Preprint typeset using LATEX style emulateapj v. 5/2/11 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 result-ing 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 can-didates that will allow us to better understand extreme star-formation and massive cluster formation in the Local Universe