The completed SDSSIV extended baryon oscillation spectroscopic survey: pairwiseinverse probability and angular correction for fibre collisions in clustering measurements
Abstract
The completed extended Baryon Oscillation Spectroscopic Survey (eBOSS) catalogues contain redshifts of 344 080 quasars at 0.8 < z < 2.2, 174 816 luminous red galaxies between 0.6 < z < 1.0, and 173 736 emissionline galaxies over 0.6 < z < 1.1 in order to constrain the expansion history of the Universe and the growth rate of structure through clustering measurements. Mechanical limitations of the fibrefed spectrograph on the Sloan telescope prevent two fibres being placed closer than 62 arcsec in a single pass of the instrument. These 'fibre collisions' strongly correlate with the intrinsic clustering of targets and can bias measurements of the twopoint correlation function resulting in a systematic error on the inferred values of the cosmological parameters. We combine the new techniques of pairwiseinverse probability and the angular upweighting (PIP+ANG) to correct the clustering measurements for the effect of fibre collisions. Using mock catalogues, we show that our corrections provide unbiased measurements, within data precision, of both the projected $\rm {\mathit{ w}_p}\left(\mathit{ r}_p\right)$ and the redshiftspace multipole ξ^{(ℓ = 0, 2, 4)}(s) correlation functions down to $0.1\, h^{1}{\rm Mpc}$ , regardless of the tracer type. We apply the corrections to the eBOSS DR16 catalogues. We find that, on scales $s\gtrsim 20\, h^{1}{\rm Mpc}$ for ξ^{ℓ}, as used to make baryon acoustic oscillation and largescale redshiftspace distortion measurements, approximate methods such as nearestneighbour upweighting are sufficiently accurate given the statistical errors of the data. Using the PIP method, for the first time for a spectroscopic program of the Sloan Digital Sky Survey, we are able to successfully access the onehalo term in the clustering measurements down to $\sim 0.1\, h^{1}{\rm Mpc}$ scales. Our results will therefore allow studies that use the smallscale clustering to strengthen the constraints on both cosmological parameters and the halo occupation distribution models.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 October 2020
 DOI:
 10.1093/mnras/staa2344
 arXiv:
 arXiv:2007.09005
 Bibcode:
 2020MNRAS.498..128M
 Keywords:

 galaxies: distances and redshifts;
 largescale structure of Universe;
 cosmology: observations;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 Submitted to MNRAS. 17 Pages, 20 Figures. A description of eBOSS and links to all associated publications can be found here: https://www.sdss.org/surveys/eboss/