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ISO observations of spirals: modelling the FIR emission

Bianchi, Simone, Alton, Paul B. and Davies, Jonathan Ivor 2000. ISO observations of spirals: modelling the FIR emission. Presented at: ISO beyond point sources : studies of extended infrared emission workshop, Madrid, Spain, 14-17 September 1999. Published in: Laureijs, R. J., Leech, K. and Kessler, M. F. eds. ISO beyond point sources : studies of extented infrared emission workshop : ISO Data centre, Villafranca del Castillo, Madrid, Spain, 14-17 September 1999. ESA. SP , vol.455 Noordwijk: ESA Publications Division, pp. 149-154.

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ISO observations at 200micron have modified our view of the dust component in spiral galaxies. For a sample of seven resolved spirals we have retrieved a mean temperature of 20K, about 10K lower than previous estimates based on IRAS data at shorter wavelengths. Because of the steep dependence of far-infrared emission on the dust temperature, the dust masses inferred from ISO fluxes are a factor of 10 higher than those derived from IRAS data only, leading to gas-to-dust ratios close to the value observed in the Galaxy. The scale-length of the 200micron emission is larger than for the IRAS 100micron emission, with colder dust at larger distances from the galactic centre, as expected if the interstellar radiation field is the main source of dust heating. The 200micron scale-length is also larger than the optical, for all the galaxies in the sample. This suggests that the dust distribution is more extended than that of the stars. A model of the dust heating is needed to derive the parameters of the dust distribution from the FIR emission. Therefore, we have adapted an existing radiative transfer code to deal with dust emission. Simulated maps of the temperature distribution within the dust disk and of the dust emission at any wavelength can be produced. The stellar spectral energy distribution is derived from observations in the ultraviolet, optical and near infrared. The parameters of the dust distribution (scale-lengths and optical depth) are chosen to reproduce the observed characteristics of the FIR emission, i.e. the shape of the spectrum, the flux and the spatial distribution. We describe the application of the model to one of the galaxies in the sample, NGC~6946.

Item Type: Conference or Workshop Item (Paper)
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Uncontrolled Keywords: Isophot ; Spiral galaxies ; Extended emission ; Cold dust ; FIR:observations ;FIR:models
Publisher: ESA Publications Division
ISBN: 9290926619
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Last Modified: 04 Jun 2017 04:24

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