Isabel Sands (Caltech)

Over the last few decades, observations of diffuse gamma-ray emission in the Milky Way– in particular, the excess of GeV gamma-rays detected in the Milky Way’s galactic center, and the massive gamma-ray bubbles (the “Fermi bubbles”) centered about the Milky Way’s disk– have challenged astrophysical models. Nearly all past studies of galactic gamma-ray emission make simplifying assumptions about cosmic ray (CR) propagation that may not be valid (e.g., steady-state equilibrium), but recent numerical breakthroughs have enabled fully time-dependent dynamical evolution of CRs in magnetohydrodynamic (MHD) simulations with resolved, multi-phase small-scale structure in the interstellar medium (ISM), allowing self-consistent comparisons to the Milky Way observations. In this talk, I will present new work in which we model diffuse gamma-ray emission in simulations of Milky Way-mass galaxies with fully-resolved, multi-species CR spectra. We find that the gamma-ray spectrum in the galactic center can fluctuate by up to an order of magnitude on million-year timescales due to highly variable star formation and losses from variable structure in the turbulent ISM. I will also show that Fermi bubble-like features arise from stellar feedback in these simulations. Finally, I will briefly discuss how this work connects to the circumgalactic medium, and will enable new constraints on cosmic ray transport.