Molecular and Atomic Gas in the Large Magellanic Cloud II.
  Three-dimensional Correlation between CO and HI
  We compare the CO J =(1-0) and HI emission in the Large Magellanic Cloud
(LMC) in three dimensions, i.e. including a velocity axis in addition to the
two spatial axes, with the aim of elucidating the physical connection between
giant molecular clouds (GMCs) and their surrounding HI gas. The CO J =1-0
dataset is from the second NANTEN CO survey and the HI dataset is from the
merged Australia Telescope Compact Array (ATCA) and Parkes Telescope surveys.
The major findings of our analysis are: 1) GMCs are associated with an envelope
of HI emission, 2) in GMCs [average CO intensity] is proportional to [average
HI intensity]^[1.1+-0.1] and 3) the HI intensity tends to increase with the
star formation activity within GMCs, from Type I to Type III. An analysis of
the HI envelopes associated with GMCs shows that their average linewidth is 14
km s-1 and the mean density in the envelope is 10 cm-3. We argue that the HI
envelopes are gravitationally bound by GMCs. These findings are consistent with
a continual increase in the mass of GMCs via HI accretion at an accretion rate
of 0.05 Msun/yr over a time scale of 10 Myr. The growth of GMCs is terminated
via dissipative ionization and/or stellar-wind disruption in the final stage of
GMC evolution.
