The SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Quasar
  Target Selection
  As part of the Sloan Digital Sky Survey IV the extended Baryon Oscillation
Spectroscopic Survey (eBOSS) will improve measurements of the cosmological
distance scale by applying the Baryon Acoustic Oscillation (BAO) method to
quasar samples. eBOSS will adopt two approaches to target quasars over 7500 sq.
deg. First, a "CORE" quasar sample will combine optical selection in ugriz
using a likelihood-based routine called XDQSOz, with a mid-IR-optical
color-cut. eBOSS CORE selection (to g < 22 OR r < 22) should return ~ 70
quasars per sq. deg. at redshifts 0.9 < z < 2.2 and ~7 z > 2.1 quasars per sq.
deg. Second, a selection based on variability in multi-epoch imaging from the
Palomar Transient Factory should recover an additional ~3-4 z > 2.1 quasars per
sq. deg. to g < 22.5. A linear model of how imaging systematics affect target
density recovers the angular distribution of eBOSS CORE quasars over 96.7%
(76.7%) of the SDSS North (South) Galactic Cap area. The eBOSS CORE quasar
sample should thus be sufficiently dense and homogeneous over 0.9 < z < 2.2 to
yield the first few-percent-level BAO constraint near z~1.5. eBOSS quasars at z
> 2.1 will be used to improve BAO measurements in the Lyman-alpha Forest.
Beyond its key cosmological goals, eBOSS should be the next-generation quasar
survey, comprising > 500,000 new quasars and > 500,000 uniformly selected
spectroscopically confirmed 0.9 < z < 2.2 quasars. At the conclusion of eBOSS,
the SDSS will have provided unique spectra of over 800,000 quasars.
