Volume 442, Number 3, November II 2005
|Page(s)||L39 - L43|
|Published online||14 October 2005|
Letter to the Editor
Spitzer IRS spectroscopy of 3CR radio galaxies and quasars: testing the unified schemes
Astronomisches Institut, Ruhr-Universität, Universitätsstr. 150 / NA7, 44780 Bochum, Germany e-mail: email@example.com
2 European Southern Observatory, Karl-Schwarzschildstr. 2, 85748 Garching b. München, Germany
3 IPAC, California Institute of Technology (Caltech), Pasadena, CA 91125, USA
4 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, Postfach 2024, 53010 Bonn, Germany
Accepted: 11 September 2005
With the Spitzer Space Telescope Infrared Spectrograph (IRS) we have observed seven powerful FR 2 radio galaxies and seven quasars. Both samples, the galaxies and the quasars, are comparable in isotropic 178 MHz luminosity (10 W/Hz W/Hz) and in redshift range (0.05 z 1.5). We find for both samples similar distributions in the luminosity ratios of high- to low-excitation lines ([NeV]14.3~ \mu m / [NeII]12.8~ \mu m) and of high-excitation line to radio power ([NeV]24.3~ \mu m / P178\,MHz). This solves the long debate about the apparent difference of quasars and radio galaxies in favor of the orientation-dependent unified schemes. Furthermore, the luminosity ratio [OIII]500.7~ nm / [OIV]25.9~ \mu m of most galaxies is by a factor of ten lower than that of the quasars. This suggests that the optical emission from the central NLR is essentially absorbed (AV 3) in the powerful FR 2 galaxies and that the [OIII]500.7~ nm luminosity does not serve as isotropic tracer for testing the unified schemes.
Key words: galaxies: active / galaxies: nuclei / galaxies: quasars: general / infrared: galaxies
© ESO, 2005
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