Kinematics of the CO Gas in the Inner Regions of the TW Hya Disk
  We present a detailed analysis of the spatially and spectrally resolved 12CO
J=2-1 and J=3-2 emission lines from the TW Hya circumstellar disk, based on
science verification data from the Atacama Large Millimeter/Submillimeter Array
(ALMA). These lines exhibit substantial emission in their high-velocity wings
(with projected velocities out to 2.1 km/s, corresponding to intrinsic orbital
velocities >20 km/s) that trace molecular gas as close as 2 AU from the central
star. However, we are not able to reproduce the intensity of these wings and
the general spatio-kinematic pattern of the lines with simple models for the
disk structure and kinematics. Using three-dimensional non-local thermodynamic
equilibrium molecular excitation and radiative transfer calculations, we
construct some alternative models that successfully account for these features
by modifying either (1) the temperature structure of the inner disk (inside the
dust-depleted disk cavity; r < 4 AU); (2) the intrinsic (Keplerian) disk
velocity field; or (3) the distribution of disk inclination angles (a warp).
The latter approach is particularly compelling because a representative warped
disk model qualitatively reproduces the observed azimuthal modulation of
optical light scattered off the disk surface. In any model scenario, the ALMA
data clearly require a substantial molecular gas reservoir located inside the
region where dust optical depths are known to be substantially diminished in
the TW Hya disk, in agreement with previous studies based on infrared
spectroscopy. The results from these updated model prescriptions are discussed
in terms of their potential physical origins, which might include dynamical
perturbations from a low-mass companion with an orbital separation of a few AU.
