Zooming in on high-redshift star formation with the Planck's Dusty GEMS sample
Strong gravitational lensing offers a unique opportunity to probe the history of mass assembly. In particular, by characterizing the most strongly lensed sub-mm galaxies at z~2-3, we can study the vigorous star formation (up to 1000 Msun/yr) in massive galaxies during their rapid formation phase with unprecedented details. Fortuitous alignments with foreground galaxies or galaxy groups/clusters that offer magnification factors >> 10 allow us to probe individual star-forming regions in these sub-mm galaxies on spatial scales <100 pc, and to constrain the mechanisms regulating the star formation efficiency in extreme environments. I will discuss the discovery and properties of the Planck's Dusty GEMS (Gravitationally Enhanced sub-Millimeter Sources), a small set of extremely bright lensed high-redshift galaxies selected in the FIR/sub-mm regime with the Planck all-sky survey. I will also present long-baseline ALMA observations of the brightest source in this sample that exhibits local star formation rate densities up to 4000 Msun/yr/kpc², corresponding to the regime of maximal starbursts.