Properties of compact 250 \mu m emission and HII regions in M33
  (HERM33ES)
  Within the framework of the HERM33ES Key Project, using the high resolution
and sensitivity of the Herschel photometric data, we study the compact emission
in the Local Group spiral galaxy M33 to investigate the nature of the compact
SPIRE emission sources. We extracted a catalogue of sources at 250um in order
to investigate the nature of this compact emission. Taking advantage of the
unprecedented Herschel resolution at these wavelengths, we also focus on a more
precise study of some striking Halpha shells in the northern part of the
galaxy. We present a catalogue of 159 compact emission sources in M33
identified by SExtractor in the 250um SPIRE band that is the one that provides
the best spatial resolution. We also measured fluxes at 24um and Halpha for
those 159 extracted sources. The morphological study of the shells also
benefits from a multiwavelength approach including Halpha, far-UV from GALEX,
and infrared from both Spitzer IRAC 8um and MIPS 24um in order to make
comparisons. For the 159 compact sources selected at 250um, we find a very
strong Pearson correlation coefficient with the MIPS 24um emission (r24 = 0.94)
and a rather strong correlation with the Halpha emission, although with more
scatter (rHa = 0.83). The morphological study of the Halpha shells shows a
displacement between far-ultraviolet, Halpha, and the SPIRE bands. The cool
dust emission from SPIRE clearly delineates the Halpha shell structures. The
very strong link between the 250um compact emission and the 24um and Halpha
emissions, by recovering the star formation rate from standard recipes for HII
regions, allows us to provide star formation rate calibrations based on the
250um compact emission alone. The different locations of the Halpha and
far-ultraviolet emissions with respect to the SPIRE cool dust emission leads to
a dynamical age of a few Myr for the Halpha shells and the associated cool
dust.
