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Structure and kinematics of shocked gas in Sgr B2: further evidence of a cloud–cloud collision from SiO emission maps

Armijos, Jairo, Banda-Barrigan, W. E., Martin-Pintado, J., Denes, H., Federrath, C. and Requena-Torres, M. A. 2020. Structure and kinematics of shocked gas in Sgr B2: further evidence of a cloud–cloud collision from SiO emission maps. Monthly Notices of the Royal Astronomical Society 499 (4) 10.1093/mnras/staa3119

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We present SiO J = 2–1 maps of the Sgr B2 molecular cloud, which show shocked gas with a turbulent substructure comprising at least three cavities at velocities of [10,40]kms−1 and an arc at velocities of [−20,10]kms−1⁠. The spatial anticorrelation of shocked gas at low and high velocities, and the presence of bridging features in position-velocity diagrams suggest that these structures formed in a cloud–cloud collision. Some of the known compact H ii regions spatially overlap with sites of strong SiO emission at velocities of [40,85]kms−1⁠, and are between or along the edges of SiO gas features at [100,120]kms−1⁠, suggesting that the stars responsible for ionizing the compact H ii regions formed in compressed gas due to this collision. We find gas densities and kinetic temperatures of the order of nH2∼105cm−3 and ∼30K⁠, respectively, towards three positions of Sgr B2. The average values of the SiO relative abundances, integrated line intensities, and line widths are ∼10−9, ∼11Kkms−1⁠, and ∼31kms−1⁠, respectively. These values agree with those obtained with chemical models that mimic grain sputtering by C-type shocks. A comparison of our observations with hydrodynamical simulations shows that a cloud–cloud collision that took place ≲0.5Myr ago can explain the density distribution with a mean column density of N¯H2≳5×1022cm−2⁠, and the morphology and kinematics of shocked gas in different velocity channels. Colliding clouds are efficient at producing internal shocks with velocities ∼5−50kms−1⁠. High-velocity shocks are produced during the early stages of the collision and can readily ignite star formation, while moderate- and low-velocity shocks are important over longer time-scales and can explain the widespread SiO emission in Sgr B2.

Item Type: Article
Status: Published
Schools: Physics and Astronomy
Publisher: Oxford University Press
ISSN: 1365-2966
Last Modified: 21 Jun 2023 12:00

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