The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: measurements of the growth of structure and expansion rate at z=0.57 from anisotropic clustering

TL;DR

This work leverages the anisotropic clustering of CMASS galaxies from SDSS-III BOSS DR9 to jointly constrain the expansion history and growth of structure at z≈0.57. Using a nonlinear RSD+AP model validated with extensive mocks and a WM A7-based prior on the linear power spectrum, the authors extract D_A, H, and fσ8 from the monopole and quadrupole moments of the two-point correlation function. They find results consistent with ΛCDM and CMB measurements, with Ω_Λ ≈ 0.74 and a robust, largely model-independent determination of the geometry and growth, enhanced when combining galaxy clustering with CMB priors. The analysis demonstrates the power of full-shape anisotropic clustering to test dark energy and gravity, and provides a public tool for future survey analyses.

Abstract

We analyze the anisotropic clustering of massive galaxies from the Sloan Digital Sky Survey III Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 9 (DR9) sample, which consists of 264,283 galaxies in the redshift range 0.43 < z < 0.7 spanning 3,275 square degrees. Both peculiar velocities and errors in the assumed redshift-distance relation ("Alcock-Paczynski effect") generate correlations between clustering amplitude and orientation with respect to the line-of-sight. Together with the sharp baryon acoustic oscillation (BAO) standard ruler, our measurements of the broadband shape of the monopole and quadrupole correlation functions simultaneously constrain the comoving angular diameter distance (2190 +/- 61 Mpc) to z=0.57, the Hubble expansion rate at z=0.57 (92.4 +/- 4.5 km/s/Mpc), and the growth rate of structure at that same redshift (d sigma8/d ln a = 0.43 +/- 0.069). Our analysis provides the best current direct determination of both DA and H in galaxy clustering data using this technique. If we further assume a LCDM expansion history, our growth constraint tightens to d sigma8/d ln a = 0.415 +/- 0.034. In combination with the cosmic microwave background, our measurements of DA, H, and growth all separately require dark energy at z > 0.57, and when combined imply Ω_Λ = 0.74 +/- 0.016, independent of the Universe's evolution at z<0.57. In our companion paper (Samushia et al. prep), we explore further cosmological implications of these observations.

Figures (11)

• Figure 1: Number density as a function of redshift for the CMASS galaxies used in this analysis. After accounting for our weighting scheme, the effective redshift for galaxy pairs in this sample is $z_{\rm eff} = 0.57$.
• Figure 2: BOSS DR9 sky coverage. The light gray region shows the expected total footprint of the survey, while the colors indicate completeness in the DR9 spectroscopy for regions included in our analysis. Dark grey regions are removed from the analysis by completeness or redshift failure cuts; see Sec. 3.5 of Aardvark for further details.
• Figure 3: Left panel: Two-dimensional correlation function of CMASS galaxies (color) compared with the best fit model described in Section \ref{['sec:goodfitLCDM']} (black lines). Contours of equal $\xi$ are shown at [0.6, 0.2, 0.1, 0.05, 0.02, 0]. Right panel: Smaller-scale two-dimensional clustering. We show model contours at [0.14, 0.05, 0.01, 0]. The value of $\xi_0$ at the minimum separation bin in our analysis is shown as the innermost contour. The $\mu \approx 1$ "finger-of-god" effects are small on the scales we use in this analysis.
• Figure 4: $\xi_0(s)$ and $\xi_2(s)$ measured from BOSS CMASS galaxies. The errorbars correspond to diagonal elements of the covariance matrix. The best-fitting model described in Section \ref{['sec:goodfitLCDM']} is shown as the solid curve. We use 23 logarithmically spaced bins and include pairs between 25 and 160 $h^{-1}$ Mpc.
• Figure 5: Upper panels: Diagonal elements of the monopole and quadrupole components of the covariance matrix computed from the LPT-based mocks (points) compared with the linear theory prediction (solid lines). Lower panels: Two slices through the reduced covariance matrices $C^{00,{\rm red}}_{ij}$ and $C^{22,{\rm red}}_{ij}$ for separation bins of 33 and 103 $h^{-1}$ Mpc. Linear theory predictions for the reduced covariance matrices in the lower panels have been scaled by a constant factor to produce good agreement between linear theory and mock covariances for off-diagonal elements, demonstrating that the scale dependence of the off-diagonal terms matches the mock covariance matrix well, but that there is extra diagonal covariance in the mocks compared with linear theory. Elements of $C^{02}$ are small (not shown).