The molecular clump towards the eastern border of SNR G18.8+0.3

TL;DR

This study investigates the molecular environment near SNR G18.8+0.3, revealing a dense molecular clump associated with an HII region complex, and finds no direct contact between the SNR shock front and this clump, suggesting different distances.

Contribution

The paper provides new molecular line observations and archival data analysis that clarify the nature of the region and the relationship between the SNR and surrounding molecular structures.

Findings

The HII region complex is embedded in a molecular clump not in contact with the SNR.

Young stellar objects are embedded in the molecular clump, indicating recent star formation.

The molecular clump and SNR are likely at different distances, with no direct interaction.

Abstract

The eastern border of the SNR G18.8+0.3, close to an HII regions complex, is a very interesting region to study the molecular gas that it is probably in contact with the SNR shock front. We observed the aforementioned region using the Atacama Submillimeter Telescope Experiment (ASTE) in the 12CO J=3-2, 13CO J=3-2, HCO+ J=4-3, and CS J=7-6 lines with an angular resolution of 22". To complement these observations, we analyzed IR, submillimeter and radio continuum archival data. In this work, we clearly show that the radio continuum "protrusion" that was early thought to belong to the SNR is an HII regions complex deeply embedded in a molecular clump. The new molecular observations reveal that this dense clump, belonging to an extended molecular cloud that surrounds the SNR southeast border, is not physically in contact with SNR G18.8+0.3, suggesting that the SNR shock front have not yet reached it or maybe they are located at different distances. We found some young stellar objects embedded in the molecular clump, suggesting that their formation should be approximately coeval with the SN explosion.