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Astron. Astrophys. 344, L1-L4 (1999)

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Letter to the Editor

Dust emissivity in the far-infrared

Simone Bianchi, Jonathan I. Davies and Paul B. Alton

Department of Physics and Astronomy, University of Wales, P.O. Box 913, Cardiff CF2 3YB, UK

Received 4 December 1998 / Accepted 18 February 1999


We have derived the dust emissivity in the Far-Infrared (FIR) using data available in the literature. We use two wavelength dependences derived from spectra of Galactic FIR emission (Reach et al. 1995). A value for the emissivity, normalised to the extinction efficiency in the V band, has been retrieved from maps of Galactic FIR emission, dust temperature and extinction (Schlegel et al. 1998).

Our results are similar to other measurements in the Galaxy but only marginally consistent with the widely quoted values of Hildebrand (1983) derived on one reflection nebula. The discrepancy with measurements on other reflection nebulae (Casey 1991) is higher and suggests a different grain composition in these environments with respect to the diffuse interstellar medium.

We measure dust masses for a sample of six spiral galaxies with FIR observations and obtain gas-to-dust ratios close to the Galactic value.

Key words: ISM: dust, extinction – infrared: ISM: continuum – infrared: galaxies

Send offprint requests to: Simone.Bianchi@astro.cf.ac.uk

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© European Southern Observatory (ESO) 1999

Online publication: March 10, 1999