Baryon Acoustic Oscillations in the Lyα forest of BOSS DR11 quasars (1404.1801v2)

Abstract: We report a detection of the baryon acoustic oscillation (BAO) feature in the flux-correlation function of the Ly{\alpha} forest of high-redshift quasars with a statistical significance of five standard deviations. The study uses 137,562 quasars in the redshift range $2.1\le z \le 3.5$ from the Data Release 11 (DR11) of the Baryon Oscillation Spectroscopic Survey (BOSS) of SDSS-III. This sample contains three times the number of quasars used in previous studies. The measured position of the BAO peak determines the angular distance, $D_A(z=2.34)$ and expansion rate, $H(z=2.34)$, both on a scale set by the sound horizon at the drag epoch, $r_d$. We find $D_A/r_d=11.28\pm0.65(1\sigma)^{+2.8}_{-1.2}(2\sigma)$ and $D_H/r_d=9.18\pm0.28(1\sigma)\pm0.6(2\sigma)$ where $D_H=c/H$. The optimal combination, $\sim D_H^{0.7}D_A^{0.3}/r_d$ is determined with a precision of $\sim2\%$. For the value $r_d=147.4~{\rm Mpc}$, consistent with the CMB power spectrum measured by Planck, we find $D_A(z=2.34)=1662\pm96(1\sigma)~{\rm Mpc}$ and $H(z=2.34)=222\pm7(1\sigma)~{\rm km\,s^{-1}Mpc^{-1}}$. Tests with mock catalogs and variations of our analysis procedure have revealed no systematic uncertainties comparable to our statistical errors. Our results agree with the previously reported BAO measurement at the same redshift using the quasar-Ly{\alpha} forest cross-correlation. The auto-correlation and cross-correlation approaches are complementary because of the quite different impact of redshift-space distortion on the two measurements. The combined constraints from the two correlation functions imply values of $D_A/r_d$ and $D_H/r_d$ that are, respectively, 7% low and 7% high compared to the predictions of a flat $\Lambda$CDM cosmological model with the best-fit Planck parameters. With our estimated statistical errors, the significance of this discrepancy is $\approx 2.5\sigma$.

• The paper presents a robust detection of the BAO feature in the Lyα forest using a threefold larger quasar sample, reaching over five sigma significance.
• It measures key cosmological parameters with 2% precision, reporting D_A/r_d = 11.28 ± 0.65 and D_H/r_d = 9.18 ± 0.28 at z = 2.34.
• The study validates its results through extensive tests with mock catalogs and comparisons with Planck CMB data, reinforcing the reliability of its high-redshift cosmology insights.

Baryon Acoustic Oscillations in the Lyα Forest of BOSS DR11 Quasars

The paper entitled "Baryon Acoustic Oscillations in the Lyα Forest of BOSS DR11 Quasars" presents a comprehensive analysis of baryon acoustic oscillations (BAO) within the Lyman-alpha (Lyα) forest observed in high-redshift quasars. The paper utilizes data from 137,562 quasars within the redshift range of 2.1 to 3.5, part of the Data Release 11 (DR11) of the Baryon Oscillation Spectroscopic Survey (BOSS) under the Sloan Digital Sky Survey (SDSS-III). This sample is three times larger than those employed in previous studies, enhancing the statistical significance of the BAO detection to five standard deviations.

Key Findings

1. BAO Feature Detection: The paper successfully detects the BAO feature in the flux-correlation function of the Lyα forest. This detection provides insight into both the angular diameter distance, $D_A(z=2.34)$, and the expansion rate, $H(z=2.34)$, using the sound horizon at the drag epoch, $r_d$, as a reference scale.
2. Measured Parameters: The paper reports that $D_A/r_d = 11.28 \pm 0.65$ at 1σ confidence and $D_H/r_d = 9.18 \pm 0.28$ at 1σ confidence, where $D_H = c/H$. These measurements were achieved with a precision of approximately 2% when optimally combined.
3. Comparison with Planck CMB: When adopting $r_d = 147.4 \, \text{Mpc}$, consistent with the Planck cosmic microwave background power spectrum measurements, they find $D_A(z=2.34) = 1662 \pm 96 \, \text{Mpc}$ and $$H(z=2.34) = 222 \pm 7 \, \text{km}\,\text{s}^{-1}\text{Mpc}^{-1}$$.
4. Mock Catalog Analysis: To ensure robustness, the research involved a variety of tests using mock catalogs. No systematic uncertainties equivalent to the statistical errors were identified, reinforcing the reliability of the measurements.
5. Comparison with Existing Measurements: Results align well with previously reported BAO measurements in a similar redshift range conducted through the quasar-Lyα forest cross-correlation method. The correlation between the angular and radial BAO measurements from both autocorrelation and cross-correlation approaches is noteworthy since the redshift space distortions differ in their impact on each method.
6. Statistical Significance and Discrepancy: The combined constraints from the two correlation functions suggest deviation of the measured values of $D_A/r_d$ and $D_H/r_d$ from predictions of a cosmological model based on the best-fit parameters from Planck data with a discrepancy significance around $2.5\sigma$.

Implications and Future Directions

The findings of this paper provide important data that enhances the comprehension of the universe's expansion history at high redshifts. The constraints on $D_A$ and $H$ at $z = 2.34$ furnish essential calibration for models exploring high-redshift cosmology and the constituents of the universe, such as dark energy and dark matter.

The results, indicating a notable but not overwhelming discrepancy from the Planck best-fit cosmological parameters, may prompt further exploration into the assumptions underlying the cosmological model, particularly in the curvature of the universe and the properties of dark energy.

Future work could extend these correlations to even higher precision, leveraging upcoming data releases and improvements in the understanding of systematic effects. This research paves the way for more extensive surveys and deeper analyses, enhancing our ability to precisely chart the universe's expansion and refine cosmological models.