A radio continuum survey of Shapley-Ames galaxies at λ2.8 cm III. The radio – far infrared correlation

Radio flux densities of Shapley-Ames galaxies at λ2.8 cm from Niklas et al. (1995a, Paper I) and at λ20 cm from Condon (1987, C87) have been used to investigate the radio – far infrared (FIR) correlation at two different radio wavelengths. The correlation between monochromatic radio and the FIR luminosity was found to be non-linear (P2.8cm ∝ L1.09±0.04 FIR and P20cm ∝ L1.23±0.05 FIR ). Galaxies with Seyfert activity often exhibit enhanced radio emission compared to the FIR. Interacting and Starburst Galaxies do not show significant deviations from the correlation. For 74 galaxies with separated thermal and nonthermal radio emission the thermal radio luminosity was found to be proportional to the FIR luminosity. At both frequencies the non-thermal radio luminosity is non-linearly connected to the FIR luminosity (Pnth ∝ L1.25±0.08 FIR ). From the ratio Pth/LFIR one can conclude that' 30 % of the FIR emission can be attributed to dust associated with massive star-forming regions.