Tracing the Formation of Molecular Clouds in a Low-Metallicity Galaxy: A HI Narrow Self-Absorption Survey of the Large Magellanic Cloud

Abstract

Cold atomic hydrogen clouds are the precursors of molecular clouds. Due to self-absorption, the opacity of cold atomic hydrogen may be high, and this gas may constitute an important mass component of the interstellar medium (ISM). Atomic hydrogen gas can be cooled to temperatures much lower than found in the cold neutral medium (CNM) through collisions with molecular hydrogen. In this paper, we search for HI Narrow Self-Absorption (HINSA) features in the Large Magellanic Cloud (LMC) as an indicator of such cold HI clouds, and use the results to quantify atomic masses and atomic-to-molecular gas ratio. Our search for HINSA features was conducted towards molecular clouds in the LMC using the ATCA+Parkes HI survey and the MAGMA CO survey. HINSA features are prevalent in the surveyed sightlines. This is the first detection of HINSA in an external galaxy. The HINSA-HI/${\mathrm{H}}_2$ ratio in the LMC varies from 0.5\e{-3} to 3.4\e{-3} (68\% interval), with a mean value of $(1.31\pm 0.03)$\e{-3}, after correcting for the effect of foreground HI gas. This is similar to the Milky Way value and indicates that similar fractions of cold gas exist in the LMC and the Milky Way, despite their differing metallicities, dust content and radiation fields. The low ratio also confirms that, as with the Milky Way, the formation timescale of molecular clouds is short. The ratio shows no radial gradient, unlike the case for stellar metallicity. No correlation is found between our results and those from previous HI absorption studies of the LMC.

arXiv comment25 pages, 16 figures

References in corpus (51)

• The EAGLE project: Simulating the evolution and assembly of galaxies and their environments
• The Origin of the Mass--Metallicity Relation: Insights from 53,000 Star-Forming Galaxies in the SDSS
• Theory of Star Formation
• The CO-to-H2 Conversion Factor
• Metallicity Calibrations and the Mass-Metallicity Relation for Star-Forming Galaxies
• A fundamental relation between mass, SFR and metallicity in local and high redshift galaxies
• An eclipsing binary distance to the Large Magellanic Cloud accurate to 2 per cent
• Combined CO & Dust Scaling Relations of Depletion Time and Molecular Gas Fractions with Cosmic Time, Specific Star Formation Rate and Stellar Mass
• The Millennium Arecibo 21-CM Absorption Line Survey. II. Properties of the Warm and Cold Neutral Media
• The Second Survey of the Molecular Clouds in the Large Magellanic Cloud by NANTEN I: Catalog of Molecular Clouds
• The Magellanic Mopra Assessment (MAGMA). I. The Molecular Cloud Population of the Large Magellanic Cloud
• A New Look at the Large-Scale HI Structure of the LMC
• The [C II] emission as a molecular gas mass tracer in galaxies at low and high redshift
• Non-Standard Grain Properties, Dark Gas Reservoir, and Extended Submillimeter Excess, Probed by Herschel in the Large Magellanic Cloud
• A FUSE Survey of Interstellar Molecular Hydrogen in the Small and Large Magellanic Clouds
• Clustering of Local Group distances: publication bias or correlated measurements? I. The Large Magellanic Cloud
• The Milky Way Imaging Scroll Painting (MWISP): Project Details and Initial Results from the Galactic Longitude of 25.8deg to 49.7deg
• A Fractal Analysis of the HI Emission from the Large Magellanic Cloud
• 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
• HI Narrow Line Absorption in Dark Clouds
• A Wide-field High Resolution HI Mosaic of Messier 31: I. Opaque Atomic Gas and Star Formation Rate Density
• HI Narrow Self-Absorption in Dark Clouds: Correlations with Molecular Gas and Implications for Cloud Evolution and Star Formation
• A new, large-scale map of interstellar reddening derived from HI emission
• Cosmological evolution of atomic gas and implications for 21 cm HI absorption
• Physical Properties of Giant Molecular Clouds in the Large Magellanic Cloud
• A Survey of Atomic Carbon [C I] in High-redshift Main-Sequence Galaxies
• The Rotation Curve of the Large Magellanic Cloud and the Implications for Microlensing
• Magnetically Dominated Strands of Cold Hydrogen in the Riegel-Crutcher Cloud
• An ATCA 20cm Radio Continuum Study of the Large Magellanic Cloud
• Fitting Together the HI Absorption and Emission in the SGPS
• The Outer Disk of the Milky Way Seen in 21-cm Absorption
• Interstellar H I and H_2 in the Magellanic Clouds: An Expanded Sample Based on UV Absorption-Line Data
• Photometric metallicity map of the Large Magellanic Cloud
• Strong FUV fields drive the [CII]/FIR deficit in z~3 dusty, star-forming galaxies
• Results of the ESO-SEST Key Programme on CO in the Magellanic Clouds X. CO emission from star formation regions in LMC and SMC
• Physical Conditions in the Ionized Gas of 30 Doradus
• The evolution of the mass-metallicity relation in SDSS galaxies uncovered by astropaleontology
• METAL: The Metal Evolution, Transport, and Abundance in the Large Magellanic Cloud Hubble program. I. Overview and Initial Results
• Characterizing the transition from diffuse atomic to dense molecular clouds in the Magellanic clouds with [CII], [CI], and CO
• An Improved Technique for Measurement of Cold HI in Molecular Cloud Cores
• 1420 MHz Continuum Absorption Towards Extragalactic Sources in the Galactic Plane
• Velocity profiles of [CII], [CI], CO, and [OI] and physical conditions in four star-forming regions in the Large Magellanic Cloud
• ALMA Observations of a Quiescent Molecular Cloud in the Large Magellanic Cloud
• A Neutral Hydrogen Self-Absorption Cloud in the SGPS
• A Sample of [CII] Clouds Tracing Dense Clouds in Weak FUV Fields observed by Herschel
• Distance to the SNR CTB 109/AXP 1E 2259+586 by HI absorption and self-absorption
• Physical properties of CO-dark molecular gas traced by C${}^{+}$
• Calibrating the HISA temperature: Measuring the temperature of the Riegel-Crutcher cloud
• OH Survey along Sightlines of Galactic Observations of Terahertz C+
• Catching the Birth of a Dark Molecular Cloud for the First Time
• OH as an Alternate Tracer for Molecular Gas: Quantity and Structure of Molecular Gas in W5

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• A lack of constraints on the cold opaque HI mass: HI spectra in M31 and M33 prefer multi-component models over a single cold opaque component
• Towards a multi-tracer timeline of star formation in the LMC -- II. The formation and destruction of molecular clouds
• Measuring Cosmic Density of Neutral Hydrogen via Stacking the DINGO-VLA Data