Radio-loud Active Galactic Nuclei
The highest frequency at which radio continuum sky surveys have been made is
GHz.
Since the beam area of a given radio telescope scales as
, a large, ground-based, extragalactic survey at higher frequencies
would require expensive multi-channel receivers and huge amounts of telescope
time. Above 30 GHz, ground-based observations are in any case
extremely difficult, and only very small areas can be surveyed.
In the large area of sky surveyed at the three PLANCK radio frequencies (30, 53 and 90 GHz), we expect to find several thousand flat-spectrum radiogalaxies, QSOs and blazars above the overall noise level. This prediction is based on high-frequency extrapolations of radiogalaxy counts at centimetre wavelengths (see Table 1.1).
Given the large fraction of blazars among flat-spectrum radiosources, the all-sky PLANCK survey will provide the most complete and richest catalogue of such objects, suitable for comparison with X-ray selected samples (e.g. as produced by ROSAT). A great advantage of such a radio-selected sample will be its common detailed spectral information over a wide frequency interval.
Another important outcome will be to check for the existence of strongly inverted-spectrum millimetre-peaked radiosources, i.e. very compact, radio-loud AGN, which is a matter of speculation at present.