Examining Turbulence in Galactic Molecular Clouds - II: Continuity of Turbulence Cascading in a Portion of the Local Arm

TL;DR

This study analyzes turbulence in a segment of the Local Arm using CO data, revealing a continuous turbulent cascade from large to small scales, with properties consistent with turbulence models and evidence of large-scale shear driving turbulence.

Contribution

It demonstrates the continuity of turbulence cascading across scales in a galactic molecular cloud region and links large-scale shear to turbulence maintenance.

Findings

Turbulence exhibits a continuous cascade from ~400 pc to sub-parsec scales.

Velocity and intensity structure functions show scale-dependent behavior consistent with turbulence models.

Large-scale galactic shear can supply energy to sustain observed turbulence.

Abstract

We use $^{12}$CO (J=1-0) MWISP data to study turbulence in a segment of the Local Arm. Velocity slices at different kinematic distances show similar spatial power spectra (SPSs) and structure functions (SFs), demonstrating that the entire region forms a single turbulent field with a cascade extending from $\sim 400$ pc to sub-parsec scales. The SPS slopes of both the intensity and velocity fields exhibit a systematic scale dependence that approaches the values expected from turbulence models. Cloud-to-cloud VSFs follow similar trends to the pixel-by-pixel VSFs in the extended self-similarity (ESS) scaling, indicating that velocity differences among clouds arise from large-scale turbulent motions. Velocity- and intensity-increment maps reveal filamentary, intermittent structures. The PDFs of the velocity increments display strong non-Gaussianity and are well fitted by the normal inverse gaussian (NIG) distribution, whereas the intensity increments show much weaker tails. A simple energetic estimate suggests that Galactic differential rotation is able to supply the large-scale shear required to maintain the observed turbulence.