van der Kruit to Spitzer: A New Look at the FIR-Radio Correlation
  We present an initial look at the far infrared-radio correlation within the star-forming disks of four nearby, nearly face-on galaxies (NGC~2403, NGC~3031, NGC~5194, and NGC~6946). Using {\it Spitzer} MIPS imaging and WSRT radio continuum data, we are able to probe variations in the logarithmic 70~$\mu$m/22~cm ($q_{70}$) flux density ratios across each disk at sub-kpc scales. We find general trends of decreasing $q_{70}$ with declining surface brightness and with increasing radius. We also find that the dispersion in $q_{70}$ within galaxies is comparable to what is measured {\it globally} among galaxies at around 0.2 dex. We have also performed preliminary phenomenological modeling of cosmic ray electron (CR$e^{-}$) diffusion using an image-smearing technique, and find that smoothing the infrared maps improves their correlation with the radio maps. The best fit smoothing kernels for the two less active star-forming galaxies (NGC~2403 and NGC~3031) have much larger scale-lengths than that of the more active star-forming galaxies (NGC~5194 and NGC~6946). This difference may be due to the relative deficit of recent CR$e^{-}$ injection into the interstellar medium (ISM) for the galaxies having largely quiescent disks. 
Eric J. Murphy (Yale), Robert Braun (ASTRON, Netherlands), George   Helou (Caltech), Lee Armus (Caltech), Jeff D. P. Kenney ...