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Secular Evolution of Galactic Disks

Secular Evolution of Galactic Disks. James Binney Oxford University. Evidence for Evolution. Hipparcos data for solar nhd Heating driven by (a) spiral structure (b) massive clouds. (Dehnen & Binney 98).

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Secular Evolution of Galactic Disks

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  1. Secular Evolution of Galactic Disks James Binney Oxford University

  2. Evidence for Evolution • Hipparcos data for solar nhd • Heating driven by (a) spiral structure (b) massive clouds (Dehnen & Binney 98)

  3. Effect of Spiral Structure(Sellwood & Binney 02) • Changes in angular momentum heat: • ΔL important only at resonances • At LR so • Effective heating by transient ss: then resonances broad and/or moving

  4. Numerical Experiments

  5. Conclude: L changes dominated by corotation, where no associated heating • Mechanism: horse-shoes • Non-analytic

  6. Unconstrained Simulation

  7. Much radial migration • But keeps cool

  8. 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 R~4 kpc (Clayton 97)

  9. Effect on n(v) • Hipparcos n(v) full of structure (Dehnen 98)

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

  11. Back to Heating • It’s a sideshow! • It’s driven by spirals • It happens at ILR • Clouds feed E into z motion • But make negligible contribution to heating: from σR/σz, ΔJR|wave~9.5ΔJR|cloud(Jenkins & Binney 90)

  12. Models of Heating(Binney, Dehnen & Bertelli 00) • Parameterize IMF and SFR • Get B-V and τ from Padua ss models • Results depend on Z distribution

  13. 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 σ(B-V) get SFR~const and σ~t1/3

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