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

TL;DR

This study uses 3D simulations and SiO observations to investigate a potential cloud-cloud collision in Sgr B2, revealing turbulent structures, shock velocities, and chemical signatures consistent with a recent collision that may trigger star formation.

Contribution

The paper demonstrates that a recent cloud-cloud collision can explain the observed gas turbulence, shock properties, and SiO emission in Sgr B2, combining simulations with observational data.

Findings

Collision produces turbulent density structures matching observations.

Shocks with velocities of 5-50 km/s explain SiO abundances.

Collision age estimated at less than 0.5 million years.

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 $N_{\rm H2}\gtrsim 5\times10^{22}\,\rm cm^{-2}$. Similarly, our numerical multi-channel shock study shows that colliding clouds are efficient at producing internal shocks with velocities of $5-50\,\rm km\,s^{-1}$ and Mach numbers of $\sim4-40$, 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 $\lesssim 0.5\,\rm Myr$-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.