A study of the interstellar medium towards the unidentified dark TeV $\gamma$-ray sources HESS J1614-518 and HESS J1616-508

摘要

HESS J1614$-$518 and HESS J1616$-$508 are two tera-electron volt (TeV)$\gamma$-ray sources that are not firmly associated with any known counterpartsat other wavelengths. We investigate the distribution of interstellar mediumtowards the TeV $\gamma$-ray sources using results from a 7 mm-wavelength Moprastudy, the Mopra Southern Galactic Plane CO Survey, the Millimetre Astronomer'sLegacy Team - 45 GHz survey and [CI] data from the HEAT telescope. Data in theCO(1$-$0) transition lines reveal diffuse gas overlapping the two TeV sourcesat several velocities along the line of sight, while observations in theCS(1$-$0) transition line reveal several interesting dense gas features. Toaccount for the diffuse atomic gas, archival HI data was taken from theSouthern Galactic Plane Survey. The observations reveal gas components withmasses $\sim10^3$ to $10^5$ M$_\odot$ and with densities $\sim10^2$ to $10^3$cm$^{-3}$ overlapping the two TeV sources. Several origin scenarios potentiallyassociated with the TeV $\gamma$-ray sources are discussed in light of thedistribution of the local interstellar medium. We find no strong convincingevidence linking any counterpart with HESS J1614$-$518 or HESS J1616$-$508.