Secular Evolution of Galactic Disks

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Secular Evolution of Galactic Disks

• James Binney
• Oxford University

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Evidence for Evolution

• Hipparcos data for solar nhd
• Heating driven by
  (a) spiral structure
  (b) massive clouds

(Dehnen Binney 98)
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Effect of Spiral Structure(Sellwood Binney 02)

• Changes in angular momentum heat
• ?L important only at resonances
• At LR so
• Effective heating by transient ss then
  resonances broad and/or moving

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Numerical Experiments
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• Conclude L changes dominated by corotation,
  where no associated heating
• Mechanism horse-shoes
• Non-analytic

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Unconstrained Simulation
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• Much radial migration
• But keeps cool

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Evidence for Migration

• Sun higher Z than local ISM even now
• No correlation of Z with age (Edvardsson et al
  93)
• Also 29Si/28Si in presolar dust grains suggest
  enrichment at R4 kpc (Clayton 97)

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Effect on n(v)

• Hipparcos n(v) full of structure (Dehnen 98)

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• Largest feature probably effect of bar (Raboud et
  al 98 Dehnen 99)
• Spirals probably responsible for other structure
  (De Simone, Wu Tremaine 04)

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Back to Heating

• Its a sideshow!
• Its driven by spirals
• It happens at ILR
• Clouds feed E into z motion
• But make negligible contribution to heating from
  sR/sz, ?JRwave9.5?JRcloud
  (Jenkins Binney 90)

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Models of Heating(Binney, Dehnen Bertelli 00)

• Parameterize IMF and SFR
• Get B-V and t from Padua ss models
• Results depend on Z distribution

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Conclusions

• Transient spiral structure churns disks through
  action at CR
• Directly evident in n(v)
• Fundamental for chemical evolution
• Explains Z distribution near Sun
• (Small) L changes at ILR heat disk
• Cloud scattering transfers E to z
• From s(B-V) get SFRconst and st1/3