Steve Longmore: Conversion of Gas into Stars in the Galactic Center

Is SF different in disk?
  • 5-10% of gas in CMZ
  • 5-10% of SF in CMZ
  • Density in CMZ 2 orders of magnitude higher
Suppressing Mechanisms in the CMZ
  • Stars dominate grav potential + outside "ring", gas is not self-gravitating + Within 100 pc, gas is self-grav
  • Local suppression dominated by turbulence by orders of magnitude
  • Dense gas PDF from Kritsuk + dispersion set by Mach number
  • Threshold for SF in CMZ very high: ~10^8 cm^-3
Turbulence
  • dissipates in a crossing time + what drives it? + MRI, GI, outflows, Sne all orders of magnitude too low + steady-state gas inflow also too small
  • "acoustic instabilities" large enough + outside inner lindblad resonance, spiral waves driven by grav instabilities
  • Montenegro, Yuan, Elmegreen 1999 model + gas falling into stellar potential + "acoustic instability"
Quiescent vs Starburst phase
  • "simple idea"
CMZ in Cosmological Context
  • velocity dispersion vs density? + high redshift clouds and CMZ clouds occupy same parameter space
  • "CMZ is inditinguishable from high-redshift starburst"
Details of stellar mass assembly
  • Molinari Ring picture: 2 vertical oscillations per orbit
  • map mass density along orbit
  • gas compressed at pericenter
  • PPV structure extraction... + orbital fitting + can't fit Molinari ring + closed orbits not possible: precession + can't fit P-V wiggle + doesn't fit Sgr B2
  • Pericenter passage SPH sim + VERTICAL compression + retrograde, counterrotating gas due to shear
  • dense gas fraction vs orbit... + prediction of density vs orbital position + Plug for Ginsburg et al VLA/GBT H2CO densitometry
  • IMF variation interesting future avenue

Questions

  • Q: On pc scales, fits with Ken-Schmidt relation
  • A: Depends on geometry. Donut vs pancake geometry.
  • Q: Isn't there gas that is more efficient at forming stars?
  • A: Doesn't fit...
  • Q: KS relation doesn't work for CMZs in other galaxies. How did you measure dispersion for high-Z clouds?
  • A: Some high-z clouds with direct measurements. Otherwise, assume virial equilibrium. Robust no matter how you derive it.
  • Q: Struggling in nearby galaxies, particularly because of outflows.
  • A: best we can do
  • Q: CMZ is similar to high-z objects. GC in pre-starburst phase. So we should have a starburst soon.
  • A: Either gas won't form stars, or will do so in bursty fashion
  • Q: Predicts lots of very dense gas in Galactic center, n~10^8.
  • A: See Jill's talk.
  • Q Wardle: Turbulence damps on vertical crossing time (0.5 Myr). 20km/s linewidth disappear in 0.5 Myr? Do you see dead clouds? Don't travel very far, so should damp.
  • A: [should have answered: it's driven!]

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