Ubiquitous velocity fluctuations throughout the molecular interstellar medium

Abstract

The density structure of the interstellar medium (ISM) determines where stars form and release energy, momentum, and heavy elements, driving galaxy evolution. Density variations are seeded and amplified by gas motion, but the exact nature of this motion is unknown across spatial scale and galactic environment. Although dense star-forming gas likely emerges from a combination of instabilities, convergent flows, and turbulence, establishing the precise origin is challenging because it requires quantifying gas motion over many orders of magnitude in spatial scale. Here we measure the motion of molecular gas in the Milky Way and in nearby galaxy NGC 4321, assembling observations that span an unprecedented spatial dynamic range ($10^{-1}-10^3$ pc). We detect ubiquitous velocity fluctuations across all spatial scales and galactic environments. Statistical analysis of these fluctuations indicates how star-forming gas is assembled. We discover oscillatory gas flows with wavelengths ranging from $0.3-400$ pc. These flows are coupled to regularly-spaced density enhancements that likely form via gravitational instabilities. We also identify stochastic and scale-free velocity and density fluctuations, consistent with the structure generated in turbulent flows. Our results demonstrate that ISM structure cannot be considered in isolation. Instead, its formation and evolution is controlled by nested, interdependent flows of matter covering many orders of magnitude in spatial scale.

Published in Nature Astronomy on July 6th 2020. This is the authors' version before final edits. Includes methods and supplementary information. Link to the NA publication: https://www.nature.com/articles/s41550-020-1126-z

References in corpus (26)

• Theory of Star Formation
• Trigonometric Parallaxes Of High-Mass Star Forming Regions: Our View Of The Milky Way
• The Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey
• Fast and inefficient star formation due to short-lived molecular clouds and rapid feedback
• The dynamical evolution of molecular clouds near the Galactic Centre - I. Orbital structure and evolutionary timeline
• Spatial distribution of interstellar gas in the innermost 3 kpc of our Galaxy
• Chains of dense cores in the Taurus L1495/B213 complex
• The Bones of the Milky Way
• The dynamical properties of dense filaments in the infrared dark cloud G035.39-00.33
• On the frequency of N2H+ and N2D+
• The Origin of Diffuse X-ray and $\gamma$-ray Emission from the Galactic Center Region: Cosmic Ray Particles
• A cluster in the making: ALMA reveals the initial conditions for high-mass cluster formation
• 'The Brick' is not a brick: A comprehensive study of the structure and dynamics of the Central Molecular Zone cloud G0.253+0.016
• The Survey of Water and Ammonia in the Galactic Center (SWAG): Molecular Cloud Evolution in the Central Molecular Zone
• Complex, Quiescent Kinematics in a Highly Filamentary Infrared Dark Cloud
• G0.253+0.016: A centrally condensed, high-mass protocluster
• Seeding the Galactic Centre gas stream: gravitational instabilities set the initial conditions for the formation of protocluster clouds
• Investigating the structure and fragmentation of a highly filamentary IRDC
• Unveiling the Early-Stage Anatomy of a Protocluster Hub with ALMA
• Abundant Methanol Masers but no New Evidence for Star Formation in GCM0.253+0.016
• Star formation in a high-pressure environment: An SMA view of the Galactic centre dust ridge
• Origins of Scatter in the Relationship Between HCN 1-0 and Dense Gas Mass in the Galactic Center
• Kinematics and properties of the Central Molecular Zone as probed with [C II]
• Autonomous Gaussian decomposition of the Galactic Ring Survey. I. Global statistics and properties of the 13CO emission data
• Multicomponent kinematics in a massive filamentary IRDC
• Spatial Power Spectra of Dust across the Local Group: No Constraint on Disc Scale Height