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Aaron Bryant
Deutsches SOFIA Institut

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 (CMZ) 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 10^3-8 cm−3 with an average of 10^4 cm−3, two orders of magnitude above that of the galactic disk. The CMZ contains ~3-5 × 10^7 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. Across various spatial scales, episodic cycles of star formation, matter transport and feedback can be identified. The evolutionary states of molecular clouds, star forming regions and stellar clusters can be linked to their positions along orbits spanning the CMZ, and may be regulated by episodic processes such as material inflow or feedback. A concentric series of expanding bubbles and fronts can be related to echoes of past activity in the central cluster and Sgr A*. The ensemble of stellar ages and populations in the highly inhospitable environment of the central few parsecs points towards a series of accretion and starburst events. Many of these processes are potentially linked in a nested series of episodic cycles occurring concurrently, in which shorter timescale cycles regulate longer ones. The resulting complex and highly time-variable picture can help to explain many of the currently observed characteristics of the Galactic Centre, such as its deficient star forming efficiency. We have hence been provided with a unique stellar and interstellar laboratory practically on our observable doorstep. Observations of both individual features and the region as a whole can improve our understanding of the formation and evolution of this region of the Milky Way - Knowledge that we can then apply to the nuclei of other galaxies. I will review some of the historical and recent advancements in our observational and theoretical interpretations of the Galactic Centre, and identify some of the more tantalising open questions and areas of interest that may be addressed by both current and future infrared/sub-mm platform capabilities.