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D.S. Theil (U. Colorado)
I present evidence that a large OB association (Cas-Tau), centered on \alpha Per open cluster, formed about 40 million years ago. The kinetic energy deposited by the massive stars of Cas-Tau generated gravitational instabilities in the Interstellar Medium (ISM). These instabilities became the Giant Molecular Clouds (GMCs) associated with the nearby (< 2 kiloparsecs) star forming regions in Orion, Scorpius-Centaurus, Perseus, Lacertae and the rest of the Gould's Belt stars.
The creation of GMCs associated with star forming regions is a long standing, unsolved problem in modern astronomy. The popular theories (Jeans type instabilities in a rotating disk) produce condensations that are at least an order of magnitude too massive to be the seeds of the galactic Giant Molecular Cloud population, and on timescales far longer than the lifetimes of GMCs. Expanding superbubbles (kiloparsec scaled, multiple supernova remnants that form around large clusters) in the ISM sweep up 'supershells' of higher density material. These shells can theoretically become gravitationally unstable over appropriate timescales to GMC mass instabilities. Observational evidence in support of this theory has been lacking until now.
The distribution and dynamics of molecular gas predicted by supershell instability theory is clearly evident in my study of local molecular gas using a galactic plane 12CO survey. Results demonstrate the earlier formation (compared to other nearby regions) of the oldest star forming region in Gould's Belt (Orion) is due to the interaction of the Gould's Belt Supershell with the recently discovered nearby supershell GSH238+00+09 (the Vela Supershell). I also discuss possible origins of the Taurus clouds, which are well inside the large low-density volume swept out by the Cas-Tau association superbubble.
This work was supported in part by the Center for Astrophysics and Space Astronomy (CASA) at the University of Colorado.
The author(s) of this abstract have provided an email address for comments about the abstract: dtheil@du.edu