Gas Kinematics of the Massive Protocluster G286.21+0.17 Revealed by ALMA
  We study the gas kinematics and dynamics of the massive protocluster
G286.21+0.17 with the Atacama Large Millimeter/submillimeter Array using
spectral lines of $C^{18}O$(2-1), $N_2D^+$(3-2), $DCO^+$(3-2) and $DCN$(3-2).
On the parsec clump scale, $C^{18}O$ emission appears highly filamentary around
the systemic velocity. $N_2D^+$ and $DCO^+$ are more closely associated with
the dust continuum. $DCN$ is strongly concentrated towards the protocluster
center, where no or only weak detection is seen for $N_2D^+$ and $DCO^+$,
possibly due to this region being at a relatively evolved evolutionary stage.
Spectra of 76 continuum defined dense cores, typically a few 1000 AU in size,
are analysed to measure their centroid velocities and internal velocity
dispersions. There are no statistically significant velocity offsets of the
cores among the different dense gas tracers. Furthermore, the majority (71\%)
of the dense cores have subthermal velocity offsets with respect to their
surrounding, lower density $C^{18}O$ emitting gas. Within the uncertainties,
the dense cores in G286 show internal kinematics that are consistent with being
in virial equilibrium. On clumps scales, the core to core velocity dispersion
is also similar to that required for virial equilibrium in the protocluster
potential. However, the distribution in velocity of the cores is largely
composed of two spatially distinct groups, which indicates that the dense
molecular gas has not yet relaxed to virial equilibrium, perhaps due to there
being recent/continuous infall into the system.
