The episodic and multiscale Galactic Centre

Within the central few hundred parsecs of the Milky Way, extending from longitude l = −1° to 1.5°, lies the Central Molecular Zone of the Galactic Centre. This extraordinary region is defined by a diverse variety of ISM features in numerous stages of evolution. Molecular cloud H2 volume densities range from 103-8 cm−3 with an average of 104 cm−3, two orders of magnitude above that of the galactic disk. The CMZ contains ∼3-5 × 107 M☉ of molecular gas, corresponding to around 5-10% of the content of the entire galaxy, and a similar fraction of its infrared luminosity. Gas temperatures, pressures and turbulent mach numbers are also significantly raised here, providing one of the more extreme environments for star formation within our observational reach.