The Radio Spectral Energy Distribution and Star Formation Rate
  Calibration in Galaxies
  We study the spectral energy distribution (SED) of the radio continuum
emission from the KINGFISH sample of nearby galaxies to understand the
energetics and origin of this emission. Effelsberg multi-wavelength
observations at 1.4GHz, 4.8GHz, 8.5GHz, and 10.5GHz combined with archive data
allow us, for the first time, to determine the mid-radio continuum (1-10 GHz,
MRC) bolometric luminosities and further present calibration relations vs. the
monochromatic radio luminosities. The 1-10 GHz radio SED is fitted using a
Bayesian Markov Chain Monte Carlo (MCMC) technique leading to measurements for
the nonthermal spectral index and the thermal fraction f_th with mean values of
alpha_nt=0.97+-0.16 (0.79+-0.15 for the total spectral index) and f_th= 10% +-
9% at 1.4 GHz. The MRC luminosity changes over ~3 orders of magnitude in the
sample. The thermal emission is responsible for ~23% of the MRC on average. We
also compare the extinction-corrected diagnostics of star formation rate with
the thermal and nonthermal radio tracers and derive the first star formation
calibration relations using the MRC radio luminosity. The nonthermal spectral
index flattens with increasing star formation rate surface density, indicating
the effect of the star formation feedback on the cosmic ray electron population
in galaxies. Comparing the radio and IR SEDs, we find that the FIR-to-MRC ratio
could decrease with star formation rate, due to the amplification of the
magnetic fields in star forming regions. This particularly implies a decrease
in the ratio at high redshifts, where mostly luminous/star forming galaxies are
detected.
