Strong lensing reveals jets in a sub-microJy radio quiet quasar
  We present e-MERLIN and EVN observations which reveal unambiguous jet
activity within radio quiet quasar HS~0810+2554. With an intrinsic flux density
of 880~nJy, this is the faintest radio source ever imaged. The findings present
new evidence against the idea that radio loud and radio quiet quasars are
powered by different underlying radio emission mechanisms, showing instead that
the same AGN mechanism can operate as the dominant source of radio emission
even in the very lowest radio luminosity quasars. Thanks to strong
gravitational lensing, our source is not only visible, but with VLBI is imaged
to a scale of just 0.27~pc: the highest ever resolution image of a radio quiet
quasar. Brightness temperatures of at least $8.4\times 10^6$~K are associated
with two highly compact components, and subsequent modelling of the lensed
system has revealed that the components are linearly aligned on opposing sides
of the optical quasar core, with the typical morphology of a compact symmetric
object (CSO). Given that this source has been found to fall on the radio--FIR
correlation, we suggest that the radio--FIR correlation cannot always be used
to rule out AGN activity in favour of star-formation activity. The correlation
-- or at least its scatter -- may conceal the coexistence of kinetic and
radiative feedback modes in AGN. Modelling of the lensing mass itself points to
a non-smooth mass distribution, hinting at the presence of dark matter
substructure which has manifested as astrometric perturbations of the VLBI
lensed images, posing no threat to the CDM paradigm.
