Cosmological simulations of galaxy formation : toward a robust accounting of galaxy populations and star formation across the Universe ?

Séminaire IPAG de Frédéric Bournaud (CEA Saclay), jeudi 11 mars 2021, 11h00, IPAG seminar room

Cosmological simulations of galaxy formation are reaching a high level of accuracy and can finely reproduce some of the main properties of galaxy populations : stellar masses, angular momentum, colors, etc. However, most galaxy formation simulations still fail to account for the detailed structure of galaxies and their global star formation history. Using high-resolution, idealized simulations of galactic dynamics and star formation, I will show that these disagreements are not cosmetic details but point toward a fundamental tension between observations and galaxy formation models.

Historically, galaxy formation models predicted galaxies with unrealistically large stellar masses : in modern cosmological simulations, this issue is generally solved though energetic feedback from young stars and supermassive black holes. I will nevertheless show that feedback, as implemented in such simulations, is generally excessive, leading to the early and unrealistic exhaustion of interstellar gas reservoirs.

Comparisons to idealized simulations and observations of galactic winds support the conclusion that energetic stellar and black hole feedback cannot be entirely responsible for the regulation of star formation and galaxy growth. Other physical processes likely emerge from sub-galactic scales in the interstellar medium, such as subtle coupling between galactic dynamics and star formation through instabilities and turbulence.

Nevertheless, some cosmological simulations can now successfully describe the re-distribution of baryons from galaxies to the intergalactic medium, and I will show that these simulations are a crucial tool not just for galaxy formation but also for modern cosmological surveys.

I will finally review how simulations of galaxy formation, evolution and star formation could gain strength in the years to come, in relation with the arrival of exascale supercomputers.