Radio Evidence for AGN Activity: Relativistic as Tracers of SMBHs
  Although the radio emission from most quasars appears to be associated with
star forming activity in the host galaxy, about ten percent of optically
selected quasars have very luminous relativistic jets apparently powered by a
SMBH which is located at the base of the jet. When these jets are pointed close
to the line of sight their apparent luminosity is enhanced by Doppler boosting
and appears highly variable. High resolution radio interferometry shows
directly the outflow of relativistic plasma jets from the SMBH. Apparent
transverse velocities in these so called blazars are typically about 7c but
reach as much as 50c indicating true velocities within one percent of the speed
of light. The jets appear to be collimated and accelerated in regions as much
as a hundred parsecs downstream from the SMBH. Measurements made with Earth to
space interferometers indicate apparent brightness temperatures of about 10E14
K or more. This is well in excess of the limits imposed by inverse Compton
cooling. The modest Doppler factors deduced from the observed ejection speeds
appear to be inadequate to explain the high observed brightness temperatures in
terms of relativistic boosting.
