# Python 2D Jean Instability in Spiral Galaxy Simulation

I have ~1000 snapshots of a spiral galaxy simulation (from Molecular cloud perturbations t=0 to t>1Gyr. What I need to do is determine whether any position at any of the snapshot times meets criteria for Jeans instability.

The simulation is 2D, and the snapshot script can read position, velocity and surface density ∑, but not temperature. The simulation also has no gas, instead the simulation was modeled by giving each individual star extra mass which corresponds to gas. I looked online and several site state the Jeans mass in 2d equal to c$_{s}$$^4$ / G$^2$*∑. But I have no clue how to determine speed of sound c$_{s}$. Also I am not really interested in Jeans mass, more so whether any position can collapse to make stars, i.e. satisfy Jeans instability.

• It seems like the model is inadequate to the question you want to answer. It seems to assume that the gas and the stars have the same distribution, whereas you are interested in finding clumps of gas that could form stars. – David Ketcheson Oct 29 '14 at 17:58
• You want to look at Toomre s number : if it's larger than one your disc will be stable to radial instabilities Q= kappa c_s/pi/G/Sigma – chris Jul 8 '17 at 9:25