Baryonic Features in the Matter Transfer Function

We provide scaling relations and fitting formulae for adiabatic cold darkmatter cosmologies that account for all baryon effects in the matter transferfunction to better than 10% in the large-scale structure regime. They are basedupon a physically well-motivated separation of the effects of acousticoscillations, Compton drag, velocity overshoot, baryon infall, adiabaticdamping, Silk damping, and cold-dark-matter growth suppression. We also find asimpler, more accurate, and better motivated form for the zero baryon transferfunction than previous works. These descriptions are employed to quantify theamplitude and location of baryonic features in linear theory. While baryonicoscillations are prominent if the baryon fraction exceeds $\Omega_0 h^2 + 0.2$,the main effect in more conventional cosmologies is a sharp suppression in thetransfer function below the sound horizon. We provide a simple but accuratedescription of this effect and stress that it is not well approximated by achange in the shape parameter $\Gamma$.