In the ΛCDM paradigm, dark matter halos form hierarchically and provide the ‘skeleton’ on which the baryonic components of galaxies form, grow, and evolve through the hierarchical assembly of subhalos. Halo stars can have multiple, distinct origins - accreted from disrupted satellites, formed in situ, or dynamically ejected from the inner galaxy - and each pathway is expected to imprint characteristic chemical abundance patterns (e.g., metallicity and detailed element ratios) across the halo.
The Andromeda Galaxy (M31) and Triangulum Galaxy (M33) offer an ideal combination of proximity and an external vantage point, enabling a detailed yet global view of halo assembly. The J-ATLAS survey adds a crucial dimension to this picture: a wide-area, homogeneous map of stellar chemical enrichment across the disks, halos, and satellite systems of M31 and M33. Leveraging the 56 J-PAS narrowband filters across the optical down to m ≈ 23 mag, J-ATLAS will complement previous broadband efforts (e.g., Pan-Andromeda Archaeological Survey) by delivering low-resolution photo-spectra for millions of resolved stars. These photo-spectra enable robust SED fitting analyses that go beyond global metallicity, providing constraints on key abundance dimensions (e.g., [Fe/H] and multiple element-sensitive features that trace α-elements and other nucleosynthetic channels) across distinct structural components and substructures. The resulting catalog of stellar parameters and abundance estimates at unprecedented scale will allow us to chemically tag disrupted debris, distinguish accreted versus in situ populations, and directly test ΛCDM driven halo formation scenarios through their predicted chemo structural signatures.
We have already begun this effort with a pilot survey targeting the Giant Stellar Stream, using it as a benchmark substructure to validate the abundance methodology and quantify chemical gradients within tidal debris. Finally, the synergy between J-ATLAS and RomAndromeda will enable chemo-dynamical studies by combining our abundance constraints with the high-fidelity proper motions delivered by the Nancy Grace Roman Space Telescope.
24/02/2026
Speaker: Borja Anguiano (Centro de Estudios de Física del Cosmos de Aragon - CEFCA)
Aula Gratton and streamed live.