Lecturer: Dr. Fangzhou Jiang Affiliation: Racah Institute of Physics, The Hebrew University of Jerusalem Abstract: Hierarchical structure formation in the standard LCDM model produces clumpy dark matter halos with abundant substructure, which are the remnants of halos that have been accreted by their host halo over time, and have survived tidal destruction. Understanding halo substructure is key to understanding satellite galaxies, the boost factor of dark matter annihilation, tidal heating of fragile stellar structures. The demographics of subhalos contain information of the Universe, providing a stringent testbed for the cosmological model. We study subhalos using a combination of cosmological N-body simulations and semi-analytic modeling. We develop a semi-analytic model describing halo assembly and subhalo evolution: it combines Monte-Carlo techniques of generating halo merging histories and simple analytical descriptions for the evolution of subhalos, thus offering extremely fast computation, the agility to experiment with different cosmologies, and the control of specific physical processes. The model accurately predicts the distributions of subhalo mass and structural parameters in cosmological simulations, and outperforms simulations in terms of mass resolution and statistical power. Unleashing the power of the semi-analytic model, we generate thousands of Milky-Way(MW)-size halos with well-resolved subhalo populations, and explicitly demonstrate that a reliable assessment of the "too-big-to-fail" problem requires such large samples. We demonstrate that 1.4+3.3−1.1% of MW-size host halos have a subhalo population in statistical agreement with that of the MW. We also present a study of unprecedented statistical power regarding the halo-to-halo variance of substructure. Finally, the model is being upgraded for predicting the spatial distribution of subhalos and being extended to generate satellite galaxy populations, aiming for a study of the influence of the host galaxy's disk on the satellite population. Additional details of the upcoming Astrophysics' seminars can be found on the following link. ‏האירוע הזה כולל שיחת וידאו ב-Google Hangouts. הצטרף: https://plus.google.com/hangouts/_/mail.huji.ac.il/astrophysics?hceid=bWFpbC5odWppLmFjLmlsX2c0czhydDlpcmhwZzRvdGNybWIzZGFqcjdvQGdyb3VwLmNhbGVuZGFyLmdvb2dsZS5jb20.1r9g6npuk5ac0kgf5294pa4hk0&hs=121