The initial conditions for young massive cluster formation in the Galactic Centre: convergence of large-scale gas flows

Young massive clusters (YMCs) are compact (less than or similar to 1 pc), high-mass (>10(4) M-circle dot) stellar systems of significant scientific interest. Due to their rarity and rapid formation, we have very few examples of YMC progenitor gas clouds before star formation has begun. As a result, the initial conditions required for YMC formation are uncertain. We present high resolution (0.13 arcsec, similar to 1000 au) ALMA observations and Mopra single-dish data, showing that Galactic Centre dust ridge 'Cloud d' (G0.412 + 0.052, mass = 7.6 x 10(4) M-circle dot, radius = 3.2 pc) has the potential to become an Arches-like YMC (10(4) M-circle dot, r similar to 1 pc), but is not yet forming stars. This would mean it is the youngest known pre-star-forming massive cluster and therefore could be an ideal laboratory for studying the initial conditions of YMC formation. We find 96 sources in the dust continuum, with masses less than or similar to 3 M-circle dot and radii of similar to 10(3) au. The source masses and separations are more consistent with thermal rather than turbulent fragmentation. It is not possible to unambiguously determine the dynamical state of most of the sources, as the uncertainty on virial parameter estimates is large. We find evidence for large-scale (similar to 1 pc) converging gas flows, which could cause the cloud to grow rapidly, gaining 10(4) M-circle dot within 10(5) yr. The highest density gas is found at the convergent point of the large-scale flows. We expect this cloud to form many high-mass stars, but find no high-mass starless cores. If the sources represent the initial conditions for star formation, the resulting initial mass function will be bottom heavy.