Surveying Galaxy Clusters (in formation) in the Distant Universe

Present-day galaxy clusters are the largest virialized structures in the Universe, yet their early assembly remains poorly understood. At z$>$2, clusters in formation span tens of Mpc and host gas-rich, dust-obscured galaxies embedded in extended, low-surface-brightness gaseous environments. Current (sub-)millimeter facilities lack the mapping speed, sensitivity, and contiguous field of view needed to trace the cold gas and dust driving rapid galaxy growth across such scales. A future large single-dish observatory with degree-scale coverage, broad spectral access, and high-multiplex capability would enable comprehensive and uniform mapping of entire protoclusters, revealing where star formation is triggered or quenched, and quantifying the cold gas budget, thus providing information on gas cooling within protocluster environments. In synergy with wide-sky optical/NIR surveys such as Euclid, LSST, and Roman, this facility would provide the missing multi-scale and multiphase submillimeter view needed to uncover how the stellar, gaseous, and dark-matter components assemble in protoclusters, completing our view of early structure formation.

💡 Research Summary

The paper addresses a fundamental gap in our understanding of how the largest virialized structures in the Universe—galaxy clusters—assemble during the first few billion years after the Big Bang. At redshifts greater than two, the progenitors of present‑day clusters, known as protoclusters, span tens of megaparsecs and consist of gas‑rich, dust‑obscured galaxies embedded in low‑surface‑brightness gaseous environments that trace the cosmic web. Existing (sub‑)millimeter facilities such as Herschel, LABOCA, and Planck provide wide‑field coverage but lack the sensitivity and angular resolution needed to identify individual galaxies and diffuse gas simultaneously. Interferometers like ALMA deliver exquisite sensitivity and sub‑arcsecond resolution, yet their primary beam (~1 arcmin) is far too small to map the full extent of protoclusters, and they filter out the extended, low‑surface‑brightness emission that connects galaxies to the surrounding circumgalactic and intergalactic medium (CGM/IGM).

To overcome these limitations, the authors propose a next‑generation, 50‑meter single‑dish submillimeter telescope—embodied in the Atacama Large Aperture Submillimetre Telescope (AtLAST) concept. The instrument would operate at a high, dry site comparable to the ALMA plateau and cover the full 30–950 GHz atmospheric window. Its key specifications include: (i) a diffraction‑limited resolution of ~2 arcseconds at 700 GHz, sufficient to resolve individual galaxies while reducing confusion noise; (ii) an instantaneous field of view of roughly 2 degrees in diameter, corresponding to ~50 × 50 Mpc at z > 2, enabling a single observation to capture an entire protocluster and its surrounding filaments; (iii) a multi‑band spectroscopic suite capable of simultaneous observations of CO,