Morphology of the $^{13}$CO(3-2) millimeter emission across the gas disc
  surrounding the triple protostar GG Tau A using ALMA observations
  Observations by the Atacama Large Millimeter/sub-millimeter Array of the dust
continuum and $^{13}$CO(3-2) millimeter emissions of the triple stellar system
GG Tau A are analysed, giving evidence for a rotating gas disc and a concentric
and coplanar dust ring. The present work complements an earlier analysis (Tang
et al. 2016) by exploring detailed properties of the gas disc. A 95% confidence
level upper limit of 0.24 arcsec (34 au) is placed on the disc scale height at
a distance of 1 arcsec (140 au) from the central stars. Evidence for Keplerian
rotation of the gas disc is presented, the rotation velocity reaching ~3.1
kms$^{-1}$ at 1 arcsec from the central stars, and a 99% confidence level upper
limit of 9% is placed on a possible in-fall velocity relative contribution.
Variations of the intensity across the disc area are studied in detail and
confirm the presence of a hot spot in the south-eastern quadrant. However
several other significant intensity variations, in particular a depression in
the northern direction, are also revealed. Variations of the intensity are
found to be positively correlated to variations of the line width. Possible
contributions to the measured line width are reviewed, suggesting an increase
of the disc temperature and opacity with decreasing distance from the stars.
