THE SECOND SURVEY OF THE MOLECULAR CLOUDS IN THE LARGE MAGELLANIC CLOUD BY NANTEN. II. STAR FORMATION

By A. Kawamura, Y. Mizuno, T. Minamidani, Miroslav D. Fillipović, L. Staveley-Smith, Sungeun Kim, N. Mizuno, T. Onishi, A. Mizuno, Y. Fukui. 2009

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We studied star formation activities in the molecular clouds in the Large Magellanic Cloud. We have utilized the second catalog of 272 molecular clouds obtained by NANTEN to compare the cloud distribution with signatures of massive star formation including stellar clusters, and optical and radio H ii regions. We find that the molecular clouds are classified into three types according to the activities of massive star formation: Type I shows no signature of massive star formation; Type II is associated with relatively small H ii region(s); and Type III with both H ii region(s) and young stellar cluster(s). The radio continuum sources were used to confirm that Type I giant molecular clouds (GMCs) do not host optically hidden H ii regions. These signatures of massive star formation show a good spatial correlation with the molecular clouds in the sense that they are located within ∼100 pc of the molecular clouds. Among possible ideas to explain the GMC types, we favor that the types indicate an evolutionary sequence; i.e., the youngest phase is Type I, followed by Type II, and the last phase is Type III, where the most active star formation takes place leading to cloud dispersal. The number of the three types of GMCs should be proportional to the timescale of each evolutionary stage if a steady state of massive star and cluster formation is a good approximation. By adopting the timescale of the youngest stellar clusters, 10 Myr, we roughly estimate the timescales of Types I, II, and III to be 6 Myr, 13 Myr, and 7 Myr, respectively, corresponding to a lifetime of 20–30 Myr for the GMCs with a mass above the completeness limit, 5 × 104 M☉.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

• The lifecycle of molecular clouds in nearby star-forming disc galaxies (2019, methodology): “…lifetimes with similarly short values as in the present study (10−30 Myr) have been measured by counting clouds or classifying clouds based on their stellar content (e.g. Elmegreen 2000; Hartmann et al. 2001; Engargiola et al. 2003; Kawamura et al. 2009; Meidt et al. 2015; Corbelli et al. 2017).”
• Modeling UV Radiation Feedback from Massive Stars. II. Dispersal of Star-forming Giant Molecular Clouds by Photoionization and Radiation Pressure (2018, background): “…on the fraction of GMCs that are spatially coincident with H II regions and young star clusters in nearby galaxies favor lifetimes of a few tens of Myrs (Engargiola et al. 2003; Blitz et al. 2007; Kawamura et al. 2009; Miura et al. 2012; see also Murray 2011; Meidt et al. 2015; Lee et al. 2016).”
• The exciting lives of giant molecular clouds (2013, background): “More recent results have estimated cloud lifetimes in the LMC and M33 to be 20-30 Myr (Kawamura et al. 2009; Miura et al. 2012).”
• Global hierarchical collapse in molecular clouds. Towards a comprehensive scenario (2019, background): “Observational evidence for this mass evolution of the clouds has been presented by Kawamura et al. (2009), who showed that GMCs in the Large Magellanic Cloud with more evolved stellar populations tend to have larger masses.”
• THE SCALE DEPENDENCE OF THE MOLECULAR GAS DEPLETION TIME IN M33 (2010, background): “Fukui et al. (1999), Blitz et al. (2007), Kawamura et al. (2009), and Chen et al. (2010) showed that in the LMC, the amount of Hα and young stars associated with a GMC evolves significantly across its lifetime.”
• The Formation and Destruction of Molecular Clouds and Galactic Star Formation (2015, background): “This tendency is actually observed in Milky Way outer disk, LMC, M33, and M51 (Rosolowsky 2005; Wong et al. 2011; Gratier et al. 2012; Hughes et al. 2010; Colombo et al. 2014) .”
• LOW CO LUMINOSITIES IN DWARF GALAXIES (2012, background): “On small scales this shows as offsets between Hα, a tracer of recent star formation, and CO, and induces large scatter in the respective ratios (e.g., Schruba et al. 2010; Onodera et al. 2010) which can be linked to the evolution of starforming regions (Kawamura et al. 2009).”
• A Herschel/PACS Far-infrared Line Emission Survey of Local Luminous Infrared Galaxies (2017, background): “…we are able to see a significant number of star-forming regions that are likely matter-bounded and still embedded in their molecular cocoon (e.g., Kawamura et al. 2009; Miura et al. 2012; Whitmore et al. 2014), seems 19 Here we do not imply a change in the initial mass function, but rather refer…”
• A MOLECULAR STAR FORMATION LAW IN THE ATOMIC-GAS-DOMINATED REGIME IN NEARBY GALAXIES (2011, background): “The typical 20 − 30 Myr timescale (Salim et al. 2007) over which most UV emission (and dust heating from B stars) occurs is well matched to current estimates for the lifetimes of giant molecular clouds (Kawamura et al. 2009).”
• Turbulent molecular clouds (2012, background): “Kawamura et al. (2009) propose that this is an evolutionary sequence and they estimate that each phase lasts, respectively, 6, 13 and 7 Myr.”
• MOLECULAR GAS AND STAR FORMATION IN NEARBY DISK GALAXIES (2013, background): “These individual elements have distinct ages and evolutionary sequences (e.g. Kawamura et al. 2009; Fukui & Kawamura 2010) so that the ratio of molecular gas to stars in a region and the emission of star formation rate tracers both evolve as a function of time (see discussion and plots in L12).”
• PHYSICAL PROPERTIES OF MOLECULAR CLOUDS FOR THE ENTIRE MILKY WAY DISK (2016, background): “This is also found in the LMC by Kawamura et al. (2009).”
• Molecular Clouds in the Milky Way (2015, methodology): “A similar track of cloud evolution is compiled by Fukui et al. (1999) and Kawamura et al. (2009) based on CO studies of molecular clouds in the Large Magellanic Cloud.”
• The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, background): “…to take from this calculation is that the timescale for H2 formation is shorter than the observationally-estimated lifetime of a molecular cloud (Kawamura et al. 2009; Koda et al. 2009), but not by a huge margin, suggesting that non-equilibrium effects might be important in some circumstances.”
• Why are most molecular clouds not gravitationally bound (2011, background): “This may mean that discussing clouds lifetimes, which are thought to be 20-30 Myr (Leisawitz et al. 1989; Kawamura et al. 2009), may not make sense.”
• THE MAGELLANIC MOPRA ASSESSMENT (MAGMA). I. THE MOLECULAR CLOUD POPULATION OF THE LARGE MAGELLANIC CLOUD (2011, background): “Recently, Kawamura et al. (2009) compared the locations of CO clouds with optical catalogs of young stellar clusters, finding that∼2/3 of the.10 Myr old clusters are associated with GMCs, the remainder having apparently dispersed their natal clouds.”