A 2% Distance to z = 0.35 by Reconstructing Baryon Acoustic Oscillations - III : Cosmological Measurements and Interpretation

TL;DR

This paper demonstrates that reconstructing BAO signals in SDSS DR7 LRGs yields a precise low-redshift distance measure that, when combined with CMB data from WMAP7 and SNLS3, robustly constrains a broad class of cosmological models. Using an inverse distance ladder anchored by the CMB sound horizon and BAO distances, the authors derive a precise Hubble constant $H_0 = 69.8 \pm 1.2$ km s$^{-1}$ Mpc$^{-1}$ and matter density $\Omega_m = 0.280 \pm 0.014$ in flat ΛCDM, with consistent results across extended models including curvature and time-varying dark energy. The work also explores the impact of relativistic species $N_{\rm REL}$ and reports a mild tension with local $H_0$ measurements, suggesting a possible but not required extension to the relativistic energy density. Overall, BAO reconstruction proves a powerful tool for breaking degeneracies in cosmological parameters and reinforcing the standard cosmological model while highlighting avenues for addressing small tensions with local measurements.

Abstract

We use the 2% distance measurement from our reconstructed baryon acoustic oscillations (BAOs) signature using the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) Luminous Red Galaxies (LRGs) from Padmanabhan et al. (2012) and Xu et al. (2012) combined with cosmic microwave background (CMB) data from Wilkinson Microwave Anisotropy Probe (WMAP7) to measure parameters for various cosmological models. We find a 1.7% measurement of H_0 = 69.8 +/- 1.2 km/s/Mpc and a 5.0% measurement of Omega_m = 0.280 +/- 0.014 for a flat Universe with a cosmological constant. These measurements of H_0 and Omega_m are robust against a range of underlying models for the expansion history. We measure the dark energy equation of state parameter w = -0.97 +/- 0.17, which is consistent with a cosmological constant. If curvature is allowed to vary, we find that the Universe is consistent with a flat geometry (Omega_K = -0.004 +/- 0.005). We also use a combination of the 6 Degree Field Galaxy Survey BAO data, WiggleZ Dark Energy Survey data, Type Ia supernovae (SN) data, and a local measurement of the Hubble constant to explore cosmological models with more parameters. Finally, we explore the effect of varying the energy density of relativistic particles on the measurement of H_0.

Figures (14)

• Figure 1: Relative difference (in $\%$) between the sound horizon scale ($r_s/r^{\rm fid}_s)_{\rm CAMB}$ from CAMB and ($r_s/r^{\rm fid}_s)_{\rm EH98}$ from EH98, for a given combination of ($\Omega_m h^2, \Omega_b h^2$). Both definitions agree to within $0.2\%$ level even for cosmologies $5 \sigma$ away from the current WMAP7 constraints. Our fiducial cosmology with the WMAP7 1-sigma errors are shown as the grey cross.
• Figure 2: 6dFGS, reconstructed SDSS DR7, and WiggleZ BAO data points. The black line represents the $\rm {\Lambda CDM}$ prediction using WMAP7 data only komatsu11. The shaded gray region is the effect of varying $\Omega_m h^2$ within the $1 \sigma$ measurement errors of WMAP7. We see that the BAO data is consistent with the $\rm {\Lambda CDM}$ cosmological model.
• Figure 3: Plot of $D_V/r_s$ normalized by the fiducial value. The open square is the percival10 BAO measurement. The black line is the WMAP7 $\rm {\Lambda CDM}$ model, red line shows the effect of varying $w$ and the blue line, the effect of varying $\Omega_K$. The shaded regions around these lines correspond to $1 \sigma$ uncertainty in $\Omega_m h^2$ around the WMAP7 measurement. We see that the BAO data has the power to distinguish between various cosmological models. The $H_0$ point is the direct $H_0$ measurement from riess11.
• Figure 4: $68\%$ and $95\%$ confidence level contours for $H_0$ vs $\Omega_m$ using WMAP7 data (dashed gray lines) and then combining it with the reconstructed SDSS DR7 LRG BAO data (solid black lines).
• Figure 5: $68\%$ and $95\%$ confidence level contours for $H_0$ vs $\Omega_m$ (top), $\Omega_K$ vs $\Omega_m$ (middle) and $\Omega_K$ vs $H_0$ (bottom) for the oCDM model. The gray dashed lines represent the "CMB" dataset, and the solid black lines represent the "CMB+BAO" dataset. We see the vast improvement in the parameter measurements by adding BAO data to the WMAP7 measurements.