Inadequate turbulent support in low-metallicity molecular clouds

Abstract

The dynamic properties of molecular clouds are set by the interplay of their self-gravity, turbulence, external pressure and magnetic fields. Extended surveys of Galactic molecular clouds typically find that their kinetic energy ($E_{\mathrm{k}}$) counterbalances their self-gravitational energy ($E_{\mathrm{g}}$), setting their virial parameter ${\alpha }_{\mathrm{vir}}=2E_{\mathrm{k}}/|E_{\mathrm{g}}|\approx 1$. However, past studies either have been biased by the use of optically-thick lines or have been limited within the solar neighborhood and the inner Galaxy (Galactocentric radius $R_{\mathrm{gc}}<R_{\mathrm{gc},\odot }\approx 8$ kpc). Here we present sensitive mapping observations of optically thin ${}^{13}$CO lines towards molecular clouds in the low-metallicity Galactic outer disk ($R_{\mathrm{gc}}\sim 9-24$ kpc). By combining archival data from the inner Galaxy and four nearby metal-poor dwarf galaxies, we reveal a systematic trend of ${\alpha }_{\mathrm{vir}}$, which declines from supervirial dynamic states in metal-rich clouds to extremely subvirial dynamic states in metal-poor clouds. In these metal-poor environments, turbulence alone is insufficient to counterbalance the self-gravity of a cloud. A cloud-volumetric magnetic field may replace turbulence as the dominant cloud-supporting mechanism in low-metallicity conditions, for example, the outermost galactic disks, dwarf galaxies and galaxies in the early Universe, which would then inevitably impact the initial conditions for star formation in such environments.

Published in Nature Astronomy. Comments are welcome! Supplementary data are available via Figshare (https://doi.org/10.6084/m9.figshare.27282924), including the 13CO line cubes/profiles, the H2 surface density maps, infrared/radio images and cloud distance probability density functions

References in corpus (68)

• The CO-to-H2 Conversion Factor
• The Neutral Atomic Phases of the ISM in the Galaxy
• Cool Gas in High Redshift Galaxies
• The Formation of Massive Stars from Turbulent Cores
• Trigonometric Parallaxes Of High-Mass Star Forming Regions: Our View Of The Milky Way
• A distance to the Large Magellanic Cloud that is precise to one per cent
• Re-examining Larson's Scaling Relationships in Galactic Molecular Clouds
• The Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey
• The Resolved Properties of Extragalactic Giant Molecular Clouds
• The Critical Density and the Effective Excitation Density of Commonly Observed Molecular Dense Gas Tracers
• How to Calculate Molecular Column Density
• Physical properties of molecular clouds for the entire Milky Way disk
• Physical Properties and Galactic Distribution of Molecular Clouds identified in the Galactic Ring Survey
• The Physical Conditions for Massive Star Formation: Dust Continuum Maps and Modeling
• The Equilibrium State of Molecular Regions in the Outer Galaxy
• Low Virial Parameters in Molecular Clouds: Implications for High Mass Star Formation and Magnetic Fields
• The ISM in distant star-forming galaxies: Turbulent pressure, fragmentation and cloud scaling relations in a dense gas disk at z=2.3
• Cloud-Scale Molecular Gas Properties in 15 Nearby Galaxies
• Equilibrium Star Cluster Formation
• A distance determination to the Small Magellanic Cloud with an accuracy of better than 2 percent based on late-type eclipsing binary stars
• Inefficient Star Formation In Extremely Metal Poor Galaxies
• The link between turbulence, magnetic fields, filaments, and star formation in the Central Molecular Zone cloud G0.253+0.016
• Supernova Driving. I. The Origin of Molecular Cloud Turbulence
• Observational Evidence of Dynamic Star Formation Rate in Milky Way Giant Molecular Clouds
• Star formation in metal-poor gas clouds
• Six Myths on the Virial Theorem for Interstellar Clouds
• Duchamp: a 3D source finder for spectral-line data
• Physical Properties of Giant Molecular Clouds in the Large Magellanic Cloud
• The evolution of CNO isotopes: the impact of massive stellar rotators
• A Model for the Onset of Self-gravitation and Star Formation in Molecular Gas Governed by Galactic Forces: I. Cloud-scale Gas Motions
• Molecular clouds and clumps in the Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey
• Physical Properties of Molecular Clouds at 2 parsec Resolution in the Low-Metallicity Dwarf Galaxy NGC 6822 and the Milky Way
• Feedback Effects on Low-Mass Star Formation
• A Possible Extension of the Scutum-Centaurus Arm into the Outer Second Quadrant
• Opacity broadening and interpretation of suprathermal CO linewidths: Macroscopic Turbulence and Tangled Molecular Clouds
• Massive Quiescent Cores in Orion: Dynamical State Revealed by High-Resolution Ammonia Maps
• The Star Formation Rate of the Milky Way as seen by Herschel
• Magnetic fields in the nearby spiral galaxy IC 342: A multi-frequency radio polarization study
• The ${}^{12}$CO/${}^{13}$CO ratio in turbulent molecular clouds
• Magnetic fields in nearby normal galaxies: Energy equipartition
• Gradients of chemical abundances in the Milky Way from HII regions: distances derived from Gaia EDR3 parallaxes and temperature inhomogeneities
• Characterization of Infrared Dark Clouds -- NH${}_3$ Observations of an Absorption-contrast Selected IRDC Sample
• The Elongations and Supersonic Motions of Molecular Clouds
• CHIMPS: Physical properties of molecular clumps across the inner Galaxy
• The state of the molecular gas in a luminous starburst/Seyfert 2 galaxy: NGC 1068 revisited
• Outflows and Bubbles in Taurus: Star-formation Feedback Sufficient to Maintain Turbulence
• ALMA observations of cool dust in a low-metallicity starburst, SBS0335-052
• An Early Transition to Magnetic Supercriticality in Star Formation
• First Results from the $Herschel$ and ALMA Spectroscopic Surveys of the SMC: The Relationship Between [CII]-bright Gas and CO-bright Gas at Low Metallicity
• Physical conditions of molecular gas in the Circinus galaxy: Multi-J CO and CI 1-0 observations
• WISDOM Project -- IX Giant Molecular Clouds in the Lenticular Galaxy NGC4429: Effects of Shear and Tidal Forces on Clouds
• Kinetic temperature of massive star forming molecular clumps measured with formaldehyde
• A New Cepheid Distance Measurement and Method for NGC 6822
• H2, CO, and Dust Absorption through Cold Molecular Clouds
• Relations Between Molecular Cloud Structure Sizes and Line Widths in the Large Magellanic Cloud
• First detection of 13CH in the interstellar medium
• Molecular clouds in the extreme outer Galaxy between $l=34.75^{\circ }$ to $45.25^{\circ }$
• The PNe and H II regions in NGC 6822 revisited. Clues to AGB nucleosynthesis
• Dense Molecular Clumps associated with the LMC Supergiant Shells LMC 4 \& LMC 5
• Molecular cloud catalogue from ${}^{13}$CO(1-0) data of the Forgotten Quadrant Survey
• Over-sized gas clumps in an extremely-metal-poor molecular cloud revealed by ALMA's pc-scale maps
• CO(2-1) Survey at 9 parsec resolution in the SMC
• An Unbiased CO Survey Toward the Northern Region of the Small Magellanic Cloud with the Atacama Compact Array. II. CO Cloud Catalog
• Turbulence in Zeeman Measurements from Molecular Clouds
• Coupling local to global star formation in spiral galaxies: the effect of differential rotation
• Star formation in evolving molecular clouds
• Kinematics of Galactic Centre clouds shaped by shear-seeded solenoidal turbulence
• Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages

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• Molecular Clouds at the Edge of the Galaxy I. Variation of CO J=2-1/1-0 Line Ratio
• Molecular Clouds at the Edge of the Galaxy II. Physical properties and scaling relations