Emulating Power Spectra for Prereconstructed and Postreconstructed Galaxy Samples

The small-scale linear information in galaxy samples typically lost during nonlinear growth can be restored to a certain level by the density field reconstruction, which has been demonstrated for improving the precision of the baryon acoustic oscillation (BAO) measurements. As proposed in the literature, a joint analysis of the power spectrum before and after the reconstruction enables an efficient extraction of information carried by high-order statistics. However, the statistics of the postreconstruction density field are difficult to model. In this work, we circumvent this issue by developing an accurate emulator for the prereconstructed, postreconstructed, and cross-power spectra ( ${P}_{\mathrm{pre}}$ , P _post , P _cross ) up to k = 0.5 h Mpc ^−1 based on the Dark Quest N -body simulations. The accuracy of the emulator is at the percent level; namely, the error of the emulated monopole and quadrupole of the power spectra is less than 1% and 10% of the ground truth, respectively. A fit to an example power spectrum using the emulator shows that the constraints on cosmological parameters get largely improved using ${P}_{\mathrm{pre}}$ + P _post + P _cross with ${k}_{\max }=0.25\,h\,{\mathrm{Mpc}}^{-1}$ , compared to that derived from ${P}_{\mathrm{pre}}$ alone; namely, the constraints on (Ω _m , H _0 , σ _8 ) are tightened by ∼41%–55%, and the uncertainties of the derived BAO and RSD parameters ( α _⊥ , α _∣∣ , f σ _8 ) shrink by ∼28%–54%, respectively. This highlights the complementarity among ${P}_{\mathrm{pre}}$ , P _post , and P _cross , which demonstrates the efficiency and practicability of a joint ${P}_{\mathrm{pre}}$ , P _post , and P _cross analysis for cosmological implications.