The filamentary structures in the CO emission toward the Milky Way disk

TL;DR

This study analyzes the orientation of filamentary structures in CO emission within the Milky Way, revealing that their alignment varies with local conditions and differs from atomic hydrogen, indicating complex shaping processes.

Contribution

It provides the first statistical analysis of CO filament orientations across a significant Galactic region, highlighting the influence of local physical factors on molecular cloud structures.

Findings

Most CO filaments lack a global preferential orientation.

Certain Galactic regions show filaments aligned with the Galactic plane.

Filament orientations differ from those of HI emission, implying different shaping mechanisms.

Abstract

We present a statistical study of the filamentary structure orientation in the CO emission observations obtained in the Milky Way Imaging Scroll Painting (MWISP) survey in the range $25.8\deg < l < 49.7\deg$, $|b| \leq 1.25\deg$, and $-100 < v_{\rm LSR} < 135$ km/s. We found that most of the filamentary structures in the $^{12}$CO and $^{13}$CO emission do not show a global preferential orientation either parallel or perpendicular to the Galactic plane. However, we found ranges in Galactic longitude and radial velocity where the $^{12}$CO and $^{13}$CO filamentary structures are parallel to the Galactic plane. These preferential orientations are different from those found for the HI emission. We consider this an indication that the molecular structures do not simply inherit these properties from parental atomic clouds. Instead, they are shaped by local physical conditions, such as stellar feedback, magnetic fields, and Galactic spiral shocks.