THE HEATING OF DUST IN STARBURST GALAXIES - THE CONTRIBUTION OF THE NONIONIZING RADIATION

The IUE UV and optical spectra and the far-infrared (FIR) IRAS flux de nsities of a sample of starburst and blue compact galaxies are used to investigate the relationship between dust obscuration and dust emissi on. The amount of dust obscuration at UV wavelengths correlates with t he FIR-to-blue ratio; and an analysis of the correlation indicates tha t not only the ionizing but also the nonionizing radiation contribute to the FIR emission. The amount of UV and optical energy lost to dust obscuration accounts for most of the cool dust FIR emission and for ab out 70% of the warm dust FIR emission The remaining 30% of the warm du st FIR flux is probably due to dust emission from regions of star form ation which are embedded in opaque giant molecular clouds and do not c ontribute to the integrated UV and optical spectrum. The use of the FI R emission as an indicator of high-mass star formation rate in star-fo rming galaxies can be problematic, since the contribution to the FIR f lux from cool dust emission heated by relatively old stars is nonnegli gible (similar to 30%).