Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chemical & dynamical evolution of the Galaxy James Binney Oxford University outline • Secular heating • Radial mixing • Origin of the thin disc 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 Modelling heating • Assume – SFR / e-t/t0 – ¾ / t¯ • Fit ¾(B-V) and N(B-V) Aumer & B 09 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 Radial mixing • Dominant effect of spiral structure is scattering @ corotation • Does not heat disc but drives radial migration Sellwood & B 02 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¯ Schoenrich & B (09) model 10 Flow over R 5 From IGM per area Schoenrich & B (09) ISM • Leads to – inhomogeneous solar nhd – steep Z gradient d[Fe/H]/dR=-0.08 Local stars Schoenrich & B (09) • Parameters fitted to GenevaCopenhagen sample of Hipparcos stars • Selection effects crucial GCS cylinder Chiappini 97 No churning 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 B 09 thin 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 Disc divided Many predictions to test Chemistry vs z Rotation vs chemistry 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