The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: Measuring D_A and H at z=0.57 from the Baryon Acoustic Peak in the Data Release 9 Spectroscopic Galaxy Sample (1303.4666v1)

Abstract: We present measurements of the angular diameter distance to and Hubble parameter at z=0.57 from the measurement of the baryon acoustic peak in the correlation of galaxies from the Sloan Digital Sky Survey III Baryon Oscillation Spectroscopic Survey. Our analysis is based on a sample from Data Release 9 of 264,283 galaxies over 3275 square degrees in the redshift range 0.43<z<0.70. We use two different methods to provide robust measurement of the acoustic peak position across and along the line of sight in order to measure the cosmological distance scale. We find D_A(0.57) = 1408 +/- 45 Mpc and H(0.57) = 92.9 +/- 7.8 km/s/Mpc for our fiducial value of the sound horizon. These results from the anisotropic fitting are fully consistent with the analysis of the spherically averaged acoustic peak position presented in Anderson et al, 2012. Our distance measurements are a close match to the predictions of the standard cosmological model featuring a cosmological constant and zero spatial curvature.

Analysis of Baryon Acoustic Oscillation Measurements in SDSS-III BOSS DR9

The research paper under discussion presents measurements of the angular diameter distance and the Hubble parameter at a redshift of 0.57 using the Baryon Acoustic Oscillation (BAO) feature in the clustering of galaxies. The data was drawn from the Sloan Digital Sky Survey III (SDSS-III) Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 9, which includes a sample of 264,283 galaxies spanning 3275 square degrees within the redshift range of 0.43 to 0.70. The primary aim of the paper was to determine the BAO scale anisotropically, utilizing different methodological approaches to derive cosmological distances.

The paper's authors employed both the monopole-quadrupole decomposition of the anisotropic correlation function and the clustering wedges method to extract the BAO signal. These methods allow for the independent determination of the angular diameter distance, $D_A(z)$, and the Hubble parameter, $H(z)$, which are crucial for understanding the cosmic expansion and probing dark energy properties. This analysis builds upon previous work on spherically averaged BAO measurements, seeking higher precision in cosmological parameter estimation by leveraging the anisotropic features of the BAO.

Numerical Findings and Cosmological Implications

The results demonstrate that at a redshift of $z = 0.57$, the angular diameter distance $D_A$ was measured to be 1408 ± 45 Mpc, while the Hubble parameter $H$ was found to be 92.9 ± 7.8 km/s/Mpc. These measurements were derived assuming a fiducial sound horizon and exhibit a robust agreement with the predictions of the $\Lambda$CDM cosmological model, with a correlation coefficient between $D_A$ and $H$ of around 0.55.

The paper confirms the consistency of BAO measurements with the standard cosmological model, aligning with results obtained from spherically averaged analyses. The anisotropic nature of the analysis allows for the separate assessment of $D_A$ and $H$, which is vital for breaking degeneracies inherent in cosmological models, particularly when constraining spatial curvature $\Omega_k$ and the dark energy equation of state $w$.

The research also establishes the efficacy of BAO as a standard ruler by which cosmological distances can be precisely measured. This provides a significant avenue for future studies, particularly with upcoming survey data expected to further refine measurements of the cosmic expansion history across different epochs.

Future Directions

As BAO surveys increase in size and resolution, it is anticipated that anisotropic analyses will increasingly dominate the search for cosmological constraints. The methodologies refined in this paper set a benchmark for future analyses that can be applied to larger datasets expected from evolving cosmological surveys. Such analyses hold the potential to yield even more stringent constraints on the properties of dark energy and the geometry of the Universe. The BOSS dataset represents only a portion of the data anticipated from next-generation surveys, which are expected to significantly enhance our understanding of the Universe's expansion history and the nature of dark energy.

In conclusion, the findings from the SDSS-III BOSS DR9 galaxy sample underscore the consistency of BAO-based measurements with standard cosmological paradigms, paving the way for more precise and expansive future investigations into the dynamics of cosmic expansion.