A dense gas survey of the gamma-ray sources HESS J1731-347 and HESS J1729-345

TL;DR

This study uses molecular spectral line observations to map dense gas around gamma-ray sources HESS J1731-347 and HESS J1729-345, providing insights into their potential hadronic gamma-ray production mechanisms.

Contribution

It presents the first detailed survey of dense molecular gas in these regions using CS(1-0) lines, revealing gas masses and dynamics relevant to gamma-ray emission models.

Findings

Dense gas mass of ~10^5 solar masses detected overall.

Significant dense gas found near HESS J1729-345, but not near HESS J1731-347.

Results support hadronic interaction scenarios for gamma-ray production.

Abstract

The results of Mopra molecular spectral line observations towards the supernova remnant HESSJ1731-347 (G353.6-0.7) and the unidentified gamma-ray source HESSJ1729-345 are presented. Dense molecular gas in three different velocity-bands (corresponding to three Galactic arms) are investigated using the CS(1-0) line. The CS-traced component provides information about the dense target material in a hadronic scenario for gamma-ray production (cosmic rays interacting with gas) and an understanding of the dynamics. Furthermore, the effects of cosmic ray diffusion into dense gas may alter the gamma-ray spectrum to cause a flattening of spectra towards such regions. Dense molecular gas mass at a level of ~10^5 Mo was revealed in this survey, with mass of the order of ~10^3 Mo towards HESSJ1729-345 in each coincident Galactic arm, but no significant detection of dense molecular gas towards HESSJ1731-347 at the currently-preferred distance of ~5.2-6.2 kpc was discovered.