Estimating Galactic gas content using different tracers: Compatibility
  of results, dark gas, and unidentified TeV sources
  A large fraction of Galactic very-high energy (VHE; E$\gtrsim$100 GeV)
$\gamma$-ray sources is cataloged as unidentified. In this work we explore the
possibility that these unidentified sources are located in ambients
particularly rich in material content unaccounted by traditional tracers. In a
scenario where the VHE emission is due to the interaction of the accelerated
particles with a target mass, a large mass of untraced material could be
substantially contributing to the VHE emission from these regions. Here, we use
three tracers for the commonly explored components: intensity of the
$^\textrm{12}$CO(1$\rightarrow$0) line to trace the molecular material, HI
hyperfine transition at 21cm to trace atomic hydrogen, and dust emission to
trace the total hydrogen content. We show that the estimates of material
content from these three tracers are compatible if the uncertainty on the
respective conversion factors is taken into account. No additional gas
component is found in these regions. However, a simple mass estimation from the
$^\textrm{12}$CO(1$\rightarrow$0) line intensity might underestimate the total
mass component in some locations.
