The jet and arc molecular clouds toward Westerlund 2, RCW 49, and HESS J1023-575; 12CO and 13CO (J=2-1 and J=1-0) observations with NANTEN2 and Mopra Telescope

摘要

We have made new CO observations of two molecular clouds, which we call "jet"and "arc" clouds, toward the stellar cluster Westerlund 2 and the TeV gamma-raysource HESS J1023-575. The jet cloud shows a linear structure from the positionof Westerlund 2 on the east. In addition, we have found a new counter jet cloudon the west. The arc cloud shows a crescent shape in the west of HESSJ1023-575. A sign of star formation is found at the edge of the jet cloud andgives a constraint on the age of the jet cloud to be ~Myrs. An analysis withthe multi CO transitions gives temperature as high as 20 K in a few places ofthe jet cloud, suggesting that some additional heating may be operatinglocally. The new TeV gamma-ray images by H.E.S.S. correspond to the jet and arcclouds spatially better than the giant molecular clouds associated withWesterlund 2. We suggest that the jet and arc clouds are not physically linkedwith Westerlund 2 but are located at a greater distance around 7.5 kpc. Amicroquasar with long-term activity may be able to offer a possible engine toform the jet and arc clouds and to produce the TeV gamma-rays, although none ofthe known microquasars have a Myr age or steady TeV gamma-rays. Alternatively,an anisotropic supernova explosion which occurred ~Myr ago may be able to formthe jet and arc clouds, whereas the TeV gamma-ray emission requires amicroquasar formed after the explosion.