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4MOST (4-meter Multi-Object Spectroscopic Telescope)

Overview   References

4MOST will be the largest spectroscopic survey facility of its kind in the Southern hemisphere and address today's most pressing astronomical questions in the fields of Galactic archeology, high-energy astrophysics, galaxy evolution and cosmology. 1) 2) 3)

Spectroscopy will always be a primary tool of ground-based astronomy yielding unique astrophysical insight into the chemical composition and radial velocities of stars in the Milky Way and nearby resolved galaxies, and accurate redshifts, measures of internal motions, the nature of stellar populations, non-thermal sources and the ionizing radiation field in a variety of extragalactic sources over cosmic time. 4)

4MOST is a new wide-field spectroscopic survey facility of ESO (European Southern Observatory) under development for the four-meter-class VISTA (Visible and Infrared Survey Telescope for Astronomy) near the Paranal Observatory in Chile. It is on one of the best observatory sites in the world and provides access to unique objects in the southern hemisphere, most notably the Galactic Center and the Magellanic Clouds. The 4MOST design allows tens of millions of spectra to be obtained via five-year surveys, even for targets distributed over a significant fraction of the sky.

The instrument is under construction at a number of consortium institutes, coordinated by the Leibniz Institute for Astrophysics Potsdam (AIP), Germany. On the operations side, the proposal selection process starts while the manufacturing will continue into 2021. Once the subsystems are finished at the different institutes, they will all be transported to Potsdam and extensively tested as a full system. In 2022, they will be shipped to Chile and installed on the VISTA telescope.

The 4MOST operations scheme differs from other ESO instrument operations in that it allows many different science cases to be scheduled simultaneously during one observation. The science program itself is organized into surveys centered on stellar objects to perform Galactic archeology of different components of the Milky Way and the Magellanic Clouds, on extragalactic objects aiming to characterize cosmological parameters, the nature of dark energy and dark matter, and the formation history of galaxies and black holes. All surveys on 4MOST will be public surveys, which means that the raw data and higher-level survey products will be published in the ESO archive.

The 4MOST Consortium consists of 15 institutes in Germany, Australia, France, the Netherlands, Sweden, Switzerland, and the UK, under leadership of the Leibniz-Institut für Astrophysik Potsdam (AIP). More than 330 scientists and engineers are working on 4MOST and contributed to the now published articles. 5)

4MOST consortium members are:

- Leibniz-Institut für Astrophysik Potsdam (AIP)

- Australian Astronomical Optics, Macquarie University (AAO)

- Centre de Recherche Astrophysique de Lyon (CRAL)

- European Southern Observatory (ESO)

- Institute of Astronomy, Cambridge (IoA), UK

- Max-Planck-Institut für Astronomie, Heidelberg (MPIA)

- Max-Planck-Institut für extraterrestrische Physik, Garching (MPE)

- Zentrum für Astronomie der Universität Heidelberg (ZAH)

- NOVA/ASTRON, Dwingeloo, The Netherlands

- Rijksuniversiteit Groningen (RuG), The Netherlands

- Lunds Universitet (LU), Sweden

- Uppsala Universitet (UU), Sweden

- Universität Hamburg (UHH)

- University of Western Australia (UWA)

- École polytechnique fédérale de Lausanne (EPFL), Switzerland.

The 4MOST consortium has been selected by ESO (European Southern Observatory) to provide the ESO community with a fibre-fed spectroscopic survey facility on the VISTA telescope with a large enough FOV (Field of View) to survey a large fraction of the southern sky in a few years. The facility will be able to simultaneously obtain spectra of ~2400 objects distributed over an hexagonal FOV of 4 x 4 degrees. This high multiplex of 4MOST, combined with its high spectral resolution, will enable detection of chemical and kinematic substructure in the stellar halo, bulge and thin and thick discs of the Milky Way, thus help unravel the origin of our home galaxy. The instrument will also have enough wavelength coverage to secure velocities of extra-galactic objects over a large range in red­shift, thus enabling measurements of the evolution of galaxies and the structure of the cosmos. 6)

This exceptional instrument enables many science goals, but the design is especially intended to complement three key all-sky, space-based observatories of prime European interest: Gaia, Euclid, and eROSITA. Such a facility has been identified as of critical importance in a number of recent European strategic documents (Bode et al., 2008; de Zeeuw & Molster, 2007; Drew et al., 2010; Turon et al., 2008) and forms the perfect complement to the many all-sky survey projects around the world.


Figure 1: The 4MOST Facility comprises the instrument as well as the software to schedule and observe many surveys in parallel, and the data management system to reduce, analyze, validate and publish all data, including higher-level data products (radial velocities/redshifts, stellar parameters, abundances, etc.), image credit: 4MOST consortium

4MOST is currently in its Manufacturing Phase with an expected start of science operations in 2022. The ESO community will be able to express their interest to use the 4MOST Facility for Public Surveys through a Call for Letters of Intent expected to be released in the summer of 2019. To prepare the community for this opportunity ESO and the 4MOST Consortium have published a 4MOST issue of The Messenger and are organizing a workshop in Garching on 6-8 May 2019.



Figure 2: This view of the reddish, Mars-like landscape of the Atacama Desert around the VISTA (Visible and Infrared Survey Telescope for Astronomy), was taken from the neighboring Cerro Paranal, home of ESO's Very Large Telescope (VLT). VISTA started operations at the end of 2009 and the latest telescope to be added to ESO's Paranal Observatory, located some 120 km south from Antofagasta, in the II Region of Chile. VISTA is the largest telescope in the world dedicated to surveying the sky and works at near-infrared wavelengths (image credit: ESO/José Francisco Salgado) 7) 8)



4MOST Overview

The March 2019 issue of ESO's The Messenger, published on 6 March, is dedicated entirely to 4MOST. It contains 13 articles, written by the 4MOST Consortium, which introduce 4MOST to the ESO community. Three overview articles describe the 4MOST project and instrument, the 4MOST science operations and its current survey plan, while another ten articles, one for each of the Consortium Surveys, describe the scientific plans of the 4MOST Consortium. 9)

4MOST is a new high-multiplex, wide-field spectroscopic survey facility under development for the four-meter-class VISTA (Visible and Infrared Survey Telescope for Astronomy) at Paranal. Its key specifications are: a large FOV (Field of View) of 4.2 x 4.2 degrees and a high multiplex capability, with 1624 fibres feeding two low-resolution spectrographs (R = λ/Δλ ~ 6500), and 812 fibres transferring light to the high-resolution spectrograph (R ~ 20 000). After a description of the instrument and its expected performance, a short overview is given of its operational scheme and planned 4MOST Consortium science; these aspects are covered in more detail in other articles in this edition of The Messenger. Finally, the processes, schedules, and policies concerning the selection of ESO Community Surveys are presented, commencing with a singular opportunity to submit Letters of Intent for Public Surveys during the first five years of 4MOST operations.

4MOST is being developed to address a broad range of pressing scientific questions in the fields of Galactic archeology, high-energy astrophysics, galaxy evolution and cosmology. Its design allows tens of millions of spectra to be obtained via five-year surveys, even for targets distributed over a significant fraction of the sky.

4MOST enables many science goals, but the design is especially intended to complement a number of key large-area, spaceborne observatories of prime European interest: Gaia, eROSITA, Euclid, and PLATO, and future ground-based, wide-area survey facilities like LSST (Large Synoptic Survey Telescope) on Cerro Pachón, Chile and SKA (Square Kilometer Array) in Africa and Australia. 4MOST will unfold maximum impact by operating continuously for an initial five-year Public Survey program delivering spectra for ≥25 million objects over ≥15 000 square degrees.


Figure 3: Spaceborne and ground-based facilities complementing 4MOST (image credit: 4MOST consortium)

Multiple science cases must be carried out simultaneously in order to efficiently fill all the fibres in a high multiplex instrument like 4MOST. This necessitates effective coordination between different science teams. To enable this, the 4MOST Consortium will perform Public Surveys using 70% of the available fibrehours in the first five years of operation.

These Public Surveys are Guaranteed Time Observations (GTO) that the Consortium receives in return for building the facility and for supporting ESO in the operation of 4MOST. Public Surveys of the ESO and the Chilean host country communities will fill the other 30% of available fibre-hours in the first five years of operation. These surveys will be chosen by a one-time, competitive, peer-reviewed selection process, similarly to other ESO Calls for Public Surveys. Here, a fibre-hour is defined as one hour of observing time, including overheads, with one fibre; hence 4MOST offers 2436 fibre-hours every hour that it is observing.

Following this overview, which contains information on instrument performance and on the procedures associated with the use of 4MOST by the community, this issue of The Messenger includes additional articles on the 4MOST science operations model, the survey plan of the 4MOST Consortium, and a description of the ten Public Surveys that the Consortium intends to carry out. Together these articles are intended to prepare the ESO community for the proposal process that will commence in the second half of 2019. The process will start with a one-off opportunity for the submission of Letters of Intent to apply for Public Surveys to be executed during the first five years of 4MOST operation.

Organization: The 4MOST project is organized along three branches:

1) Instrument — responsible for the development, construction, and commissioning of the instrument hardware and associated software;

2) Operations — for the planning, data reduction, archiving, and publishing of the observations including the associated data-flow;

3) Science — the branch that develops the different Surveys and is responsible for science analysis and publication.

The instrument and operations branches are mainly performed by the 4MOST Consortium and are jointly called the 4MOST Facility.

The instrument is under construction at a number of Consortium institutes, coordinated by the 4MOST Project Office located at the Leibniz-Institut für Astrophysik Potsdam (AIP). Once the subsystems are finished at the different institutes, they will all be transported to Potsdam and extensively tested there as a full system before being shipped to Paranal. At Paranal the 4MOST instrument will be installed, tested, and commissioned on the VISTA telescope.

The operations branch is led by the Operations Development Group, consisting of the leads of the different subsystems and working groups involved in observation planning and data-flow. It also contains the 4MOST Helpdesk activities.

The science program is organized into several surveys. The members of the survey teams are spread over all participating institutes and each team is led by one or more Survey Principal Investigators (Survey PIs). Coordination between all participating surveys is performed by the Science Coordination Board (SCB), consisting of all Survey PIs. The science branch is overseen by two Project Scientists, one for Galactic and one for extragalactic science, who have both a science guidance and a managerial role.



The 4MOST instrument design was driven by the science requirements of its key Consortium Surveys. Within a 2-hour observation 4MOST has the sensitivity to obtain redshifts of r = 22.5 magnitudes (AB) galaxies and active galactic nuclei (AGN), radial velocities of any Gaia source (G < 20.5 magnitudes [Vega]), stellar parameters and selected key elemental abundances with accuracy better than 0.15 dex of G < 18-magnitude stars, and abundances of up to 15 elements of G < 15.5-magnitude stars. Furthermore, in a five-year survey 4MOST can cover > 17,000 square degrees at least twice and obtain spectra of more than 20 million sources with a resolution of R ~ 6500 and more than three million spectra with a resolution of R ~ 20 000 for the typical science cases proposed. The main instrument parameters enabling these science requirements are summarized in Table 1.

Instrument parameter

Design value

FOV (Field of View), hexagon

~ 4.2 square degrees (Ø = 2.6 degrees)

Accessible sky (zenith angle < 55º)

> 30,000 square degrees

Expected on-target fibre-hours per year

LRS (Low Resistance State): > 3,200,000 h yr–1, HRS > 1600,000 h yr–1

Multiplex fibre positioner


Low-Resolution Spectrographs LRS (x 2)
- Resolution
- Number of fibres
- Passband
- Velocity accuracy
- Mean sensitivity 6 x 20 min, mean seeing
- new moon, S/N = 10 Å–1 (AB-magnitude)

<R> = 6500
812 fibres
3700–9500 Å
< 1 km s–1
4000 Å: 20.2, 5000 Å: 20.4, 6000 Å: 20.4,
7000 Å: 20.2, 8000 Å: 20.2, 9000 Å: 19.8

High-Resolution Spectrograph HRS (x 1)
- Resolution
- Number of fibres
- Passband
- Velocity accuracy
- Mean sensitivity 6 × 20 min, mean seeing,
- 80% moon, S/N = 100 Å–1 (AB-magnitude)

<R> = 20 000
812 fibres
3926–4355, 5160–5730, 6100–6790 Å
< 1 km s–1
4200 Å: 15.7, 5400 Å: 15.8, 6500 Å: 15.8

Smallest target separation

15 arcseconds on any side

# of fibres in random Ø = 2 arcminute circle

≥ 3

Fibre diameter

Ø = 1.45 arcseconds

Table 1: 4MOST key instrument specifications

Figure 4 provides an overview of the main instrument subsystems. A new Wide Field Corrector (WFC) equipped with an Atmospheric Dispersion Compensator (ADC) that provides corrections to a 55º zenith angle distance creates a focal surface with a 2.6º diameter. Two Acquisition and Guiding (A&G) cameras ensure correct pointing, while four Wave Front Sensing (WFS) cameras steer the active optics system of the telescope.


Figure 4: Layout of the different subsystems of 4MOST on the VISTA telescope (image credit: ESO, 4MOST consortium)

The AESOP [Australian Astronomical Observatory (AAO) Project] fibre positioning system based on the tilting spine principle can, within 2 minutes, simultaneously position all of the 2436 science fibres that are arranged in a hexagonally shaped grid at the focal surface. The accuracy of fibre positioning is expected to be better than 0.2 arcseconds thanks to a four-camera metrology system observing the fibre tips back-illuminated from the spectrograph. The tilting spine positioner has the advantage that each fibre has a large patrol area; each target in the science field of view can be reached by at least three fibres that go to one of the Low-Resolution Spectrographs (LRS) and one or two fibres that go to the High-Resolution Spectrograph (HRS). This ensures a high allocation efficiency of the fibres to targets, even when targets are clustered.

Each spectrograph accepts 812 science fibres and six simultaneous calibration fibres attached to either end of the spectrograph entrance slit. The covered wavelength range and resolution of the LRS and HRS spectrographs are as listed in Table 1 and depicted in Figure 5. Each type of spectrograph has three channels in fixed configurations covering three wavelength bands, and is thermally invariant and insulated (HRS) or temperature controlled (LRS) for stability. Each channel is equipped with a 6 k x 6 k CCD detector with low read noise (< 2.3 electrons per read) and with high, broadband quantum efficiency. The spectra are sampled with about three pixels per resolution element.


Figure 5: Spectral resolution in the three channels of the 4MOST High-Resolution (HRS, upper lines) and Low-Resolution Spectrographs (LRS; lower lines), image credit: ESO, 4MOST consortium

A calibration system equipped with a continuum source, a Fabry-Perot etalon, and ThAr (Thorium-Argon) lamps can feed light through the telescope plus science fibres combination and also directly through the simultaneous calibration fibres into the spectrograph slit to ensure accurate wavelength calibration. This will ensure that we can typically reach better than1 km/s accuracy on stellar radial velocities. The expected sensitivity is depicted in Figure 6. The estimated observing overheads are currently conservatively estimated to be 3.5 minutes per repointing of the telescope and 4.4 minutes per science exposure for repositioning of the fibres, obtaining attached calibration frames, and performing detector readout. We aim to reduce these overhead numbers in the future by executing more exposure setup activities in parallel and by reducing the number of attached night-time calibration exposures once we have established the stability and calibration reproducibility of the full system.


Figure 6: The expected 4MOST pointsource sensitivities for the signal-to-noise levels and lunar conditions indicated in the legend. The solid lines are for a total exposure time of 120 minutes, whereas the dashed lines are the limits for 20-minute exposures. The approximate conversion to signal-to-noise per pixel is obtained by dividing the HRS values by 3.3 and the LRS values by 1.7. For clarity, sky emission lines are removed — this mostly affects results redward of 7000 Å. Mean (not median) seeing conditions, airmass values, fibre quality and positioning errors, etc., are used, in order to ensure that this plot is representative for an entire 4MOST survey, not just for the optimal conditions. Typical science cases for obtaining detailed elemental abundances of stars (orange), stellar parameters and some elemental abundances (dark blue), stellar radial velocities (light blue), and galaxy and AGN redshifts (black: 90% complete, grey: 50% complete) are shown (image credit: ESO, 4MOST consortium)



The 4MOST operations scheme differs from other ESO instrument operations in that it allows many different science cases to be scheduled simultaneously during one observation. To accommodate the range of exposure times required for different targets, the same part of the sky will be observed with multiple exposures and visits. Objects that require longer exposures will be exposed several times until their stacked spectra reach the required signal-to-noise. 4MOST operations also differ from the standard ESO scheme in that the 4MOST Consortium plays a primary role in planning the observations (Phase 2) and in reducing, analyzing and publishing the data (Phase 3).

These Consortium activities are closely monitored by ESO to ensure uniform progress and data quality for all surveys. The details of 4MOST operations are described in the accompanying article in this edition of The Messenger.



The 4MOST science program formulated by the Consortium has been organized into the ten surveys listed in Table 2. There are five surveys centered on stellar objects to perform Galactic archeology of different components of the Milky Way and the Magellanic Clouds, with the goal of understanding their current structure and their assembly history. There are four surveys of extragalactic objects aiming to characterize cosmological parameters, the nature of dark energy and dark matter, and the formation history of galaxies and black holes. Finally, there is a survey dedicated to time domain discoveries, mainly in synergy with the LSST (Large Synoptic Survey Telescope) facility where supernova transients and quasar luminosity variations will be complemented with spectroscopic observations.

For most of these surveys, millions of spectra will be obtained, having a huge legacy value for the community and creating an enormous potential for serendipitous discoveries. Being the only facility in the south with such a large field of view and multiplex capability creates numerous unique opportunities for 4MOST. Of special interest are synergies with new southern hemisphere facilities under construction such as LSST, SKA, and ESO's E-ELT (European Extremely Large Telescope). The southern sky is of particular interest for Galactic archeology, with good access to the Milky Way bulge and the Magellanic Clouds. For this science, the R ~ 20,000 of the HRS enables accurate abundance measurements of many elements; the R ~ 6500 LRS spectra also have higher spectral resolution and better sampling of the spectral resolution elements than similar high-multiplex, wide-field facilities, thereby allowing better stellar elemental abundance determinations. 4MOST provides an unprecedentedly large volume coverage of all Galactic components, thereby expanding on the legacy of the ESA Gaia mission.

This Messenger edition contains sufficiently detailed descriptions of the Consortium Surveys and the overall observing strategy (Guiglion et al., see Ref. 9) to enable the ESO community to develop complementary surveys using the roughly 4.8/2.4 million LRS/HRS fibrehours available to them in the first 5-year survey. The process of integrating community observing programs into the 4MOST survey program is described in the next section.


Survey Name

Survey (Co-)PI


Milky Way Halo LR Survey

Irwin (IoA), Helmi (RuG)


Milky Way Halo HR Survey

Christlieb (ZAH)


Milky Way Disc and Bulge LR Survey (4MIDABLE LR)

Chiappini, Minchev, Starkenburg (AIP)


Milky Way Disc and Bulge HR Survey (4MIDABLE HR)

Bensby (Lund), Bergemann (MPIA)


Galaxy Clusters Survey

Finoguenov (MPE)


AGN Survey

Merloni (MPE)


Galaxy Evolution Survey (WAVES)

Driver (UWA), Liske (UHH)


Cosmology Redshift Survey

Richard (CRAL), Kneib (EPFL)


Magellanic Clouds Survey (1001MC)

Cioni (AIP)


Time-Domain Extragalactic Survey (TiDES)

Sullivan (Southampton)

Table 2: 4MOST Consortium Surveys and their Principal Investigators


Community programs

In designing the 4MOST operations system, the aim has been to follow normal ESO operations as much as possible. This means that 4MOST follows the ESO Public Surveys sequence of program selection (Phase 1), observation preparation (Phase 2), program execution at the telescope, and finally data reduction, analysis, and publication (Phase 3). However, 4MOST, being a survey facility running typically many science programs simultaneously in each observation, has required some modifications to the normal process, as described below.

As highlighted earlier, 4MOST Surveys have a duration of five years. This ensures that large projects can be accomplished with carefully crafted completeness goals and well understood selection functions. New programs will be selected and started only once every five years and, after a short run-in period, the observing strategy will stay as stable as possible during each five-year survey program. All surveys on 4MOST will be Public Surveys, which means that the raw data will be published immediately in the ESO archive and that the science teams of the surveys have an obligation to release higher-level data products that have legacy value for the community.

The community can propose for one of two types of Survey programs with 4MOST.

1) Participating Surveys from the ESO community will join the Consortium Surveys in a common observing program, where they share the available fibres in each observing block and are "charged" fibre-hours only for their fraction of fibres used. They also share the time spent on any duplicate targets in common between surveys, get full access to all data from the Consortium and participating community programs, and are invited to collaborate in the higher-level data analysis and publication efforts.

2) Non-Participating Surveys get their own (half) nights on the telescope and will be "charged" fibre-hours for the full 2436 fibres during that time regardless of whether they can all be filled. These surveys will receive calibrated and extracted spectra from the Consortium data management system, but will not have access to any data other than their own and they will be responsible for delivering higher-level data products to the ESO archive on their own. While many aspects are the same for Participating and Non-Participating Surveys, critical differences during the various execution phases of the Surveys are highlighted below.

Phase 1

4MOST Phase 1 will begin with a Call for Letters of Intent. Each Letter of Intent is expected to set out: the science goals of the proposed survey; a description of its scope (for example, the number of targets and their distribution on the sky, the targets' luminosity range, the approximate number of fibre-hours needed); an initial list of Survey team members and their roles (i.e., a simple management plan); and whether the proposal is for a Participating or Non-Participating Survey. To estimate the feasibility and scope of the observations an Exposure Time Calculator (ETC) will be provided through an ESO web interface for single targets, and through an ETC tool from the 4MOST Consortium for many targets at once. After a peer review of the Letters of Intent that will be managed by ESO, a number of teams will be invited to respond to the 4MOST Call for Proposals, at which time ESO may suggest that some of the community proposals merge with other community or Consortium proposals.

At this stage a more detailed science case will be required as well as a full (mock) target catalogue with template spectra, spectral success criteria, and a total survey goal encapsulated by a figure of merit. A web-based version of the 4MOST Facility Simulator (4FS) will be provided, allowing proposers to check the feasibility of their proposed survey. 4FS will provide an estimate of the number of successfully observed targets in a five-year survey when run either standalone (Non-Participating proposals) or in conjunction with the Consortium Surveys (Participating proposals) and the required number of fibre-hours. Clearly, proposals that are well matched to the overall observing strategy of 4MOST as described in the 4MOST Survey Plan article in this edition (for example, surveys with sparsely distributed targets or with looser completeness requirements) have a higher chance of being successfully executed in the amount of time available.

After selection of all Consortium and Community Surveys through ESO's peer review process for Public Surveys proposals, the selected programs will be invited to submit survey management plans, approval of which by the ESO Director General is mandatory before the final acceptance of a Public Survey. The survey management plan will contain a detailed list of science data products and timeline for their release. For Consortium and Participating Community Surveys a single, joint survey management plan will be delivered. For Non-Participating Community Surveys, each Survey PI will be responsible for the delivery of a survey management plan.

Phase 2

After selection, the members of the Participating Community Surveys will join the Consortium Surveys to form the joint Science Team. The Community Survey PIs will become members of the Science Coordination Board and it is expected that the Community Surveys will provide staff effort to the different 4MOST working groups, most notably those on survey strategy, selection functions, quality assurance, and, if they so wish, higher-level pipelines. The target catalogues of the Community Surveys will be merged with those of the Consortium and through an iterative process a joint survey plan will be developed to observe all targets. Once the final observing strategy has been agreed upon, only small changes in strategy will be allowed during the operations phase without approval by the SCB and/or ESO. The 4MOST Operations Group provided by the Consortium will create all Observing Blocks running on 4MOST.

Non-Participating Surveys will not join the Science Team, but will be provided with software to create and submit their own Observing Blocks which will be scheduled on their assigned (half) nights. Any significant changes from the original Non-Participating Survey plan will have to be approved by ESO.

Phase 3

As with ESO's Public Survey policies, 4MOST Survey programs have data delivery obligations to ESO and its community. All 4MOST raw data will become available as soon as they have been ingested into the ESO archive at the end of each night. The raw data will be processed by the Consortium Data Management System to remove instrumental effects and create one-dimensional, flux and wavelength-calibrated Level 1 (L1) spectra. The L1 data will be released yearly through the ESO archive. For Participating Surveys, dedicated classification, stellar and extragalactic pipelines run by Consortium working groups will produce Level 2 (L2) data products like object type likelihoods, stellar parameters, elemental abundances and redshifts, etc. These products will be released through the ESO archive on a schedule to be agreed upon with ESO before the start of the observations. All L1 and L2 products will also be released through the 4MOST World Archive operated by the Consortium, which will also contain matched catalogues from other facilities and added value catalogues with data processed beyond the standard pipelines. While the Consortium will take care of uploading the L1 and L2 products to the ESO archive for the joint Science Team, Non-Participating Surveys will have to produce and upload their own L2 products to ESO.


Given the joint use of the available fibres and the corresponding mixed nature of the data products, members of the Consortium Surveys and Participating Community Surveys, i.e., members of the joint Science Team, have to abide by a number of policies to ensure fair use of data and a fair return on investment. Community Survey membership will be limited to those on the original proposal plus up to 15 additional members added at a later stage if a certain capability or expertise is needed that is not available within the Science Team. Participating Community Survey targets may overlap by a maximum of 20% with Consortium targets, but will share the required "cost" in exposure time for the overlap, allowing both surveys to do more in their allotted amount of fibre-hours. All data products are shared among all Science Team members. However, all science exploitation shall take place in projects announced to the whole Science Team and restrictions regarding this exploitation may be applied when a new project overlaps significantly with an existing PhD project or with the core science of a Survey that the project proposer is not a member of. Full details of these Science Team policies as approved by ESO will be released alongside a Code of Conduct when the Call for Letters of Intent is published. By submitting a Participating Survey program the proposers implicitly agree to comply with these policies.

For Non-Participating Surveys there may be at most a 30% overlap in targets with other Surveys and they will not share exposure time with other Surveys. This means that any duplicate targets in Non-Participating Surveys will be observed twice as there is no means to coordinate the effort with other Surveys. Non-Participating Surveys are free to devise their own membership, data access, and publication policies.


The 4MOST Project moved into full construction after passing Final Design Review-1 in May 2018. Major milestones in further development and construction are the release of the Call for Letters of Intent in the second half of 2019 which will have a submission deadline about 2 months later, completion of the system integration in Potsdam in July 2021, passing the full system test including operations rehearsals for the Preliminary Acceptance Europe by February 2022, and the installation and commissioning of the facility at VISTA for Provisional Acceptance Chile in November 2022, after which the first five year survey will start.

Consortium and Minor Participants Institutes

The 4MOST Consortium institutes and their main roles in the project are listed in Table 3. The following Minor Participant institutes are also contributing to the development of 4MOST: Durham University, University of Sussex, University College London, Institute for Astrophysics Göttingen (IAG), University of Warwick, University of Hull, Universität Potsdam, Laboratoire d'Etudes des Galaxies, Etoiles, Physique et Instrumentation (GEPI), IN2P3/Laboratoire des Matériaux Avancés (L.M.A.); and for the TiDES Survey: Lancaster University, Queen's University Belfast, University of Portsmouth, and University of Southampton.


Instrument responsibility

Science lead responsibility

Leibniz-Institut für Astrophysik Potsdam (AIP)

Management and system engineering,
telescope interface (including WFC),
metrology, fibre system, instrument control
software, System AIV and commissioning

Milky Way Disc and Bulge LR Survey, Cosmology
Redshift Survey, Magellanic Clouds Survey

Australian Astronomical Optics – Macquarie (AAO)

Fibre positioner

Galaxy Evolution Survey

Centre de Recherche Astrophysique de Lyon (CRAL)

Low-resolution spectrographs

Cosmology Redshift Survey

European Southern Observatory (ESO)

Detectors system

Institute of Astronomy, Cambridge (IoA)

Data management system

Milky Way Halo LR Survey

Max-Planck-Institut für Astronomie (MPIA)

Instrument control system hardware

Milky Way Disc and Bulge HR Survey

Max-Planck-Institut für extraterrestrische
Physik (MPE)

Science operations system

Galaxy Clusters Survey, AGN Survey

Zentrum für Astronomie der Universität Heidelberg

High-resolution spectrograph,
Instrument control system software

Milky Way Halo HR Survey


Calibration system

Rijksuniversiteit Groningen (RuG)


Milky Way Halo LR Survey

Lund University (Lund),


Milky Way Disc and Bulge HR Survey

Lund University (Lund)


Milky Way Disc and Bulge HR Survey

Universität Hamburg (UHH)


Galaxy Evolution Survey

University of Western Australia (UWA)


Galaxy Evolution Survey

École polytechnique fédérale de Lausanne (EPFL)


Cosmology Redshift Survey

Table 3: 4MOST Consortium institutes and their main roles in the Project


Figure 7: The Milky Way arches over the VLT (clearly deploying its laser guide star capability) and VISTA (on the right). By 2022, VISTA will have transformed into 4MOST with operations beginning towards the end of the year (image credit: ESO, G. Hüdepol)


1) "Milky Way and beyond: Next Generation Survey Telescope," AIP, 6 March 2019, URL:

2) Roelof S. de Jong, Samuel C. Barden, Olga Bellido-Tirado, Joar G. Brynnel, Steffen Frey, Domenico Giannone, Roger Haynes, Diana Johl, Daniel Phillips, Olivier Schnurr, Jakob C. Walcher, Roland Winkler, Wolfgang R. Ansorge, Sofia Feltzing, Richard G. McMahon, Gabriella Baker, Patrick Caillier, Tom Dwelly, Wolfgang Gaessler, Olaf Iwert, Holger G. Mandel, Nikolai A. Piskunov, Johan H. Pragt, Nicholas A. Walton, Thomas Bensby, Maria Bergemann, Cristina Chiappini, Norbert Christlieb, Maria-Rosa L. Cioni, Simon Driver, Alexis Finoguenov, Amina Helmi, Michael J. Irwin, Francisco-Shu Kitaura, Jean-Paul Kneib, Jochen Liske, Andrea Merloni, Ivan Minchev, Johan Richard, Else Starkenburg, "4MOST: the 4-meter Multi-Object Spectroscopic Telescope project at preliminary design review," Proceedings of SPIE, Volume 9908, 'Ground-based and Airborne Instrumentation for Astronomy VI'; 99081O (2016) ,, SPIE Astronomical Telescopes + Instrumentation, Edinburgh, UK, 9 August 2016, URL:

3) Roelof S. de Jong, Sam Barden, Olga Bellido-Tirado, Joar Brynnel, Cristina Chiappini, Éric Depagne, Roger Haynes, Diana Johl, Daniel P. Phillips, Olivier Schnurr, Axel D. Schwope, Jakob Walcher, et al., "4MOST: 4-meter Multi-Object Spectroscopic Telescope", Proceedings of SPIE, Vol. 9147, 'Ground-based and Airborne Instrumentation for Astronomy V,' 91470M (24 July 2014), doi: 10.1117/12.2055826,

4) Richard S Ellis, Joss Bland-Hawthorn, Malcolm Bremer, Jarle Brinchmann, Luigi Guzzo, Johan Richard, Hans-Walter Rix, Eline Tolstoy, Darach Watson, "ESO Future of Multi-Object Spectroscopy Working Group Report," 6 September, 2016, URL:

5) "4MOST articles in the ESO messenger," Messenger No 175, March 2019, URL:

6) "4MOST — 4-meter Multi-Object Spectroscopic Telescope," URL:

7) "The desert around VISTA," ESO, 26 July 2010, URL:


9) Roelof S. de Jong, Oscar Agertz, et al., "4MOST: Project overview and information for the First Call for Proposals," 4MOST issue of The Messenger, No. 175 ,March 6, 2019, URL:

The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (

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