# Dense molecular gas at 12 mm towards Galactic TeV gamma-ray sources

## TL;DR

This study investigates dense molecular gas around Galactic TeV gamma-ray sources using 12 mm observations, revealing dense gas counterparts and unusual emission features that suggest interactions influencing gamma-ray production.

## Contribution

It provides the first extensive survey of dense gas tracers near TeV sources, identifying potential hadronic origins and shock activity indicators in the gas.

## Key findings

- Dense gas detected near 38 of 49 TeV sources.
- Unusual emission features indicating shock activity.
- Dense gas counterparts found near unidentified TeV sources.

## Abstract

The High Energy Stereoscopic System (H.E.S.S.) has revealed many TeV (10 12 eV) gamma-ray sources along the Galactic Plane and around 30 percent of these sources remain unidentified. The morphology and dynamics of dense gas coincident and surrounding the gamma-ray emission can provide clues about the nature of the TeV emission. The H2O Southern Galactic Plane Survey (HOPS) undertaken with the Mopra radio telescope, includes several dense gas tracers, such as NH3 (n,n) transitions and HC3N (3-2), star formation tracers including H2O masers, and radio recombination lines which trace ionised gas. A search for dense gas, traced by NH3 (1,1) emission seen in HOPS and additional observations, towards Galactic TeV sources has been undertaken. Of the 49 Galactic TeV sources covered by 12 mm observations, NH3 (1,1) is detected towards or adjacent to 38 of them. Dense gas counterparts have been detected near several unidentified Galactic TeV sources which display morphology pointing to a hadronic origin to the TeV gamma-rays. The dense gas detected towards some TeV sources displays unusual emission characteristics, including very broad linewidths and enhanced ortho-to-para NH3 abundance ratios towards HESS J1745-303 and HESS J1801-233, which reflects previous shock activity within the gas.