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

Abstract

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] km s${}^{-1}$ and an arc at velocities of [-20,10] km s${}^{-1}$. The spatial anti-correlation 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 HII regions spatially overlap with sites of strong SiO emission at velocities of [40,85] km s${}^{-1}$, and are between or along the edges of SiO gas features at [100,120] km s${}^{-1}$, suggesting that the stars responsible for ionizing the compact HII regions formed in compressed gas due to this collision. We find gas densities and kinetic temperatures of the order of $n_{{\mathrm{H}}_2}\sim 10^5\mathrm{c}{\mathrm{m}}^{-3}$ and $\sim$30 K, respectively, towards three positions of Sgr B2. The average values of the SiO relative abundances, integrated line intensities, and line widths are $\sim$10${}^{-9}$, $\sim$11 K km s${}^{-1}$, and $\sim$31 km s${}^{-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 $\lesssim$ 0.5 Myr ago can explain the density distribution with a mean column density of ${\bar{N}}_{{\mathrm{H}}_2}\gtrsim 5\times 10^{22}$ cm${}^{-2}$, and the morphology and kinematics of shocked gas in different velocity channels. Colliding clouds are efficient at producing internal shocks with velocities $\sim$5-50 km $s^{-1}$. 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 timescales and can explain the widespread SiO emission in Sgr B2.

Accepted for publication in MNRAS. 22 pages, 17 figures. Movies of the simulations can be found here: https://tinyurl.com/y5bc3smn

References in corpus (31)

• The NumPy array: a structure for efficient numerical computation
• PLUTO: a Numerical Code for Computational Astrophysics
• The Density Probability Distribution in Compressible Isothermal Turbulence: Solenoidal versus Compressive Forcing
• An Improved Distance and Mass Estimate for Sgr A* from a Multistar Orbit Analysis
• The dynamical evolution of molecular clouds near the Galactic Centre - I. Orbital structure and evolutionary timeline
• SiO line emission from C-type shock waves : interstellar jets and outflows
• The Fractal Density Structure in Supersonic Isothermal Turbulence: Solenoidal versus Compressive Energy Injection
• The link between turbulence, magnetic fields, filaments, and star formation in the Central Molecular Zone cloud G0.253+0.016
• Do cloud-cloud collisions trigger high-mass star formation? I. Small cloud collisions
• Parametrization of C-shocks. Evolution of the Sputtering of Grains
• Tracing shocks and photodissociation in the Galactic center region
• Isolating signatures of major cloud-cloud collisions using position-velocity diagrams
• Triggered O star formation in M20 via cloud-cloud collision: Comparisons between high-resolution CO observations and simulations
• The dynamical evolution of molecular clouds near the Galactic Centre - II. Spatial structure and kinematics of simulated clouds
• Cloud-cloud collision as drivers of the chemical complexity in Galactic Centre molecular clouds
• Autonomous Gaussian Decomposition
• Phosphorus-bearing molecules in the Galactic Center
• APEX mapping of H3O+ in the Sgr B2 region
• Wind bubbles within H II regions around slowly moving stars
• Spectral imaging of the Sagittarius B2 region in multiple 3-mm molecular lines with the Mopra telescope
• Filament formation in wind-cloud interactions. II. Clouds with turbulent density, velocity, and magnetic fields
• Tracing extended low-velocity shocks through SiO emission - Case study of the W43-MM1 ridge
• On the dynamics and survival of fractal clouds in galactic winds
• The Launching of Cold Clouds by Galaxy Outflows III: The Influence of Magnetic Fields
• Shocks in dense clouds. IV. Effects of grain-grain processing on molecular line emission
• High-mass star formation possibly triggered by cloud-cloud collision in the HII region RCW 34
• A SiO J = 5 - 4 Survey Toward Massive Star Formation Regions
• 3 mm spectral line survey of two lines of sight toward two typical cloud complexes in the Galactic Center
• The effect of photoionising feedback on star formation in isolated and colliding clouds
• SHOCKFIND - An algorithm to identify magnetohydrodynamic shock waves in turbulent clouds
• IRAS 18153-1651: an H II region with a possible wind bubble blown by a young main-sequence B star

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