A Large Scale 12CO (J=1−0) Survey toward the Chamaeleon Region with NANTEN

Abstract

Abstract We carried out a large-scale survey for molecular clouds in 12CO ($J = 1-0$) emission toward the Chamaeleon region with the NANTEN 4-meter radio telescope at Las Campanas Observatory in Chile. The survey covered $\sim 491 \,\mathrm{deg}^2$ toward $284 {{}^{\circ }} \lesssim l \lesssim 320 {{}^{\circ }}$ and $-34 {{}^{\circ }} \lesssim b \lesssim-6 {{}^{\circ }}$ at an $8^{\prime}$ grid spacing. The total molecular mass in the observed area is estimated to be $\sim 8300 \,{{{M}_{\odot}}}$. More than 60% of the total mass is concentrated in and around the previously known Cha I, II, and III dark clouds. Two cloud complexes having molecular hydrogen masses of $\sim 430 \,{{{M}_{\odot}}}$ and $\sim 1300 \,{{{M}_{\odot}}}$, respectively, have been found at $\sim 10 {{}^{\circ }}$ galactic-east of the Chamaeleon major clouds. We have identified a prominent filament extending from Cha I to the galactic-east direction, which is remarkably long ($\gtrsim 40 \,\mathrm{pc}$) compared with filamentary features found in other dark-cloud complexes. A correlation study between the CO distribution and isolated X-ray emitting T Tauri stars (TTSs) indicates that $\gtrsim 65\%$ of the TTSs are located within 1 pc of the 12CO cloud boundaries. This suggests that low-density parental molecular gas still remains around the isolated TTSs, although the dense parts with density greater than $10^3 \,\mathrm{cm}^{-3}$ have almost dissipated. This provides further support for the local formation of “isolated” T Tauri stars in small clouds.