A 2% Distance to z=0.35 by Reconstructing Baryon Acoustic Oscillations - I : Methods and Application to the Sloan Digital Sky Survey (1202.0090v1)

Abstract: We apply the reconstruction technique to the clustering of galaxies from the SDSS DR7 LRG sample, sharpening the baryon acoustic oscillation (BAO) feature and achieving a 1.9% measurement of the distance to z=0.35. This is the first application of reconstruction of the BAO feature in a galaxy redshift survey. We update the reconstruction algorithm of Eisenstein et al, 2007 to account for the effects of survey geometry as well as redshift-space distortions and validate it on 160 LasDamas simulations. We demonstrate that reconstruction sharpens the BAO feature in the angle averaged galaxy correlation function, reducing the nonlinear smoothing scale \Sigma_nl from 8.1 Mpc/h to 4.4 Mpc/h. Reconstruction also significantly reduces the effects of redshift-space distortions at the BAO scale, isotropizing the correlation function. This sharpened BAO feature yields an unbiased distance estimate (< 0.2%) and reduces the scatter from 3.3% to 2.1%. We demonstrate the robustness of these results to the various reconstruction parameters, including the smoothing scale, the galaxy bias and the linear growth rate. Applying this reconstruction algorithm to the SDSS LRG DR7 sample improves the significance of the BAO feature in these data from 3.3 sigma for the unreconstructed correlation function, to 4.2 sigma after reconstruction. We estimate a relative distance scale D_V/r_s to z=0.35 of 8.88+/-0.17, where r_s is the sound horizon and D_V = (D_A^2/H)^{1/3} is a combination of the angular diameter distance D_A and Hubble parameter H. Assuming a sound horizon of 154.25 Mpc, this translates into a distance measurement D_V (z=0.35) = 1.356+/-0.025 Gpc. We find that reconstruction reduces the distance error in the DR7 sample from 3.5% to 1.9%, equivalent to a survey with three times the volume of SDSS.

• The paper applies an updated baryon acoustic oscillation reconstruction method to Sloan Digital Sky Survey DR7 data to achieve a 1.9% distance measurement error at redshift z=0.35.
• The study's reconstruction algorithm significantly sharpens the BAO peak and reduces the scatter of distance estimates from 3.3% to 2.1% in redshift space.
• This work demonstrates that BAO reconstruction significantly enhances precision, which is crucial for future cosmological surveys and constraining dark energy models.

Analysis of a 2% Distance Measure to z=0.35 via Baryon Acoustic Oscillations

The paper "A 2% Distance to $z=0.35$ by Reconstructing Baryon Acoustic Oscillations - I: Methods and Application to the Sloan Digital Sky Survey" by Padmanabhan et al. presents an important advancement in cosmological distance measurements with the application of a reconstruction technique to baryon acoustic oscillations (BAO). This work is pioneering in its application to a galaxy redshift survey, specifically using data from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7). The authors manage to achieve a distance measurement error of only 1.9% to a redshift of $z=0.35$.

Methodological Innovations

One core contribution of this research is the updated reconstruction algorithm used to analyze galaxy clustering in the SDSS DR7 Luminous Red Galaxy (LRG) sample. This technique aims at reversing the non-linear smoothing of the BAO feature, a challenge posed by the large-scale flows in the density field associated with cosmic structure formation. The adapted algorithm addresses survey geometry and redshift-space distortions—a significant step given previous BAO detections were not applied to real data until this paper.

Critical to the methodology is the use of LasDamas simulations that mirror the SDSS survey's geometry and clustering properties, serving as a validation tool for the reconstruction's efficacy. The paper demonstrates that the reconstruction yields a sharper BAO peak, evident in both real and redshift spaces, by reducing the non-linear smoothing scale from 8.1 Mpc/$h$ to 4.4 Mpc/$h$.

Numerical Results and Improvements

The authors reveal that applying reconstruction techniques significantly enhances the detection and precision of the BAO feature, thereby improving cosmological distance estimates. The paper reports a reduction in the scatter of distance estimates from 3.3% to 2.1% in redshift space. This enhancement not only confirms the feature more prominently but also minimizes the number of outliers in distance estimations due to increased detection significance.

The distance measurements achieved reflect a relative distance scale, $D_{V}/r_{s}$, of $8.88 \pm 0.17$ to $z=0.35$. With an assumed sound horizon of 154.25 Mpc, this translates to a distance of $1.356 \pm 0.025$ Gpc. Notably, these results show consistency across variations in parameters like smoothing scales, galaxy bias, and growth rates, highlighting the robustness of the reconstruction.

Implications and Future Directions

This methodological innovation significantly enhances the precision of cosmological distance measurements, echoing its implications for future BAO surveys which largely count on reconstruction for improved measurement precision. This work underscores the importance of density field reconstruction in disentangling the isotropic parameter information from BAO, facilitating more accurate constraints on the angular diameter distance and Hubble parameter.

In view of the demonstrated robustness and effectiveness, future avenues of research could focus on anisotropic BAO signal reconstructions to further exploit the capability of these methodological advancements in cosmological interpretations. Such enhanced measurements are crucial to constraining models of dark energy and understanding the universe's accelerated expansion.

Overall, the research detailed in this paper illustrates not only a substantial methodological advancement in the field of cosmology but also sets a precedent for integrating reconstruction techniques into standard analyses within future large-scale structure surveys.