In today standard picture of the universe, the Λ Cold Dark Matter (ΛCDM) model, the largest cosmic structures are vast, invisible clumps of dark matter that grow by merging under the pull of gravity. Dark matter outweighs ordinary matter by a factor of five to six, making it the dominant form of matter in the cosmos. As it gathers into dark matter halos, their gravity forms a cosmic scaffold that draws in ordinary matter, much of it hydrogen, the fuel for star formation. As this gas falls into halos, it cools and condenses, eventually igniting stars and giving rise to galaxies. At the same time, energetic processes such as supernova explosions and activity from supermassive black holes inject energy into the gas, decreasing (i.e. regulating) how efficiently stars can form.
In this framework, structures grow hierarchically: small systems form first, then merge into larger ones. The most massive galaxies are therefore expected to appear relatively late in cosmic history.
Over the past decade, however, astronomers have discovered surprisingly massive and bright galaxies from when the universe was only one to two billion years old, and in some cases even earlier. Even more striking, since the very first observations from the James Webb Space Telescope (JWST), it has become clear that unexpectedly large numbers of bright, possibly massive, and seemingly mature galaxies already existed much earlier. These findings suggest a far more extreme picture of galaxy formation in the first few hundred million years after the Big Bang.
The implication is remarkable: large galaxies were already taking shape just a few hundred million years after the universe began. According to current theories, building such enormous systems should take much longer. Yet these early galaxies appear to have formed stars at a breathtaking pace, more efficiently than predicted from the growth of their dark matter halos.
In this context, SFEER is designed to uncover the physical processes that enabled the rapid build-up of the first massive galaxies and, guided by these insights, to extend the exploration to lower masses and earlier cosmic epochs. ALMA observations from the REBELS survey already provide the first systematic view of cold gas and dust in ~30 massive galaxies at only 700–800 Myr after the Big Bang, in the heart of the Epoch of Reionization, revealing the reservoirs that fuel early star formation. Through a JWST program I lead, we have just secured exquisite spatially resolved spectroscopy for twelve of the brightest REBELS sources. Together, JWST and ALMA establish an unprecedented reference sample, delivering the most comprehensive characterization to date of primordial galaxy properties. Building on this foundation, SFEER will exploit deep JWST surveys to push to fainter, less extreme systems and to even earlier times, back to when the Universe was only few hundred million years old.
By combining the unique capabilities of JWST and ALMA with complementary datasets and next-generation surveys, SFEER will provide a transformative, end-to-end view of how stars, gas, and dust first assembled into galaxies, setting a new benchmark for models of galaxy formation.
