VLBI observations of the CORALZ sample: young radio sources at low
  redshift
  Young radio-loud active galactic nuclei form an important tool to investigate
the evolution of extragalactic radio sources. To study the early phases of
expanding radio sources, we have constructed CORALZ, a sample of 25 compact
($\theta<2"$) radio sources associated with nearby ($z<0.16$) galaxies. In this
paper we determine the morphologies, linear sizes, and put first constraints on
the lobe expansion speeds of the sources in the sample. We observed the radio
sources from the CORALZ sample with MERLIN at 1.4 GHz or 1.6 GHz, the EVN at
1.6 GHz, and global VLBI at 1.6 GHz and/or 5.0 GHz. Radio maps, morphological
classifications, and linear sizes are presented for all sources in the CORALZ
sample. We have determined a first upper limit to the expansion velocity of one
of the sources, which is remarkably low compared to the brighter GPS sources at
higher redshifts, indicating a relation between radio luminosity and expansion
speed, in agreement with analytical models. In addition we present further
strong evidence that the spectral turnovers in GPS and CSS sources are caused
by synchrotron self-absorption (SSA): the CORALZ sources are significantly
offset from the well-known correlation between spectral peak frequency and
angular size, but this correlation is recovered after correcting for the
flux-density dependence, as predicted by SSA theory.
