SPACE: the SPectroscopic All-sky Cosmic Explorer

TL;DR

SPACE envisions a space-based near-infrared spectroscopic all-sky survey to map the 3D evolution of the Universe out to z~2 (and a deep field to z>10) by obtaining redshifts for >5×10^8 galaxies. The mission leverages a 1.5 m Ritchey-Chrétien telescope and MEMS-based DMD multiplexing to achieve ~6000 targets per pointing at R~400, with 0.8–1.8 μm spectral coverage and imaging down to AB~26. It aims to constrain dark energy through BAO measurements, growth-rate studies from redshift-space distortions, high-redshift SNe, and galaxy clusters, while also enabling galaxy formation and evolution studies and a Milky Way survey, all in comparison and synergy with Planck, JWST, and future facilities. The SPACE concept includes a robust simulation-backed design, a four-channel payload, operation from a large L2 halo orbit, and a comprehensive data-analytic pipeline through MOC/SOC/SDC structures to deliver high-value cosmological and astrophysical results.

Abstract

We describe the scientific motivations, the mission concept and the instrumentation of SPACE, a class-M mission proposed for concept study at the first call of the ESA Cosmic-Vision 2015-2025 planning cycle. SPACE aims to produce the largest three-dimensional evolutionary map of the Universe over the past 10 billion years by taking near-IR spectra and measuring redshifts for more than half a billion galaxies at 0<z<2 down to AB~23 over 3πsr of the sky. In addition, SPACE will also target a smaller sky field, performing a deep spectroscopic survey of millions of galaxies to AB~26 and at 2<z<10+. These goals are unreachable with ground-based observations due to the ~500 times higher sky background. To achieve the main science objectives, SPACE will use a 1.5m diameter Ritchey-Chretien telescope equipped with a set of arrays of Digital Micro-mirror Devices (DMDs) covering a total field of view of 0.4 deg2, and will perform large-multiplexing multi-object spectroscopy (e.g. ~6000 targets per pointing) at a spectral resolution of R~400 as well as diffraction-limited imaging with continuous coverage from 0.8mum to 1.8mum.

Figures (11)

• Figure 1: A simulated $5�\times7�$ field showing the location of the spectra of the selected targets.
• Figure 2: Simulated spectrum of an early-type passively evolving galaxy at $z>2$. The D4000 break and the main absorption lines (CaII H&K) are clearly detected. It is impossible to obtain such a spectrum with ground-based near-IR spectroscopy due to the sky background, OH line contamination and telluric absorptions.
• Figure 3: Optical Telescope Assembly and fore-optics system (four channels).
• Figure 6: Left: typical substructure of a TI DMD; center: DMD array with an ant leg for comparison; 3: packaged DMD CINEMA (2048$\times$1080) device.
• Figure 7: Estimated SNR of SPACE spectra in 900s integration. We used detector parameters typical of WFC3/IR flight candidates. Transmission efficiencies of all reflective and refractive components are those of the WFC3/IR optical coating. Light losses due to the prism thickness are included, together with the most recent zodiacal background prediction for the SNAP mission also at L2.