The most compact bright radio-loud AGN -- I. A new target sample
  selected for the space VLBI
  We investigated the archival ground-based VLBI images of the extragalactic
radio sources included in both the {\it Wilkinson Microwave Anisotropy Probe
(WMAP)} and the {\it Planck} catalogues, and selected 49 bright and compact
sources as potential targets for space Very Long Baseline Interferometry (VLBI)
observations at mm wavelengths. These sources have a flat radio continuum
spectrum between 33 and 94~GHz. They are identified as core-dominated active
galactic nuclei (AGN), located at declinations above $-40\degr$, and have never
been observed with ground-based VLBI at 86~GHz. The radio properties of the 49
new sources are presented. We compare this new sample with similar samples of
compact AGN available from earlier studies. The new candidates, together with
the existing bright compact AGN sample identified from 86-GHz ground-based VLBI
imaging surveys, form a catalogue of more than 160 AGN. These could be primary
targets for mm-VLBI observations on the ground, as well as for future
mm-wavelength space VLBI missions such as the project with two satellites
currently under study in China.
