Sub-mm/mm studies of the molecular gas in the Galactic disk; the TeV gamma ray SNR RXJ1713.7-3946 and the W28 high mass star forming region

TL;DR

This study uses sub-mm/mm observations to explore the molecular gas in the Galactic disk, focusing on the gamma-ray emitting SNR RXJ1713.7-3946 and the W28 star forming region, revealing interactions that influence cosmic ray acceleration and gamma-ray production.

Contribution

It provides new high-resolution molecular gas data linking gas structures with gamma-ray sources, highlighting the role of molecular clouds in cosmic ray acceleration and gamma-ray emission.

Findings

Molecular gas correlates with gamma-ray emission in RXJ1713.7-3946.

A dense molecular core is associated with hard gamma rays and X-ray emission.

High excitation conditions are observed in the W28 star forming core.

Abstract

Interstellar molecular clouds are gamma ray sources through the interactions with cosmic ray protons followed by production of neutral pions which decay into gamma rays. We present new NANTEN2 observations of the TeV gamma ray SNR RXJ1713.7-3946 and the W28 region in the 12CO J=2-1, 4-3 and 7-6 emission lines. In RXJ1713.7-3946 we confirm that the local molecular gas having velocities around -10 km/s shows remarkably good spatial correlations with the SNR. We show that the X ray peaks are well correlated with the molecular gas over the whole SNR and suggest that the interactions between the SNR and the molecular gas play an important role in cosmic ray acceleration via several ways including magnetic field compression. The CO J=4-3 distribution towards peak C shows a compact and dense cloud core having a size of about 1 pc as well as a broad wing. The core shows a notable anti-correlation with the Suzaku X ray image and is also associated with hard gamma rays as observed with HESS. Based on these findings, we present a picture that peak C is a molecular clump survived against the impact of the SN blast waves and is surrounded by high energy electrons emitting the X ray. The TeV gamma ray distribution is, on the other hand, more extended into the molecular gas, supporting the hadronic origin of gamma ray production. W28 is one of the most outstanding star forming regions exhibiting TeV gamma rays as identified through a comparison between the NANTEN CO dataset and HESS gamma ray sources. In the W28 region, we show the CO J=2-1 distribution over the whole region as well as the detailed image of the two TeV gamma ray peaks. One of them show strong CO J=7-6 emission, suggesting high excitation conditions in this high mass star forming core. A pursuit for the detailed mechanism to produce gamma rays is in progress.