Atsushi Nishimura

Molecular Clumps and Infrared Clusters in the S247, S252, and BFS52 Regions

We present results of the observations carried out toward the S247, S252, and BFS52 H II regions with various molecular lines using the 1.85?m radio telescope and the 45?m telescope at Nobeyama Radio Observatory. There are at least 11 young infrared clusters (IR clusters) within the observed region. We found that there are two velocity components in 12CO?(J = 2-1), and also that their spatial distributions show an anti-correlation. The IR clusters are located at their interfaces, suggesting that two distinct clouds with different velocities are colliding with each other, which may have induced the cluster formation. Based on 13CO?(J = 1-0) and C18O (J = 1-0) observations, we identified 16 clumps in and around the three H II regions. Eleven of the clumps are associated with the IR clusters and the other five clumps are not associated with any known young stellar objects. We investigated variations in the velocity dispersions of the 16 clumps as a function of the distance from the center of the clusters or the clumps. Clumps with clusters tend to have velocity dispersions that increase with distance from the cluster center, while clumps without clusters show a flat velocity dispersion over the clump extents. A 12CO?outflow has been found in some of the clumps with IR clusters but not in the other clumps, supporting a strong relation of these clumps to the broader velocity dispersion region. We also estimated a mean star formation efficiency of ~30% for the clumps with IR clusters in the three H II regions.

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

Molecular clouds in the NGC 6334 and NGC 6357 region: Evidence for a 100 pc-scale cloud–cloud collision triggering the Galactic mini-starbursts

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FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45 m telescope (FUGIN): Molecular clouds toward W 33; possible evidence for a cloud–cloud collision triggering O star formation

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Molecular clouds toward three Spitzer bubbles S116, S117, and S118: Evidence for a cloud–cloud collision which formed the three H ii regions and a 10 pc scale molecular cavity

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Formation of the young compact cluster GM 24 triggered by a cloud–cloud collision

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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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SPATIAL VARIATIONS OF PAH PROPERTIES IN M17SW REVEALED BY SPITZER/IRS SPECTRAL MAPPING

2-1, and

Discovery of Molecular and Atomic Clouds Associated with the Gamma-Ray Supernova Remnant Kesteven 79

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