Cosmic rays ( CRs ) have recently re-emerged as attractive candidates for mediating feedback in galaxies because of their long cooling timescales .
Simulations have shown that the momentum and energy deposited by CRs moving with respect to the ambient medium can drive galactic winds .
However , simulations are hampered by our ignorance of the details of CR transport .
Two key limits previously considered model CR transport as a purely diffusive process ( with constant diffusion coefficient ) and as an advective streaming process .
With a series of GADGET simulations , we compare the results of these different assumptions .
In idealised three-dimensional galaxy formation models , we show that these two cases result in significant differences for the galactic wind mass loss rates and star formation suppression in dwarf galaxies with halo masses M \approx 10 ^ { 10 } n { M } _ { \odot } : diffusive CR transport results in more than ten times larger mass loss rates compared to CR streaming models .
We demonstrate that this is largely due to the excitation of Alfvén waves during the CR streaming process that drains energy from the CR population to the thermal gas , which is subsequently radiated away .
By contrast , CR diffusion conserves the CR energy in the absence of adiabatic changes and if CRs are efficiently scattered by Alfvén waves that are propagating up the CR gradient .
Moreover , because pressure gradients are preserved by CR streaming , but not diffusion , the two can have a significantly different dynamical evolution regardless of this energy exchange .
In particular , the constant diffusion coefficients usually assumed can lead to unphysically high CR fluxes .