Secular Evolution of Galactic Disks James Binney Oxford University

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

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

Numerical Experiments

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

Unconstrained Simulation

Much radial migration Much radial migration But keeps cool But keeps cool

Evidence for Migration Sun higher Z than local ISM even now Sun higher Z than local ISM even now No correlation of Z with age (Edvardsson et al 93) No correlation of Z with age (Edvardsson et al 93) Also 29 Si/ 28 Si in presolar dust grains suggest enrichment at R~4 kpc (Clayton 97) Also 29 Si/ 28 Si in presolar dust grains suggest enrichment at R~4 kpc (Clayton 97)

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

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

Back to Heating Its a sideshow! Its a sideshow! Its driven by spirals Its driven by spirals It happens at ILR It happens at ILR Clouds feed E into z motion Clouds feed E into z motion But make negligible contribution to heating: from σ R /σ z, ΔJ R | wave ~9.5ΔJ R | cloud (Jenkins & Binney 90) But make negligible contribution to heating: from σ R /σ z, ΔJ R | wave ~9.5ΔJ R | cloud (Jenkins & Binney 90)

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

Conclusions Transient spiral structure churns disks through action at CR Transient spiral structure churns disks through action at CR Directly evident in n(v) Directly evident in n(v) Fundamental for chemical evolution Fundamental for chemical evolution Explains Z distribution near Sun Explains Z distribution near Sun (Small) L changes at ILR heat disk (Small) L changes at ILR heat disk Cloud scattering transfers E to z Cloud scattering transfers E to z From σ(B-V) get SFR~const and σ~t 1/3 From σ(B-V) get SFR~const and σ~t 1/3