Abstract:

The importance of cosmic rays (CRs) in galaxy evolution has become increasingly recognized over the past decade. Yet, a key unknown in CR physics that dictates their impact is the effective diffusion coefficient of GeV CR protons. Historically, the primary constraint on this diffusion coefficient has come from the observed scaling relation between gamma-ray luminosity (Lγ) and far-infrared luminosity (LIR). However, comparisons between simulations and observations in the literature have largely been conducted in a simplistic manner, which could potentially bias our interpretation.

In this talk, I will first provide a general overview of cosmological simulations, the FIRE collaboration, and the role of CRs in galaxy evolution. I will then focus on introducing how I used a suite of
cosmic ray magnetohydrodynamic (CR-MHD) simulations with FIRE-2 feedback models to investigate this issue, which includes modeling the γ ray emission as well as post-processing the simulated galaxies with 3D radiative transfer code SKIRT to obtain their LIR. In short, we find that the complex star formation rate (SFR)-LIR relation can bias the interpretation of whether the diffusion coefficient used in the simulation successfully reproduces the observed scaling relation. Moreover, we found a hint that a higher diffusion coefficient may be needed in dwarf galaxies to match the observations.