The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Growth rate of structure measurement from anisotropic clustering analysis in configuration space between redshift 0.6 and 1.1 for the Emission Line Galaxy sample

TL;DR

The study analyzes anisotropic clustering of SDSS-IV eBOSS DR16 Emission Line Galaxies in configuration space (0.6 < z < 1.1) to measure the growth rate f(z) through RSD and BAO signals. It develops a CLPT-GS-based RSD model and a modified 2PCF estimator to suppress unknown angular systematics, validating the approach with EZmocks and N-body mocks. The joint RSD+BAO analysis at z_eff ≈ 0.85 yields fσ8 ≈ 0.35 ± 0.10, with DH/r_drag ≈ 19.1 and DM/r_drag ≈ 19.9, consistent with ΛCDM Planck predictions; a Fourier-space consensus tightens these constraints. The work demonstrates robust configuration-space techniques and systematic-error mitigation essential for future ELG-dominated surveys like DESI, Euclid, PFS, and WFIRST.

Abstract

We present the anisotropic clustering of emission line galaxies (ELGs) from the Sloan Digital Sky Survey IV (SDSS-IV) extended Baryon Oscillation Spectroscopic Survey (eBOSS) Data Release 16 (DR16). Our sample is composed of 173,736 ELGs covering an area of 1170 deg$^2$ over the redshift range $0.6 \leq z \leq 1.1$. We use the Convolution Lagrangian Perturbation Theory in addition to the Gaussian Streaming Redshift-Space Distortions to model the Legendre multipoles of the anisotropic correlation function. We show that the eBOSS ELG correlation function measurement is affected by the contribution of a radial integral constraint that needs to be modelled to avoid biased results. To mitigate the effect from unknown angular systematics, we adopt a modified correlation function estimator that cancels out the angular modes from the clustering. At the effective redshift, $z_{\rm eff}=0.85$, including statistical and systematical uncertainties, we measure the linear growth rate of structure $fσ_8(z_{\rm eff}) = 0.35\pm0.10$, the Hubble distance $D_H(z_{\rm eff})/r_{\rm drag} = 19.1^{+1.9}_{-2.1}$ and the comoving angular diameter distance $D_M(z_{\rm eff})/r_{\rm drag} = 19.9\pm1.0$. These results are in agreement with the Fourier space analysis, leading to consensus values of: $fσ_8(z_{\rm eff}) = 0.315\pm0.095$, $D_H(z_{\rm eff})/r_{\rm drag} = 19.6^{+2.2}_{-2.1}$ and $D_M(z_{\rm eff})/r_{\rm drag} = 19.5\pm1.0$, consistent with $Λ$CDM model predictions with Planck parameters.

Figures (11)

• Figure 1: Redshift density of the eBOSS ELG sample per Galactic cap and for the combined sample.
• Figure 2: Two-dimensional correlation function in the directions perpendicular and parallel to the line-of-sight. Panels from left to right are for: standard 2PCF (Equation \ref{['eq:LS']}), shuffled 2PCF (Equation \ref{['eq:shuffle2PCF']}), modified 2PCF with no cut (Equation \ref{['eq:mod2pcf']}) and modified 2PCF with a cut (Equation \ref{['eq:mod2pcffinal']}). The top row displays the measurement from the eBOSS ELG data sample, the middle row displays the mean of the 1000 'shuffled-z' EZmocks with systematics (100 mocks for the shuffled 2PCF), and the bottom row shows the difference between the mean of the 1000 'shuffled-z' EZmocks with and without systematics (100 mocks for the shuffled 2PCF). For the modified 2PCF, all parameters are taken at their fiducial values (see text). The black circles illustrate our fiducial fitting range in $s$ for the multipoles.
• Figure 3: Multipoles of the standard 2PCF as measured from the eBOSS ELG data sample in each cap and from the mean of the shuffled-z EZmocks with and without systematics. The bands represent the one sigma dispersion around the mean of the mocks. Errors on data points come from one sigma dispersion of mocks with systematics. Vertical dashed lines define the baseline fitting range.
• Figure 4: Multipoles of the modified 2PCF as measured from the eBOSS ELG data sample in each cap and from the mean of the shuffled-z EZmocks with and without systematics. The bands represent the one sigma dispersion around the mean of the mocks. We note that EZmocks with and without systematics mostly overlap, as a result of angular systematics being removed by the modified 2PCF. Errors on data points come from one sigma dispersion of mocks with systematics. Vertical dashed lines define the baseline fitting range.
• Figure 5: The complete RSD+BAO correlation matrices from 1000 EZmocks computed in 8$\, h^{-1}$Mpc bins from 0 to 200$\, h^{-1}\mathrm{Mpc}$ for the combined NGC+SGC sample, using the standard (top) and modified (bottom) RSD 2PCF. The latter is computed with $s_{\rm min}^{\rm cut}=32\, h^{-1}\mathrm{Mpc}$, $z_{\rm mod}=0.83$, $s_{\parallel}^{\rm max}=190$$\, h^{-1}$Mpc as in the baseline analysis. The post-reconstruction monopole for BAO is always computed from the standard 2PCF. On both axes we show the fiducial range of the RSD analysis, from 36 to 156$\, h^{-1}$Mpc in central bin values.