Extragalactic Surveys

Galaxy Clusters Survey

Survey PI: Alexis Finoguenov (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 below) will perform all-sky X-ray surveys in the years 2017 to 2021 to a limiting depth that is a factor of 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 redshifts 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.


AGN Survey

Survey PI: 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 Evolution Survey (WAVES)

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

waves_cylinderWAVES 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 survey design is not yet fully fixed, but at this stage the survey is proposed to comprise of two distinct sub-surveys: WAVES-Deep and WAVES-Wide.

WAVES-Deep will cover 100 deg² 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 10¹²M_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 1500 deg² to r < 22 mag with photo-z pre-selection (z < 0.13). 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 10¹¹ – 10¹² 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 Mpc³.

Further information is available at https://wavesurvey.org/ .

Cosmology Redshift Survey

Survey PI: Jean-Paul Kneib (EPFL),  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.

Time-Domain Extragalactic Survey (TiDES)

Survey PI: Bob Nichol (Portsmouth)

The next-generation of wide-field sky surveys, such as the Large Synoptic Survey Telescope (LSST) and the Zwicky Transient Factory (ZTF), will revolutionise our understanding of the extragalactic variable sky by discovering millions of transient detections per night (supernovae, tidal disruption events, optical counterparts to gravitational waves, AGN variability, etc.). The key to fully exploiting this exciting science will be rapid spectroscopic classification of transients, combined with a systematic and unbiased follow-up strategy. Our goal is to do exactly this by harnessing the multiplex capabilities of 4MOST with an allocation to TiDES of a few percent of fibres per extragalactic pointing over the survey.

The science aims of TiDES are: i) rapid classification of unusual live extragalactic transients discovered by wide-field sky surveys, ii) obtain host galaxy redshifts for Type Ia supernovae so that they can be used as cosmological distance indicators, and iii) spectroscopically monitor AGN variability to perform a large AGN broad emission line reverberation mapping experiment. TiDES will provide both tight constraints on the cosmological parameters from the local Universe out to redshift of ~2.5 and constrain the astrophysics of explosive transients.


Left figure: Type Ia supernova Hubble Diagram showing the best-fit ΛCDM cosmology (solid black line) compared with data from z ~ 0 – 1.3 (Betoule et al. 2014). Next-generation discovery surveys, such as LSST, combined with extensive spectroscopic followup of supernovae with 4MOST will significantly improve the cosmological constraints. Right figure: Hubble diagram based on AGN broad emission line lags of 700 objects from a TiDES mock catalogue. The red line with orange error region represents the best-fit ΛCDM model.