The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: BAO and RSD measurements from the anisotropic power spectrum of the Quasar sample between redshift 0.8 and 2.2

TL;DR

The paper analyzes the final five-year eBOSS DR16 quasar sample to extract cosmological information from large-scale clustering. Using both BAO-only and Full-Shape RSD analyses on the anisotropic power spectrum, the authors measure distance scales D_H/r_drag and D_M/r_drag, as well as the linear growth rate fσ8 at z_eff ≈ 1.48, with a consensus combining Fourier- and configuration-space results. They validate their modeling with EZmocks for covariance and observational systematics and with OuterRim mocks for BAO/RSD model testing, and they carefully quantify systematic uncertainties dominated by power-spectrum modeling and fibre collisions. The results provide high-redshift constraints compatible with a flat ΛCDM cosmology and offer important benchmarks for upcoming quasar surveys.

Abstract

We measure the clustering of quasars of the final data release (DR16) of eBOSS. The sample contains $343\,708$ quasars between redshifts $0.8\leq z\leq2.2$ over $4699\,\mathrm{deg}^2$. We calculate the Legendre multipoles (0,2,4) of the anisotropic power spectrum and perform a BAO and a Full-Shape (FS) analysis at the effective redshift $z{\rm eff}=1.480$. The errors include systematic errors that amount to 1/3 of the statistical error. The systematic errors comprise a modelling part studied using a blind N-Body mock challenge and observational effects studied with approximate mocks to account for various types of redshift smearing and fibre collisions. For the BAO analysis, we measure the transverse comoving distance $D_{\rm M}(z_{\rm eff})/r_{\rm drag}=30.60\pm{0.90}$ and the Hubble distance $D_{\rm H}(z_{\rm eff})/r_{\rm drag}=13.34\pm{0.60}$. This agrees with the configuration space analysis, and the consensus yields: $D_{\rm M}(z_{\rm eff})/r_{\rm drag}=30.69\pm{0.80}$ and $D_{\rm H}(z_{\rm eff})/r_{\rm drag}=13.26\pm{0.55}$. In the FS analysis, we fit the power spectrum using a model based on Regularised Perturbation Theory, which includes Redshift Space Distortions and the Alcock-Paczynski effect. The results are $D_{\rm M}(z_{\rm eff})/r_{\rm drag}=30.68\pm{0.90}$ and $D_{\rm H}(z_{\rm eff})/r_{\rm drag}=13.52\pm{0.51}$ and we constrain the linear growth rate of structure $f(z_{\rm eff})σ_8(z_{\rm eff})=0.476\pm{0.047}$. Our results agree with the configuration space analysis. The consensus analysis of the eBOSS quasar sample yields: $D_{\rm M}(z_{\rm eff})/r_{\rm drag}=30.21\pm{0.79}$, $D_{\rm H}(z_{\rm eff})/r_{\rm drag}=3.23\pm{0.47}$ and $f(z_{\rm eff})σ_8(z_{\rm eff})=0.462\pm{0.045}$ and is consistent with a flat $Λ{\rm CDM}$ cosmological model using Planck results.

Figures (16)

• Figure 1: Top panel: Power spectrum of the SGC data with all weights applied (solid circle) or without the photometric weight (open circle); the effect on the NGC (not shown here) is smaller. Represented are the multipoles of the power spectrum: monopole (blue), quadrupole (red), and hexadecapole (green). Lower panel: Impact of the NGC (dashed line), and SGC (dotted line) window function on the power spectrum multipoles of a baseline power spectrum (solid line, same color scheme as in the top panel)
• Figure 2: Multipoles of the power spectrum measured with the DR16 eBOSS quasar sample (dots) compared to the EZmocks (dashed line). The standard deviation of the mocks is indicated by the shaded area. The NGC and SGC are shown in the top and bottom panels, respectively. The monopole is shown in blue and the shot noise contribution is subtracted, the quadrupole in red and the hexadecapole in green.
• Figure 3: Comparison of the BAO wiggles in the power spectrum of the data and mocks. The dots represent the DR16 data, the dashed lines are the best-fit, the black line shows the mean of the NGC EZmocks. The green line shows the mean of one realisation of the OuterRim mock challenge (mock3) with realistic smearing. For the latter, the BAO feature appears shifted as a consequence of their intrinsic cosmology being different.
• Figure 4: Best-fit values of $\alpha_\parallel$ and $\alpha_\perp$ for the tests performed on DR16 quasar sample for the BAO-analysis (values are taken from Table \ref{['results:test-data-bao']}). Green points show the impact of taking into account the different weights while blue points are for consistency/robustness tests.
• Figure 5: $\chi^2$ profile of the $\alpha_{\rm iso}$ BAO parameter in Fourier and configuration space. We show the $\chi^2$ profile for the BAO model (solid curves) and the $\chi^2$ difference between a model without BAO peak and the minimum of the BAO model (dashed lines)