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

Wong, Tony; Hughes, Annie; Tokuda, Kazuki; Indebetouw, R.; Bernard, J. P.; Onishi, Toshikazu; Wojciechowski, Evan; Bandurski, Jeffrey; Kawamura, Akiko; Roman-Duval, Julia; Cao, Yixian; Chen, C.-H. Rosie; Chu, You‐Hua; Cui, Chaoyue; Fukui, Y.; Montier, L.; Müller, Erik; Ott, J.; Paradis, D.; Pineda, J. L.; Rosolowsky, Erik; Sewiło, M.

doi:10.3847/1538-4357/aa9333

Cited by 35 publications

(43 citation statements)

References 65 publications

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“…For the first time, it is possible to resolve individual sites of high-mass star formation within the structured natal gas that characterizes the earliest stages. Recent ALMA observations of multiple high-mass star-forming regions in the LMC show protostars forming in dense, filamentary molecular gas with complex dynamics (e.g., Indebetouw et al 2013;Fukui et al 2015;Nayak et al 2016;Saigo et al 2017;Wong et al 2017;Nayak et al 2018;Naslim et al 2018).…”

Section: Introductionmentioning

confidence: 99%

Unveiling the nature of candidate high-mass young stellar objects in the Magellanic Clouds with near-IR spectroscopy

Reiter

Nayak

Meixner

et al. 2019

Monthly Notices of the Royal Astronomical Society

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As nearby neighbors to the Milky Way, the Large and Small Magellanic Clouds (LMC and SMC) provide a unique opportunity to study star formation in the context of their galactic ecosystems. Thousands of young stellar objects (YSOs) have been characterized with large-scale Spitzer and Herschel surveys. In this paper, we present new near-IR spectroscopy of five high-mass YSOs in the LMC and one in the SMC. We detect multiple hydrogen recombination lines, as well as He i 2.058 µm, H 2 , [Fe ii], and [S iii] in these highly excited sources. We estimate the internal extinction of each source and find that it is highest for sources with the youngest evolutionary classifications. Using line ratios, we assess the dominant excitation mechanism in the three sources where we detect both H 2 2.12 µm and [Fe ii] 1.64 µm. In each case, photoexcitation dominates over shock excitation. Finally, we detect CO bandhead absorption in one of our LMC sources. While this feature is often associated with evolved stars, this object is likely young with strong PAH and fine-structure emission lines tracing an H ii region detected at longer wavelengths. Compared to high-mass YSOs in the Galaxy, our sources have higher bolometric and line luminosities, consistent with their selection as some of the brightest sources in the LMC and SMC.

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Section: Introductionmentioning

confidence: 99%

Unveiling the nature of candidate high-mass young stellar objects in the Magellanic Clouds with near-IR spectroscopy

Reiter

Nayak

Meixner

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…The source number is labeled at the top-left corner. Solid black: HI emission spectra (Kim et al 2003); red: CO spectra (Wong et al 2011(Wong et al , 2017; blue: HINSA(this work); dotted black: "original spectrum", i.e. the calculated spectrum "before" HINSA absorption(this work, see Section 3.2.1).…”

Section: Discussionmentioning

confidence: 99%

“…We employ the third data release of MAGMA for this study (Wong et al 2011(Wong et al , 2017. It contains the CO J=1-0 cube described in Wong et al (2011).…”

Section: Comentioning

confidence: 99%

Tracing the Formation of Molecular Clouds in a Low-metallicity Galaxy: An H i Narrow Self-absorption Survey of the Large Magellanic Cloud

Liu¹,

Li²,

Qian³

et al. 2019

ApJ

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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/H 2 ratio in the LMC varies from 0.5×10 −3 to 3.4×10 −3 (68% interval), with a mean value of (1.31 ± 0.03)×10 −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.

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“…We do not account for potential beam dilution, which could decrease our measurements of T ex from CO 12 and cause us to overestimate CO 13 t and N 13 CO and overestimate X CO . Wong et al (2017) make similar estimates of the molecular gas mass using CO 12 and CO…”

Section: [O Iii] and Highly Ionized Materialsmentioning

confidence: 99%

First Results from the Herschel and ALMA Spectroscopic Surveys of the SMC: The Relationship between [C ii]-bright Gas and CO-bright Gas at Low Metallicity*

Jameson

Bolatto

Wolfire

et al. 2018

ApJ

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The Small Magellanic Cloud (SMC) provides the only laboratory to study the structure of molecular gas at high resolution and low metallicity. We present results from the Herschel Spectroscopic Survey of the SMC (HS   ( 3 < pc) scales. We estimate A V using far-IR thermal continuum emission from dust and find that the CO/[C II] ratios reach the Milky Way value at high A V in the centers of the clouds and fall to 1 5 1 10-the Milky Way value in the outskirts, indicating the presence of translucent molecular gas not traced by bright CO 12 emission. We estimate the amount of molecular gas traced by bright [C II] emission at low A V and bright CO 12 emission at high A V . We find that most of the molecular gas is at low A V and traced by bright [C II] emission, but that faint CO 12 emission appears to extend to where we estimate that the H 2 -to-H I transition occurs. By converting our H 2 gas estimates to a CO-to-H 2 conversion factor (X CO ), we show that X CO is primarily a function of A V , consistent with simulations and models of low-metallicity molecular clouds.

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

Cited by 35 publications

References 65 publications

Unveiling the nature of candidate high-mass young stellar objects in the Magellanic Clouds with near-IR spectroscopy

Unveiling the nature of candidate high-mass young stellar objects in the Magellanic Clouds with near-IR spectroscopy

Tracing the Formation of Molecular Clouds in a Low-metallicity Galaxy: An H i Narrow Self-absorption Survey of the Large Magellanic Cloud

First Results from the Herschel and ALMA Spectroscopic Surveys of the SMC: The Relationship between [C ii]-bright Gas and CO-bright Gas at Low Metallicity*

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