The clustering of the SDSS-IV extended Baryon Oscillation Spectroscopic Survey DR14 quasar sample: First measurement of Baryon Acoustic Oscillations between redshift 0.8 and 2.2

TL;DR

This paper presents the first BAO measurement from the auto-correlation of eBOSS DR14 quasars in the redshift range 0.8 < z < 2.2, yielding D_V(z=1.52) = 3843 ± 147 Mpc (in units of r_d). Using both configuration-space ξ(s) and Fourier-space P(k) analyses, the authors detect BAO at >2.8σ and achieve ~3.8% isotropic distance precision after combining estimators. They validate their approach with 1400 mock catalogs (EZmocks and QPM), show robustness to systematics and redshift treatments, and place the DR14 quasar BAO result in the context of Planck ΛCDM and the BAO distance ladder. The study demonstrates that quasars are reliable tracers of large-scale structure and that BAO measurements from quasars significantly enhance constraints on cosmic geometry, particularly when combined with other BAO data, reinforcing a flat ΛCDM cosmology and strengthening the evidence for dark energy.

Abstract

We present measurements of the Baryon Acoustic Oscillation (BAO) scale in redshift-space using the clustering of quasars. We consider a sample of 147,000 quasars from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) distributed over 2044 square degrees with redshifts $0.8 < z < 2.2$ and measure their spherically-averaged clustering in both configuration and Fourier space. Our observational dataset and the 1400 simulated realizations of the dataset allow us to detect a preference for BAO that is greater than 2.8$σ$. We determine the spherically averaged BAO distance to $z = 1.52$ to 3.8 per cent precision: $D_V(z=1.52)=3843\pm147 \left(r_{\rm d}/r_{\rm d, fid}\right)\ $Mpc. This is the first time the location of the BAO feature has been measured between redshifts 1 and 2. Our result is fully consistent with the prediction obtained by extrapolating the Planck flat $Λ$CDM best-fit cosmology. All of our results are consistent with basic large-scale structure (LSS) theory, confirming quasars to be a reliable tracer of LSS, and provide a starting point for numerous cosmological tests to be performed with eBOSS quasar samples. We combine our result with previous, independent, BAO distance measurements to construct an updated BAO distance-ladder. Using these BAO data alone and marginalizing over the length of the standard ruler, we find $Ω_Λ > 0$ at 6.6$σ$ significance when testing a $Λ$CDM model with free curvature.

Figures (15)

• Figure 1: The redshift distribution of the DR14 quasar sample, for 111,633 quasars in the NGC and 75,887 in the SGC. We use the data with $0.8 < z < 2.2$ for clustering statistics; this redshift region is marked with dotted lines. The $n(z)$ is slightly different in the NGC and SGC, due to known differences in the targeting efficiency, and we thus treat the two regions separately.
• Figure 2: The footprint of the eBOSS DR14 quasar sample. The top panel displays the portion of the footprint in the NGC and the bottom panel the SGC. The colour mapping indicates the observational completeness, C$_{\rm eBOSS}$, as defined in the text.
• Figure 3: The relationship between the number density of the DR14 quasar sample and various potential systematics before (dashed crimson curves, labeled 'raw') and after (grey squares, labeled 'corrected') weighting for limiting magnitude (depth) and Galactic extinction (E[B-V]). Weighting for limiting magnitude and E[B-V] removes correlations with other potential systematic quantities.
• Figure 4: The relationship between the number density of the DR14 quasar sample and the $i$-band 5$\sigma$ limiting magnitude ('depth') for four slices in redshift, after weights for depth and Galactic extinction have been applied. No systematic trends with redshift are apparent.
• Figure 5: Top panel: The spherically averaged redshift-space correlation function of the DR14 quasar sample, for data in the SGC (blue squares) and NGC (red diamonds). The dashed curves display the mean of the 1000 EZmock samples. The data in each region are broadly consistent with the mean of the mocks and with each other. Bottom panel: The NGC and SGC data have been combined (solid black curve) and are now compared to both the EZ and QPM mocks (points with error-bars). The agreement is excellent. The dashed grey curve displays the result for the data when not applying systematic weights; the difference is dramatic and has $\chi^2$ significance of more than 180. The covariance matrix is dominated by the low number density of the DR14 quasar sample and the correlation between data points is low, e.g., the correlation between neighboring $s$ bins is $\sim$0.2.