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

TL;DR

This study investigates the interstellar medium around two unidentified TeV gamma-ray sources using multi-wavelength data, revealing overlapping gas components but no definitive counterparts, thus informing potential origin scenarios.

Contribution

It provides a detailed analysis of the interstellar medium near HESS J1614-518 and HESS J1616-508 using new and archival data, offering insights into their possible origins.

Findings

Diffuse and dense gas components overlap the sources.

No strong evidence linking known counterparts to the gamma-ray sources.

Gas masses range from 10^3 to 10^5 solar masses.

Abstract

HESS J1614$-$518 and HESS J1616$-$508 are two tera-electron volt (TeV) $\gamma$-ray sources that are not firmly associated with any known counterparts at other wavelengths. We investigate the distribution of interstellar medium towards the TeV $\gamma$-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 [CI] data from the HEAT telescope. Data in the CO(1$-$0) transition lines reveal diffuse gas overlapping the two TeV sources at several velocities along the line of sight, while observations in the CS(1$-$0) transition line reveal several interesting dense gas features. To account for the diffuse atomic gas, archival HI data was taken from the Southern Galactic Plane Survey. The observations reveal gas components with masses $\sim10^3$ to $10^5$ M$_\odot$ and with densities $\sim10^2$ to $10^3$ cm$^{-3}$ overlapping the two TeV sources. Several origin scenarios potentially associated with the TeV $\gamma$-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.