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

We present the large-scale clustering 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 multipoles. Purely angular photometric systematics are mitigated by nulling angular signal in pixels of appropriate size. Variations of the redshift distribution with photometric conditions are accounted for by splitting and measuring the radial selection function of the survey in regions of homogeneous imaging. Both techniques result in integral constraints which we model consistently. At the effective redshift z_eff = 0.845 we measure D_V(z_eff)/r_drag = 18.33 +0.57−0.62, with D_V the volume averaged distance and r_drag the comoving sound horizon at the drag epoch. In combination with the RSD measurement, at z_eff = 0.85 we find ƒσ₈(z_eff) = 0.289 +0.085−0.096, with ƒ the growth rate of structure and σ₈ the normalisation of the linear power spectrum, D_H(z_eff)/r_drag = 20.0 +2.4−2.2 and D_M(z_eff)/r_drag = 19.17 ±0.99 with D_H and D_M the Hubble and comoving angular distances, respectively. Quoted errors include statistical and systematic contributions. We find good agreement with the results obtained in configuration space, thus allowing a consensus measurement of ƒσ₈(z_eff) = 0.315 ±0.095, D_H(z_eff)/r_drag = 19.6 +2.2−2.1 and D_M(z_eff)/r_drag = 19.5 ±1.0. This measurement is in agreement with a flat ΛCDM model with Planck parameters.