Cosmology and the Halo Occupation Distribution from Small-Scale Galaxy Clustering in the Sloan Digital Sky Survey
Abstract
We use the projected correlation function w_p(r_p) of a volume-limited subsample of the Sloan Digital Sky Survey (SDSS) main galaxy redshift catalogue to measure the halo occupation distribution (HOD) of the galaxies of the sample. Simultaneously, we allow the cosmology to vary within cosmological constraints imposed by cosmic microwave background experiments in a LCDM model. We find that combining w_p(r_p) for this sample alone with the observations by WMAP, ACBAR, CBI and VSA provides one of the most sensitive techniques available to measure cosmological parameters. For a minimal flat six-parameter LCDM model with an HOD with two free parameters (and a third fixed by the mean galaxy density), we find Omega_m=0.271^+0.026_-0.027, sigma_8=0.821^+0.028_ -0.028, and H_0=70.6^+2.6_-2.6 km s^-1 Mpc^-1; these errors are significantly smaller than from CMB alone and similar to those obtained by combining CMB with the large scale galaxy power spectrum assuming scale-independent bias. The corresponding HOD parameters describing the minimum halo mass and the normalization and cutoff of the satellite mean occupation are Mmin=(2.94^+0.33_-0.33)x 10^12 h^-1 M_odot, M_1 = (4.51^+0.54_-0.54)x 10^13 h^-1 M_o, and kappa=4.70^+0.53_-0.75. These HOD parameters thus have small fractional uncertainty when cosmological parameters are allowed to vary within the range permitted by the data. Similar modeling for other galaxy samples could reduce the statistical errors on these results, while more thorough investigations of the cosmology dependence of nonlinear halo bias and halo mass functions are needed to eliminate remaining systematic uncertainties, which may be comparable to statistical uncertainties. (abridged)Keywords
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