[Paper Review] An Overview of the SPACE Mission Proposal

Massimo Robberto, A. Cimatti+1 more|arXiv (Cornell University)|Oct 22, 2007

Galaxies: Formation, Evolution, Phenomena1 references3 citations

TL;DR

SPACE proposes a class-M space mission to conduct the first all-sky near-infrared spectroscopic survey of over 500 million galaxies using MEMS-based slit spectroscopy at R ~ 400 across 0.8–1.8 µm. It will deliver sub-0.001 redshift accuracy, enabling definitive measurements of baryon acoustic oscillations and cosmic structure growth, with 0.5% precision on the BAO scale and unprecedented constraints on dark energy and modified gravity theories.

ABSTRACT

SPACE (SPectroscopic All-sky Cosmic Explorer) is a class-M mission proposed to ESA for the Cosmic Vision 2015-2025 call and recently promoted to the next assessment study phase. SPACE will produce the first all-sky spectroscopic survey of the Universe, taking spectra of more than 500 million galaxies over a wide range of redshifts. SPACE will operate in slit mode (MEMS) at R~400 between 0.8 and 1.8micron down to AB~23, providing redshifts to an accuracy of Delta z~0.001, regardless on the presence of bright emission lines, together with the most relevant physical and evolutionary properties. The catalog of spectroscopic redshift will allow to place the ultimate constraints on the Baryon Acoustic Oscillations and the nature of Dark Energy. By obtaining the first 3-D all-sky map of the Universe at z~2 and beyond, SPACE will trace the growth rate of cosmic structures, the large scale structure of luminous baryons and its cosmic evolution. Besides the all-sky survey, SPACE will carry out a deep extragalactic survey over an area of ~10 sq. deg., enabling a most powerful supernova search program, and a galactic plane survey in integral field mode. Approximately 30% of the time will be open. Due to its versatility, SPACE is a ``self-sufficient'' observatory which can attack and solve the most compelling questions on the nature of the Dark Energy without complementary data from the Earth or space. Its unique wide-field capabilities in the near-IR make SPACE the ideal complement to JWST, ALMA, and the future 25-50 m telescopes.

Motivation & Objective

• To overcome the limitations of photometric redshifts by delivering precise spectroscopic redshifts for hundreds of millions of galaxies across the extragalactic sky.
• To measure baryon acoustic oscillations (BAOs) with sub-0.001 accuracy in redshift, enabling the tightest constraints on dark energy and cosmic geometry.
• To trace the growth of large-scale structure from z ~ 2 to the present, distinguishing between dark energy and modified gravity models.
• To discover and characterize primordial galaxies, Ly-α emitters, and early-type galaxies at z > 2, including the first QSOs and Type Ia supernovae.
• To create a legacy dataset through a 5-year mission with 30% guest observer time, enabling long-term data mining across all fields of astronomy.

Proposed method

• Utilizes a 1.5 m space telescope at the Sun-Earth L2 point to minimize thermal and atmospheric interference in the near-IR.
• Employs MEMS micromirror devices for multi-object slit spectroscopy, enabling simultaneous observation of ~6,000 galaxies per pointing across a 0.4 deg² field of view.
• Operates at resolving power R ~ 400 in the 0.8–1.8 µm range, with spectral resolution sufficient to measure redshifts to Δz ~ 0.001 regardless of emission-line presence.
• Performs initial H-band imaging (AB ~ 23) at each pointing to select sources for spectroscopy, producing the deepest all-sky near-IR imaging survey to date.
• Switches to integral field mode using Hadamard transforms for a Galactic plane survey, enabling 3D spectroscopy of a 1 deg² strip.
• Combines a wide-area all-sky survey (covering ~70% of the sky), a deep extragalactic survey (10 deg² to AB ~ 26), and a galactic plane survey, with ~30% of observing time allocated to guest observer programs.

Experimental results

Research questions

• RQ1 Can a space-based near-IR spectroscopic survey achieve sub-0.001 redshift accuracy for 500 million galaxies across the extragalactic sky?
• RQ2 What is the precision with which baryon acoustic oscillations can be measured across multiple redshift bins using a single all-sky spectroscopic survey?
• RQ3 How accurately can the growth rate of cosmic large-scale structure be measured from z ~ 2 to the present using a wide-field spectroscopic survey?
• RQ4 What is the yield of high-redshift galaxies (z > 2), including Ly-α emitters and early QSOs, in a deep spectroscopic survey covering 10 deg² to AB ~ 26?
• RQ5 Can a space-based spectroscopic survey discover Type Ia supernovae with an efficiency an order of magnitude higher than previous missions due to its wide field of view?

Key findings

• SPACE will achieve a 0.5% accuracy in measuring the BAO scale across redshift slices of Δz ~ 0.5, surpassing the statistical power of all other planned surveys.
• The mission will deliver the definitive measurement of the baryon acoustic oscillation signature, with statistical power approximately an order of magnitude higher than WFMOS.
• The all-sky survey will enable the first 3D all-sky map of the Universe at z ~ 2 and beyond, tracing the large-scale structure of luminous baryons and their cosmic evolution.
• The deep extragalactic survey will discover approximately 2,300 Type Ia supernovae, with spectral observations at an efficiency 10× higher than SNAP, due to its wide field of view.
• The mission will produce the deepest all-sky near-IR imaging survey to date (AB ~ 23), serving as a byproduct of source selection for spectroscopy.
• Joint constraints on the dark energy equation of state (w₀ and wₐ) will improve dramatically, with SPACE providing the tightest constraints on w₀ and wₐ from any single survey.