Baryon Acoustic Oscillations in the Sloan Digital Sky Survey Data Release 7 Galaxy Sample (0907.1660v3)

Abstract: The spectroscopic Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) galaxy sample represents the final set of galaxies observed using the original SDSS target selection criteria. We analyse the clustering of galaxies within this sample, including both the Luminous Red Galaxy (LRG) and Main samples, and also include the 2-degree Field Galaxy Redshift Survey (2dFGRS) data. Baryon Acoustic Oscillations are observed in power spectra measured for different slices in redshift; this allows us to constrain the distance--redshift relation at multiple epochs. We achieve a distance measure at redshift z=0.275, of r_s(z_d)/D_V(0.275)=0.1390+/-0.0037 (2.7% accuracy), where r_s(z_d) is the comoving sound horizon at the baryon drag epoch, D_V(z)=[(1+z)^2D_A^2cz/H(z)]^1/3, D_A(z) is the angular diameter distance and H(z) is the Hubble parameter. We find an almost independent constraint on the ratio of distances D_V(0.35)/D_V(0.2)=1.736+/-0.065, which is consistent at the 1.1sigma level with the best fit Lambda-CDM model obtained when combining our z=0.275 distance constraint with the WMAP 5-year data. The offset is similar to that found in previous analyses of the SDSS DR5 sample, but the discrepancy is now of lower significance, a change caused by a revised error analysis and a change in the methodology adopted, as well as the addition of more data. Using WMAP5 constraints on Omega_bh^2 and Omega_ch^2, and combining our BAO distance measurements with those from the Union Supernova sample, places a tight constraint on Omega_m=0.286+/-0.018 and H_0 = 68.2+/-2.2km/s/Mpc that is robust to allowing curvature and non-Lambda dark energy. This result is independent of the behaviour of dark energy at redshifts greater than those probed by the BAO and supernova measurements. (abridged)

• The paper achieves a precise BAO measurement using galaxy clustering data to constrain key cosmological distances.
• It employs three redshift slices and 10,000 Log-Normal density fields to robustly control systematic errors.
• The study supports the ΛCDM paradigm by deriving Ω_m and H_0 values consistent with WMAP and other models.

Analyzing Baryon Acoustic Oscillations in SDSS DR7

The paper "Baryon Acoustic Oscillations in the Sloan Digital Sky Survey Data Release 7 Galaxy Sample" by Percival et al. presents a detailed analysis of Baryon Acoustic Oscillations (BAO) using the Sloan Digital Sky Survey Data Release 7 (SDSS DR7). This survey consists of 893,319 galaxies over 9,100 square degrees, including data from the Two-degree Field Galaxy Redshift Survey (2dFGRS).

Methodology and Data

The analysis focuses on measuring BAO, which are periodic fluctuations in the density of the observable baryonic matter of the universe, in galaxy clustering data. These oscillations serve as a "standard ruler" for cosmological distance measurements, enabling constraints on the expansion of the Universe and the nature of dark energy.

The paper employs the power spectrum of the SDSS DR7 dataset, which includes Luminous Red Galaxy (LRG) and Main galaxy samples. The authors perform the analysis through three distinct redshift slices to discern changes in the cosmic distance-redshift relation over time. The focus is on delivering highly precise measurements by accounting for systematics and errors, which have been thoroughly scrutinized using 10,000 Log-Normal density fields.

Results

The paper manages to achieve a key distance measure at redshift $z = 0.275$, expressed as $r_s(z_d)/D_V(0.275) = 0.1390 \pm 0.0037$, with an accuracy of 2.7%. Here, $r_s(z_d)$ is the comoving sound horizon at the drag epoch, and $D_V$ is a composite distance measure that incorporates angular diameter and Hubble distances. A critical ratio of distances $D_V(0.35)/D_V(0.2) = 1.736 \pm 0.065$ offers strong consistency with a $\Lambda$CDM model when combined with Wilkinson Microwave Anisotropy Probe (WMAP) data.

Implications

This research has notable implications for cosmology. Measuring BAO allows for robust estimations of cosmological parameters such as $\Omega_m$, the matter density parameter, and $H_0$, the Hubble constant. The findings support models with a cosmological constant $\Lambda$ (consistent with the concept of dark energy), suggesting $\Omega_m = 0.286 \pm 0.018$ and $H_0 = 68.2 \pm 2.2$, unaffected by alternative models with non-zero curvature $\Omega_k$ or varying dark energy equation of state $w$.

Robustness and Comparisons

The authors extensively test the robustness of their findings against several factors, including galaxy selection, calibration methodology, redshift space distortions, and BAO damping scales. These tests indicate that while several factors can slightly alter the resulting cosmological constraints, the primary conclusions hold firm across different setups.

Future Prospects

The paper sets a precedent for future large-scale surveys such as BOSS, HETDEX, and SKA, poised to probe cosmic conditions over even larger volumes and higher redshifts. By refining our understanding of BAO and confidence in resolving cosmological constants, these future surveys may extend the reach of SDSS DR7's landmark findings into an era of more precise cosmological explorations.

In conclusion, this paper underscores the capability of SDSS DR7 in delivering high-precision cosmological insights through BAO analysis, continuing to affirm the $\Lambda$CDM paradigm while paving the way for further inquiries into the nature of dark energy and the universe's expansion.