Speaker
Description
Cosmic rays (CRs) are a pivotal non-thermal component of galaxy formation and evolution. However, the intricacies of CR physics, particularly how they propagate in the circumgalactic medium (CGM), remain largely unconstrained. In this work, we study CGM observables in FIRE-2 (Feedback in Realistic Environments) simulations of the same Milky Way (MW)-mass halo
at 𝑧 = 0 with different CR transport models that gave similar diffuse ∼ GeV 𝛾-ray emission. We study the CGM gas properties, and generate synthetic observations of rest-frame UV ion absorption columns and X-ray emission (for both inner CGM/near-ISM region and extended CGM). We find that CRs lower galaxy masses and star formation rates (SFRs), while supporting more cool CGM gas. This boosts the HI and OVI column densities in the CGM, while lowering X-ray luminosities consistent with observed scalings with mass/star formation rate (SFR), but there can be large differences between CR transport models and resolution levels. X-ray emission within and close to galaxies is consistent with thermal (free-free and metal line) emission plus X-ray binaries, while more extended (∼ 100 kpc) CGM emission is potentially dominated by inverse Compton (IC) scattering, motivating future work on the spatially-resolved profiles. Although comparisons with X-ray observations are sensitive to the details of sample selection and disk subtraction, and they do not impose strong constraints on CR models, the run-to-run difference is clear and could be used as a framework for future studies. Overall, the inclusion of CRs and detailed transport models brings simulations more in line with observations and builds support for their accurate treatment in modern cosmological simulations of galaxy evolutions.