(Io) Yat-Tien's Update on CND project

Circum Nuclear Disk (CND) in the Galactic Center (GC)

Brief Intro: CND is a Keplerian ring of inner radius 1pc and outer radii 3-7 pc or more (probably not more) around the supermassive blackhole in the GC, having a mass ~4.2e6 M_sun. It contains 10e4 - 10e5 solar masses of very warm, turbulent and clumpy molecular and atomic gas. There is a luminous young cluster of massive stars located within a few tenths of a pc from the blackhole, outputting strong spherical stellar wind. A torodial magnetic field of 1 milliGauss exists in the disk.

Run time and Environment: A batch job was submitted and run in the UCLA *Hoffman2 Cluster. 40 CPUs were requested and It took ~1 week on queuing. Interactive mode with maximum CPU=8 and maximum run time=24hours also available for users. [*The maximum # of CPUs and maximum run time that a normal user can request for are 128 and 24 hours respectively] The total integration time was only 15% of a revolution time on the outer edge of the disk (t~54,000 yr & total frames=20). The computational run time was ~15.5 hours. 40 cores were used.

Setup of the Problem: (Problem was set up with the BasicDisk module by Jonathan) A molecular ring with of an inner radius of 1pc and an outer radius of 4pc, and a constant thickness of 1pc was set up. To prevent inflow/outflow of matter in the z direction to the disk, the disk and the envelope are in hydrostatic and pressure equilibrium . The outflow module was used to simulate the ionized stellar wind from the center of the ring. The ionization module was also used. Moreover, we imposed a torodial B field of magnitude 1mG in the disk. 

Some important  global/physical parameters are shown as the following: Resolution: 32, 32, 16 AMRlevel: 2

Outflow

  • outflow radius: 0.4pc (from the central blackhole)
  • outflow velocity: 700km/s
  • outflow density: *1000 /cc

(*from observation: total mass loss rate from the central cluster ~3e-2 solar masses per year)

  • outflow temperature: 1e4 K

Disk

  • density: 1e5 /cc

(=total mass ~2.5e4 Msun)

  • temperature: 300 K 

Result: 1) Flaring Disk started to form in the 3rd frame (t=8,100 yr) after the ionized wind hit the inner edge of the CND

2) As the outflow compressed the inner region of the disk, dense equatorial region formed

3) A density wave propagating outwards radially, a second wave was seen in the 18th frame.

4) Rotational KH instability? (4-fold symmetrical feature that was attributable to the gridding, need a further check with better resolution)

Image of the simulation attached (Face-on & Edge-on)

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