Name : kyung Kiu Kim Hit : 1,628 jtang_IEU.pptx (2.4M) [11] DATE : 2011-04-06 04:00:30 Title: Likelihood reconstruction method of real-space density and velocity power spectra from a redshift galaxy survey Speaker: Dr. Jiayu Tang(IPMU)  Date & Time: 4:00 PM, March 21 (Mon.), 2011 Place: International Education Building(국제교육관)  615 Host: Eric Linder Abstract : We develop a maximum likelihood based method of reconstructing the real-space density and velocity power spectra from the measured galaxy clustering in redshift space.  Our method reconstructs band powers of the real-space power spectra, each of which depends on the redshift-space power spectrum with different powers of angular modulations $\mu^{2n}$ ($n=0,1,2$) at each wavenumber bins, including marginalization over uncertainties in the band powers at different wavenumber bins and the parameters to model the nonlinear redshift distortion effect, the so-called Fingers-of-God effect. We show that the method can well recover the power spectrum of $\mu^0$, equivalently the density power spectrum , up to $k\simeq 0.3~h{\rm Mpc}^{-1}$ to a few percent accuracies in amplitudes, for both dark matter (N-body particles) and halos, if we use the FoG model that has sufficient degrees of freedom to capture the scale- and angular-dependences seen in simulations. However, for the halo spectrum that is least affected by the FoG effect, the reconstructed spectrum shows greater amplitudes than the spectrum inferred from the simulations. We argue that the disagreement is ascribed to nonlinearity effects that arise from the cross-bispectra of density and velocity perturbations and become important at $k> 0.1~h{\rm Mpc}^{-1}$.  We find that adding the nonlinearity correction term to the measured density-velocity power spectrum can fairly well reproduce the reconstructed spectra for halos. These results imply that such nonlinearity corrections need to be included when using the reconstructed power spectra of halos or galaxies to constrain cosmological models or gravity theory.