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The Extended Baryon Oscillation Spectroscopic Survey (eBOSS) will conductnovel cosmological observations using the BOSS spectrograph at Apache PointObservatory. Observations will be simultaneous with the Time DomainSpectroscopic Survey (TDSS) designed for variability studies and theSpectroscopic Identification of eROSITA Sources (SPIDERS) program designed forstudies of X-ray sources. eBOSS will use four different tracers to measure thedistance-redshift relation with baryon acoustic oscillations (BAO). Using morethan 250,000 new, spectroscopically confirmed luminous red galaxies at a medianredshift z=0.72, we project that eBOSS will yield measurements of $d_A(z)$ toan accuracy of 1.2% and measurements of H(z) to 2.1% when combined with thez>0.6 sample of BOSS galaxies. With ~195,000 new emission line galaxyredshifts, we expect BAO measurements of $d_A(z)$ to an accuracy of 3.1% andH(z) to 4.7% at an effective redshift of z= 0.87. A sample of more than 500,000spectroscopically-confirmed quasars will provide the first BAO distancemeasurements over the redshift range 0.9<z<2.2, with expected precision of 2.8%and 4.2% on $d_A(z)$ and H(z), respectively. Finally, with 60,000 new quasarsand re-observation of 60,000 quasars known from BOSS, we will obtain newLyman-alpha forest measurements at redshifts z>2.1; these new data will enhancethe precision of $d_A(z)$ and H(z) by a factor of 1.44 relative to BOSS.Furthermore, eBOSS will provide improved tests of General Relativity oncosmological scales through redshift-space distortion measurements, improvedtests for non-Gaussianity in the primordial density field, and new constraintson the summed mass of all neutrino species. Here, we provide an overview of thecosmological goals, spectroscopic target sample, demonstration of spectralquality from early data, and projected cosmological constraints from eBOSS.

The SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Overview and Early Data