Baryonic Features in the Matter Transfer Function

We provide scaling relations and fitting formulae for adiabatic cold dark matter cosmologies that account for all baryon effects in the matter transfer function to better than 10% in the large-scale structure regime. They are based upon a physically well-motivated separation of the effects of acoustic oscillations, Compton drag, velocity overshoot, baryon infall, adiabatic damping, Silk damping, and cold-dark-matter growth suppression. We also find a simpler, more accurate, and better motivated form for the zero baryon transfer function than previous works. These descriptions are employed to quantify the amplitude and location of baryonic features in linear theory. While baryonic oscillations 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 the transfer function below the sound horizon. We provide a simple but accurate description of this effect and stress that it is not well approximated by a change in the shape parameter $\Gamma$.Comment: 20 pages, LaTeX, 7 Postscript figures included. Submitted to ApJ. Electronic versions of formulae are available at http://www.sns.ias.edu/~whu/transfer/transfer.htm