EDP Sciences
Free access
Volume 404, Number 1, June II 2003
Page(s) 1 - 19
Section Cosmology
DOI http://dx.doi.org/10.1051/0004-6361:20030427

A&A 404, 1-19 (2003)
DOI: 10.1051/0004-6361:20030427

New radiative transfer models for obscuring tori in active galaxies

I. M. van Bemmel1 and C. P. Dullemond2

1  Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands
2  Max-Planck Institut für Astronomie, PO Box 1317, 85741 Garching, Germany

(Received 10 June 2002 / Accepted 17 March 2003)

Two-dimensional radiative transfer is employed to obtain the broad-band infrared spectrum of active galaxies. In the models we vary the geometry and size of the obscuring medium, the surface density, the opacity and the grain size distribution. Resulting spectral energy distributions are constructed for different orientations of the toroid. Colour-colour comparisons with observational data are consistent with previous observations that the emission longward of 60  ${\rm\mu}$m is produced by star-formation and unrelated to the presence of an obscuring torus. We also find that the toroid cannot be flat, but is rather conical or flaring. The density is most likely constant with radius, and the size is relatively large with an inner radius around 10 pc. A direct comparison with radio galaxy Cygnus A yields a best fit for a conical disk with constant surface density, and a size from 10 to 30 pc, assuming the far-infrared emission is due to star-formation in the host galaxy.

Key words: galaxies: active -- galaxies individual: Cygnus A -- infrared: galaxies -- infrared: ISM -- quasars: general -- ISM: dust

Offprint request: I. M. van Bemmel, bemmel@stsci.edu

SIMBAD Objects

© ESO 2003