Diffuse and dense gas in the Central Molecular Zone
With the HOPS and MALT90 surveys we are mapping a significant fraction of the dense molecular gas in the Galaxy in over 20 dense-gas-tracing transitions (e.g. from H2O, NH3, HC3N, HC5N, N2H+, HCN, HNC, HCO+,
CH3CN, SiO, C2H, ..). Combining this with the far-IR continuum emission from Hi-GAL we can derive the physical/chemical/kinematic properties and evolutionary state of much of the molecular gas in the Galaxy destined to form stars. In this talk I will present preliminary results from three science projects based on this combined dataset, namely: i) looking for variations in the star formation rate across the Galaxy as a function of environment, in particular, comparing the central molecular zone with the rest of the Galactic disk; ii) seeing if Galactic dense molecular clouds follow the empirical relations observed in extragalactic systems (e.g. the Kennicutt-Schmidt and Gao & Solomon relations) and what this implies for interpreting the extragalactic relations; iii) searching for molecular cloud progenitors of the most extreme (massive and dense) stellar clusters. I will finish by showing one cloud lying close to the Galactic center which is clearly extreme compared to the rest of the Galactic molecular cloud population. With a mass of 105 M¤, a radius of only ~3 pc and almost no signs of star formation it appears to be the progenitor of an Arches-like stellar cluster. As such, we speculate this molecular cloud may be a local-universe-analogue of the initial conditions of a super star cluster or potentially even a small globular cluster.