GG Tau A: gas properties and dynamics from the cavity to the outer disk
  We used new ALMA $^{13}$CO and C$^{18}$O(3-2) observations obtained at high
angular resolution ($\sim$0.2") together with previous CO(3-2) and (6-5) ALMA
data and continuum maps at 1.3 and 0.8 mm in order to determine the gas
properties (temperature, density, and kinematics) in the cavity and to a lesser
extent in the outer disk of GG Tau A, the prototype of a young triple T Tauri
star that is surrounded by a massive and extended Keplerian outer disk. By
deprojecting, we studied the radial and azimuthal gas distribution and its
kinematics. We also applied a new method to improve the deconvolution of the CO
data and in particular better quantify the emission from gas inside the cavity.
We perform local and nonlocal thermodynamic equilibrium studies in order to
determine the excitation conditions and relevant physical parameters inside the
ring and in the central cavity. Residual emission after removing a smooth-disk
model indicates unresolved structures at our angular resolution, probably in
the form of irregular rings or spirals. The outer disk is cold, with a
temperature $<20$ K beyond 250 au that drops quickly (r$^{-1}$). The kinematics
of the gas inside the cavity reveals infall motions at about 10% of the
Keplerian speed. We derive the amount of gas in the cavity, and find that the
brightest clumps, which contain about 10% of this mass, have kinetic
temperatures 40$-$80 K, CO column densities of a few 10$^{17}$ cm$^{-2}$, and
H$_2$ densities around 10$^7$ cm$^{-3}$. Although the gas in the cavity is only
a small fraction of the disk mass, the mass accretion rate throughout the
cavity is comparable to or higher than the stellar accretion rate. It is
accordingly sufficient to sustain the circumstellar disks on a long timescale.
