ORCID Profile
0000-0002-2062-1600
Current Organisations
National Astronomical Observatory of Japan
,
Kyushu University
,
自然科学研究機構国立天文台/National Astronomical Observatory of Japan
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Publisher: American Astronomical Society
Date: 06-2022
Abstract: We present results of a wide-field (approximately 60 × 90 pc) Atacama Large Millimeter/submillimeter Array mosaic of CO(2–1) and 13 CO(2–1) emission from the molecular cloud associated with the 30 Doradus star-forming region in the Large Magellanic Cloud (LMC). Three main emission complexes, including two forming a bow-tie-shaped structure extending northeast and southwest from the central R136 cluster, are resolved into complex filamentary networks. Consistent with previous studies, we find that the central region of the cloud has higher line widths at a fixed size relative to the rest of the molecular cloud and to other LMC clouds, indicating an enhanced level of turbulent motions. However, there is no clear trend in gravitational boundedness (as measured by the virial parameter) with distance from R136. Structures observed in 13 CO are spatially coincident with filaments and are close to a state of virial equilibrium. In contrast, 12 CO structures vary greatly in virialization, with low CO surface brightness structures outside of the main filamentary network being predominantly unbound. The low surface brightness structures constitute ∼10% of the measured CO luminosity they may be shredded remnants of previously star-forming gas clumps, or alternatively the CO-emitting parts of more massive, CO-dark structures.
Publisher: American Astronomical Society
Date: 08-2021
Publisher: American Astronomical Society
Date: 14-08-2019
Publisher: American Astronomical Society
Date: 25-10-2018
Publisher: Oxford University Press (OUP)
Date: 12-06-2020
DOI: 10.1093/PASJ/PSAA045
Abstract: We report the first evidence for high-mass star formation triggered by collisions of molecular clouds in M 33. Using the Atacama Large Millimeter/submillimeter Array, we spatially resolved filamentary structures of giant molecular cloud 37 in M 33 using 12CO(J = 2–1), 13CO(J = 2–1), and C18O(J = 2–1) line emission at a spatial resolution of ∼2 pc. There are two in idual molecular clouds with a systematic velocity difference of ∼6 km s−1. Three continuum sources representing up to ∼10 high-mass stars with spectral types of B0V–O7.5V are embedded within the densest parts of molecular clouds bright in the C18O(J = 2–1) line emission. The two molecular clouds show a complementary spatial distribution with a spatial displacement of ∼6.2 pc, and show a V-shaped structure in the position–velocity diagram. These observational features traced by CO and its isotopes are consistent with those in high-mass star-forming regions created by cloud–cloud collisions in the Galactic and Magellanic Cloud H ii regions. Our new finding in M 33 indicates that cloud–cloud collision is a promising process for triggering high-mass star formation in the Local Group.
Publisher: American Astronomical Society
Date: 27-11-2020
Publisher: American Astronomical Society
Date: 10-2021
Publisher: American Astronomical Society
Date: 27-11-2017
Publisher: American Astronomical Society
Date: 09-2021
Publisher: American Astronomical Society
Date: 09-08-2018
Publisher: American Astronomical Society
Date: 12-10-2020
Publisher: American Astronomical Society
Date: 03-2019
Publisher: American Astronomical Society
Date: 21-07-2022
Abstract: We present a comparison of low- J 13 CO and CS observations of four different regions in the LMC—the quiescent Molecular Ridge, 30 Doradus, N159, and N113, all at a resolution of ∼3 pc. The regions 30 Dor, N159, and N113 are actively forming massive stars, while the Molecular Ridge is forming almost no massive stars, despite its large reservoir of molecular gas and proximity to N159 and 30 Dor. We segment the emission from each region into hierarchical structures using dendrograms and analyze the sizes, masses, and line widths of these structures. We find that the Ridge has significantly lower kinetic energy at a given size scale and also lower surface densities than the other regions, resulting in higher virial parameters. This suggests that the Ridge is not forming massive stars as actively as the other regions because it has less dense gas and not because collapse is suppressed by excess kinetic energy. We also find that these physical conditions and energy balance vary significantly within the Ridge and that this variation appears only weakly correlated with distance from sites of massive-star formation such as R136 in 30 Dor, which is ∼1 kpc away. These variations also show only a weak correlation with local star formation activity within the clouds.
Publisher: Oxford University Press (OUP)
Date: 21-10-2021
Abstract: Studying the driving modes of turbulence is important for characterizing the impact of turbulence in various astrophysical environments. The driving mode of turbulence is parameterized by b, which relates the width of the gas density PDF to the turbulent Mach number b ≈ 1/3, 1, and 0.4 correspond to driving that is solenoidal, compressive, and a natural mixture of the two, respectively. In this work, we use high-resolution (sub-pc) ALMA 12CO (J = 2–1), 13CO (J = 2–1), and C18O (J = 2–1) observations of filamentary molecular clouds in the star-forming region N159E (the Papillon Nebula) in the Large Magellanic Cloud (LMC) to provide the first measurement of turbulence driving parameter in an extragalactic region. We use a non-local thermodynamic equilibrium (NLTE) analysis of the CO isotopologues to construct a gas density PDF, which we find to be largely log-normal in shape with some intermittent features indicating deviations from lognormality. We find that the width of the log-normal part of the density PDF is comparable to the supersonic turbulent Mach number, resulting in b ≈ 0.9. This implies that the driving mode of turbulence in N159E is primarily compressive. We speculate that the compressive turbulence could have been powered by gravo-turbulent fragmentation of the molecular gas, or due to compression powered by H I1.2ex flows that led to the development of the molecular filaments observed by ALMA in the region. Our analysis can be easily applied to study the nature of turbulence driving in resolved star-forming regions in the local as well as the high-redshift Universe.
Location: No location found
Location: Japan
No related grants have been discovered for Kazuki Tokuda.