Measurement of Baryon Acoustic Oscillations in the Lyman-alpha Forest Fluctuations in BOSS Data Release 9 (1301.3459v2)

Abstract: We use the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 9 (DR9) to detect and measure the position of the Baryonic Acoustic Oscillation (BAO) feature in the three-dimensional correlation function in the Lyman-alpha forest flux fluctuations at a redshift z=2.4. The feature is clearly detected at significance between 3 and 5 sigma (depending on the broadband model and method of error covariance matrix estimation) and is consistent with predictions of the standard LCDM model. We assess the biases in our method, stability of the error covariance matrix and possible systematic effects. We fit the resulting correlation function with several models that decouple the broadband and acoustic scale information. For an isotropic dilation factor, we measure 100x(alpha_iso-1) = -1.6 ^{+2.0+4.3+7.4}_{-2.0-4.1-6.8} (stat.) +/- 1.0 (syst.) (multiple statistical errors denote 1,2 and 3 sigma confidence limits) with respect to the acoustic scale in the fiducial cosmological model (flat LCDM with Omega_m=0.27, h=0.7). When fitting separately for the radial and transversal dilation factors we find marginalised constraints 100x(alpha_par-1) = -1.3 ^{+3.5+7.6 +12.3}{-3.3-6.7-10.2} (stat.) +/- 2.0 (syst.) and 100x(alpha_perp-1) = -2.2 ^{+7.4+17}{-7.1-15} +/- 3.0 (syst.). The dilation factor measurements are significantly correlated with cross-correlation coefficient of ~ -0.55. Errors become significantly non-Gaussian for deviations over 3 standard deviations from best fit value. Because of the data cuts and analysis method, these measurements give tighter constraints than a previous BAO analysis of the BOSS DR9 Lyman-alpha forest sample, providing an important consistency test of the standard cosmological model in a new redshift regime.

• The paper demonstrates a robust detection of BAO in the Lyman-alpha forest using BOSS DR9 data, achieving a significance between 3 and 5 sigma.
• It employs a three-dimensional correlation function and multiple broadband models to effectively separate acoustic signals from systematic biases.
• The findings strengthen the constraints on the ΛCDM model and set a benchmark for future high-redshift BAO studies in cosmic expansion research.

Analysis of Baryon Acoustic Oscillations in Lyman-$\alpha$ Forest Fluctuations

The paper "Measurement of Baryon Acoustic Oscillations in the Lyman-$\alpha$ Forest Fluctuations in BOSS Data Release 9" contributes to cosmological research by utilizing data from the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 9 to analyze baryon acoustic oscillations (BAO) in the Lyman-$\alpha$ forest fluctuations at a redshift of $z_{\rm eff}=2.4$. The paper addresses the significance of BAO as a comoving standard ruler to probe the expansion history of the Universe, grounded in the $\Lambda$CDM model.

Key Findings and Methodology

The research employs DR9 data to detect the BAO feature with high statistical significance, achieving between 3 and 5 sigma depending on the methods applied. This robustness is crucial for validating the $\Lambda$CDM model in a new high-redshift regime. The analysis systematically deals with biases, error covariance matrix stability, and potential systematic effects.

The paper uses a three-dimensional correlation function to assess the presence of the BAO feature. Special attention is paid to the role of instrumental effects and theoretical modeling, integral to measuring the dilation factors that relate BAO features to cosmic distances. It adopts multiple models and broadband methods to dissociate broadband and acoustic information effectively. For the isotropic dilation factor, the measurement aligns closely with predictions of the fiducial model, indicating a consistent BAO peak detection.

Implications and Future Directions

This paper not only reinforces the understanding of cosmic expansion at high redshift but also advances methodologies in BAO measurements using Lyman-$\alpha$ forest data. The findings establish tighter constraints on BAO parameters compared to previous DR9 analyses, thus providing a new benchmark for testing standard cosmological models.

Moreover, this work speculates on the applicability of these methodologies to future data releases and survey enhancements, indicating the potential for more precise and accurate constraints on dark energy's role and behavior. Such measures are critical for addressing existing tensions between BAO measurements from different cosmological observables at diverse redshifts, like those from CMB data by the SPT or BOSS galaxy surveys.

Conclusion

The research delineates an advanced framework for detecting BAO in Lyman-$\alpha$ forest fluctuations, pushing the frontiers of high-redshift cosmology. As large-scale structure surveys evolve, leveraging similar methodologies promises a deeper understanding of cosmological parameters and the nature of dark energy. These insights are pertinent not only for enhancing cosmological models but also for refining the techniques used in large-scale astrophysical surveys.