The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: BAO and RSD measurements from anisotropic clustering analysis of the Quasar Sample in configuration space between redshift 0.8 and 2.2 (2007.08998v2)

Abstract: We measure the anisotropic clustering of the quasar sample from Data Release 16 (DR16) of the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey (eBOSS). A sample of $343,708$ spectroscopically confirmed quasars between redshift $0.8<z<2.2$ are used as tracers of the underlying dark matter field. In comparison with DR14 sample, the final sample doubles the number of objects as well as the survey area. In this paper, we present the analysis in configuration space by measuring the two-point correlation function and decompose using the Legendre polynomials. For the full-shape analysis of the Legendre multipole moments, we measure the BAO distance and the growth rate of the cosmic structure. At an effective redshift of $z_{\rm eff}=1.48$, we measure the comoving angular diameter distance $D_{\rm M}(z_{\rm eff})/r_{\rm drag} = 30.66\pm0.88$, the Hubble distance $D_{\rm H}(z_{\rm eff})/r_{\rm drag} = 13.11\pm0.52$, and the growth rate $f\sigma_8(z_{\rm eff}) = 0.439\pm0.048$. The accuracy of these measurements is confirmed using an extensive set of mock simulations developed for the quasar sample. The uncertainties on the distance and growth rate measurements have been reduced substantially ($\sim 45\%$ and $\sim30\%$) with respect to the DR14 results. We also perform a BAO-only analysis to cross check the robustness of the methodology of the full-shape analysis. Combining our analysis with the Fourier space analysis, we arrive at $D^{\bf{c}}_{\rm M}(z_{\rm eff})/r_{\rm drag} = 30.22 \pm 0.79$, $D^{\bf{c}}_{\rm H}(z_{\rm eff})/r_{\rm drag} = 13.26 \pm 0.47$, and $f\sigma_8^{\bf{c}}(z_{\rm eff}) = 0.464 \pm 0.045$.

• The paper measures BAO and RSD in a quasar sample at z=1.48 using the two-point correlation function and Legendre polynomial decomposition.
• It improves cosmic distance and growth rate accuracy by approximately 45% and 30% over DR14 through extensive mock simulations.
• The results support ΛCDM predictions while revealing a 2σ tension in growth rates, indicating potential avenues for alternative cosmological models.

Overview of the Completed SDSS-IV eBOSS DR16 Quasar Analysis

This paper provides a comprehensive analysis of the clustering measurements from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS) Data Release 16 (DR16) conducted as part of the Sloan Digital Sky Survey IV (SDSS-IV). The paper focuses on the anisotropic clustering of quasars in the redshift range of 0.8 to 2.2, using a sample of 343,708 spectroscopically confirmed quasars. This work represents the final release of eBOSS data, doubling both the quantity of objects and the survey area compared to the DR14 sample.

Methodology and Analysis

The analysis is performed in configuration space by measuring the two-point correlation function and employing Legendre polynomials for decomposition. This approach allows for the extraction of both the Baryon Acoustic Oscillation (BAO) signature and Redshift Space Distortion (RSD) measurements.

• BAO and RSD Measurements: At an effective redshift of 1.48, the paper reports a comoving angular diameter distance of $D_{\rm M}(z_{\rm eff})/r_{\rm drag} = 30.66\pm0.88$, a Hubble distance $D_{\rm H}(z_{\rm eff})/r_{\rm drag} = 13.11\pm0.52$, and a growth rate of the cosmic structure given by $f\sigma_8(z_{\rm eff}) = 0.439\pm0.048$.
• Accuracy and Systematic Tests: The robustness of these measurements is confirmed using extensive mock simulations. The paper emphasizes a significant improvement in the accuracy of distance and growth rate measurements, with reductions in uncertainties of approximately 45% and 30% respectively, compared to previous results from DR14.
• BAO-only Analysis: The paper also performs a BAO-only analysis to verify the robustness of the full-shape analysis methodology. When combined with a Fourier space analysis, parameters converge to $D^{\bf{c}_{\rm M}(z_{\rm eff})/r_{\rm drag} = 30.21 \pm 0.79$, $D^{\bf{c}_{\rm H}(z_{\rm eff})/r_{\rm drag} = 13.23 \pm 0.47$, and $f\sigma_8^{\bf{c}(z_{\rm eff}) = 0.462 \pm 0.045$.

Implications

This research offers vital implications for cosmological models, particularly concerning the ΛCDM model predicted by Planck CMB measurements. The paper's results are largely consistent with this model, though a noted 2σ discrepancy in the growth rate $f\sigma_8$ suggests possible areas for further investigation. This provides avenues for testing alternative gravitational models and dark energy constructs.

Future Directions

The results from DR16 enrich our understanding and offer tighter constraints on cosmological parameters. They pave the way for next-generation surveys with higher precision demands. Future surveys may continue to exploit techniques for configuration and Fourier space analysis collaboratively for optimal parameter constraints. The findings also underscore the significance of addressing systematic errors comprehensively, an area where future efforts can build upon this paper's robust methodological framework.

In conclusion, the paper effectively advances the understanding of the universe's expansion and large-scale structure, illustrating the eBOSS program's importance in cosmological research. The methodologies applied and the results achieved provide a benchmark for ongoing and future astronomical surveys.