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

Very cold dust in galaxies ^*

R. Siebenmorgen ¹, E. Krügel ² and R. Chini <sup>3

1</sup> 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

Abstract

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 K. The ratio of infrared luminosity to gas mass, , where the latter quantity has been obtained from 1.3 mm observations within the central is about 90 / . In contrast, the spectral energy distributions of inactive spirals require, apart from warm dust of K, an additional very cold component of at most K. Determining the gas mass from 1.3 mm dust continuum maps that cover the optical extent of the inactive spirals we find / , a factor 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

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations
  • 2.1. ISOPHOT photometry
  • 2.2. The color correction
  • 2.3. Integrated millimeter wave photometry
• 3. Results
  • 3.1. Remarks on individual galaxies
• 4. A lower limit to grain temperature
• 5. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: November 3, 1999
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