Non-ideal magnetohydrodynamics vs turbulence I: Which is the dominant
  process in protostellar disc formation?
  Non-ideal magnetohydrodynamics (MHD) is the dominant process. We investigate
the effect of magnetic fields (ideal and non-ideal) and turbulence (sub- and
transsonic) on the formation of circumstellar discs that form nearly
simultaneously with the formation of the protostar. This is done by modelling
the gravitational collapse of a 1~M$_\odot$ gas cloud that is threaded with a
magnetic field and imposed with both rotational and turbulent velocities. We
investigate magnetic fields that are parallel/anti-parallel and perpendicular
to the rotation axis, two rotation rates and four Mach numbers. Disc formation
occurs preferentially in the models that include non-ideal MHD where the
magnetic field is anti-parallel or perpendicular to the rotation axis. This is
independent of the initial rotation rate and level of turbulence, suggesting
that subsonic turbulence plays a minimal role in influencing the formation of
discs. Aside from first core outflows which are influenced by the initial level
of turbulence, non-ideal MHD processes are more important than turbulent
processes during the formation of discs around low-mass stars.
