Using strong gravitational lensing to zoom in on high-redshift galaxies
  The centres of galaxies are powerful laboratories to test the current
$\Lambda$CDM model for structure formation and evolution. While these
sub-galactic scales can be directly investigated in the local Universe, it is
observationally extremely difficult to access them at high redshift. The
combination of strong gravitational lensing and VLBI observations allows us to
access these scales to study both the baryonic and the dark matter distribution
at the largest distances. For example, it becomes possible to unveil complex
mass density distribution of lensing galaxies, faint cold molecular gas
reservoirs, offset and binary AGN candidates at $z>1$. Currently, these
detailed studies are limited by the small number of known radio-loud lensed
sources. Wide-field VLBI observations may provide a viable way to search for
many more radio-loud systems and test strategies in preparation for the future
surveys with the next generation of interferometers.
