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.
Download