Secular Evolution of Secular Evolution of Galactic DisksGalactic Disks

James BinneyJames Binney

Oxford UniversityOxford University

Evidence for EvolutionEvidence for Evolution Hipparcos data for solar nhdHipparcos data for solar nhd Heating driven by Heating driven by

(a) spiral structure (a) spiral structure (b) massive clouds(b) massive clouds

(Dehnen & Binney 98)

Effect of Spiral StructureEffect of Spiral Structure(Sellwood & Binney 02)(Sellwood & Binney 02)

Changes in angular momentum heat:Changes in angular momentum heat:

ΔΔL important only at resonancesL important only at resonances At LR soAt LR so Effective heating by transient ss: Effective heating by transient ss:

then resonances broad and/or movingthen resonances broad and/or moving

Numerical ExperimentsNumerical Experiments

Conclude: L changes dominated by Conclude: L changes dominated by corotation, where no associated corotation, where no associated heatingheating

Mechanism: horse-shoesMechanism: horse-shoes Non-analyticNon-analytic

Unconstrained SimulationUnconstrained Simulation

Much radial migrationMuch radial migration But keeps coolBut keeps cool

Evidence for MigrationEvidence for Migration Sun higher Z than local ISM even nowSun higher Z than local ISM even now

No correlation of Z with age No correlation of Z with age (Edvardsson et al (Edvardsson et al 93)93)

Also Also 2929Si/Si/2828Si in presolar dust grains Si in presolar dust grains suggest enrichment at R~4 kpc suggest enrichment at R~4 kpc (Clayton 97)(Clayton 97)

Effect on n(Effect on n(vv))

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

Largest feature probably effect of bar Largest feature probably effect of bar (Raboud et al 98; Dehnen 99)(Raboud et al 98; Dehnen 99)

Spirals probably responsible for other Spirals probably responsible for other structure structure (De Simone, Wu & Tremaine 04)(De Simone, Wu & Tremaine 04)

Back to HeatingBack to Heating

It’s a sideshow!It’s a sideshow! It’s driven by spiralsIt’s driven by spirals It happens at ILRIt happens at ILR Clouds feed E into z motionClouds feed E into z motion But make negligible contribution to But make negligible contribution to

heating: from heating: from σσRR//σσzz, , ΔΔJJRR||wavewave~9.5~9.5ΔΔJJRR||

cloudcloud (Jenkins & Binney 90)(Jenkins & Binney 90)

Models of HeatingModels of Heating(Binney, Dehnen & Bertelli 00)(Binney, Dehnen & Bertelli 00)

Parameterize IMF and SFRParameterize IMF and SFR

Get B-V and Get B-V and ττ from Padua ss models from Padua ss models Results depend on Z distributionResults depend on Z distribution

ConclusionsConclusions

Transient spiral structure churns disks Transient spiral structure churns disks through action at CRthrough action at CR

Directly evident in n(Directly evident in n(vv)) Fundamental for chemical evolutionFundamental for chemical evolution Explains Z distribution near SunExplains Z distribution near Sun (Small) L changes at ILR heat disk(Small) L changes at ILR heat disk Cloud scattering transfers E to zCloud scattering transfers E to z From From σσ(B-V) get SFR~const and (B-V) get SFR~const and σσ~t~t1/31/3