The surveys listed below are the GTO surveys that will be carried out by the 4MOST consortium. However, ample time will be available to public surveys accessible through ESO proposals.

The observational consortium surveys are split into Galactic Surveys and Extragalactic Surveys, while Survey Simulations are predicting the progress of these surveys.

Galactic Surveys

Milky Way Halo (LR)

Survey PIs: Amina Helmi (Groningen), Mike Irwin (IoA)

LRhaloThe Milky Way is thought to be embedded in an elongated dark matter halo, and surrounded by thousands of dark clumps. The only way to detect these is using thin stellar streams such as that shown in red. The black circles are clumps “colliding” now with the stream and leading to its fragmented appearance. Gaia will detect hundreds of such streams, and the characterization of how their stars move with 4MOST will allow us to pin-down the nature of the mysterious dark matter.

Milky Way Halo (HR)

Survey PIs: Norbert Christlieb (LSW)

The Galactic halo contains some of the oldest and most metal-poor stars known in our Galaxy. These stars conserve, to a large extend, the chemical composition and kinematics of the gas cloud from which they have formed.
With the 4MOST high-resolution spectrograph, we want to acquire spectra of at least 100,000 such stars, and determine their chemical abundance patterns, using stellar atmosphere models. These chemical “fingerprints”
will help us in disentangling the contributions of various nucleosynthesis processes that were occurring in the first generation(s) of stars, which chemically enriched the Universe shortly after the Big Bang, as is illustrated in the figure below.GCE_summary_highres_English

In addition, complementary astrometry to be collected with the Gaia satellite will allow us to determine the orbits of the metal-poor stars, and identify the remnants of smaller galaxies that were attracted by the large gravitational force of our galaxy, and eventually merged with it. These observations can then be compared with numerical simulations of spiral galaxy formation, to check how realistic these are, and whether any
physics is missing in these simulations.


Survey PIs: Cristina Chiappini (AIP), Ivan Minchev (AIP), Else Starkenburg (AIP)

The mechanisms of the formation and evolution of the Milky Way are encoded in the location, kinematics, and chemistry of its stars. Moreover, the Milky Way serves as a template for understanding other galaxies, and hence galaxy formation in general. With the 4MOST low-resolution mode we aim at studying the kinematical and chemical substructures in the Milky Way disks and bulge out to larger distances apic1_diskLRnd greater precision than conceivable with the Gaia mission alone, or with any other ongoing or planned survey. The main goals of this survey are as follows: (i) To understand the current Milky Way disk structure and dynamics (bar, spiral arms, stellar radial migration); (ii) To study the chemo-dynamics of the disk, which, when combined with (i) above will allow us to recover the disk evolutionary history; and (iii) To constrain the formation of the Milky Way bulge using both chemical and dynamical information. To accomplish the above goals and to cover the entire visible disk from the South, we have designed several stellar subsamples consisting of dwarf or giant stars, depending on the distances from the Sun.


Milky Way Bulge/Disk (HR)

Survey PIs: Thomas Bensby (Lund Observatory), Maria Bergemann (MPIA)

The 4MOST DRS4 is the largest high-resolution spectroscopic survey of stars in the Milky Way disk
and bulge to date. The survey will complement astrometric information from Gaia with high-precision chemical abundances for 2 million stars. We will provide abundances of all chemical elements, which are critical for testing nucleosynthesis at different epochs of galaxy formation: Li, CNO, p-process, Fe-peak elements such as Cr, Mn, Fe, Ni produced in supernovae, light and heavy neutron-capture such as Sr, Ba, Eu. These extensive chemical abundance maps will trace the time evolution of abundance gradients in the disk, putting new stringent constraints on models of stellar evolution and Galaxy formation.

Our goal is to provide metallicity-unbiased and volume-limited samples of stars throughout the disk at all galactocentric radii, and, in particular, a comprehensive description of the inner Galactic disk. This will be possible by drawing on the positions, distances, and stellar pre-classification from the Gaia space mission.


Extra Galactic Surveys


Survey PIs: Andrea Merloni (MPE)

The 4MOST AGN survey will represent one of the largest, and most complete spectroscopic survey of Active Galactic Nuclei ever undertaken. Built around the sample of X-ray selected AGN detected by the eROSITA X-ray all-sky survey, it aims at obtaining highly complete spectroscopic follow-up of about 1 million sources, smoothly distributed over a very wide redshift range 0<z<6. The X-ray selection for the majority of the AGN guarantees minimal bias against obscured accretion and objects with significant contamination from stellar light from the host galaxy. Combining X-ray, optical and IR AGN selection criteria, we will also be able to probe the history of accretion onto supermassive black holes also for the most heavily obscured AGN, while at the same time probing the Large Scale structure with enough accuracy to test the geometry of the Universe via QSO BAO studies.


Galaxy Clusters

Survey PIs: Andrea Merloni (MPE)

Clusters of galaxies are exquisite probes of the growth of structures in the Universe and very sensitive tracers of structure formation in current cosmological models. eROSITA (see figure above) will perform all-sky X-ray surveys in the years 2017 to 2021 to a limiting depth that is a factor 30 deeper than the ROSAT all-sky survey, and with broader energy coverage, better spectral resolution and better spatial resolution. Redshift information is critical to exploit the full potential of the eROSITA cluster samples. We will use 4MOST to survey the >50,000 southern X-ray galaxy clusters that will be discovered by eROSITA, measuring redshift for 3–50 galaxies in each cluster. Thanks to these measurements, we will be able not only to provide stringent tests of the cosmological paradigm, but also to calibrate the cluster mass via velocity dispersion estimates, study the large scale distribution of clusters, and determine the evolution of galaxy populations in high density environments up to z~1.


Galaxy Evolution (WAVES)

Survey PIs: Simon Driver (UWA), Jochen Liske (ESO)

WAVES is a massively multiplexed spectroscopic survey of 2 million galaxies addressing galaxy evolution. The survey is led by a European-Australian team and will build upon the excellent imaging data provided by two of the European Southern Observatory’s ongoing Public Surveys: VST KiDS and VISTA VIKING. The current survey design is fluid and will remain so until operations commence, but at this stage is proposed to comprise of two distinct sub-surveys DEEP-WAVES and WIDE-WAVES.

waves_cylinderWAVES-DEEP will cover 100deg^2 to r < 22 mag and extend the power of SDSS-like population statistics out to z~1. The deep survey will yield ~1.2 million galaxies allowing for the detection of ~50,000 dark matter halos (to 10^12M_sun) and 5000 filaments, representing the largest group and filament catalogue ever constructed, and forming the first detailed study of galaxy evolution as a function of halo mass. The groups themselves will be used in turn as telescopes in their own right to probe to the most distant corners of the Universe using gravitational lensing.

WAVES-WIDE will cover 750 deg^2 to r < 22 mag with photo-z pre-selection (z < 0.25). This will result in ~0.9 million galaxy targets and uncover a further 85,000 dark matter halos, allowing a detailed study of the halo occupancy in 10^11 – 10^12 M_sun halos to a stellar mass limit of 10^7 M_sun, and providing a field dwarf galaxy sample over a volume of > 10 Mpc^3.

Further information is available at .

Cosmology Redshift Survey

Survey PI: Francisco Kitaura (AIP),  Johan Richard (CRAL)

The 4MOST cosmology survey aims at studying the nature of gravity and dark energy, responsible for the structure formation in the Universe and its expansion, respectively.

To this end, it will map the three dimensional matter distribution in the southern galactic sky. It aims at performing precise measurements of baryon acoustic oscillations and redshift space distortions from the three dimensional distribution of galaxies with an unprecedented accuracy at redshifts up to about 1.

4MOST_eLGplusLRGIn particular it aims at measuring redshifts for 1-2 Million Luminous Red Galaxies (LRGs) and 13-20 Million emission Line Galaxies (eLGs) on 13-15k sqdeg. While LRGs are massive red galaxies tracing the high density peaks of the dark matter density field, eLGs are blue galaxies distributed across the cosmic web, which redshifts can be determined thanks to their OII doublet emission line caused by their star forming activity. The combination of both LRGs and eLGs permits to set tight constraints on the cosmological parameters performing a multitracer analysis.

Additionally it will measure the distribution of quasars and the Lyman alpha forest between redshift 2.2-3.5.

It will allow for a number of additional projects cross correlating with weak lensing surveys, studying secondary anisotropies in the cosmic microwave background, and studying the cosmic web.
The 4MOST survey will be complementary to EUCLID and other galaxy redshift surveys focusing on the southern galactic sky and on a lower redshift range.

Survey Simulations

Operations Model

4MOST has an unique operations model where the potential targets from many different science surveys are combined into one master catalogue. In any given pointing a mixture of targets from the
different surveys are observed simultaneously. This allows for an efficient use of all fibres and accommodates smaller surveys that require relatively few targets per pointing but have targets spread
over the entire sky.


A map of the fraction of targets from one DRS that are predicted to have been successfully observed by the end of the 4MOST sky survey.

To ensure that science surveys having very different observational requirements can be observed simultaneously, a few constraints are imposed on the targets and the observing strategy:

The sky is divided into regions that will be observed as much as possible in similar observing conditions (sky brightness, seeing) such that targets in the appropriate magnitude range can be chosen. Bright time will be primarily devoted to the area dominated by stellar targets (i.e. the Galactic plane and bulge, plus the Magellanic Clouds), while dark/grey time is devoted to the extragalactic sky. A large fraction of the sky in the range -70<Dec<+20deg will be observed by 4MOST. The 4MOST survey footprint will be visited multiple times, with an expectation that each field will be observed for a minimum of six times 20min exposures (or “tiles”). Some fields with high target densities will receive many more than six tiles. After each 20min tile, any fibre previously placed on a target that has received sufficient exposure time to reach its signal-to-noise requirement will be moved to a new target. Targets that need more exposure time will be assigned a fibre in subsequent tiles until the required time has been reached.


Predicted sky coverage of the 4MOST sky survey after 5 years of operations illustrating the number of 20min tiles delivered per field.

4MOST Facility Simulator

To demonstrate the feasibility of the above operations concept, and to prepare for the actual observations, a detailed simulator has been developed. The 4MOST Facility Simulator (4FS) consists of two main components: the Throughput Simulator and the Operations Simulator.

4FS Throughput Simulator

The Throughput Simulator (TS) is a software tool used to fold spectral templates through the system response of the 4MOST facility taking account of the range of possible atmospheric conditions.
The TS derives its description of the 4MOST instrument response using outputs of the full instrument simulator TOAD.

The TS is used to make estimates of the exposure time that will be required (under a range of observing conditions) to obtain spectra of science targets that have a sufficiently high signal-to-noise ratio to satisfy the specific data quality requirements associated with each target. The TS is coded in such a way to allow rapid bulk processing of a large number of spectral templates through a large parameter space of observing conditions.

4FS Operations Simulator

The Operations Simulator (OpSim) is a software tool used to simulate the progress of the 5-year 4MOST survey. The OpSim is used to plan, optimise and verify many aspects of operations planning. The OpSim is also used as a system engineering tool, to examine the impact of instrument design choices on science survey outcomes. The OpSim contains a detailed parameterised model of the 4MOST facility, including representations of the instrument focal plane, the various constraints/limitations, and a statistical model of the operating environment (e.g. the long-term atmospheric/environmental conditions at Paranal). Where possible, the OpSim uses prototype versions of the various algorithms that will be used to operate the real 4MOST survey, e.g fibre-> target assignment, survey strategy, survey scheduling and progress balancing/feedback algorithms. The OpSim serves as the primary test-bed for development and optimisation of these algorithms and
their optimal control parameters.


Progress of survey FoMs for the seven original design reference surveys over the 5-years of the 4MOST survey.

The OpSim takes as its main input a set of target catalogues associated with the science surveys, together with a description of how the success of each science survey may be quantified, a so called
“survey figure-of-merit” (FoM). One “run” of the OpSim simulates the night-time tile-to-tile operations of 4MOST over the 5-year survey duration, right down to the decision tree that results in the placement of individual fibres on individual science targets. The OpSim outputs a large quantity of diagnostic information, both high-level and detailed. At one end of the scale, the OpSim reports
the survey success FoMs that can be readily compared when for example the parameters describing the survey strategy have been adjusted. At the other extreme the OpSim outputs very detailed information, such as catalogues describing which targets have been observed and for how long, together with detailed diagnostic information about fibre movements and usage.

Simulation Results

We show some example figures produced by the OpSim that provide diagnostic information about survey success, fibre usage, predicted survey sky coverage and target completeness.


Distribution of fibre offsets (from fibre base position) averaged over all fibres, illustrating the choices of fibre allocation algorithm and fibre collision avoidance on the small scale selection function.