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Astron. Astrophys. 351, 495-505 (1999)

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Very cold dust in galaxies *

R. Siebenmorgen 1, E. Krügel 2 and R. Chini 3

1 ISO Data Centre, Astrophysics Division of ESA, Villafranca del Castillo, P.O. Box 50727, 28080 Madrid, Spain
2 MPIfR, Auf dem Hügel, 53121 Bonn, Germany
3 Astronomisches Institut der Ruhr-Universität Bochum, Universitätsstrasse 150 NA7, 44780 Bochum, Germany

Received 29 April 1999 / Accepted 3 August 1999


We present multi-filter far infrared photometry of active and inactive galaxies obtained with ISOPHOT. We find that the far infrared and submillimeter spectrum of the active galaxies can be described by a single modified black-body at a color temperature of [FORMULA] K. The ratio of infrared luminosity to gas mass, [FORMULA], where the latter quantity has been obtained from 1.3 mm observations within the central [FORMULA] is about 90 [FORMULA]/ [FORMULA]. In contrast, the spectral energy distributions of inactive spirals require, apart from warm dust of [FORMULA] K, an additional very cold component of at most [FORMULA] K. Determining the gas mass from 1.3 mm dust continuum maps that cover the optical extent of the inactive spirals we find [FORMULA] [FORMULA]/ [FORMULA] , a factor [FORMULA] lower than for the active galaxies.

Key words: galaxies: spiral – galaxies: ISM

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA.

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

© European Southern Observatory (ESO) 1999

Online publication: November 3, 1999