AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 64. Shells in the Global ISM
Topical, Oral, Wednesday, June 2, 1999, 8:30-10:00am, 10:45am-12:30pm, 2:00-3:30pm, Continental Ballroom B

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[64.12] Influence of Shells on the Global SFR

E. Vazquez-Semadeni (Instituto de Astronomia, UNAM), T. Passot (Obs. of Nice), A. Gazol (Instituto de Astronomia, UNAM)

We discuss the feedback from large-scale stellar energy injection into the ISM, mainly through shells and supershells, on the global star formation rate (SFR), in terms of environmental parameters such as the strength of the magnetic field, the cooling laws of the flow, and the rotation rate of the host galaxy. Shells promote star formation by inducing compressive motions in the ambient gas, and hence we discuss criteria for the the production of self-gravitating structures through compression. On the other hand, supershells can disperse the molecular complexes in which they originate, supressing star formation over extended periods of time. We discuss the balance between these two effects. Strong uniform magnetic fields prevent shells from expanding, decreasing their dispersing effect, and increasing the global SFR. High rotation rates render the SFR more uniform over time because they decrease the effective compressibility of the medium. The presence of thermal instabilities in the warm medium, on the other hand, increases the SFR, thus increasing the number of shells present at any one time in the medium. Finally, we discuss recent models suggesting that the rate of kinetic energy increase in the ISM is proportional to 2/3 power of the stellar energy injection rate.

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