A Study of the Interstellar Medium Towards the Unidentified Dark TeV γ-Ray Sources HESS J1614-518 and HESS J1616-508

HESS J1614-518 and HESS J1616-508 are two tera-electron volt γ-ray sources that are not firmly associated with any known counterparts at other wavelengths. We investigate the distribution of interstellar medium towards the tera-electron volt γ-ray sources using results from a 7-mm-wavelength Mopra study, the Mopra Southern Galactic Plane CO Survey, the Millimetre Astronomer's Legacy Team-45 GHz survey and [C i] data from the HEAT telescope. Data in the CO(1-0) transition lines reveal diffuse gas overlapping the two tera-electron volt sources at several velocities along the line of sight, while observations in the CS(1-0) transition line reveal several interesting dense gas features. To account for the diffuse atomic gas, archival H i data was taken from the Southern Galactic Plane Survey. The observations reveal gas components with masses 10³ to 10⁵ M_⊙ and with densities 10² to 10³ cm^-3 overlapping the two tera-electron volt sources. Several origin scenarios potentially associated with the tera-electron volt γ-ray sources are discussed in light of the distribution of the local interstellar medium. We find no strong convincing evidence linking any counterpart with HESS J1614-518 or HESS J1616-508.