[Paper Review] MOONRISE: The Main MOONS GTO Extragalactic Survey

R. Maiolino, M. Cirasuolo+35 more|arXiv (Cornell University)|Jan 1, 2020

Astronomy and Astrophysical Research38 citations

TL;DR

MOONRISE is a guaranteed-time extragalactic survey using the MOONS spectrograph on the VLT to conduct a deep, wide-area spectroscopic survey of ~500,000 galaxies at z ≈ 0.9–2.6, focusing on Cosmic Noon (z ~ 1–2.5), enabling unprecedented measurements of galaxy metallicity, star formation, and environmental dependence through multi-epoch observations and high-fidelity spectral diagnostics across optical to near-infrared wavelengths.

ABSTRACT

The MOONS instrument possesses an exceptional combination of large multiplexing, high sensitivity, broad simultaneous spectral coverage (from optical to near-infrared bands), large patrol area and high fibre density. These properties provide the unprecedented potential of enabling, for the very first time, SDSS-like surveys around Cosmic Noon (z~1-2.5), when the star formation rate in the Universe peaked. The high-quality spectra delivered by MOONS will sample the same nebular and stellar diagnostics observed in extensive surveys of local galaxies, providing an accurate and consistent description of the evolution of various physical properties of galaxies, and hence a solid test of different scenarios of galaxy formation and transformation. Most importantly, by spectroscopically identifying hundreds of thousands of galaxies at high redshift, the MOONS surveys will be capable of determining the environments in which primeval galaxies lived and will reveal how such environments affected galaxy evolution. In this article, we specifically focus on the main Guaranteed Time Observation (GTO) MOONS extragalactic survey, MOONRISE, by providing an overview of its scientific goals and observing strategy.

Motivation & Objective

• To measure the redshift evolution of galaxy metallicity scaling relations, including the mass-metallicity and Fundamental Metallicity Relations, across cosmic time.
• To determine how galaxy properties—especially star formation and quenching—depend on large-scale environment at z ≈ 1–2.5.
• To achieve high completeness (80% in COSMOS, 70% in VIDEO fields) for mass- and magnitude-limited samples to enable robust statistical tests of galaxy evolution models.
• To identify and spectroscopically confirm high-redshift galaxies (z ≈ 6–8) and AGN using targeted observations of Lyman-break and Lyα emitter candidates.
• To provide a legacy dataset of high-quality, consistent spectroscopic diagnostics across a broad redshift range, enabling direct comparison with local surveys like SDSS and GAMA.

Proposed method

• Utilizes the MOONS multi-object spectrograph on the VLT, which provides simultaneous coverage from optical to near-infrared (0.8–2.4 µm) with high multiplexing (up to 1000 fibres) and high fibre density.
• Employs a dual observing strategy: Xswitch mode (nodding for sky subtraction) and Stare mode (dedicated sky fibres), optimizing completeness and background subtraction.
• Applies a dual selection function: galaxies are selected by stellar mass (log M* > 9.5) or apparent magnitude (HAB < 23–24) in three redshift bins (0.9 < z < 1.1, 1.2 < z < 1.7, 2.0 < z < 2.6) to maximize sample diversity.
• Allocates 25% of fibres per pointing to passive galaxies for repeated 8-hour integrations to achieve high completeness, while the rest target star-forming galaxies with shorter exposures (1–2 hours).
• Uses mock simulations and photometric samples to optimize fibre allocation and survey design, ensuring 80% completeness in COSMOS and 70% in VIDEO fields.
• Targets high-redshift candidates (z > 5) and AGN with dedicated 8-hour integrations, using broad- and narrow-band photometry for selection.

Experimental results

Research questions

• RQ1 How does the mass-metallicity relation evolve from z ≈ 1 to z ≈ 2.5, and does it remain constant or evolve significantly?
• RQ2 What is the role of environment (clusters, filaments, voids) in quenching star formation and transforming galaxies at Cosmic Noon?
• RQ3 How do the physical properties of galaxies—such as metallicity, star formation rate, and stellar mass—correlate with their large-scale environment at z ≈ 1–2.5?
• RQ4 Can MOONS achieve high completeness (≥80%) for mass-limited samples in deep fields like COSMOS and VIDEO, and how does observing mode (Xswitch vs. Stare) affect this?
• RQ5 What is the spectroscopic confirmation rate and redshift accuracy for high-redshift Lyman-break and Lyα emitter candidates at z ≈ 6–8?

Key findings

• MOONS can detect key nebular lines such as [OII] at z = 3.8, [OIII] at z = 2.6, and Ha at z = 1.74, enabling spectroscopic redshifts and diagnostics across the full Cosmic Noon redshift range.
• The survey is expected to obtain high-quality spectra for up to 54,500 galaxies in the 0.9 < z < 1.1 bin, 12,900 in 1.2 < z < 1.7, and 88,700 in 2.0 < z < 2.6, with a total of ~200,000 galaxies in Xswitch mode over 4 square degrees.
• In the COSMOS field, the survey aims for 80% completeness with ~480 passive galaxies and ~4,350 star-forming galaxies per pointing, requiring ~38 nights of observing time including overheads.
• The Stare mode could nearly double the number of observed galaxies, reaching ~460,000 total in 7 square degrees, assuming acceptable background subtraction.
• High-redshift candidates (z > 5) will be observed with 8-hour integrations, and a few tens of fibres per pointing will be allocated to these targets to enable confirmation of early galaxies.
• The survey design achieves high completeness through repeated observations with reconfigured fibre layouts, with up to 40 hours on source for some targets, ensuring robust statistical power for environmental and scaling relation studies.