Title: Dark matter clues from the faintest Milky Way satellites

Speaker: Isabel Santos-Santos (Leibniz Institute for Astrophysics Potsdam)

Time: 15:00, Thursday, 15 October 2026

Tencent Meeting: 46822606747 password: 6360

Location: Lecture Hall, 3rd floor

Invited by: Peng Wang

Abstract：

The cold dark matter (CDM) cosmological model successfully reproduces the large-scale distribution of galaxies and has been established as the standard paradigm. On small scales, it makes robust predictions, yet these remain to be fully tested against observational data of dwarf galaxies. The last decade has seen a rise in the number of known Milky Way (MW) satellites, primarily thanks to the discovery of closeby ultrafaint systems, opening a new avenue for testing the standard model. These ultra-faints are located very close to the MW centre, present compact sizes, and have high central densities; characteristics a priori challenging to reconcile with traditional cosmological simulations.

I will review CDM's small-scale predictions and present a new model to predict the abundance and present-day properties of the complete population of MW satellite galaxies in LCDM. Our framework combines the highest-resolution simulation of a MW-mass halo with a semi-analytic galaxy formation model which assumes that galaxies form in the "cuspy" centres of CDM halos massive enough to allow atomic hydrogen to cool. The key novelties of our approach are the explicit tracking of "orphan" satellites (galaxies artificially disrupted due to limited numerical resolution), and the accurate modelling of tidal stripping of both dark matter and stars.

This framework predicts a large population of undiscovered satellite galaxies at close distances, with properties resembling those of recently detected ambiguous ultra-faint compact satellites, that blur the line between dwarf galaxies and globular clusters. Upcoming deep surveys like LSST have the potential to fully reveal this ultrafaint population, providing an unprecedented test of the nature of the elusive dark matter.

CV：I am a postdoctoral researcher at the Leibniz Institute for Astrophysics Potsdam (Germany) working in the group of Dr Noam Libeskind. Previously, I was a postdoc at the Institute for Computational Cosmology in Durham (UK) working with Prof Frenk, and before then, I was a postdoc in the University of Victoria (Canada) working with Prof Navarro. I completed my Ph.D. in Astrophysics and Cosmology at the Universidad Autónoma de Madrid (Spain). My research explores the cosmological role played by dwarf galaxies to uncover the nature of dark matter.