Sunday, April 14, 2013

Dobbs, C. L.; Pringle, J. E.; The exciting lives of giant molecular clouds

The exciting lives of giant molecular clouds
by: Dobbs, C. L.; Pringle, J. E.
[arXiv:1303.4995v1, pdf, first author, second]
This paper does a particle simulation with 8 million particles with each particle having a mass of ~300 Msun. They include heating and cooling following the method of Glover and Mac Low (2007), with cooling being switched off at 50K. Each particle contains a fraction of H2 which they recalculate each timestep based on expected formation and destruction events. They also include stellar feedback with the feedback relation given in equation (1) of their paper. It depends on an arbitrarily chosen parameter (ε), the  H2 mass, and a factor that comes from their chosen IMF. This is multiplied by 10^51 ergs, which comes from the average energy of a supernova events. The energy is deposited half in thermal energy, half in kinetic. No explanation on how they choose the deposit of kinetic energy, but that may be covered in a previous paper (actually a lot of what they are doing is covered in previous papers, they are always referring to previous papers for their set up). They also had a background stellar potential, with perturbations for the spiral arms.

They ran their simulations for ~300 Myr, and found that giant molecular clouds form in the spiral arms through the conglomeration of smaller clouds. The GMCs are then disrupted mostly through sheer effects, but in the smaller clouds there is more disruption through stellar feedback. The larger clouds can also stretch out into a spur in the spiral arm which in turn can form its own GMCs, from the remnants of the original cloud. Below is figure 1 from the paper which shows column density at 250 Myr. One particular GMC that they studied in detail is marked with a red square.
Below is figure 3 from the paper which shows the evolution of the cloud marked in figure 1.