[Paper Review] MUltiplexed Survey Telescope: Perspectives for Large-Scale Structure Cosmology in the Era of Stage-V Spectroscopic Survey

Cheng Zhao, Song Huang+42 more|arXiv (Cornell University)|Nov 12, 2024

Astronomy and Astrophysical Research4 citations

TL;DR

The MUltiplexed Survey Telescope (MUST) is a proposed 6.5-meter spectroscopic telescope designed to conduct the first Stage-V cosmological survey in the 2030s, mapping over 100 million galaxies and quasars from redshift z ≈ 0 to z ≈ 5.5 using 20,000+ simultaneous targets across a 5 deg² field of view. Using Fisher forecasts, the study demonstrates that MUST will enable sub-percent-level constraints on dark energy, 2% precision on structure growth, and sub-eV sensitivity to neutrino mass, surpassing current limits on primordial non-Gaussianity and warm dark matter mass.

ABSTRACT

The MUltiplexed Survey Telescope (MUST) is a 6.5-meter telescope under development. Dedicated to highly-multiplexed, wide-field spectroscopic surveys, MUST observes over 20,000 targets simultaneously using 6.2-mm pitch positioning robots within a ~5 deg$^2$ 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, ranging from local bright galaxies and luminous red galaxies to 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 the series of science white papers for MUST, with subsequent developments focusing on additional scientific cases such as galaxy and quasar evolution, Milky Way physics, and dynamic phenomena in the time-domain Universe.

Motivation & Objective

• To design a next-generation spectroscopic survey telescope capable of mapping the 3D large-scale structure of the universe from z ≈ 0 to z ≈ 5.5.
• To address unresolved questions in cosmology, including the nature of dark energy, gravity, primordial non-Gaussianity, and neutrino properties.
• To develop a conceptual target selection strategy for diverse tracers across low- and high-redshift regimes.
• To forecast the cosmological power of MUST using Fisher matrix methods, establishing its scientific potential for Stage-V surveys.
• To position MUST as a cornerstone for future cosmological experiments, complementing imaging, CMB, and gravitational wave probes.

Proposed method

• Utilizes a 6.5-meter telescope with a multiplexed focal plane using 6.2-mm pitch positioning robots to observe over 20,000 targets simultaneously within a ~5 deg² field of view.
• Employs a multi-tracer approach: bright galaxies, luminous red galaxies (LRGs), emission-line galaxies (ELGs), Lyman-break galaxies (LBGs), Lyα emitters (LAEs), and quasars (QSOs) for redshift coverage from z ≈ 0 to z ≈ 5.5.
• Applies a conceptual target selection algorithm based on multi-band imaging and spectroscopic validation data to ensure sufficient source density across redshifts.
• Uses Fisher forecast methodology to project cosmological constraints on dark energy, structure growth, primordial non-Gaussianity, neutrino mass, and warm dark matter.
• Models survey design with two components: a dark time survey for primary cosmological mapping and a grey time survey for complementary science.
• Integrates forecasts with external probes—CMB (Planck, Simons Observatory), imaging surveys, radio surveys, and gravitational wave sources—to assess synergy and enhanced sensitivity.

Experimental results

Research questions

• RQ1 Can MUST achieve sub-percent-level precision in geometric measurements of the universe using low-redshift galaxy tracers (z < 1.6)?
• RQ2 To what extent can MUST improve constraints on the growth rate of structure and test theories of gravity at z > 2?
• RQ3 Can MUST provide the first cosmological measurement of primordial non-Gaussianity (fNL^local) with precision surpassing Planck’s constraints?
• RQ4 What is the expected sensitivity of MUST to the total neutrino mass, and can it confirm non-zero neutrino mass with statistical error < 0.03 eV?
• RQ5 What lower limit on warm dark matter particle mass can be set using Lyα forest data from a 14,000 deg² survey?

Key findings

• MUST will achieve ~1% precision on geometric measurements of the universe at low redshifts (z < 1.6), enabling robust discrimination between dark energy models.
• Structure growth measurements at z > 2 will reach 2% precision, allowing for strong tests of gravity theories beyond General Relativity.
• MUST will provide the first cosmological constraint on the primordial non-Gaussianity parameter fNL^local with precision on the order of unity, surpassing Planck’s sensitivity.
• Combined with CMB data, MUST will achieve a statistical error on the total neutrino mass of ~0.03 eV, enabling confirmation of non-zero neutrino mass.
• With a 14,000 deg² survey area, MUST will set a lower limit on warm dark matter particle mass of ~10.5 keV, exceeding current best constraints.
• The survey will map over 100 million galaxies and quasars across a redshift range from z ≈ 0 to z ≈ 5.5, covering ~1 billion years after the Big Bang.