Wednesday, May 6, 2009 - 3:15pm
Robi Banerjee (ITA):
"Formation and Evolution of Molecular Clouds in Numerical Simulations"
Abstract. Molecular clouds are the birthplaces of stars in galaxies. Despite this well established fact, our knowledge of how these dense and cold clouds condense out of the warm atomic interstellar gas, and how such clouds evolve over time, is still deficient. In this talk, I'll present results from our numerical investigations of molecular cloud formation by transonic converging flows in the magnetized, warm neutral medium (WNM). Here, star-forming (molecular) clumps form through triggered thermal instability (TI). These cold clumps coexsist with the warm atomic gas and grow by outward propagation of their phase transition fronts and through accretion of the WMN. At later times they also grow by coalescence while the entire cloud begins to contract. The clumps are almost in pressure balance with their surroundings and have internal turbulent Mach numbers comparable to the bulk motions of the WNM. These turbulent motions seed the density fluctuations that are sufficient to become gravitationally unstable and start to collapse. The entire molecular cloud is highly dynamic and is continously forming stars. During its global collapse, the central region of the cloud achieves the properties that are necessary to form massive stars.