Synchrotron emission from hot accretion flows and the cosmic microwave background anisotropy

Current estimates of number counts of radio sources in the frequency range in which the most sensitive cosmic microwave background (CMB) experiments a re carried out significantly underrepresent sources with strongly inverted spectra. Hot accretion flows around supermassive black holes in the nuclei of nearby galaxies are expected to produce inverted radio spectra by therma l synchrotron emission. We calculate the temperature fluctuations and power spectra of these sources in the Planck Surveyor 30 GHz energy channel, whe re their emission is expected to peak. We find that their potential contrib ution is generally comparable to the instrumental noise, and approaches the CMB anisotropy level at small angular scales. Forthcoming missions, which will provide a large statistical sample of inverted-spectra sources, will b e crucial for determining the distribution of hot accretion flows in nearby quiescent galactic nuclei. Detection of these sources in different frequen cy channels will help constrain their spectral characteristics, and hence t heir physical properties.