Self Gravity sims

I've started running some hires 3D simulations of gravitationally induced turbulence. Here are a couple images of the column density at 17 Myr

as well as a ​movie

I went with a cloud at a density of 10 particles/cc and a temperature of 160 K and a radius of 20 pc for a total cloud volume of about 8500 MSolar. The cloud material initially has a Jeans Length of 80 pc. I was able to get pressure equilibrium by using the Inuoue and Inutsuka cooling/heating curve which gives an equilibrium temperature (pressure) for a given density plotted below. x-axis is log10 number density and y-axis is log10 pressure in units of (Kelvin/cc) (ignore the horizontal line)

This curve allows for gas at 10 particles/cc and 160 K to be in pressure balance with gas at .23 particles/cc and 6784 K.

It would be possible to raise the density to 100 particles/cc and still be in pressure balance with gas at 1 particle/cc if we wanted to make the cloud more massive.

The cloud is initially kicked with a solenoidal velocity perturbation with a k-2 spectra and a total kinetic energy that is only about 1/3 the gravitational binding energy although there is plenty of internal energy to support the cloud

Gravitational Energy -17.3e46 ergs
Thermal Energy 32.6e46 ergs
Kinetic Energy 6.14e46 ergs

Since the Kinetic energy is 1/5 of the thermal energy, the initial perturbations are sub sonic. There is still structure that initially appears, but given the scales, I believe it is driven by thermal instabilities rather than gravitational.

Here are some histograms of density at approximately 8 Myr (red line) and 16 Myr (green line).

and density weighted histograms of the Jeans Length

Eventually the central part of the cloud collapses and forms 4 sink particles at around 17 Myr, while the rest of the cloud is still fairly whispy.

Given that the resolution is 100 pc / 2048 the code should form particles when the jeans length is .2 pc which should occur at densities of 1e5 with a corresponding jeans mass of about 10 solar masses. Given that the cloud contains 8000 MSolar eventually there should form 100s of 10 solar mass cores - provided there are mechanisms for increasing the density to 1e5. Global contraction may be necessary to provide the density enhancement - as the cooling instabilities can only compress the material to 120 particles/cc or so…

Image showing typical astrophysical scales

In the colliding flows, we are embedding dense small clumps in the colliding streams to provide perturbations. We want these clumps to be in pressure equilibrium with the stream, and for the stream and the clumps to be in a thermally stable region (n < 1 or n > 10). It is also good if the clumps are large enough to be resolved, but be light enough to not plow through the opposing flow. The two stable densities allowed with the minimum density contrast occurs at arround 10 and .23 particles/cc. We decided to have a mean density of 1 particle/cc and a flow radius of 20 pc which gives a Mass flux of 523 m_sun/Myr for about 15 Myr or a total mass about 8000 MSolar which would be comparable to the mass in the spherical cloud.

It would also be interesting comparing this to an isothermal run at 160 K or perhaps much lower… I was also thinking it would be good to always refine the Jeans length by 64 cells or so - until some maximum resolution. Also I've noticed that these runs are rotationally symmetric which is due to a difference in bluegene's compiler handling certain random number generating functions differently. That issue has been fixed.

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