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

Abstract

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), Halpha, far-ultraviolet and integrated H I 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 Halpha morphology (sub-structured versus not-substructured) and on whether they have a significant CO detection (S/N > 3sigma). We find that the sources have dust masses in the range 102-104 M&sun; and that they present significant differences in their inferred dust/star formation/gas parameters depending on their Halpha morphology and CO detection classification. The results suggests differences in the evolutionary states or in the number of embedded H II regions between the sub-samples. 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 Halpha 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 Halpha 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 Halpha luminosity for the age of the young stellar populations in the star-forming regions.