Spitzer photometry of YSC in M33

The properties of young stellar clusters (YSCs) in M33, identified from the center out to about twice the size of the bright star-forming disk, are investigated to determine possible spatial and time variations of the star formation process in this Local Group blue galaxy. 915 MIR sources have been extracted from the Spitzer 24um image. Upon inspection of H{alpha} and GALEX images and exclusion of evolved AGB stars, a sample of 648 objects is selected as candidate YSCs and their luminosity function is examined.

The spectral energy distribution of each object, based on aperture photometry, is compared with Starburst99 models to derive age, mass and AV of individual clusters. In the analysis we allow for different values of the upper mass cutoff of the stellar initial mass function (IMF), the porosity of the ISM, and the dustiness of HII regions. We also examine the influence of different dust models and include corrections for incompleteness of the IMF.