  We investigate spectroscopic properties of galaxy systems identified based on
deep X-ray observations in the COSMOS field. The COSMOS X-ray system catalog we
use George et al. (2011) includes 180 X-ray systems to a limiting flux of $1.0
\times 10^{-15}$ erg cm$^{-2}$ s$^{-1}$, an order of magnitude deeper than
future e-ROSITA survey. We identify spectroscopic members of these X-ray
systems based on the spectroscopic catalog constructed by compiling various
spectroscopic surveys including 277 new measurements; 137 X-ray systems are
spectroscopically identified groups with more than three spectroscopic members.
We identify 1843 spectroscopic redshifts of member candidates in these X-ray
systems. The X-ray luminosity ($L_{X}$) - velocity dispersion ($\sigma_{v}$)
scaling relation of the COSMOS X-ray systems is consistent with that of massive
X-ray clusters. One of the distinctive features of the COSMOS survey is that it
covers the X-ray luminosity range where poor groups overlap the range for
extended emission associated with individual quiescent galaxies. We assess the
challenges posed by the complex morphology of the distribution of low X-ray
luminosity systems, including groups and individual quiescent galaxies, in the
$L_{x} - \sigma_{v}$ plane.
