The completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Large-scale Structure Catalogues and Measurement of the isotropic BAO between redshift 0.6 and 1.1 for the Emission Line Galaxy Sample

TL;DR

This work delivers the final DR16 eBOSS emission-line galaxy sample and constructs large-scale structure catalogues to measure the isotropic BAO signal in the 0.6<z<1.1 range. Using redrock for reliable redshifts, extensive angular vetoes, and a comprehensive weighting scheme to correct systematics, the authors validate their catalogues with OuterRim and EZmock mocks and apply reconstruction to sharpen the BAO feature. They report a 3.2% precision measurement of D_V(z_eff)/r_drag = 18.23 ± 0.58 at z_eff = 0.845, with results broadly consistent with Fourier-space analyses, underscoring the robustness of ELG-based BAO measurements. The publicly released LSS catalogues and the extensive mock challenges provide valuable tools for current and future ELG clustering analyses in next-generation surveys like DESI, 4MOST, and Euclid.

Abstract

We present the Emission Line Galaxy (ELG) sample of the extended Baryon Oscillation Spectroscopic Survey (eBOSS) from the Sloan Digital Sky Survey IV Data Release 16 (DR16). After describing the observations and redshift measurement for the 269,243 observed ELG spectra over 1170 deg$^2$, we present the large-scale structure catalogues, which are used for the cosmological analysis. These catalogues contain 173,736 reliable spectroscopic redshifts between 0.6 and 1.1, along with the associated random catalogues quantifying the extent of observations, and the appropriate weights to correct for non-cosmological fluctuations. We perform a spherically averaged baryon acoustic oscillations (BAO) measurement in configuration space, with density field reconstruction: the data 2-point correlation function shows a feature consistent with that of the BAO, providing a 3.2-percent measurement of the spherically averaged BAO distance $D_V(z_{\rm eff})/r_{\rm drag} = 18.23\pm 0.58$ at the effective redshift $z_{\rm eff}=0.845$.

Figures (15)

• Figure 1: Geometry of the ELG program. The NGC tiling is presented in the top panel: chunk eboss23 is at lower Dec. and chunk eboss25 at higher Dec. The SGC tiling is presented in the bottom panel: chunk eboss21 is at R.A.<0$^\circ$. and chunk eboss22 at R.A.>0$^\circ$. The colour-coding is the tiling completeness (COMP_BOSS), which represents the fraction of resolved fibres per sector (see Section \ref{['sec:cp']}). Additionally, we overlay some a posteriori angular veto masks, which are detailed in Section \ref{['sec:vetomask']}: Mira star (light gray), DECam pointings with bad photometric calibration (dark gray), and two low-quality spectroscopic plates (black). The regions without targets at R.A$\sim$130$^\circ$ and Dec.$\sim$20$^\circ$ corresponds to the open cluster NGC 2632.
• Figure 2: Illustration of the DECaLS-related, bright objects and stars masks for a given DECaLS brick ($0.25^\circ \times 0.25^\circ$, $3600 \times 3600$ pixels, with 0.262 arcsec/pixel). The xybug mask is the symmetric along the brick diagonal of the not g+r+z mask. The decam_anymask mask mostly follows the CCD edges along R.A. (horizontal in the figure).
• Figure 3: Fraction of reliable $z_{\rm spec}$ (SSR) per plate, as a function of the plate SN: each dot represent a PLATE-MJD reduction. For the NGC/SGC, the SSR before weighting by $1/f_{\text{noz,pSN}}$ is displayed in green/magenta dots and the SSR after weighting by $1/f_{\text{noz,pSN}}$ is displayed in blue/red triangles. The model is fitted to each half-spectrograph for each chunk.
• Figure 4: Fraction of reliable $z_{\rm spec}$ (SSR) as a function of XFOCAL and YFOCAL for the NGC, before (top panels) and after (bottom panels) weighting by $1/f_{\text{noz,XYFOCAL}}$. The top- and right-side panels show the SSR as a function of XFOCAL and YFOCAL; the top-right histograms display the distribution of the normalised SSR. The model is fitted to each half-spectrograph for each chunk.
• Figure 5: Same as Figure \ref{['fig:xyfoc_ngc']}, but for the SGC.