The thermodynamic evolution of GMCs and the formation of clusters
Institut für Theoretische Astrophysik, Heidelberg, Germany
GMCs are not characterised by 10K isothermal gas, yet much of our modelling of star formation to date has used such an assumption. The vast majority of the mass in a GMC resides at densities where the thermodynmics are dominated by the balance between atomic line emission and heating from the interstellar radiation field. In the high density regions of star formation, the thermodynamics are largely controlled by coupling to the dust. Although Larson presented a piece-wise polytropic fit to roughly model these these two regimes, it is unlikely that such a tight fit would exist in reality. To study the thermodynamics properly, one needs to track the chemical evolution of the gas and the relevant heating and cooling processes in the GMC.
We present the results of new calculations of cluster formation which follow the self-consistent effects of non-equilibrium chemistry on the thermodynamics of the gas, as well as a treatment for the dust cooling. These conditions take two extreme cases, highlighting the differences between clusters formed by strongly self-gravitating gas and those formed by extreme ram pressure. This includes a discussion of the relative roles of competitive accretion and gravitational fragmentation in the formation of the mass function in both cases. We will also address the ability of the flows to 'drive' the turbulence in the growing young cluster, and attempt to answer the question of "How fast is 'rapid' star formation?".