Jay Gallagher: Lessons from Comparisons between the Nuclear Region of the Milky Way and Those in Nearby Spirals

Investigation to understand assumptions made in extragalactic obs

  • MW single example - what is unique, what general?
  • SNR / CR interaction model works in M82 & NGC 253, not in MW
  • MW SFR? Is it right?
  • lots of nearby SAB moderately-barred spirals moderately analogous to MW
  • Maffei 2 + 5x10^7 msun mol gas in rotating core
  • NGC 253 + 10^8 msun molecular gas
  • MW + 3-4x10^7

Similar molecular and stellar content

Major differences
  • MW: SFR 0.01 Msun/yr [my comment: this seems low?]
  • IC 342 & Maffei 2: 1 Msun/yr
  • NGC 253, M82: 3-8 msun/yr + nuclei don't follow CO vs SFR
  • NGC 253: huge wind (almost naked eye) + 10-100x MW CMZ thermal pressure
  • Gamma rays: MW overluminous at low energies?

Statement: "No correlation. Extragalactic relation totally fails" on a plot with 5 data points...

  • not tied to CO
  • Must be a large range in SF efficiency
  • SFR not correlated with nuclear stellar mass
  • MW in SFR low-state
Episodic SF
  • Physical state varies + Chemical transition? + driven by chemistry rather than mass?
  • SF bimodal? Need larger sample
  • Unexpected SMBH impacts?

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Questions

  • Q: Comment - SF adequate to explain energetics seen
  • Q Longmore: Idea for what's stopping SF in our own galaxy. Rate limiting factor is that gas is not self-gravitating.
  • A: turbulent, yeah.
  • Q Mitch: Positive feedback. SF starts, gets intensified. Squeezed by external pressures.
  • A: Agree
  • Q: SFR density of mol gas.
  • A: Cloud production mechanism is different (rather than SF "relation" breaking down)
  • Q: Large range in star formation. Is wind/outflow to SFR more constant?
  • A: would like to know. Outflows not well-measured.
  • Q: Constant at what value?
  • A: Outflow/SFR constant
  • Q Farhad: Dense gas in other galaxies?
  • A: Not known yet. Need to know dense gas fractions
  • Q Farhad: Need to know fraction of dense gas.
  • A: Bigger debate in N253

Comments