TRAO Survey of Nearby Filamentary Molecular Clouds, the Universal Nursery of Stars (TRAO-FUNS). III. Filaments and Dense Cores in the NGC 2068 and NGC 2071 Regions of Orion B

Abstract

We present the results of molecular line observations performed toward the NGC 2068 and NGC 2071 regions of the Orion B cloud as the TRAO-FUNS project to study the roles of the filamentary structure in the formation of dense cores and stars in the clouds. Gaussian decomposition for the C ^18 O spectra with multiple velocity components and the application of a friends-of-friends algorithm for the decomposed components allowed us to identify a few tens of velocity-coherent filaments. We also identified 48 dense cores from the observations of N _2 H ^+ using a core finding tool, FellWalker. We performed a virial analysis for these filaments and dense cores, finding that the filaments with N _2 H ^+ dense core are thermally supercritical, and the filaments with a larger ratio between the line mass and the thermal critical line mass tend to have more dense cores. We investigated the contribution of the nonthermal motions in dense cores and filaments, showing the dense cores are mostly in transonic/subsonic motions while their natal filaments are mostly in supersonic motions. This may indicate that gas turbulent motions in the filaments have been dissipated at the core scale to form the dense cores there. The filaments with (dynamically evolved) dense cores in infalling motions or with NH _2 D bright (or chemically evolved) dense cores are all found to be gravitationally critical. Therefore, the criticality of the filament is thought to provide a key condition for its fragmentation, the formation of dense cores, and their kinematical and chemical evolution.

Keywords

• Interstellar medium
• Interstellar filaments
• Molecular clouds
• Star formation
• Radio astronomy