SDSS-IV eBOSS Spectroscopy of X-ray and WISE AGN in Stripe 82X: Overview
  of the Demographics of X-ray and Mid-Infrared Selected Active Galactic Nuclei
  We report the results of a Sloan Digital Sky Survey-IV eBOSS program to
target X-ray sources and mid-infrared-selected WISE AGN candidates in a 36.8
deg$^2$ region of Stripe 82. About half this survey (15.6 deg$^2$) covers the
largest contiguous portion of the Stripe 82 X-ray survey. This program
represents the largest spectroscopic survey of AGN candidates selected solely
by their WISE colors. We combine this sample with X-ray and WISE AGN in the
field identified via other sources of spectroscopy, producing a catalog of 4847
sources that is 82% complete to $r\sim22$. Based on X-ray luminosities or WISE
colors, 4730 of these sources are AGN, with a median sample redshift of
$z\sim1$. About 30% of the AGN are optically obscured (i.e., lack broad lines
in their optical spectra). BPT analysis, however, indicates that 50% of the
WISE AGN at $z<0.5$ have emission line ratios consistent with star-forming
galaxies, so whether they are buried AGN or star-forming galaxy contaminants is
currently unclear. We find that 61% of X-ray AGN are not selected as MIR AGN,
with 22% of X-ray AGN undetected by WISE. Most of these latter AGN have high
X-ray luminosities ($L_{\rm x} > 10^{44}$ erg s$^{-1}$), indicating that MIR
selection misses a sizable fraction of the highest luminosity AGN, as well as
lower luminosity sources where AGN heated dust is not dominating the MIR
emission. Conversely, $\sim$58% of WISE AGN are undetected by X-rays, though we
do not find that they are preferentially redder than the X-ray detected WISE
AGN.
