Gas and dust properties in the Chamaeleon molecular cloud complex based on the optically thick H I.
HAYASHI K., OKAMOTO R., YAMAMOTO H., HAYAKAWA T., TACHIHARA K. and FUKUI Y.
Abstract (from CDS):
Gas and dust properties in the Chamaeleon molecular cloud complex have been investigated with emission lines from the atomic hydrogen (H I) and 12CO molecules, dust optical depth at 353 GHz (τ353), and J-band infrared extinction (AJ). We have found a scatter correlation between the H I integrated intensity (W_H I_) and τ353 in the Chamaeleon region. The scattering has been examined in terms of a possible large optical depth in H I emission (τ_H I_) using a total column density (NH) model based on τ353. A nonlinear relation of τ353 with the ∼1.2 power of AJ has been found in opaque regions (AJ >= 0.3 mag), which may indicate a dust evolution effect. If we apply this nonlinear relation to the NH model (i.e., NH ∝ τ3531/1.2) allowing arbitrary τ_H I_, the model curve reproduces well the W_H I–τ353_ scatter correlation, suggesting optically thick H I (τ_H I_ ∼ 1.3) extended around the molecular clouds. Based on the correlations between the CO integrated intensity and the NH model, we have derived the CO-to-H2 conversion factor (XCO) on ∼1.°5 scales (corresponding to ∼4 pc) and found spatial variations of XCO ∼ (0.5-3) x 1020 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.