How to Find Young Massive Cluster Progenitors
  We propose that bound, young massive stellar clusters form from dense clouds
that have escape speeds greater than the sound speed in photo-ionized gas. In
these clumps, radiative feedback in the form of gas ionization is bottled up,
enabling star formation to proceed to sufficiently high efficiency so that the
resulting star cluster remains bound even after gas removal. We estimate the
observable properties of the massive proto-clusters (MPCs) for existing
Galactic plane surveys and suggest how they may be sought in recent and
upcoming extragalactic observations. These surveys will potentially provide a
significant sample of MPC candidates that will allow us to better understand
extreme star-formation and massive cluster formation in the Local Universe.
