JWST Breakthrough in Galaxy Formation: Mass Build-up Efficiency at Cosmic Dawn

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We present SFEER (Star Formation Efficiency in the Epoch of Reionization), an ambitious project to enable one of the most significant and long-lasting leaps in our understanding of early galaxy formation. The discovery of exceptionally massive galaxies in the distant Universe has confronted us with puzzling questions about how galaxies could assemble so efficiently at early cosmic times. Unfortunately, significant instrumental limitations have prevented us from robustly reconstructing their physical properties. The recent launch of the James Webb Space Telescope (JWST) has ignited a revolution. Its exquisite sensitivity and spatial resolution are going to provide dramatically new information on massive galaxies in the the Epoch of Reionization (EoR) and beyond. SFEER is set to play a dominant role in this process. At its core is a cycle 1 JWST/NIRSpec program I am leading which will obtain spatially resolved spectroscopy for 12 exceptionally bright galaxies in the EoR. Remarkably, estimates of the interstellar medium (ISM) reservoirs of this sample are already in our hands thanks to recent Atacama Large Millimeter Array (ALMA) observations, providing information on their molecular gas and dust content, and the fraction of obscured star formation. This joint dataset clearly stands out in the panorama of current JWST programs, and constitutes an important benchmark. SFEER will enable to probe the assembly history of these tantalizing objects through the characterization of their ages, stellar mass, energy-balanced star-formation rates, metallicity, merging fractions and gas kinematics, and their relationship with the host dark matter halos. Taking advantage of complementary JWST programs and wide-area multi-wavelength data from ground and Euclid, we will extend our results to higher and lower masses, and probe galaxy formation from the earliest points in cosmic time.