The structure of molecular clouds from large scale surveys of CO and CS

The molecular gas lying in the interior of the Orion superbubble consists of sheets, filaments and bubbles in which the dense active star forming cloud cores are embedded. Many regions have a wind-swept or cometary appearance suggesting strong interaction with the Orion OB association. External heating dominates the cloud energy budget, resulting in cold (∼10K) cloud cores surrounded by hot (>20K) envelopes. Non-ionizing UV radiation emitted by late B and A stars may be the source of the kinetic energy needed to form some of the large scale cavities and contributes to the supersonic line widths seen in many clouds.