Abstract:
The radio-farinfrared correlation holds within galaxies down to scales of
about 50 pc. It indicates a close relation between star formation and the
generation of magnetic fields and cosmic rays. We developed a new method
to compute an extinction map (from a dust model derived from the Spitzer
FIR data) which is used to correct H-alpha and to separate the radio
thermal and nonthermal components. Our scale-by-scale analysis in M33
using wavelet functions showed that the correlation is almost perfect on all scales between the radio thermal emission and the warm dust emission. The non-thermal (synchrotron) radio emission is correlated with the FIR emission at scales below 2 kpc, because magnetic fields and cosmic rays are enhanced
in star-forming regions. - A similar analysis for M31 revealed significant
differences to M33: The high correlation between radio thermal and FIR
emission only holds at scales beyond 1 kpc, the high synchrotron-FIR cor-
relation only at scales larger than 2 kpc. These results indicate that dust
heating sources are different in the two galaxies and show the important
role of magnetic fields for the radio-FIR correlation.