Milky Way Halo Low Resolution Survey
Survey PIs: Amina Helmi (Groningen), Mike Irwin (IoA)
The 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 High Resolution Survey
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.
In addition, complementary astrometry to be collected with the Gaia satellite will allow us to determine the orbits of the metal-poor stars, and to 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.
The Thousands and One Magellanic Clouds fields Low and High Resolution Survey (1001MC)
Survey PI: Maria-Rosa Cioni (AIP)
The Magellanic Clouds are the largest satellite galaxies of the Milky Way and they are a typical example of an early stage of accretion. Their important role has justified numerous multi-wavelength photometric investigations of their stellar content in the past decade and many of these are still ongoing.
This survey provides a comprehensive spectroscopic study of the stars in the Magellanic Clouds to improve our knowledge of their origin and evolution, but also to remove potential biases. The main goals are to measure the radial velocity and the iron abundance of many different stellar populations, as well as additional chemical elements for the brightest stars. These stars should sample all structures (bar, disc, halo) and substructures (streams) associated with the interactions among the Magellanic Clouds and with the Milky Way. The stellar spectra are necessary to match the high quality proper motions that become available, e.g., from Gaia and VISTA. The information from spectra and proper motions is crucial to obtain accurate star formation histories and geometrical parameters, as well as to design dynamical models that reproduce the history of formation and evolution of the system.
The 1001MC observations will provide an invaluable database for a wide range of scientific applications and the survey will have true legacy value.
Milky Way Bulge and Disk Low Resolution Survey
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 and 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 and Disk High Resolution Survey
Survey PIs: Thomas Bensby (Lund Observatory), Maria Bergemann (MPIA)
This survey will be 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.