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Astron. Astrophys. 328, 510-516 (1997)

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Anisotropic [OIII] emission in radio loud AGN *

S. di Serego Alighieri 1, A. Cimatti 1, R.A.E. Fosbury 2, 3 and R. Hes 4, 5

1 Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy (sdiserego@arcetri.astro.it, acimatti@arcetri.astro.it)
2 Space Telescope-European Coordinating Facility, Karl-Schwarzschild Str.2, D-85748 Garching bei München, Germany (rfosbury@eso.org)
3 Affiliated to the Astrophysics Division of the Space Science Dept., European Space Agency
4 Dunsink Observatory, School of Cosmic Physics, Castleknock, Dublin 15, Ireland
5 Present address: Faculty of Systems Engineering, Group of Information and Communication Technology, Delft Univ. of Technology, P.O. Box 5015, 2600 GA Delft, The Netherlands (rhes@sepa.tudelft.nl)

Received 22 May 1997 / Accepted 29 July 1997

Abstract

We present the results of spectropolarimetry of a sample of 7 powerful radio galaxies and 2 quasars with [FORMULA] obtained to detect possible anisotropies in the [OIII] line emission, which could explain the higher [OIII] luminosity of quasars than that of radio galaxies within the framework of the Unified Model of radio-loud AGN. We detect polarized [OIII] in 4 radio galaxies, consistent with the possibility that a considerable fraction ([FORMULA]) of the observed [OIII] emission is scattered in a similar way to the hidden nuclear continuum. However, small but detectable rotation between the polarization direction of the line and of the continuum in two radio galaxies shows that the geometry of the emitting regions can be different.

Key words: line: formation – scattering – techniques: polarimetric – galaxies: active – radio continuum: galaxies

* Based on observations obtained at the European Southern Observatory, La Silla, Chile, and at the Isaac Newton Group of Telescopes, La Palma, Canary Islands, Spain

Send offprint requests to: S. di Serego Alighieri

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© European Southern Observatory (ESO) 1997

Online publication: March 26, 1998

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