The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: measurement of the BAO and growth rate of structure of the emission line galaxy sample from the anisotropic power spectrum between redshift 0.6 and 1.1

TL;DR

The paper analyzes large-scale clustering of the SDSS-IV eBOSS DR16 emission line galaxy sample in Fourier space to jointly constrain the BAO-based distance scale and the growth rate via redshift-space distortions. It deploys a sophisticated RSD model (TNS with RegPT two-loop corrections) alongside an isotropic BAO template, carefully accounting for irregular survey geometry, window functions, and radial/angular integral constraints. Validation against extensive mock catalogs (MultiDark, OuterRim, EZ, GLAM-QPM) quantifies systematic uncertainties, enabling a consensus measurement when combined with configuration-space results. The final constraints are consistent with Planck flat ΛCDM, demonstrating the viability of ELGs as tracers for both cosmic expansion and structure growth in upcoming surveys.

Abstract

We analyse the large-scale clustering in Fourier space of emission line galaxies (ELG) from the Data Release 16 of the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey. The ELG sample contains 173,736 galaxies covering 1,170 square degrees in the redshift range $0.6 < z < 1.1$. We perform a BAO measurement from the post-reconstruction power spectrum monopole, and study redshift space distortions (RSD) in the first three even multipoles. Photometric variations yield fluctuations of both the angular and radial survey selection functions. Those are directly inferred from data, imposing integral constraints which we model consistently. The full data set has only a weak preference for a BAO feature ($1.4σ$). At the effective redshift $z_{\rm eff} = 0.845$ we measure $D_{\rm V}(z_{\rm eff})/r_{\rm drag} = 18.33_{-0.62}^{+0.57}$, with $D_{\rm V}$ the volume-averaged distance and $r_{\rm drag}$ the comoving sound horizon at the drag epoch. In combination with the RSD measurement, at $z_{\rm eff} = 0.85$ we find $fσ_8(z_{\rm eff}) = 0.289_{-0.096}^{+0.085}$, with $f$ the growth rate of structure and $σ_8$ the normalisation of the linear power spectrum, $D_{\rm H}(z_{\rm eff})/r_{\rm drag} = 20.0_{-2.2}^{+2.4}$ and $D_{\rm M}(z_{\rm eff})/r_{\rm drag} = 19.17 \pm 0.99$ with $D_{\rm H}$ and $D_{\rm M}$ the Hubble and comoving angular distances, respectively. These results are in agreement with those obtained in configuration space, thus allowing a consensus measurement of $fσ_8(z_{\rm eff}) = 0.315 \pm 0.095$, $D_{\rm H}(z_{\rm eff})/r_{\rm drag} = 19.6_{-2.1}^{+2.2}$ and $D_{\rm M}(z_{\rm eff})/r_{\rm drag} = 19.5 \pm 1.0$. This measurement is consistent with a flat $Λ$CDM model with Planck parameters.

Figures (17)

• Figure 1: Window function multipoles (top: NGC, bottom: SGC) of the EZ mocks (reproducing the eBOSS ELG sample), before (dashed lines) and after (continuous lines) application of the veto masks. Contrary to previous clustering analyses imposing window functions to converge to $1$ on small scales, we properly normalise these window functions by the same term as the power spectrum estimation. The height difference between the window function monopoles is explained by the area covered by veto masks (see text).
• Figure 2: Power spectrum multipoles (top: NGC, bottom: SGC; blue: monopole, red: quadrupole, green: hexadecapole) of the RSD model. The window function effect only is taken into account in continuous lines, and the additional impact of the global and radial integral constraints (IC) are shown in dashed and dotted lines, respectively. For this figure we choose $f=0.8$, $b_{1}=1.4$, $b_{2}=1$, $\sigma_{v}=4 \, \mathrm{Mpc}/h$.
• Figure 3: Ratio of the RSD best fits to the OuterRim-based mocks (of type 1, 4, 5, 6 with SHOD and HMQ HODs, using three line-of-sight axes --- $x$, $y$, $z$) to their expected values, using different template cosmologies. The gray shaded area represents an error of $3\%$ on $f\sigma_{8}$ and $1\%$ on the scaling parameters on either side of the reference values in the OuterRim cosmology.
• Figure 4: Ratio of the isotropic BAO best fits to the OuterRim-based mocks (of type 1, 4, 5, 6 with SHOD and HMQ HODs, using three line-of-sight axes --- $x$, $y$, $z$) to their expected values, using different template cosmologies. The gray shaded area represents an error of $0.5\%$ on $\alpha$ on either side of the reference value in the OuterRim cosmology.
• Figure 5: eBOSS ELG footprint. Top left: comoving redshift density. Top right: tiling completeness in NGC. Bottom: tiling completeness in SGC.