2019/05/10 by Katsuhiro Hayashi, Ryuji Okamoto, Hiroaki Yamamoto +4
Chemistry · Earth and Planetary Sciences · Physics and Astronomy · #Astrophysics #Astrophysics and Star Formation Studies #Atmospheric Ozone and Climate #Molecular cloud #Opacity #Optics #Physics #Spectroscopy and Laser Applications #Stars #astro-ph.GA
paper · pdf · doi:10.3847/1538-4357/ab2051
30 pages, 21 figures, Accepted for ApJ
arxiv created 2019/05/10 · openalex publication_date 2019/06/20 · arxiv updated 2019/06/26 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Abstract Gas and dust properties in the Chamaeleon molecular cloud complex have been investigated with emission lines from the atomic hydrogen (H i ) and 12 CO molecules, dust optical depth at 353 GHz ( τ 353 ), and J -band infrared extinction ( A J ). We have found a scatter correlation between the H i integrated intensity ( W H i ) and τ 353 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 ( N H ) model based on τ 353 . A nonlinear relation of τ 353 with the ∼1.2 power of A J has been found in opaque regions ( A J ≳ 0.3 mag), which may indicate a dust evolution effect. If we apply this nonlinear relation to the N H model (i.e., N H ∝ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>τ</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>353</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mn>1.2</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> ) allowing arbitrary τ H i , the model curve reproduces well the W H i – τ 353 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 N H model, we have derived the CO-to-H 2 conversion factor ( X CO ) on ∼1.°5 scales (corresponding to ∼4 pc) and found spatial variations of X CO ∼ (0.5–3) × 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.