Examinations of CO completeness based on three independent CO surveys
  We report the global properties recovered by an ongoing CO survey of the
Milky Way Imaging Scroll Painting (MWISP) toward the Galactic outskirts. %To
better understand the observational biases, Our results are also compared to
those extracted by a uniform decomposition method from the CfA 1.2 m CO survey
and the FCRAO 14 m outer Galaxy survey (OGS). We find that more extended and
unseen structures are present in the MWISP data. The total flux across the disk
recovered by the MWISP survey is 1.6 times larger than those recovered by the
CfA and OGS surveys in the case of the same resolution. The discrepancies are
scaling with distance. For example, in the outermost OSC arm, the flux ratios
for MWISP-to-CfA and MWISP-to-OGS increase up to 43.8 and 7.4, respectively.
Nonetheless, the census of molecular gas in our Galaxy is still far from
complete by the MWISP, with flux completeness of $<$58%. The total mass ratios
of the tabulated molecular clouds between different surveys are similar to the
CO flux ratio. The application of these ratios to the total H$_{\rm 2}$ mass of
our Galaxy yields a correction factor of at least 1.4, meaning that the H$_{\rm
2}$ mass of our Galaxy should be at least 40% more massive than previously
determined. Including the completeness correction, an even more significant
fraction of the matter should be contributed by baryonic matter. The mass
spectrum in the outer Galactic plane is better described by a non-truncating
power-law with $\gamma$=$-$1.83$\pm$0.05, and an upper mass of
$M_0$=(1.3$\pm$0.5)$\times$10$^{\rm 6}$ $M_\odot$.
