Unveiling the Impact of Cosmic Rays on the Disc Sizes and Outflows from Dwarf Scales to Galaxy Groups

Abstract Cosmic rays (CRs) are a non-thermal energy component in the interstellar and circumgalactic medium (CGM) that provide an additional feedback channel beyond thermal and kinetic feedback from stars and AGN. They influence galaxy evolution by altering gas properties, regulating star formation, and shaping galactic outflows. We investigate these effects using cosmological zoom-in simulations, which incorporate CR transport and feedback on top of the Auriga model. Our simulations span a wide range of halo masses, from dwarf galaxies to small groups (M200c = 1010 − 1013 M⊙), allowing us to assess the mass-dependent impact of CRs in a cosmological setting. We find that CRs have the strongest impact in lower-mass galaxies (M200c 1012 M⊙), where they suppress star formation by up to 50 %, reduce gas and stellar half-light radii, and drive outflows that reach higher velocities at the virial radius compared to simulations without CRs. These CR-enhanced outflows transport metals and magnetic fields into the CGM, raising metallicity, strengthening magnetisation, and lowering temperatures. In more massive galaxies, CRs do not significantly affect star formation or outflow properties, likely because stellar and AGN feedback dominate in this regime. However, they still influence morphology across all halo masses by reducing gas half-mass and stellar half-light radii. Finally, variations in CR transport properties, such as different diffusion coefficients or excluding Alfvén cooling, significantly affect star formation, CGM properties, and outflows in lower-mass galaxies. This sensitivity makes these galaxies key environments for testing CR transport models and refining our understanding of their role in galaxy evolution.