The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: Testing gravity with redshift-space distortions using the power spectrum multipoles (1312.4611v2)

Abstract: We analyse the anisotropic clustering of the Baryon Oscillation Spectroscopic Survey (BOSS) CMASS Data Release 11 (DR11) sample, which consists of $690\,827$ galaxies in the redshift range $0.43 < z < 0.7$ and has a sky coverage of $8\,498\,\text{deg}^2$. We perform our analysis in Fourier space using a power spectrum estimator suggested by Yamamoto et al. (2006). We measure the multipole power spectra in a self-consistent manner for the first time in the sense that we provide a proper way to treat the survey window function and the integral constraint, without the commonly used assumption of an isotropic power spectrum and without the need to split the survey into sub-regions. The main cosmological signals exploited in our analysis are the Baryon Acoustic Oscillations and the signal of redshift space distortions, both of which are distorted by the Alcock-Paczynski effect. Together, these signals allow us to constrain the distance ratio $D_V(z_{\rm eff})/r_s(z_d) = 13.89\pm 0.18$, the Alcock-Paczynski parameter $F_{\rm AP}(z_{\rm eff}) = 0.679\pm0.031$ and the growth rate of structure $f(z_{\rm eff})\sigma_8(z_{\rm eff}) = 0.419\pm0.044$ at the effective redshift $z_{\rm eff}=0.57$. We did not find significant systematic uncertainties for $D_V/r_s$ or $F_{\rm AP}$ but include a systematic error for $f\sigma_8$ of $3.1\%$. Combining our dataset with Planck to test General Relativity (GR) through the simple $\gamma$-parameterisation, reveals a $\sim 2\sigma$ tension between the data and the prediction by GR. The tension between our result and GR can be traced back to a tension in the clustering amplitude $\sigma_8$ between CMASS and Planck.

• The paper quantifies redshift-space distortions using power spectrum multipoles to derive key parameters, including fσ8 (0.419±0.044) and DV/rs (13.89±0.18).
• The study employs a robust methodology that corrects for survey window functions and the Alcock-Paczynski effect on a dataset of 690,827 galaxies over 8,498 square degrees.
• The analysis reveals a notable ~2σ tension with Planck data, suggesting potential modifications to General Relativity on cosmological scales.

Overview of "The Clustering of Galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: Testing Gravity with Redshift-space Distortions using the Power Spectrum Multipoles"

The paper conducted by Florian Beutler et al. focuses on analyzing the anisotropic clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS) CMASS Data Release 11 (DR11). This analysis involves a comprehensive examination of redshift-space distortions and Baryon Acoustic Oscillations (BAOs) using the power spectrum multipoles, which are key to testing the principles of gravity through cosmological observations.

Methodology and Analysis

The data sample consists of 690,827 galaxies within a redshift range of 0.43 to 0.7, covering an expansive sky area of 8,498 square degrees. The researchers employ a Fourier space power spectrum estimator, accommodating for the survey window function and the integral constraint, which deviates from the previously common assumption of isotropy in this context. The methodology involves a meticulous calculation of multipole power spectra, including the isotropic and anisotropic components, accounting for the Alcock-Paczynski effect, which distorts these signals.

Key Results

Among the significant quantitative outcomes, they achieve:

• A distance ratio $D_V(z_{\rm eff})/r_s(z_d) = 13.89\pm 0.18$,
• An Alcock-Paczynski parameter $F_{\rm AP}(z_{\rm eff}) = 0.679\pm0.031$,
• A growth rate of structure $$f(z_{\rm eff})\sigma_8(z_{\rm eff}) = 0.419\pm0.044$$ at the effective redshift $z_{\rm eff}=0.57$.

These results are pivotal as they offer robust constraints on the cosmological model parameters and are importantly noted to be resilient against systematic uncertainties which might otherwise skew the results.

The extensive validation using mock galaxy catalogues and N-body simulations suggests that systematic uncertainties introduce a mere 3.1% error in the growth rate parameter $f\sigma_8$, highlighting the paper's methodological robustness. Notably, the uncertainties linked to the constraints on $D_V/r_s$ or $F_{\rm AP}$ remain negligible.

Implications and Theoretical Considerations

By integrating the BOSS dataset with Planck data to test General Relativity (GR), the team identifies a noticeable $\sim 2\sigma$ tension between the empirical data and GR predictions, particularly visible in the discrepancy in the clustering amplitude $\sigma_8$ between CMASS and Planck. This incongruity serves as a critical point for theoretical exploration, providing invaluable insights into potential modifications or extensions of the GR framework on cosmological scales.

The implications of these findings touch upon both practical observational strategies and the theoretical modeling of the universe's large-scale structure. As researchers grapple with modifying existing gravitational theories or integrating new components into cosmological models, these results serve as a guiding benchmark.

Future Prospects

Continued examination directed towards resolving the tension highlighted by this paper could pave the way for groundbreaking advances in theoretical physics and cosmology. Future surveys and high-precision experimental data could leverage these findings to refine our understanding of gravitational interactions on cosmic scales. The paper underscores the necessity for ongoing collaboration between observational astronomy and theoretical physics to unravel the universe's deepest mysteries.