A unique instrument for the biggest telescope

The Extremely Large Telescope (ELT), i.e., ESO's future 39 meter telescope, will probably be the most ambitious ground-based optical astronomical facility of the century. Its main scientific objectives are the detection and study of the formation of the very first structures in the early Universe, 10-13 billion years ago, and obtaining the very first images of super exo-Earths and more generally the systematic characterization of extrasolar planets and their formation process.

The ELT is particularly innovative since it proposes for the first time to integrate the concept of adaptive optics directly within the telescope (Ground Layer Adaptive Optics, GLAO), which will provide uniform image quality and reduce the dependence of the observations to atmospheric conditions. Its great collecting power will reach sensitivities unmatched by any competing american ELT project. It will provide european astronomers with the most ambitious optical astronomical observation tool and the most powerful telescope ever built.

A fundamental prediction of cosmological models is that structures evolved "hierarchically" by successive mergers of more and more massive objects from the Big Bang to the galaxies we see around us today. Questions such as what seeded the growth of the first primordial galaxies and the history of galaxies like our own Milky Way remain unclear - only the ELT can bring the answers within our reach.

A major challenge is awaiting astronomers: the Universe contains hundreds of billions of galaxies, each of which consists of hundreds of billions of stars! Surveying these systems efficiently calls for a multi-object spectrograph (MOS) know as ELT-MOS as soon as possible after first light of the ELT in 2024.

The international MOSAIC Consortium, coordinated by Paris Observatory, is gathering together efforts across Europe and Brazil to build this ELT survey machine. It includes major players in instrument development and conception, which built a number of effective and scientifically productive instruments for the VLT (FLAMES, KMOS, NACO, X-SHOOTER).

The most prominent objective of MOSAIC will be to conduct the first exhaustive inventory of matter in the distant Universe. This will lift the veil on how matter is distributed in and between distant galaxies, by accounting for all kinds of regular matter, comprising stars and different phases of gas, as well as so-called dark matter.

The MOSAIC design has also been driven by 7 core science cases (below), but with its design also strongly influenced by other cases developed by the community in the MOS White Paper to ensure we're as ready as possible for the exciting discoveries awaiting in the late 2020s.

MOSAIC will give a tremendous leap forward in our understanding of how present-day galaxies formed and evolved. This includes detecting nearby primordial stars, the very first galaxies at the epoch of re-ionization, the most exhaustive dynamical survey of distant galaxies ever undertaken, and detailed study of stars in galaxies millions of light years beyond the Milky Way.

A massive work was initiated in 2011 to establish the scientific cases (hereafter, SCs) that are driving the design of a MOS on the ELT. Going from the largest to the smallest spatial scales :

MOSAIC will detect and study the very first galaxies. Their light, which has taken more than 13 billion years to reach us, will provide us with vital clues to our understanding of the early epoch when the Universe was ‘reionised’, during which its gas changed from a universally neutral into an ionised state.

First light

The warm and hot gas between galaxies and within their halo is a reservoir of matter from which proto-galaxies can form. MOSAIC will provide an unprecedented map of the distant 3D structures of this gas as well as evaluating for the first time the distribution of the different baryonic components of the matter.

Mapping the inter-galactic medium

MOSAIC will characterise gaseous outflows in large samples of active galactic nuclei (AGN) over cosmic time and with a wide range of luminosities. The unique spectroscopic capabilities of the instrument, further enhanced by adaptive optics corrections, will allow us to map in detail the outflows of ionised and neutral gas, including their kinetic energies and mass outflow rates, and to constrain their extent and geometries. Such a comprehensive census will finally provide a self-consistent picture of the impact of SMBH-driven outflows on the regulation of star formation in galaxies.

The coevolution of supermassive black holes and galaxies

MOSAIC on ELT will carry out the first statistically significant survey of the chemo-dynamical properties of dwarf galaxies at 1 < z < 3, when the Universe was less than half its current age. The unrivalled visual acuity, sensitivity and multiplexity of the spectrograph will allow the study of spatially-resolved chemical inhomogeneities in large samples of high-z dwarfs. Their chemical maps, further complemented with detailed kinematic information of the ionised gas across the galaxy shall uncover the presence of infall-driven, turbulent star formation, as well as reveal the imprints of energetic outflows from supernovae. The dwarf irregular galaxy IC1613 Credit: NASA/JPL-Caltech/SSC

Dwarf galaxies

Lithium is the heaviest nucleus produced in the Big Bang Nucleosynthesis (BBN). The other sources of Li production operate on long time-scales (> than 2 Gyr) so that lithium observed in the old stars must come from the BBN. The lithium abundance measured in the stellar atmospheres is almost the same for all the old unevolved stars but it is one third of the standard BBN prediction. Is this a sign of "new physics", beyond the standard model? Has lithium been uniformly destroyed in all the stars? All the theories predicting lithium destruction fail to explain at the same time the homogeneity and such a large destruction. Is this behaviour unique to our Galaxy? Only with MOSAIC we will be able to observed for the first time, lithium in several external galaxies and answer this question.

Probing the first three minutes

Several fundamental questions about the inner part of our Galaxy, the Bulge, are still without answer because this region is dense and with high extinction so that present telescopes can catch only the few brightest stars there. With MOSAIC we will be able to observe unevolved stars, the largest population in the bulge. In particular, for the first time, we will be able to observe in the Bulge stars that, as our Sun, are sill on the Main Sequence. This stellar population will reveal us the kinematic and metallicity of the Bulge, and, hosting the large majority of the stars, will allow us to better estimate the mass of our Galaxy. With a good knowledge on the complete sequence of the stellar evolution in the Bulge, we will derive also stellar ages. We will then have the possibility to draw a picture on the formation and past history of our Galaxy and to understand its actual shape.

Exploring the center of the Milky way

The MOSAIC science team contains more than 140 astronomers from across the globe, with contributions from:

  • Angela Adamo
  • Jose Afonso
  • David Alexander
  • Emilio Alfaro Navarro
  • Omar Almaini
  • Leonardo Almeida
  • Philippe Amram
  • Joana Ascenso
  • Hervé Aussel
  • Beatriz Barbuy
  • Nate Bastian
  • Giuseppina Battaglia
  • Ted Bergin
  • Arjan Bik
  • Beth Biller
  • Xavier Bonfils
  • Piercarlo Bonifacio
  • Nicolas Bouche
  • Rychard Bouwens
  • Enzo Brocato
  • Andy Bunker
  • Elisabetta Caffau
  • Karina Caputi
  • John Carter
  • Africa Castillo
  • Stephane Charlot
  • Laurent Chemin
  • Cristina Chiappini
  • Ana Chies Santos
  • Andrea Cimatti
  • Michele Cirasuolo
  • Yann Clenet
  • Francoise Combes
  • Sébastien Comeron
  • Christopher Conselice
  • Thierry Contini
  • Jean-Gabriel Cuby

  • Katia Cunha
  • Emanuele Daddi
  • Massimo Dall'Ora
  • Gavin Dalton
  • Ben Davies
  • Reinaldo deCarvalho
  • Alex deKoter
  • Miroslava Dessauges-Zavadsky
  • Karen Disseau
  • James Dunlop
  • Benoit Epinat
  • Chris Evans
  • Michele Fabrizio
  • Sofia Feltzing
  • Annette Ferguson
  • Mercedes Filho
  • Alexis Finoguenov
  • Fabrizio Fiore
  • Ewan Fitzsimons
  • Hector Flores
  • Adriano Fontana
  • Dimitri Gadotti
  • Anna Gallazzi
  • Jesus Gallego
  • Paulo Garcia
  • Eric Gendron
  • Emanuele Giallongo
  • Oscar Gonzalez
  • Damian Gratadour
  • Eva Grebel
  • Eike Guenther
  • François Hammer
  • Chris Harrison
  • Marc Huertas-Company
  • Rodrigo Ibata
  • Jorge Iglesia Paramo
  • Jure Japelj

  • Lex Kaper
  • Susan Kassin
  • Carolina Kehrig
  • Pierre Kervella
  • Andreas Korn
  • Davor Krajnovic
  • Rolf Kudritzki
  • Clotilde Laigle
  • Thierry Lanz
  • Nicolas Laporte
  • Soeren Larsen
  • Bertrand Lemasle
  • Jose Manuel Vilchez
  • Claudia Maraston
  • Isabel Marquez
  • David Martinez-Delgado
  • Justyn Maund
  • Iain Mcdonald
  • Ross McLure
  • Simona Mei
  • Jens Melinder
  • Michael Meyer
  • Chris Miller
  • John Monnier
  • Simon Morris
  • Sally Oey
  • Goran Ostlin
  • Stephane Paltani
  • Jorge Iglesia Paramo
  • Lee R. Patrick
  • Thibaut Paumard
  • Roser Pello
  • Laura Pentericci
  • Celine Peroux
  • Patrick Petitjean
  • Janine Pforr
  • Nor Pirzkal

  • Henri Plana
  • Mathieu Puech
  • Hadi Rahmani
  • Philipp Richter
  • Myriam Rodrigues
  • Emmanuel Rollinde
  • Martin Roth
  • Daniel Rouan
  • Gerard Rousset
  • Lee R. Patrick
  • Heikki Salo
  • Hugues Sana
  • Ruben Sanchez
  • Daniel Schaerer
  • Ricardo Schiavon
  • Rainer Schödel
  • Raymond Simons
  • Matthias Steinmetz
  • Mark Swinbank
  • Lidia Tasca
  • William Taylor
  • Eduardo Telles
  • Goncalves Thiago
  • Christina Thöne
  • Scott Trager
  • Laurence Tresse
  • Marina Trevisan
  • Miguel Verdugo
  • Susanna Vergani
  • Aprajita Verma
  • Jose Manuel Vilchez Medina
  • Jakob Walcher
  • Jianling Wang
  • Niraj Welikala
  • Lutz Wisotzki
  • Yanbin Yang
  • Stefano Zibetti
  • Bodo Ziegler

Who are we? Infos on the MOSAIC consortium.


Scientific goals and milestones: why MOSAIC?


How do we get there? All the technology behind MOSAIC.


What performance can we expect from MOSAIC?


How will MOSAIC fit in the instrumental landscape?