The SDSS-IV eBOSS spectrograph has undertaken a survey of quasars in the almost unexplored redshift range 0.8 < z < 2.2 since fall 2014. One of its main goals is to track the BAO signature in the matter distribution, which has been seen in lower redshift galaxies but not yet in quasar samples. It also measures the growth rate of structure using RSD, which has been proved to provide a direct test of general relativity. Such a clustering analysis is essential to study the mysterious late-time acceleration of the expansion of the universe, which could be due to an exotic fluid called dark energy or which could come from a breakdown of general relativity on cosmological scales or something else. Thus, clustering analysis has received much attention from multi-object spectrographs in the last decade at low redshifts. At larger redshift (z > 1), there is a strong interest to use quasars that are among the brightest sources in the universe to trace the matter density field and probe an epoch when the universe was not yet dominated by its late-time cosmic acceleration.
In this talk, I will present the clustering analysis we performed on the 2-year data taking eBOSS DR14 quasar sample (https://arxiv.org/abs/1705.06373,https://arxiv.org/abs/1801.03062). I will first explain the BAO and RSD effects that appear in the matter distribution and that we use to extract the cosmological parameters, then I will summarize the study of potential systematics we validated using mock catalogs and eventually I will describe the cosmological results we get with this new sample.
This study is a first use of eBOSS quasars as tracers of the matter field and will be included in the analysis of the final eBOSS sample at the end of 2019 with an expected improvement on the statistical precision of a factor 2. Together with BOSS, eBOSS will pave the way for future programs such as the ground-based DESI experiment and the space-based mission Euclid. Both programs will extensively probe the intermediate redshift range 1 < z < 2 with millions of spectra, improving the cosmological constraints by an order of magnitude with respect to current measurements.