Rei Enokiya

MOLECULAR CLOUDS IN THE TRIFID NEBULA M20: POSSIBLE EVIDENCE FOR A CLOUD-CLOUD COLLISION IN TRIGGERING THE FORMATION OF THE FIRST GENERATION STARS

A large-scale study of the molecular clouds toward the Trifid Nebula, M20, has been made in the J = 2-1 and J = 1-0 transitions of 12CO and 13CO. M20 is ionized predominantly by an O7.5 star HD164492. The study has revealed that there are two molecular components at separate velocities peaked toward the center of M20 and that their temperatures—30-50 K as derived by a large velocity gradient analysis—are significantly higher than the 10 K of their surroundings. We identify the two clouds as the parent clouds of the first generation stars in M20. The mass of each cloud is estimated to be ~103 M ☉ and their separation velocity is ~8 km s–1 over ~1-2 pc. We find that the total mass of stars and molecular gas in M20 is less than ~3.2 × 103 M ☉, which is too small by an order of magnitude to gravitationally bind the system. We argue that the formation of the first generation stars, including the main ionizing O7.5 star, was triggered by the collision between the two clouds in a short timescale of ~1 Myr, a second example alongside Westerlund 2, where a super-star cluster may have been formed due to cloud-cloud collision triggering.

DISCOVERY OF POSSIBLE MOLECULAR COUNTERPARTS TO THE INFRARED DOUBLE HELIX NEBULA IN THE GALACTIC CENTER

We have discovered two molecular features at radial velocities of ?35?km?s?1 and 0?km?s?1 toward the infrared Double Helix Nebula (DHN) in the Galactic center with NANTEN2. The two features show good spatial correspondence with the DHN. We have also found two elongated molecular ridges at these two velocities distributed vertically to the Galactic plane over 0.?8. The two ridges are linked by broad features in velocity and are likely connected physically with each other. The ratio between the 12CO J = 2-1 and J = 1-0 transitions is 0.8 in the ridges which is larger than the average value 0.5 in the foreground gas, suggesting the two ridges are in the Galactic center. An examination of the K band extinction reveals a good coincidence with the CO 0?km?s?1 ridge and is consistent with a distance of 8 ? 2?kpc. We discuss the possibility that the DHN was created by a magnetic phenomenon incorporating torsional Alfv?n waves launched from the circum-nuclear disk and present a first estimate of the mass and energy involved in the DHN.

High-mass star formation possibly triggered by cloud–cloud collision in the H ii region RCW 34

We report a possibility that the high-mass star located in the HII region RCW 34 was formed by a triggering induced by a collision of molecular clouds. Molecular gas distributions of the

Magnetohydrodynamic Simulations of a Jet Drilling an H I Cloud: Shock Induced Formation of Molecular Clouds and Jet Breakup

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RCW 36 in the Vela Molecular Ridge: Evidence for high-mass star-cluster formation triggered by cloud–cloud collision

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Molecular and Atomic Gas toward HESS J1745−303 in the Galactic Center: Further Support for the Hadronic Scenario

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Detailed CO(J = 1–0, 2–1, and 3–2) observations toward an H ii region RCW 32 in the Vela Molecular Ridge

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Magnetic activity in the Galactic Centre region – fast downflows along rising magnetic loops

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Magnetohydrodynamic Simulations of the Formation of Molecular Clouds toward the Stellar Cluster Westerlund 2: Interaction of a Jet with a Clumpy Interstellar Medium

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Detailed distributions of the CO J = (2 − 1)/J = (1 − 0) intensity ratios toward a large area of the central molecular zone

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