A Hunt for Massive Starless Cores
  We carry out an ALMA $\rm N_2D^+$(3-2) and 1.3~mm continuum survey towards 32
high mass surface density regions in seven Infrared Dark Clouds with the aim of
finding massive starless cores, which may be the initial conditions for the
formation of massive stars. Cores showing strong $\rm N_2D^+$(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 C$^{18}$O(2-1), DCN(3-2) and DCO$^+$(3-2).
Over 100 $\rm N_2D^+$ cores are identified with our newly developed
core-finding algorithm based on connected structures in position-velocity
space. The most massive core has $\sim70\:M_\odot$ (potentially
$\sim170\:M_\odot$) and so may be representative of the initial conditions for
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 $\rm N_2D^+$(3-2) line
emission, finding results that are generally consistent with virial equilibrium
of pressure confined cores.
