Observing protoplanetary discs with the Square Kilometre Array -- I.
  Characterising pebble substructure caused by forming planets
  High angular resolution observations of discs at mm wavelengths (on scales of
a few au) are now commonplace, but there is a current lack of a comparable
angular resolution for observations at cm wavelengths. This presents a
significant barrier to improving our understanding of planet formation, in
particular how dust grains grow from mm to cm sizes. In this paper, we examine
the ability of the Square Kilometre Array (SKA) to observe dust substructure in
a young, planet-forming disc at cm wavelengths. We use dusty hydrodynamics and
continuum radiative transfer to predict the distribution and emission of 1 cm
dust grains (or pebbles) within the disc, and simulate continuum observations
with the current SKA1-MID design baseline at frequencies of 12.5 GHz (Band 5b,
~2.4 cm) on 5-10 au scales. The SKA will provide high-fidelity observations of
the cm dust emission substructure in discs for integration times totalling
100's of hours. Radial structure can be obtained at a sufficient resolution and
S/N from shorter (10's of hours) integration times by azimuthal averaging in
the image plane. By modelling the intensity distribution directly in the
visibility plane, it is possible to recover a similar level of (axisymmetric)
structural detail from observations with integration times 1-2 orders of
magnitude lower than required for high-fidelity imaging. Our results
demonstrate that SKA1-MID will provide crucial constraints on the distribution
and morphology of the raw material for building planets, the pebbles in
protoplanetary discs.
