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

摘要

The central molecular zone (CMZ) hosts some of the most massive and densemolecular clouds and star clusters in the Galaxy, offering an important windowinto star formation under extreme conditions. Star formation in this extremeenvironment may be closely linked to the 3-D distribution and orbital dynamicsof 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 presentthe discovery of a highly-regular, corrugated velocity field located justupstream from the dust ridge molecular clouds (which include G0.253+0.016 andSgr 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 thepredicted Toomre ($\sim17$ pc) and Jeans ($\sim6$ pc) lengths, respectively. Iconclude that gravitational instabilities are driving the formation ofmolecular clouds within the Galactic Centre gas stream. Furthermore, I suggestthat these seeds are the historical analogues of the dust ridge molecularclouds - possible progenitors of some of the most massive and dense molecularclouds in the Galaxy. If our current best understanding for the 3-D geometry ofthis system is confirmed, these clouds may pinpoint the beginning of anevolutionary sequence that can be followed, in time, from cloud condensation tostar formation.