Astrophysical observations at (sub)mm wavelengths (from ~300 micron to ~3mm) allow us to study the cold and dense material in the Universe, hence probing the formation of stars and planets, and the interstellar and circumgalactic medium within galaxies across cosmic time. The current generation of 15m-class single-dish telescopes has delivered some of the first surveys at (sub)mm wavelengths, allowing to go far beyond the previously optical-biased view of the Universe. Follow-up observations with interferometers then revealed in exquisite detail the morphology and kinematics of such (sub)mm sources. However, it is now clear that without a transformative change in the capabilities of single-dish facilities in the 2030s, interferometers will soon become source-starved. The current generation of 15m-class single- dish telescopes, with their limited fields of view, spatial resolutions, and sensitivities, can only reveal the "peak of the iceberg" of the (sub)mm source population, both for Galactic and extragalactic studies. These limitations cannot be fully mitigated by interferometers, which are all intrinsically affected by a low mapping speed and by the loss of diffuse extended signals.
The Atacama Large Aperture Submillimeter telescope (AtLAST) project is a concept for a 50m diameter single dish observatory to be built near the ALMA site. With its extremely large field of view (the goal is ~2 degrees), spatial resolution (up to ~1'' at 350 micron) and sensitivity to both point sources and large-scale structures, AtLAST will be transformational for all fields of astronomy in the 2030s. In this talk I will describe the EU Horizon2020-funded project that aims to deliver a comprehensive design study for such a next-generation single-dish facility.
