A Multiwavelength Study of the Sgr B Region: Contiguous Cloud-Cloud Collisions Triggering Widespread Star Formation Events?

TL;DR

This study re-examines the Sgr B region and proposes that contiguous cloud-cloud collisions with a relative velocity of about 20 km/s triggered widespread high-mass star formation, challenging previous models.

Contribution

It introduces a new CCC identification methodology and suggests an alternative collision scenario involving contiguous clouds with specific velocities.

Findings

Identified over 50 cloud-cloud collisions across the region.

Found two large velocity components with signatures of collision.

Proposed a collision model with a relative velocity of ~20 km/s for star formation.

Abstract

The Sgr\,B region, including Sgr\,B1 and Sgr\,B2, is one of the most active star-forming regions in the Galaxy. Hasegawa et al. (1994) originally proposed that Sgr\,B2 was formed by a cloud-cloud collision (CCC) between two clouds with velocities of $\sim$45 km~s$^{-1}$ and $\sim$75 km~s$^{-1}$. However, some recent observational studies conflict with this scenario. We have re-analyzed this region, by using recent, fully sampled, dense-gas data and by employing a recently developed CCC identification methodology, with which we have successfully identified more than 50 CCCs and compared them at various wavelengths. We found two velocity components that are widely spread across this region and that show clear signatures of a CCC, each with a mass of $\sim$10$^6$ $M_\odot$. Based on these observational results, we suggest an alternative scenario, in which contiguous collisions between two velocity features with a relative velocity of $\sim$20 km~s$^{-1}$ created both Sgr\,B1 and Sgr\,B2. The physical parameters, such as the column density and the relative velocity of the colliding clouds, satisfy a relation that has been found to apply to the most massive Galactic CCCs, meaning that the triggering of high-mass star formation in the Galaxy and starbursts in external galaxies can be understood as being due to the same physical CCC process.