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

Aims. The eastern border of the SNR G18.8+0.3, close to an HII regions complex, is a very interesting region for studying the molecular gas that it is probably in contact with the supernova remnant (SNR) shock front. Methods. We observed this 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 infrared, submillimeter, and radio continuum archival data. Results. In this work, we clearly show that the radio continuum “protrusion” that was earlier thought to belong to the SNR is an HII region complex that is 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’s southeast border, is not physically in contact with SNR G18.8+0.3, suggesting that the SNR shock front has not yet reached it or that they may be 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