Galactic Consortium Surveys
The Galactic Consortium Surveys are designed to help us understand the Milky Way and how it evolved to its present-day configuration. Which internal and external processes have shaped our Galaxy? Taking advantage of the unique characteristics of 4MOST, we have designed a set of surveys that will address key objectives in Galactic Archaeology, including: determining the density profile, shape and characteristic parameters of the dark matter halo of the Milky Way; better understanding the current Milky Way disk structure and dynamics (bar, spiral arms, vertical structure, stellar radial migration, merger history); reconstructing the growth history of the Milky Way; finding and characterizing kinematic and chemical patterns within the Magellanic Clouds system; and identifying stars that were accreted to the Galactic halo from globular clusters, and quantifying their contribution to the build-up of the halo.
These, and many more questions, will be addressed using the five Galactic Consortium Surveys to be conducted with 4MOST. In total more than 15 million low-resolution spectra and 3 million high-resolution spectra will sample the different stellar populations, providing a dense and deep map of the stellar properties in the Milky Way and the Magellanic Clouds. In addition, several tailored sub-surveys will study White Dwarfs, compact X-ray binaries, Cepheids and hot dwarf stars.
Below we provide more details on each of the five surveys (click on the survey titles).
Milky Way Halo Low Resolution Survey
Survey PIs: Else Starkenburg (Rijksunversiteit Groningen), Clare Worley (University of Cambridge)
The goal of this survey is to study the formation and evolution of the Milky Way halo to deduce its assembly history and the 3D distribution of mass in the Milky Way. The combination of multi-band photometry, Gaia proper motion and parallax data, and radial velocities, overall metallicity and elemental abundances obtained from low resolution spectra of halo giants with 4MOST will yield an unprecedented characterization of the Milky Way halo and its interface with the thick disk. The survey will produce a (volume and magnitude) complete sample of giant stars in the halo covering at least 10,000 deg2 of high latitude sky, and measure their line-of-sight velocities with a precision of 1-2 km/s as well as their metallicities to 0.2 dex precision.
Further information is provided by A. Helmi et al., 2019, The Messenger, 175, 23.
We will study the formation history of the Milky Way, and the earliest phases of its chemical enrichment, with a sample of 1.5 million stars at high galactic latitude. Elemental abundances of up to 20 elements with a precision of better than 0.2 dex will be derived for these stars. The sample will include members of kinematically coherent substructures, which we will associate with their possible birthplaces by means of their abundance signatures and kinematics, allowing us to test models of galaxy formation. Our target catalog will also contain 30,000 stars at a metallicity of less than one hundredth of that of the Sun. This sample will therefore be almost a factor of 100 larger than currently existing samples of metal-poor stars for which precise elemental abundances determined from high-resolution spectroscopy are available, hence enabling us to study the early chemical evolution of the Milky Way in unprecedented detail.
Further information is provided by N. Christlieb et al., 2019, The Messenger, 175, 26.
Milky Way Bulge and Disk Low Resolution Survey (4MIDABLE-LR)
Survey PIs: Cristina Chiappini (Leibniz-Institut für Astrophysik Potsdam), Ivan Minchev (Leibniz-Institut für Astrophysik Potsdam)
The mechanisms of the formation and evolution of the Milky Way are encoded in the orbits, chemistry and ages of its stars. With the 4MIDABLE-LR Survey we aim to study kinematic and chemical substructures in the Milky Way disk and bulge region with samples of unprecedented size out to larger distances and greater precision than conceivable with Gaia alone or any other on-going or planned survey. Gaia gives us the unique opportunity to have a target selection almost entirely based on parallax and magnitude range, hence increasing the efficiency in sampling larger Milky Way volumes with well-defined and effective selection functions.
Further information is provided by C. Chiappini et al., 2019, The Messenger, 175, 30.
Milky Way Bulge and Disk High Resolution Survey (4MIDABLE-HR)
Survey PIs: Thomas Bensby (Lunds universitet), Maria Bergemann (Max-Planck-Institut für Astronomie)
Signatures of the formation and evolution of a galaxy are imprinted in its stars. Their velocities, ages, and chemical compositions present major constraints on models of galaxy formation, and on various processes such as the gas in- and outflows, accretion of cold gas, radial migration, and variability of star formation activity. Understanding the evolution of the Milky Way requires large observational datasets of stars where these quantities have been determined with high accuracy. This is the science driver of the 4MIDABLE-HR Survey: to obtain high-resolution spectra at R ≈ 20,000 and to provide detailed elemental abundances for large samples of stars in the Galactic disk and bulge. High data quality will allow us to provide accurate spectroscopic diagnostics of millions of stellar spectra: precise radial velocities, rotation, abundances of many elements, including those that are only accessible in the optical, such as Li, s-, and r-process, as well as multi-epoch spectra for a sub-sample of stars. Synergies with complementary programs like Gaia and TESS will provide masses, stellar ages, and multiplicity, forming a multi-dimensional dataset that will allow us to explore and constrain the origin and structure of the Milky Way.
Further information is provided by T. Bensby et al., 2019, The Messenger, 175, 35.
The Thousands and One Magellanic Clouds fields Low and High Resolution Survey (1001MC)
Survey PI: Maria-Rosa Cioni (Leibniz-Institut für Astrophysik Potsdam)
This survey aims to measure the kinematics and elemental abundances of many different stellar populations that sample the history of formation and interaction of the Magellanic Clouds. The survey will collect spectra for about half a million stars with G < 19.5 mag (Vega) distributed over an area of about 1000 deg2 and will provide an invaluable dataset for a wide range of scientific applications.
Further information is provided by M.-R.L. Cioni et al., 2019, The Messenger, 175, 54.