We report on Mopra observations toward the young massive star cluster RSGC 1 , adjoined by , and possibly associated with the gamma-ray source HESS J1837–069 .
We measure the CO ( J = 1 –0 ) distribution around the cluster and gamma-ray source , and find that the cluster is slightly higher than the velocity ranges associated with the Crux-Scutum arm .
We reveal the cluster is associated with much less molecular gas compared with other young massive clusters in the Galaxy , Westerlund 1 ( Wd 1 ) and 2 ( Wd 2 ) , which also radiate gamma-rays .
We find no other structures that would otherwise indicate the action of supernova remnants , and due to the lack of material which may form gamma-rays by hadronic interaction , we conclude that the gamma-rays detected from HESS J1837–069 are not created through proton-proton interactions , and may more plausibly originate from the pulsar that was recently found near RSGC 1 .