Deep, ultra-high-resolution radio imaging of submillimetre galaxies
  using Very Long Baseline Interferometry
  We present continent-scale VLBI - obtained with the European VLBI Network
(EVN) at a wavelength of 18cm - of six distant, luminous submm-selected
galaxies (SMGs). Our images have a synthesized beam width of ~30 milliarcsec
FWHM - three orders of magnitude smaller in area than the highest resolution
VLA imaging at this wavelength - and are capable of separating radio emission
from ultra-compact radio cores (associated with active super-massive black
holes - SMBHs) from that due to starburst activity. Despite targeting compact
sources - as judged by earlier observations with the VLA and MERLIN - we
identify ultra-compact cores in only two of our targets. This suggests that the
radio emission from SMGs is produced primarily on larger scales than those
probed by the EVN, and therefore is generated by star formation rather than an
AGN - a result consistent with other methods used to identify the presence of
SMBHs in these systems.
