Lessons from the hidden Universe

Understanding when and how galaxies assemble and mature is essential to unveil the complete picture of galaxy formation and evolution throughout the history of the Universe. A robust determination of the abundance of massive (even quiescent) galaxies at high redshift and their contribution to the cosmic star formation rate density (CSFRD) is essential to constrain current galaxy formation models. In this sense, although a significant fraction of star formation in the Universe is heavily enshrouded by dust, our current knowledge of high-z (z > 3) is mainly based on galaxy samples selected in the rest frame UV. We present a new multi-wavelength approach that has allowed us to uncover a hidden population of very massive high-z galaxies that were missed by previous surveys at optical and NIR wavelengths. These elusive systems represent 30-40% of the most massive (logM > 11 M⊙) at z=4-6