Continuum spectra covering centimetre to submillimetre wavelengths are
presented for a northern sample of 104 extragalactic radio sources,
mainly active galactic nuclei, based on four-epoch Planck data. The nine
Planck frequencies, from 30 to 857 GHz, are complemented by a set of
simultaneous ground-based radio observations between 1.1 and 37 GHz. The
single-survey Planck data confirm that the flattest high-frequency radio
spectral indices are close to zero, indicating that the original
accelerated electron energy spectrum is much harder than commonly
thought, with power-law index around 1.5 instead of the canonical 2.5.
The radio spectra peak at high frequencies and exhibit a variety of
shapes. For a small set of low-z sources, we find a spectral upturn at
high frequencies, indicating the presence of intrinsic cold dust.
Variability can generally be approximated by achromatic variations,
while sources with clear signatures of evolving shocks appear to be
limited to the strongest outbursts.
- galaxies: active
- galaxies: general
- radio continuum: galaxies