Dense Molecular Clumps Associated With the Large Magellanic Cloud Supergiant Shells LMC 4 and LMC 5

Fujii, K.; Minamidani, Tetsuhiro; Mizuno, N.; Onishi, Toshikazu; Kawamura, Akiko; Müller, Erik; Dawson, J. R.; Tatematsu, Ken’ichi; Hasegawa, Tetsuo; Tosaki, Tomoka; Miura, Rie; Muraoka, Kazuyuki; Sakai, Takeshi; Tsukagoshi, Takashi; Tanaka, K.; Ezawa, H.; Fukui, Y.

doi:10.1088/0004-637x/796/2/123

Cited by 20 publications

(23 citation statements)

References 77 publications

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“…For example, Fujii et al (2014) find dense molecular clumps at early stages of star formation between the LMC 4 and LMC 5 supershells. The expansion speeds of these superbubbles, which are 21 and 36 km/sec, respectively (Kim et al 1999), are similar to what we get in our simulations, but their observed sizes are much larger (i.e., radii of about 290 and 550 pc, assuming a distance of 50 kpc to the LMC).…”

Section: Summary and Discussionmentioning

confidence: 99%

The role of magnetic fields in the structure and interaction of supershells

Ntormousi

Dawson

Hennebelle

et al. 2017

A&A

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Context. Large-scale shocks formed by clustered feedback of young OB stars are considered an important source of mechanical energy for the interstellar medium (ISM) and a trigger of molecular cloud formation. Their interaction sites are locations where kinetic energy and magnetic fields are redistributed between ISM phases. Aims. In this work we address two questions, both involving the role of galactic magnetic fields in the dynamics of supershells and their interactions. On the one hand, we study the effect of the magnetic field on the expansion and fragmentation of supershells and, on the other hand, we look for the signatures of supershell collisions on dense structures and on the kinetic and magnetic energy distribution of the ISM. Methods. We performed a series of high-resolution, three-dimensional simulations of colliding supershells. The shocks are created by time-dependent feedback and evolve in a diffuse turbulent environment that is either unmagnetized or has different initial magnetic field configurations. Results. In the hydrodynamical situation, the expansion law of the superbubbles is consistent with the radius-time relation R ∝ t 3/5 that is theoretically predicted for wind-blown bubbles. The supershells fragment over their entire surface into small dense clumps that carry more than half of the total kinetic energy in the volume. However, this is not the case when a magnetic field is introduced, either in the direction of the collision or perpendicular to the collision. In both situations, the shell surfaces are more stable to dynamical instabilities. When the magnetic field opposes the collision, the expansion law of the supershells also becomes significantly flatter than in the hydrodynamical case. Although a two-phase medium arises in all cases, in the magnetohydrodynamical (MHD) simulations the cold phase is limited to lower densities and the cold clumps are located further away from the shocks with respect to the hydrodynamical simulations. Conclusions. For the parameters we explored, self-gravity has no effect on either the superbubble expansion or the shock fragmentation. In contrast, a magnetic field, whether mostly parallel or mostly perpendicular to the collision axis, causes a deceleration of the shocks, deforms them significantly, and largely suppresses the formation of the dense gas on their surface. The result is a multi-phase medium in which the cold clumps are not spatially correlated with the supershells.

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Section: Summary and Discussionmentioning

confidence: 99%

The role of magnetic fields in the structure and interaction of supershells

Ntormousi

Dawson

Hennebelle

et al. 2017

A&A

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“…Multitransition observations of molecular clouds in the LMC Heikkilä et al 1999;Israel et al 2003;Kim et al 2004;Bolatto et al 2005;Pineda et al 2008;Mizuno et al 2010;Minamidani et al 2008Minamidani et al , 2011Fujii et al 2014;Paron et al 2016) suggest that the molecular gas traced by CO may be warmer and/or denser than in our Galaxy. NH 3 (1,1) and (2,2) lines have been surveyed toward seven star-forming regions in the LMC by Ott et al (2010) using the Australia Telescope Compact Array (ATCA).…”

Section: Introductionmentioning

confidence: 92%

“…The kinetic temperatures of molecular clumps in the LMC have been calculated by multi-transition data of CO Heikkilä et al 1999;Israel et al 2003;Kim et al 2004;Bolatto et al 2005;Pineda et al 2008;Mizuno et al 2010;Minamidani et al 2008Minamidani et al , 2011Fujii et al 2014;Paron et al 2016). These observations show that the higher temperatures (T kin 100 K) occur in cloud regions that are of lower density ( 10 3 cm −3 ) and that the gas is colder (T kin = 10 -80 K) in regions of higher density (10 4 -10 5 cm −3 ).…”

Section: Comparison Of Temperatures Derived From H 2 Co Co Nh 3 Amentioning

confidence: 99%

Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde

Tang

Henkel

Chen

et al. 2017

A&A

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Context. The kinetic temperature of molecular clouds is a fundamental physical parameter affecting star formation and the initial mass function. The Large Magellanic Cloud (LMC), the closest star forming galaxy with low metallicity, provides an ideal laboratory to study star formation in such an environment. Aims. The classical dense molecular gas thermometer NH 3 is rarely available in a low metallicity environment because of photoionization and a lack of nitrogen atoms. Our goal is to directly measure the gas kinetic temperature with formaldehyde toward six star-forming regions in the LMC. Methods. Three rotational transitions (J K A K C = 3 03 -2 02 , 3 22 -2 21 , and 3 21 -2 20 ) of para-H 2 CO near 218 GHz were observed with the Atacama Pathfinder EXperiment (APEX) 12 m telescope toward six star forming regions in the LMC. Those data are complemented by C 18 O 2-1 spectra. Results. Using non-LTE modeling with RADEX, we derive the gas kinetic temperature and spatial density, using as constraints the measured para-H 2 CO 3 21 -2 20 /3 03 -2 02 and para-H 2 CO 3 03 -2 02 /C 18 O 2-1 ratios. Excluding the quiescent cloud N159S, where only one para-H 2 CO line could be detected, the gas kinetic temperatures derived from the preferred para-H 2 CO 3 21 -2 20 /3 03 -2 02 line ratios range from 35 to 63 K with an average of 47 ± 5 K (errors are unweighted standard deviations of the mean). Spatial densities of the gas derived from the para-H 2 CO 3 03 -2 02 /C 18 O 2-1 line ratios yield 0.4 -2.9 × 10 5 cm −3 with an average of 1.5 ± 0.4 × 10 5 cm −3 . Temperatures derived from the para-H 2 CO line ratio are similar to those obtained with the same method from Galactic star forming regions and agree with results derived from CO in the dense regions (n(H 2 ) > 10 3 cm −3 ) of the LMC. A comparison of kinetic temperatures derived from para-H 2 CO with those from the dust also shows good agreement. This suggests that the dust and para-H 2 CO are well mixed in the studied star forming regions. A comparison of kinetic temperatures derived from para-H 2 CO 3 21 -2 20 /3 03 -2 02 and NH 3 (2,2)/(1,1) shows, however, a drastic difference. In the star forming region N159W, the gas temperature derived from the NH 3 (2,2)/(1,1) line ratio is ∼16 K (Ott et al. 2010), which is only half the temperature derived from para-H 2 CO and the dust. Furthermore, ammonia shows a very low abundance in a 30 ′′ beam. Apparently, ammonia only survives in the most shielded pockets of dense gas not yet irradiated by UV photons, while formaldehyde, less affected by photodissociation, is more widespread and is also sampling regions more exposed to the radiation of young massive stars. A correlation between the gas kinetic temperatures derived from para-H 2 CO and infrared luminosity, represented by the 250 µm flux, suggests that the kinetic temperatures traced by para-H 2 CO are correlated with the ongoing massive star formation in the LMC.

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“…The mass can be also estimated from the dynamical information of the size of the clumps and the linewidth of CO lines by assuming the virial equilibrium. We derived the virial masses from the 13 CO (J = 1-0) line using the procedure described by Fujii et al (2014) as follows. The virial mass is estimated as…”

Section: Virial Massmentioning

confidence: 99%

Formation of high-mass stars in an isolated environment in the Large Magellanic Cloud

Harada

Onishi

Tokuda

et al. 2019

Publications of the Astronomical Society of Japan

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The aim of this study is to characterize the distribution and basic properties of the natal gas associated with high-mass young stellar objects (YSOs) in isolated environments in the Large Magellanic Cloud (LMC). High-mass stars usually form in Giant Molecular Clouds (GMCs) as part of a young stellar cluster, but some OB stars are observed far from GMCs. By examining the spatial coincidence between the high-mass YSOs and 12 CO (J = 1-0) emission detected by NANTEN and Mopra observations, we selected ten high-mass YSOs that are located away from any of the NANTEN clouds but are detected by the Mopra pointed observations. The ALMA observations revealed that a compact molecular cloud whose mass is a few thousand solar masses or smaller is associated with the high-mass YSOs, which indicates that these compact clouds are the sites of high-mass star formation. The high-density and high-temperature throughout the clouds are explained by the severe photodissociation of CO due to the lower metallicity than in the Galaxy. The star formation efficiency ranges from several to as high as ∼ 40%, indicating efficient star formation in these environments. The enhanced turbulence may be a cause of the efficient star formation therein, as judged from the gas velocity information and the association with the lower density gas.

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Dense Molecular Clumps Associated With the Large Magellanic Cloud Supergiant Shells LMC 4 and LMC 5

Cited by 20 publications

References 77 publications

The role of magnetic fields in the structure and interaction of supershells

The role of magnetic fields in the structure and interaction of supershells

Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde

Formation of high-mass stars in an isolated environment in the Large Magellanic Cloud

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