Constraining Cosmic-Ray Transport through Synthetic Observations of the Circumgalactic Medium

Abstract

Cosmic-rays have been found to be potentially of great importance in galaxy formation in recent theoretical work. By establishing a substantial source of non-thermal pressure support in the circum-galactic medium (CGM), cosmic-rays alter the phase structure and spatial distribution of gas in the CGM, with notable ensuing effects on the star formation histories of galaxies. However, these effects rely heavily on the transport rate of cosmic-rays from the interstellar medium (ISM) into the CGM, and there remain order-of-magnitude uncertainties in the value of the macroscopic cosmic-ray diffusion coefficient from different plausible physical models. To place constraints on these theoretical models, we use high-resolution, magneto-hydrodynamic, cosmological simulations of galaxy formation from the Feedback in Realistic Environments (FIRE) project, and post process them with a novel code to compute the expected non-thermal synchrotron emission from the inner halo of these galaxies. By forward modeling the emission from simulations of galaxy formation which self-consistently evolve cosmic-rays, we are able to explore differences between models in non-thermal emission and place new constraints on models for cosmic-ray transport which may be investigated via future radio continuum observing missions.