently finished the first ground -based optical emission-line survey of a complete sample of Seyfert galaxies. Surprisingly, a large fraction of the Seyfert 2 galaxies show no evidence of the bi-conical or linear emission-line structures expected in the unified model. Rather, the morphologies of their high excitation gas are ``halo-like'', suggesting this gas is ionized by an isotropic component of nuclear ionizing radiation. Unfortunately, previous HST observations have been heavily biassed towards the small fraction of Seyfert 2's for which ground-based observations had already provided considerable support for the unified model. We now wish to observe a complete, unbiassed sample to see whether or not the structures expected in the unified model are present, but on too small a scale for ground -based resolutions. Specifically, the HST images will be used to a} determine the incidence and properties of ``ionizing cones'', b} investigate the relationship between the radio sources and the ionized gas, c} search for direct evidence of dusty tori through reddening of the continuum images, and d} investigate the ionization balance of the emission-line knots, as a probe of anisotropic nuclear ionizing radiation.
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