Woong-Tae Kim: Star Formation in Nuclear Rings

Nuclear Rings

  • Form by resonant interactions with barred potentials + but bar torque is low near inner lindbland resonances + resonance is very long timescale
  • claim that bar strength controls bar substructure
  • bar potential modeled by "Ferrers Prolates"
  • Q_B is the "controlling parameter" + Q_B = 0.23 yields really cool looking models
  • stronger bar leads to smaller radius ring + pushes more gas inward
  • range of SFR + age gradient within nuclear rings

Two models of ring SF

  • popcorn model + randomly distributed + no age gradient
  • pearls-on-a-string model + SF at contact point + age gradient
  • age gradient <-> lower SFR
  • simulation generating 10^5 msun clusters

Sim results

  • presence or absence of age gradient depends on SFR + no age gradient if SFR > 1 Myr + corresponds to maximum SFR at a contact point
  • prolonged SF requires prolonged feeding + HVCs (accretion of primordial gas) + ang mom dissipation by spiral arms + Galactic fountains
  • If corotation radius at large R, can feed spiral arms into ring

Questions

  • Q: Sims are pure hydro. Speculate on B-fields. Chuckle.
  • A: Ring would be smaller
  • Q: Typical velocity of gas along bar in model?
  • A: 50-100 km/s
  • Q: Do you mean no need for x2 orbit?
  • A: no, need X2 to form ring. Formation mechanism of ring is not related to resonance.
  • Q: Ring on x2 orbit?
  • A: yes
  • Q: is there observation evidence of age gradients in nuclear rings?
  • A: Yes, Mazzuca '08 shows gradient in H-alpha EQW
  • Q Farhad: Can you form the circumnuclear disk (2pc) with the same mechanism?
  • A: Can't answer now. Need to run the simulation with the right size-scale
  • Q: Would the bar be unstable to bending instabilities in 3D?
  • A: We ran 3D, and didn't see any difference. But, with different initial conditions, may see dynamical difference..
  • Q: Have you modeled where the bar meets the arm?
  • A: No, couldn't do that, only treated stellar.

Comments