MOSAIC on the ELT: High-multiplex Spectroscopy to Unravel the Physics of Stars and Galaxies from the Dark Ages to the Present Day

The powerful combination of the cutting-edge multi-object spectrograph named MOSAIC with the world largest visible/near-infrared telescope, ESO’s Extremely Large Telescope (ELT), will allow us to probe deeper into the Universe than ever before. MOSAIC is an extremely efficient instrument for obtaining spectra of the numerous faint sources in the Universe, including the very first galaxies and sources of cosmic reionisation. MOSAIC has a high multiplex in the near-infrared (NIR) and in the visible, and also has multi-integral field units (Multi-IFUs) in the NIR. It is therefore perfectly suited to carrying out an inventory of dark matter (from rotation curves) and baryons in the cool–warm gas phases in galactic haloes at z = 3–4. MOSAIC will enable detailed maps of the intergalactic medium at z = 3, the evolutionary history of dwarf galaxies during a Hubble time, and the chemistry as directly measured from stars up to several Mpc. It will also measure faint features in cluster gravitational lenses or in streams surrounding nearby galactic haloes. The preliminary design of MOSAIC is expected to begin next year and its level of readiness is already high, given the instrumental studies already carried out by the team.