Title: Astro-particle Phenomena from Dark Matter and Cosmic Rays in MHD Galaxy Formation Simulations

Abstract: Over the last few decades, observations of diffuse gamma-ray emission in the Milky Way have challenged astrophysical models– in particular, the excess of GeV gamma-rays detected in the Milky Way’s galactic center. Possible explanations for this signal include annihilating or decaying dark matter, or an undetected population of millisecond pulsars. However, nearly all past studies of galactic gamma-ray emission make simplifying assumptions about CR propagation that may not be valid (e.g., steady-state equilibrium). Recent numerical breakthroughs have enabled fully time-dependent dynamical evolution of CRs in magnetohydrodynamic (MHD) galaxy formation simulations, allowing self-consistent comparisons to the Milky Way observations. In this talk, I will present new work in which we model gamma-ray emission in simulations of Milky Way-mass galaxies with fully-resolved, multi-species cosmic ray 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 interstellar medium. Critically, this time-varying gamma-ray emission leads to transient enhancements in the gamma-ray spectrum consistent with the detected Fermi-LAT excess.  We also show that the inverse Compton scattering of cosmic ray leptons fuels the formation of Fermi bubble-like features in these simulations.  Finally, I will present the first results from a new suite of cosmological simulations in which a dark sector with an ultra-light mediator gives rise to a long-range (kiloparsec-scale) self-interaction. The addition of a long-range dark matter self-interaction has dramatic effects on the formation of galaxies and their host halos, and will be testable by current and upcoming astronomical surveys.

https://lbnl.zoom.us/j/94928022788?pwd=emVQWG1mTnhSbHVqekVuenk0VEVQZz09