Gas and Dust Properties in the Chamaeleon Molecular Cloud Complex based
  on the Optically Thick HI
  Gas and dust properties in the Chamaeleon molecular cloud complex have been
investigated with emission lines from atomic hydrogen (HI) and 12CO molecule,
dust optical depth at 353 GHz ($\tau_{353}$), and $J$-band infrared extinction
($A_{J}$). We have found a scatter correlation between the HI integrated
intensity ($W_{\rm HI}$) and $\tau_{353}$ in the Chamaeleon region. The
scattering has been examined in terms of possible large optical depth in HI
emission ($\tau_{\rm HI}$) using a total column density ($N_{\rm H}$) model
based on $\tau_{353}$. A nonlinear relation of $\tau_{353}$ with the $\sim$1.2
power of $A_{J}$ has been found in opaque regions ($A_{J}$ $\gtrsim$ 0.3 mag),
which may indicate dust evolution effect. If we apply this nonlinear relation
to the $N_{\rm H}$ model (i.e., $N_{\rm H} \propto \tau_{353}^{1/1.2}$)
allowing arbitrary $\tau_{\rm HI}$, the model curve reproduces well the $W_{\rm
HI}$-$\tau_{353}$ scatter correlation, suggesting optically thick HI
($\tau_{\rm HI} \sim$1.3) extended around the molecular clouds. Based on the
correlations between the CO integrated intensity and the $N_{\rm H}$ model, we
have then derived the CO-to-H$_{2}$ conversion factor ($X_{\rm CO}$) on
$\sim$1.5$^{\circ}$ scales (corresponding to $\sim$4 persec) and found spatial
variations of $X_{\rm CO}$ $\sim$(0.5-3)$\times$10$^{20}$ cm$^{-2}$ K$^{-1}$
km$^{-1}$ s across the cloud complex, possibly depending on the radiation field
inside or surrounding the molecular clouds. These gas properties found in the
Chamaeleon region are discussed through a comparison with other local molecular
cloud complexes.
