A multiwavelength analysis of the clumpy FIR–bright sources in M33

We present a multiwavelength study of a sample of far-infrared (FIR) sources detected on the Herschel broad–band maps of the nearby galaxy M33. We perform source photometry on the FIR maps as well as mid-infrared (MIR), Hα, far-ultraviolet and integrated HI and CO line emission maps. By fitting MIR/FIR dust emission spectra, the source dust masses, temperatures and luminosities are inferred. The sources are classified based on their Hα morphology (substructured versus not-substructured) and on whether they have a significant CO detection (S/N >3σ). We find that the sources have dust masses in the range 10-10 M⊙ and that they present significant differences in their inferred dust/star formation/gas parameters depending on their Hα morphology and CO detection classification. The results suggests differences in the evolutionary states or in the number of embedded HII regions between the subsamples. The source background–subtracted dust emission seems to be predominantly powered by local star formation, as indicated by a strong correlation between the dust luminosity and the dust-corrected Hα luminosity and the fact that the extrapolated young stellar luminosity is high enough to account for the observed dust emission. Finally, we do not find a strong correlation between the dust-corrected Hα luminosity and the dust mass of the sources, consistent with previous results on the breakdown of simple scaling relations at sub-kpc scales. However, the scatter in the relation is significantly reduced by correcting the Hα luminosity for the age of the young stellar populations in the star–forming regions.