A Multi-Scale Study of IR and Radio Emission from M33
  The origin of the tight radio--IR correlation in galaxies has not been fully understood. One reason is the uncertainty about which heating sources (stars or diffuse interstellar radiation field)provide the energy that is absorbed by dust and re-radiated in IR. Another problem is caused by comparing the IR emission with the thermal and nonthermal components of the radio continuum emission separated by simplistically assuming a constant nonthermal spectral index. We use the data at the $Spitzer$ MIPS wavelengths of 24, 70, and 160 $\mu$m, as well as recent radio continuum map at 3.6 cm observed with the 100--m Effelsberg telescope. Using the wavelet transformation, we separate diffuse emission components from compact sources and study the radio-IR correlation at various scales. We also investigate the IR correlations with the thermal and nonthermal radio emissions separated by our developed method. A H$\alpha$ map serves as a tracer of star forming regions. 
F. S. Tabatabaei, R. Beck, M. Krause, E. M. Berkhuijsen, R. Gehrz, K.   D. Gordon, J. L. Hinz, and G. H. Rieke