Cosmic Microwave Background Comptonization by Energetic Nonthermal Electrons in Clusters of Galaxies

Use of the Sunyaev-Zeldovich effect as a precise cosmological probenecessitates a realistic assessment of all possible contributions toComptonization of the cosmic microwave background in clusters of galaxies. Wehave calculated the additional intensity change due to various possiblepopulations of energetic electrons that have been proposed in order to accountfor measurements of intracluster radio, nonthermal X-ray and (possibly also)EUV emission. Our properly normalized estimates of (the highly model dependentvalue of) the predicted intensity change due to these electrons is well below$\sim 6%$ and $\sim 35%$ of the usual Sunyaev-Zeldovich effect due to electronsin the hot gas in Coma and A2199, respectively. These levels constitute highupper limits since they are based on energetic electron populations whoseenergy densities are {\it comparable} to those of the thermal gas. The mainimpact of nonthermal Comptonization is a shift of the crossover frequency(where the thermal effect vanishes) to higher values. Such a shift would haveimportant consequences for our ability to measure cluster peculiar velocitiesfrom the kinematic component of the Sunyaev-Zeldovich effect.Comment: 15 pages, 2 figure