SIMBAD references

We carry out an ALMA N₂D⁺(3-2) and 1.3 mm continuum survey of 32 high-mass surface density regions of seven infrared dark clouds, with the aim of finding massive starless cores that may form the initial conditions for the formation of massive stars. Cores showing strong N₂D⁺(3-2) emission are expected to be highly deuterated and indicative of early, potentially pre-stellar stages of star formation. We also present maps of these regions in ancillary line tracers, including C¹⁸O(2-1), DCN(3-2), and DCO⁺(3-2). Over 100 N₂D⁺  cores are identified with our newly developed core-finding algorithm, based on connected structures in position-velocity space. The most massive core has ∼70 M_☉ (potentially ∼170 M_☉) and so may be representative of the initial conditions or early stages of massive star formation. The existence and dynamical properties of such cores constrain massive star formation theories. We measure the line widths and thus velocity dispersion of six of the cores with strongest N₂D⁺(3-2) line emission, finding results that are generally consistent with virial equilibrium of pressure confined cores.