Offspring of SPACE: the Spectrograph Channel of the ESA DarkEnergy Mission EUCLID

摘要

The SPACE and DUNE proposals for the ESA Cosmic Vision 2015-2025 have been pre-selected for a Dark Energy Mission. An assessment study was performed in the past few months resulting in a merged mission called EUCLID. The study led to a possible concept for the mission and the payload, paving the way for the industrial studies. SPACE has now become the EUCLID spectrograph channel (EUCLID-spectro). We will discuss its science and give a description of the different studied optical designs. EUCLID-spectro aims to produce the largest three-dimensional map of the Universe by taking near-IR spectra at R=400 and 0.9um<λ<1.7μm for～200 million galaxies at z < 2 and H < 22 over 20,000 deg~2. It will measure the expansion history of the Universe and the growth rate of structure using Baryonic Acoustic Oscillations, redshift-space distortions and clusters of galaxies. It will distinguish true dark energy from a modification of Einstein's gravity. The original design had 4 channels each re-imaging with mirrors a sub-field from the Casgrain focus onto a Digital Micromirror Device (DMD). A prism spectrograph followed each array. This design was modified to adapt EUCLID-spectro to a DUNE-type telescope, to reduce the number of optics and spectrographs, and add an imaging capability. We studied grism spectrographs, especially for a slitless backup solution that have less optics but a smaller field; we also studied compact prism and lens spectrographs, telescope corrector combined with micromirror arrays at the Casgrain focus then eliminating the re-imaging, and TIR prisms over the arrays to help with packaging.