1. Chemical & dynamical evolution of the Galaxy James Binney Oxford University

2. outline Secular heating Radial mixing Origin of the thin disc

3. Secular heating Fluctuations in © from spiral structure and molecular clouds scatter stars from near-circular orbits Colour of MS stars related to mean age So random velocity of MS stars increases with B-V Aumer & B 09

4. Modelling heating Assume –SFR / e -t/t 0 – ¾ / t ¯ Fit ¾ (B-V) and N(B-V) Aumer & B 09

5. The solar neighbourhood is old ¿ max > 10.5 Gyr, best age 12.5 Gyr Peak cosmic SFR z = 1-2 $ ¿ = 7.8 – 10.5 Gyr Mean age 5.9 – 6.4 Gyr upper end of disc ages at 10 kpc in Scannapieco+09 simulations Aumer & B 09

6. Radial mixing Dominant effect of spiral structure is scattering @ corotation Does not heat disc but drives radial migration

7. Sellwood & B 02

8. Impact on chemical evolution Conventional evolution models (van den Bergh 62 ! Chiappini+97 ! Colavitti+08): –Disc a series of accreting annuli –Annuli evolve independently Schoenrich & B (09ab): –Annuli accrete from IGM & next outwards –Stars move radially on growing epicycles (blurring) and epicenters “churned” – ¾ / t ¯

9. Schoenrich & B (09) Flow over R From IGM per area model 5 10

10. Schoenrich & B (09) Leads to –inhomogeneous solar nhd –steep Z gradient ISM Local stars d[Fe/H]/dR=-0.08

11. Schoenrich & B (09) Parameters fitted to Geneva- Copenhagen sample of Hipparcos stars Selection effects crucial GCS cylinder Chiappini 97 No churning

12. Origin of thick disc Reid & Gilmore (83) identified thick disc by vertical profile Later thick-disc stars found to be old and high- ® Overlap of thin & thick discs in Fe/H (Bensby+03) suggested hiatus in SF between two thinB 09

13. Thick disc & SNIa In SB09 model infall rate declines monotonically & SFR determined by Kennicutt law so total continuity in SF But distribution of stars in (Fe/H, ® ) bimodal Reason: high SF in ~1Gyr before SNIa kick in Metal-poor stars in solar nhd not historical relic but reflect radial mixing ISM tracks

14. Disc divided

15. Many predictions to test Rotation vs chemistry Chemistry vs z

16. Conclusions We are in the middle of an era of giant Galaxy surveys (Hipparcos, UCAC2, DENIS, 2MASS, SDSS, RAVE, HERMES, APOGEE, Gaia) From these data we should infer history of the Galaxy Models have a crucial role to play Dating stars is v hard; chemistry is a more accessible proxy Chemistry & dynamics entangled Radial mixing has been too long neglected The simplest model of chemodynamical evolution with radial mixing suggests the thick disc formed quiescently and reflects dynamics of SNIa rather than lumpy accretion