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Astron. Astrophys. 325, 450-456 (1997)

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Origin of the IR continuum in the Circinus galaxy*

Ralf Siebenmorgen 1, Alan Moorwood 2, Wolfram Freudling 2, 3 and Hans Ulrich Käufl 2

1 ISO Science Operations Centre, Astrophysics Division of ESA, Villafranca del Castillo, P.O. Box 50727, E-28080 Madrid, Spain
2 European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München, Germany
3 Space Telescope - European Coordinating Facility, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München, Germany

Received 21 October 1996 / Accepted 7 March 1997


We present infrared and millimeter-wave observations of the Circinus galaxy which is at a distance of only 4 Mpc and provides the closest example of an obscured Seyfert nucleus surrounded by a starburst ring. The FWHM size of the continuum emission is found to be only [FORMULA] 0.3" (6pc) at 3-5 µm, [FORMULA] 1.3" at 10 µm, [FORMULA] 1.5" at 20µm and [FORMULA] 23" (460pc) at 1.3 mm. The 1.3 mm measurements also provide an estimate of [FORMULA] [FORMULA] for the gas mass. It is shown using a radiative transfer code that both the observed sizes and overall spectral energy distribution, including the 9.7µm silicate absorption and 3.28 - 11.3 µm PAH emission features, can be satisfactorily modelled by assuming that the total luminosity is dominated by dust heated by a central power law source.

Key words: galaxies: individual: Circinus – infrared: galaxies – Infrared: ISM: continuum – dust, extinction

* Based on observations collected at the European Southern Observatory, La Silla, Chile (ESO 53.1-069, 53.1-051)

Send offprint requests to: rsiebenm@iso.vilspa.esa.es

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© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998