Bimodal orientation distribution and head-tail asymmetry of a sample of filamentary molecular clouds

Abstract

The morphology of molecular clouds is crucial for understanding their origin and evolution. In this work, we investigate the morphology of the filamentary molecular clouds (filaments for short) using a portion of the ${}^{12}\text{CO}(J=1-0)$ data from the Milky Way Imaging Scroll Painting (MWISP) project. The data cover an area spanning $104.75^{\circ }<l<150.25^{\circ },|b|<5.25^{\circ }$ in Galactic coordinates, with $V_{\text{LSR}}$ ranging from $-95$ to 25 ${\text{km s}}^{-1}$. Our primary focus is on the orientation and morphological asymmetry of the filaments. To achieve this, we apply several criteria on the data to create a sample of filaments with well-defined straight shape, and we use elliptical fitting to obtain the orientation of each filament, with an estimated error of $\sim 1.6^{\circ }$ for the orientation. We find that the filament orientation with respect to the Galactic plane exhibits a bimodal distribution, a double-Gaussian fitting of which has two centres located at $-38.1^{\circ }$ and $42.0^{\circ }$, with 1$\sigma$ of the two Gaussian functions being $35.4^{\circ }$ and $27.4^{\circ }$. We do not find significant correlation between the orientation and other parameters, including the Galactic coordinates, radial velocity, velocity width, and physical scale. A considerable fraction of filaments ($\gtrsim 40$ per cent) display head-tail asymmetry, which suggests that mass concentration tends to occur at one end of the filaments.

16 pages, 19 figures, accepted by MNRAS

References in corpus (14)

• Filamentary structure of star-forming complexes
• The Milky Way Imaging Scroll Painting (MWISP): Project Details and Initial Results from the Galactic Longitude of 25.8deg to 49.7deg
• The Bones of the Milky Way
• Magnetically Dominated Strands of Cold Hydrogen in the Riegel-Crutcher Cloud
• A Census of Large-Scale ($\ge$ 10 pc), Velocity-Coherent, Dense Filaments in the Northern Galactic Plane: Automated Identification Using Minimum Spanning Tree
• The evolution of Giant Molecular Filaments
• Initial Conditions for Star Formation: A Physical Description of the Filamentary ISM
• Edge collapse and subsequent longitudinal accretion in Filament S242
• Star-forming sites IC 446 and IC 447: an outcome of end-dominated collapse of Monoceros R1 filament
• The relative orientation between the magnetic field and gradients of surface brightness within thin velocity slices of 12CO and 13CO emission from the Taurus molecular cloud
• Magnetic Field Orientation in Self-Gravitating Turbulent Molecular Clouds
• Distances to molecular clouds in the second Galactic quadrant
• The properties of clusters, and the orientation of magnetic fields relative to filaments, in magnetohydrodynamic simulations of colliding clouds
• The filamentary structures in the CO emission toward the Milky Way disk