The Dust Content and Opacity of Actively Star‐forming Galaxies

We present far-infrared (FIR) photometry at 150m and 205 mo f eight low-redshift starburst galaxies obtained with the Infrared Space Observatory (ISO) ISOPHOT. Five of the eight galaxies are detected in both wavebands and these data are used, in conjunction with IRAS archival photometry, to model the dust emission at >40 m. The FIR spectral energy distributions (SEDs) are best tted by a combination of two modied Planck functions, with T40{55 K (warm dust) and T20{23 K (cool dust), and with a dust emissivity index = 2. The cool dust can be a major contributor to the FIR emission of starburst galaxies, representing up to 60% of the total flux. This component is heated not only by the general interstellar radiation eld, but also by the starburst itself. The cool dust mass is up to 150 times larger than the warm dust mass, bringing the gas-to-dust ratios of the starbursts in our sample close to Milky Way values, once rescaled for the appropriate metallicity. The ratio between the total dust FIR emission in the range 1{1000 m and the IRAS FIR emission in the range 1 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.