Context :

Aims : 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 M 33 to investigate the nature of the compact SPIRE emission sources .
We extracted a catalogue of sources at 250 \mu m 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 H \alpha shells in the northern part of the galaxy .

Methods : We present a catalogue of 159 compact emission sources in M 33 identified by SExtractor in the 250 \mu m SPIRE band that is the one that provides the best spatial resolution .
We also measured fluxes at 24 \mu m and H \alpha for those 159 extracted sources .
The morphological study of the shells also benefits from a multiwavelength approach including H \alpha , far-ultraviolet from GALEX , and infrared from both Spitzer IRAC 8 \mu m and MIPS 24 \mu m in order to make comparisons .

Results : For the 159 compact sources selected at 250 \mu m , we find a very strong Pearson correlation coefficient with the MIPS 24 \mu m emission ( r _ { 24 } = 0.94 ) and a rather strong correlation with the H \alpha emission , although with more scatter ( r _ { H \alpha } = 0.83 ) .
The morphological study of the H \alpha shells shows a displacement between far-ultraviolet , H \alpha , and the SPIRE bands .
The cool dust emission from SPIRE clearly delineates the H \alpha shell structures .

Conclusions : The very strong link between the 250 \mu m compact emission and the 24 \mu m and H \alpha emissions , by recovering the star formation rate from standard recipes for H ii regions , allows us to provide star formation rate calibrations based on the 250 \mu m compact emission alone .
The different locations of the H \alpha and far-ultraviolet emissions with respect to the SPIRE cool dust emission leads to a dynamical age of a few Myr for the H \alpha shells and the associated cool dust .