MUltiplexed Survey Telescope (MUST) science white paper I: Overview of large-scale structure cosmology in the era of Stage-V spectroscopic surveys

Abstract

The MUltiplexed Survey Telescope (MUST) is a 6.5-m telescope under development. Dedicated to highly-multiplexed, wide-field spectroscopic surveys, MUST observes over 20000 targets simultaneously using 6.2-mm pitch positioning robots within a ∼5 deg² field of view. MUST aims to conduct the first Stage-V spectroscopic survey in the 2030s, mapping the 3D Universe with over 100 million galaxies and quasars, spanning from the nearby Universe to a redshift of z ∼ 5.5, corresponding to approximately 1 billion years after the Big Bang. To cover this extensive redshift range, we present an initial conceptual target-selection algorithm for different types of galaxies, including local bright galaxies, luminous red galaxies, emission-line galaxies, and high-redshift (2 < z < 5.5) Lyman-break galaxies. Using Fisher forecasts, we demonstrate that MUST can address fundamental questions in cosmology, including the nature of dark energy, tests of gravity theories, and investigations into primordial physics. This is the first paper in a series of science white papers for MUST, with subsequent papers focusing on additional scientific cases, including galaxy and quasar evolution, Milky Way physics, and dynamic phenomena in the time-domain Universe.