Extracting angular diameter distance and expansion rate of the universe from two-dimensional galaxy power spectrum at high redshifts: Baryon acoustic oscillation fitting versus full modeling

We present a method for extracting the angular diameter distances, D _A, and the expansion rates, H, of the universe from the two-dimensional baryon acoustic oscillations (BAO) in the galaxy power spectrum. Our method builds upon the existing algorithm called the "fit-and- extract" (FITEX) method, which allows one to extract only D _A/H² from a spherically averaged one-dimensional power spectrum. We develop the FITEX-2d method, an extension of the FITEX method, to include the two-dimensional information, which allows us to extract D _A and H simultaneously. We test the FITEX-2d method using the Millennium Simulation as well as simplified Monte Carlo simulations with a bigger volume. The BAOs, however, contain only a limited amount of information. We show that the full modeling, including the overall shape of the power spectrum, yields much better determinations of D_A and H, hence the dark energy equation of state parameters such as w ₀ and w _a, than the BAO-only analysis by more than a factor of 2, provided that nonlinear effects are under control.