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Free keywords:
Astrophysics, Galaxy Astrophysics, astro-ph.GA
MPINP:
Hochenergie-Astrophysik Theorie - Abteilung Hofmann
Abstract:
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-ray
source HESS J1023-575. The jet cloud shows a linear structure from the position
of Westerlund 2 on the east. In addition, we have found a new counter jet cloud
on the west. The arc cloud shows a crescent shape in the west of HESS
J1023-575. A sign of star formation is found at the edge of the jet cloud and
gives a constraint on the age of the jet cloud to be ~Myrs. An analysis with
the multi CO transitions gives temperature as high as 20 K in a few places of
the jet cloud, suggesting that some additional heating may be operating
locally. The new TeV gamma-ray images by H.E.S.S. correspond to the jet and arc
clouds spatially better than the giant molecular clouds associated with
Westerlund 2. We suggest that the jet and arc clouds are not physically linked
with Westerlund 2 but are located at a greater distance around 7.5 kpc. A
microquasar with long-term activity may be able to offer a possible engine to
form the jet and arc clouds and to produce the TeV gamma-rays, although none of
the known microquasars have a Myr age or steady TeV gamma-rays. Alternatively,
an anisotropic supernova explosion which occurred ~Myr ago may be able to form
the jet and arc clouds, whereas the TeV gamma-ray emission requires a
microquasar formed after the explosion.
