Molecular gas kinematics of the CMZ: Great oaks from little acorns grow

TL;DR

This paper investigates the 3-D structure and velocity field of the Central Molecular Zone, revealing gravitational instabilities as key to molecular cloud formation and suggesting an evolutionary sequence leading to star formation.

Contribution

It provides a new, accurate 3-D model of the CMZ and discovers a regular velocity pattern linked to cloud formation via gravitational instabilities.

Findings

Correlation of velocity corrugations with massive cloud condensations

Agreement of observed wavelengths with Toomre and Jeans lengths

Gravitational instabilities drive molecular cloud formation in the CMZ

Abstract

The central molecular zone (CMZ) hosts some of the most massive and dense molecular clouds and star clusters in the Galaxy, offering an important window into star formation under extreme conditions. Star formation in this extreme environment may be closely linked to the 3-D distribution and orbital dynamics of the gas. Here I discuss how our new, accurate description of the $\{l,b,v\}$ structure of the CMZ is helping to constrain its 3-D geometry. I also present the discovery of a highly-regular, corrugated velocity field located just upstream from the dust ridge molecular clouds (which include G0.253+0.016 and Sgr B2). The extremes in this velocity field correlate with a series of massive ($\sim10^{4}$ M$_{\odot}$) cloud condensations. The corrugation wavelength ($\sim23$ pc) and cloud separation ($\sim8$ pc) closely agree with the predicted Toomre ($\sim17$ pc) and Jeans ($\sim6$ pc) lengths, respectively. I conclude that gravitational instabilities are driving the formation of molecular clouds within the Galactic Centre gas stream. Furthermore, I suggest that these seeds are the historical analogues of the dust ridge molecular clouds - possible progenitors of some of the most massive and dense molecular clouds in the Galaxy. If our current best understanding for the 3-D geometry of this system is confirmed, these clouds may pinpoint the beginning of an evolutionary sequence that can be followed, in time, from cloud condensation to star formation.