A cloud-cloud collision in Sgr B2? 3D simulations meet SiO observations

Abstract

We compare the properties of shocked gas in Sgr B2 with maps obtained from 3D simulations of a collision between two fractal clouds. In agreement with ${}^{13}$CO(1-0) observations, our simulations show that a cloud-cloud collision produces a region with a highly turbulent density substructure with an average $N_{H2}\gtrsim 5\times 10^{22}\mathrm{c}{\mathrm{m}}^{-2}$. Similarly, our numerical multi-channel shock study shows that colliding clouds are efficient at producing internal shocks with velocities of $5-50\mathrm{km}{\mathrm{s}}^{-1}$ and Mach numbers of $\sim 4-40$, which are needed to explain the $\sim 10^{-9}$ SiO abundances inferred from our SiO(2-1) IRAM observations of Sgr B2. Overall, we find that both the density structure and the shocked gas morphology in Sgr B2 are consistent with a $\lesssim 0.5\mathrm{Myr}$-old cloud-cloud collision. High-velocity shocks are produced during the early stages of the collision and can ignite star formation, while moderate- and low-velocity shocks are important over longer time-scales and can explain the extended SiO emission in Sgr B2.

7 pages, 2 figures, accepted for publication in the Proceedings of the IAU Symposium 362 "Predictive Power of Computational Astrophysics as a Discovery Tool"

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• The dynamical evolution of molecular clouds near the Galactic Centre - I. Orbital structure and evolutionary timeline
• Shock-multicloud interactions in galactic outflows -- I. Cloud layers with log-normal density distributions