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The chemodynamical structure of the ancient galactic halo

Grant number: 21/10429-0
Support Opportunities:Scholarships in Brazil - Doctorate (Direct)
Effective date (Start): December 01, 2021
Field of knowledge:Physical Sciences and Mathematics - Astronomy - Stellar Astrophysics
Principal Investigator:Silvia Cristina Fernandes Rossi
Grantee:Guilherme Limberg
Host Institution: Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG). Universidade de São Paulo (USP). São Paulo , SP, Brazil
Associated research grant:15/50374-0 - Mosaic: the multi-object spectrograph for the ESO Extremely Large Telescope, AP.TEM
Associated scholarship(s):22/07301-5 - Chemical-abundance patterns of disrupted dwarf galaxies, BE.EP.DD


The assembly and evolution of galaxies in cosmological context remains one of the greatest challenges in contemporaneous Astrophysics. Within the › cold dark matter paradigm, galaxies and their respective dark matter halos grow in size through successive merging with other such systems. In this hierarchical framework, the milky way's halo provide the best available laboratory for us to bear witness of these phenomena in their full magnificence and complexity. In this project, we propose to study the chemical and dynamical (i.e., ""chemodynamical"") structure of the ancient galactic halo and the properties of its stellar populations, providing clues about the sequence of accretion events that took place throughout the history of the milky way as a whole. First, we analyze the orbits of very metal-poor ([Fe/H] < 2.0) stars in order to identify clusters of such objects with similarities in energy and angular-momentum spaces. These dynamically tagged groups are primary candidates to share a common progenitor, perhaps in ultra-faint dwarf galaxies. Second, we investigate the chemical-abundance patterns of a kinematically cold and metal-poor stellar stream. We examine ± and neutron-capture elements to demonstrate that stars from this substructure likely originated in a (now) destroyed galaxy similar to present-day dwarf spheroidal satellites of the milky way. We will build on these findings by comparing these data with chemical-evolution models in order to estimate the stellar mass of the parent galaxy of the stream at the epoch of the merger, its star-formation rate, the efficiency of outflows, and the expected age of its stellar population. Finally, we are conducting follow-up observations of low-metallicity members of this stream with high-resolution (R = 40,000) spectroscopy with the GRACES instrument at Gemini North (8.1m). The newly acquired data will be utilized in the determination of precise radial velocities and abundances of both light (e.g., ± and iron-peak) and heavy (neutron-capture) elements, extending our knowledge about this substructure in the very metal-poor regime. For this project, we have already been granted <25h of telescope time split between 2021A and 2021B. (AU)

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