Supernova Remnants Associated with Molecular Clouds in the Large Magellanic Cloud

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Abstract
We used the Swedish-ESO Submillimeter Telescope (SEST) to search for CO emission associated with three supernova remnants (SNRs) in the Large Magellanic Cloud: N49, N132D, and N23. Observations were carried out in the J = 2 → 1 rotational transition of CO (230.5 GHz) where the half-power beamwidth of the SEST is 23''. Molecular clouds were discovered near N49 and N132D; no CO emission was discovered in the region we mapped near N23. The N49 cloud has a peak line temperature of 0.75 K, spatial scale of ~7 pc and virial mass of ~3 × 104 M☉. The N132D cloud is brighter with a peak temperature of 5 K; it is also larger ~22 pc and considerably more massive ~2 × 105 M☉. The velocities derived for the clouds near N49 and N132D, +286.0 and +264.0 km s-1, agree well with the previously known velocities of the associated SNRs: +286 km s-1 and +268 km s-1, respectively. ROSAT X-ray images show that the ambient density into which the remnants are expanding appears to be significantly increased in the direction of the clouds. Taken together these observations indicate a physical association between the remnants and their respective, presumably natal, molecular clouds. The association of N49 and N132D with dense regions of molecular material means that both were likely products of short-lived progenitors that exploded as core-collapse supernovae.
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