ALMA Observations of a Quiescent Molecular Cloud in the Large Magellanic Cloud

Abstract

We present high-resolution (sub-parsec) observations of a giant molecular cloud in the nearest star-forming galaxy, the Large Magellanic Cloud. ALMA Band 6 observations trace the bulk of the molecular gas in ${}^{12}$CO(2-1) and high column density regions in ${}^{13}$CO(2-1). Our target is a quiescent cloud (PGCC G282.98-32.40, which we refer to as the "Planck cold cloud" or PCC) in the southern outskirts of the galaxy where star-formation activity is very low and largely confined to one location. We decompose the cloud into structures using a dendrogram and apply an identical analysis to matched-resolution cubes of the 30 Doradus molecular cloud (located near intense star formation) for comparison. Structures in the PCC exhibit roughly 10 times lower surface density and 5 times lower velocity dispersion than comparably sized structures in 30 Dor, underscoring the non-universality of molecular cloud properties. In both clouds, structures with relatively higher surface density lie closer to simple virial equilibrium, whereas lower surface density structures tend to exhibit super-virial line widths. In the PCC, relatively high line widths are found in the vicinity of an infrared source whose properties are consistent with a luminous young stellar object. More generally, we find that the smallest resolved structures ("leaves") of the dendrogram span close to the full range of line widths observed across all scales. As a result, while the bulk of the kinetic energy is found on the largest scales, the small-scale energetics tend to be dominated by only a few structures, leading to substantial scatter in observed size-linewidth relationships.

Accepted by ApJ; 21 pages in AASTeX two-column style

References in corpus (10)

• Structural Analysis of Molecular Clouds: Dendrograms
• Molecular Cloud Evolution II. From cloud formation to the early stages of star formation in decaying conditions
• Bias-free Measurement of Giant Molecular Cloud Properties
• ALMA Reveals the Molecular Medium Fueling the Nearest Nuclear Starburst
• The link between turbulence, magnetic fields, filaments, and star formation in the Central Molecular Zone cloud G0.253+0.016
• Dust and Gas in the Magellanic Clouds from the HERITAGE Herschel Key Project. I. Dust Properties and Insights into the Origin of the Submm Excess Emission
• Revealing the physical properties of molecular gas in Orion with a large scale survey in J=2-1 lines of 12CO, 13CO and C18O
• Abundances and Isotope Ratios in the Magellanic Clouds: The Star Forming Environment of N113
• Dense Clumps in Giant Molecular Clouds in the Large Magellanic Cloud: Density and Temperature Derived from ${}^{13}$CO($J=3-2$) Observations
• The location, clustering, and propagation of massive star formation in giant molecular clouds

Cited by in corpus (15)

• On the duration of the embedded phase of star formation
• The 30 Doradus Molecular Cloud at 0.4 pc Resolution with the Atacama Large Millimeter/submillimeter Array: Physical Properties and the Boundedness of CO-emitting Structures
• An Unbiased CO Survey Toward the Northern Region of the Small Magellanic Cloud with the Atacama Compact Array. I. Overview: CO Cloud Distributions
• Role of Thermal and Non-thermal Processes in the ISM of Magellanic Clouds
• Internal Structures of Molecular Clouds in the LMC Revealed by ALMA
• An Unbiased CO Survey Toward the Northern Region of the Small Magellanic Cloud with the Atacama Compact Array. II. CO Cloud Catalog
• Towards a multi-tracer timeline of star formation in the LMC -- II. The formation and destruction of molecular clouds
• ACA CO($J=2-1$) Mapping of the Nearest Spiral Galaxy M33. I. Initial Results and Identification of Molecular Clouds
• ALMA Observations of Giant Molecular Clouds in M33 III: Spatially Resolved Features of the Star-Formation Inactive Million-solar-mass Cloud
• Sequential Star Formation in the Young SMC Region NGC 602: Insights from ALMA
• Measuring Young Stars in Space and Time -- II. The Pre-Main-Sequence Stellar Content of N44
• ALMA resolves molecular clouds in the metal poor Magellanic Bridge A
• Tracing the Formation of Molecular Clouds in a Low-Metallicity Galaxy: A HI Narrow Self-Absorption Survey of the Large Magellanic Cloud
• ALMA ${}^{13}\mathrm{CO}$(J=1-0) Observations of NGC 604 in M33: Physical Properties of Molecular Clouds
• Molecular Clouds at the Edge of the Galaxy II. Physical properties and scaling relations