Letters of Intent received in 2020

LoI 2022-2128
Toward a Holistic View of the Milky Way's Early Star-Formation

Date: 12 December 2022 to 16 December 2022
Location: Kuala Lumpur, Malaysia
Contact: David Nataf (dnataf1@jhu.edu)
Coordinating division: Division G Stars and Stellar Physics
Other divisions: Division J Galaxies and Cosmology
Co-Chairs of SOC: David Moise Nataf (Johns Hopkins University)
Yuan-Sen Ting (Australian National University)
Chair of LOC: None (None)



- The chronology of the formation and assembly of the Milky Way's Halo, globular clusters, Bulge, and Thick Disk;
- The relative chronology of accretion events and the aetiology of their contributions to Galactic structure and stellar populations;
- The Local Group in a cosmology context, and a comparative study of surviving dwarf galaxies versus what we've uncovered of cannibalized dwarf galaxies;
- Interpretation of first-year JWST data and early lessons on high-redshift analogues of the early Milky Way;
- Investigation of how cosmological simulations succeed (or not) at bridging the gap between high-redshift observations from HST, JWST, and ALMA, and observations and analyses of the Milky Way and the Local Group today.



The fields of Galactic archaeology and near-field cosmology have been revolutionized by a plethora of hitherto unfathomably rich data from virtually every observational domain. This breadth runs the span from the most ancient field of astronomy (astrometry) through to one of the newest (asteroseismology). We now know the approximate ages, detailed chemical abundances, and precise kinematics for millions of stars across much of the Milky Way, from the Bulge to the Solar Neighbourhood through to the Halo. This incredible bounty of astronomical data is accompanied by increasingly sophisticated astrophysical models in each of the hierarchical galaxy assembly, galactic dynamics, stellar evolution, and nucleosynthetic yields.

These resources have led to an emerging picture of the Milky Way's first ~3 billion years. The first phase of star-formation was likely dominated by metal-poor ([Fe/H] <= -3.0), whose chemical abundances represent a zoo in their suggested diversity of early chemical polluters. Some brief time later, the Milky Way formed its first globular clusters, its Bulge, and its Thick Disk, with the earliest phases of that stage likely having been dominated by globular clusters. Simultaneous to these developments, the early Milky Way experienced several significant accretion events, such as the recently discovered Gaia-Enceladus and Sequoia streams. These accretion and dissolution events stand in contrast to its puzzlingly quiescent state today. We can trace these structures dynamically, chemically, and may even be able to identify which globular clusters belonged to them.

Magnificent data and state-of-the-art models are optimally insightful when used together. Given recent developments, the time is now to bring in experts from these areas and thus enable a more holistic understanding of the Milky Way's early star formation, a period in which the Galaxy was kinematically hotter, experiencing more massive and more frequent accretion and dissolution events, and predominantly forming stars in more massive clusters. An advantage of hosting the conference in late 2022 is that by then we will have the benefit of several findings from Cycle 1 James Webb Space Telescope Data, which will undoubtedly shed new light on the state of galaxies at redshifts 2 <~ Z <~ 10, and thus of galaxies that are analogs to the early Milky Way.