Chia-Hsun Chuang, Yun Wang
Galaxy clustering data can be used to measure H(z), D_A(z), and \beta(z). Here we present a method for using effective multipoles of the galaxy two-point correlation function (\xi_0(s), \xi_2(s), \xi_4(s), and \xi_6(s), with s denoting the comoving separation) to measure H(z), D_A(z), and \beta(z), and validate it using LasDamas mock galaxy catalogs. Our definition of effective multipoles explicitly incorporates the discreteness of measurements, and treats the measured correlation function and its theoretical model on the same footing. We find that for the mock data, \xi_0 + \xi_2 + \xi_4 captures nearly all the information, and gives significantly stronger constraints on H(z), D_A(z), and \beta(z), compared to using only \xi_0 + \xi_2. We apply our method to the sample of LRGs from the SDSS DR7 without assuming a dark energy model or a flat Universe. We find that \xi_4(s) deviates on scales of s<60\,Mpc/h from the measurement from mock data (in contrast to \xi_0(s), \xi_2(s), and \xi_6(s)), leading to a significant difference in the measured mean values of H(z), D_A(z), and \beta(z) from \xi_0 + \xi_2 and \xi_0 + \xi_2 + \xi_4, thus it should not be used in deriving parameter constraints. We obtain {H(0.35),D_A(0.35),\Omega_mh^2,\beta(z)} = {79.6_{-8.7}^{+8.3}km s^{-1}Mpc^{-1}, 1057_{-87}^{+88}Mpc, 0.103\pm0.015, 0.44\pm0.15} using \xi_0 + \xi_2. We find that H(0.35)r_s(z_d)/c and D_A(0.35)/r_s(z_d) (where r_s(z_d) is the sound horizon at the drag epoch) are more tightly constrained: {H(0.35)r_s(z_d)/c, D_A(0.35)/r_s(z_d)} = {0.0437_{-0.0043}^{+0.0041},6.48_{-0.43}^{+0.44}} using \xi_0 + \xi_2. We conclude that the multipole method can be used to isolate systematic uncertainties in the data, and provide a useful cross-check of parameter measurements from the full correlation function.
View original:
http://arxiv.org/abs/1205.5573
No comments:
Post a Comment