The Molecular Ridge Close to 30 Doradus in the Large Magellanic Cloud

Abstract

Abstract With the ATNF Mopra telescope we are performing a survey in the 12 CO(1–0) line to map the molecular gas in the Large Magellanic Cloud. For some regions we also obtained interferometric maps of the high density gas tracers HCO + and HCN with the Australia Telescope Compact Array. Here we discuss the properties of the elongated molecular complex that stretches about 2 kpc southward from 30 Doradus. Our data suggest that the complex, which we refer to as the ‘molecular ridge’, is not a coherent feature but consists of many smaller clumps that share the same formation history. Likely triggers of molecular-cloud formation are shocks and shearing forces that are present in the surrounding south-eastern H i overdensity region, a region influenced by strong ram pressure and tidal forces. The molecular ridge is at the western edge of the the overdensity region where a bifurcated velocity structure transitions into a single disk velocity component. We find that the 12 CO(1–0) and H i emission peaks in the molecular ridge are typically near each other but never coincide. A likely explanation is the conversion of warmer, low-opacity H i to colder, high-opacity H i from which H 2 subsequently forms. On smaller scales we find that very dense molecular gas, as traced by interferometric HCO + and HCN maps, is associated with star formation along shocked filaments and with rims of expanding shell-like structures, both created by feedback from massive stars.