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Astron. Astrophys. 325, 450-456

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Origin of the IR continuum in the Circinus galaxy*

Ralf Siebenmorgen1, Alan Moorwood2, Wolfram Freudling2, 3, and Hans Ulrich Käufl2

1ISO Science Operations Centre, Astrophysics Division of ESA, Villafranca del Castillo, P.O. Box 50727, E-28080 Madrid, Spain
2European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München, Germany
3Space 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 10µm, 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

© European Southern Observatory (ESO) 1997

Online publication: September 9, 1997
Last change: April 28, 1998