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Gerry Gilmore IoA Cambridge

Evolution of the Milky Way a look at just some of the bigger issues we don’t know and future prospects for progress: Gaia. Gerry Gilmore IoA Cambridge. The complexity we have available to study. Stellar populations: 4.5 `types’.

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Gerry Gilmore IoA Cambridge

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  1. Evolution of the Milky Waya look at just some of the bigger issues we don’t knowand future prospects for progress: Gaia Gerry Gilmore IoA Cambridge

  2. The complexity we have available to study Stellar populations: 4.5 `types’ • Kinematically cold, high-J (angular momentum), wide age-range, narrow abundance range - dG-`problem’  late gas accretion? -- thin disk POP I • Old, high-J, discrete? intermediate PopII, thick disk I.5 • Hot, low-J, old?, metal-rich, related to SMBH? – pseudo+bulge • Hot, low-J(???), old(??) metal-poor(?), late accretion(?), probably itself 2-component – halo classical POPII • The first early stars POPIII? +POPIV +.... • CONCLUSION: We know little about unbiased samples • BUT each type shows surprisingly little element scatter •  focus has been on extremes

  3. The Galactic disks • disk (late type) galaxies are (too?) common • Most, perhaps all, are double disks • – thin disk plus thick disk • Most disks are big – too big? • Most disks are old – too old? • Most/all are metal-rich – too metal-rich? • All have complex secular dynamical evolution

  4. What came before the thin disk? The thick disk? The halo? Both? Neither? Big challenge: understand the DF of metal-poor disk stars What created the elements at -1.5dex and high angular momentum? Where are the ancestors? Where are the minor merger consequences? Solar cylinder metallicity DF g-dwarf `problem’

  5. Chemical evolution models allow very large element ratio scatter – not seen This model from Wyse + gg Both the Thin and the Thick Disk look very homogeneous locally: hard to understand! Do few components imply few origins? Element ratio data from Fuhrmann

  6. Vertical metallicity DF with Z-height Looks like a two-component thin+thick separate population model fits best. A very old model! (Wyse&GG 1995) Consistent with thick disk formation ending prior to thin disk, and gas retained. Burnett, Binneyetal 2011: RAVE data

  7. Age  Z>500pc • Age-metallicity DF, from RAVE • The thin disk shows very small • chemical evolution over 8Gyr; • the thick disk has a narrow age • Similar to Ohta results from • Subaru/FMOS • Tight element ratios • efficient ISM mixing • SFR  ISM fountains • Burnett etal 2011 • and • Binney, nipoti, fraternali • MN 2009 397 1804 Z<500pc

  8. Ruchti et al 2010, 2011. RAVE sample follow-up MgI/FeI Thick disk merges into inner halo?? galactic field stars all see a mass-average yield, which is spatially well mixed. This continuity tells us nothing about MWG merger/assembly duilding blocks – except they perhaps did not exist. • Derived ratios of several keyα-elements to iron, for 215 red giants Blue = Halo Red = Thick Disk Black = Thin Disk Orange = Thick/Halo Green = Thin/Thick SiI/FeI CaI/FeI TiI/FeI TiII/FeII

  9. Bulge—halo —diskconnection? Which first? Bulge, halo Wyse & gg 1992 The first zero [Fe] stars should be in the bulge: are they? SMBH connection?? Thick, thin disks Bulge angular momentum distribution consistent with dissipational collapse of gaseous ejecta from stellar halo star-forming regions -- mass ratios also agree with low metallicity of stellar halo Hartwick 1979:impossible with significant late halo accretion or secular growth

  10. Current data show the power of chemistry to measure `history’ NB- ongoing star formation in very inner disk – Arches, etc – creating a pseudo-bulge? Standard IMF (#1) Well-mixed (#2) Fast recycling (#3) Renzini 2008

  11. Much focus on inner (pseudo-) bulge, not much on the very extended But it exists! Recall Ibata/Gilmore survey VISTA VHS data, b=40deg Most of the stars here are halo, or disc(s)

  12. Roederer 2009: Red=inner halo orbits Blue=outer halo orbits Plateau  universal IMF Plateau  efficient mixing Sharp break  narrow time Small scatter  good mixing ... .... ... Lots and lots of physics EMP stars are critical probes of the stellar IMF in the early Universe Their use to probe galaxy formation models is not clear -- lots of recent models. Current accretion – Sgr, SMC is making a young metal-rich Pop-II halo HALO

  13. Stellar metallicity distributions appear sequential: Halo  thick disk  thin disk Halo MDF consistent with monolithic formation in situ, with gas loss into early disk. [ELS] But this is not modern LCDM expectation. Coincidence or information? We do not know the [Fe/H] DFs of any stellar ppulation We do not know the [Fe/H] DFs of any stellar ppulation

  14. The new “field of streams”double Sgr stream, much complexityhow does this relate to the “typical” halo? Koposov, Belokurov, et al 2011

  15. Gaia astrometric mission due for launch 2013 parallaxes and proper motions for ~1 billion stars to mG<20 mag spectra for radial velocities and metallicities for 150 million stars Variability alerts from 2014 Full source data from 2016 Precise astrometry later The coming revolution: GaiaGaia needs spectroscopy RAVE meeting Coonabarabran

  16. Gaia Focal Plane Figure courtesy Alex Short 104.26cm Wave Front Sensor Wave Front Sensor Red Photometer CCDs Blue Photometer CCDs 42.35cm Radial-Velocity Spectrometer CCDs Basic Angle Monitor Basic Angle Monitor Star motion in 10 s 4.4s per CCD Sky Mapper CCDs Astrometric Field CCDs Sky mapper: - detects all objects to 20 mag - rejects cosmic-ray events - FoV discrimination Astrometry: - total detection noise: ~6 e- Total field: - active area: 0.75 deg2 - CCDs: 14 + 62 + 14 + 12 - 4500 x 1966 pixels (TDI) - pixel size = 10 µm x 30 µm = 59 mas x 177 mas Photometry: - spectro-photometer - blue and red CCDs Spectroscopy: - high-resolution spectra - red CCDs 16

  17. Science Alerts • aims: • detect unexpected and rapid changes in the flux, spectrum or position • or appearance of new objects • trigger ground-based follow-up • provide targets to the community to be studied at peculiar states • methods: • run in near-real-time: between couple of hours and 24h after observation • use photometric, spectroscopic and astrometric Gaia data • cross-match against existing information • Gaia spatial resolution makes for a real challenge – crowded fields • Motivation • Collaboration interests in special cases, esp rare objects

  18. Gaia is so many orders better than no win every parameter it is hard to appreciate, Advantage of spatial resolution: Gaia detects all sources with FWHM <0.65arcsec So all the AGN, compact galaxies,.multi-lensed QSOs, kiler asteroids,... R136 at 0.1”, 0.5”, 1.0”

  19. Photometry selection – complete to V=20, drop to 50% at G=20.5 Even in crowded fields – this is R136 (HST data) as seen by one Gaia CCD Green box = Gaia will measure that source.

  20. The Gaia-ESO Spectroscopic Survey Co-PIs Gerry Gilmore (IoA, Cambridge) & Sofia Randich (INAF-Arcetri) plus......

  21. Gaia-ESO survey overview • VLT-FLAMES public survey of all stellar populations of the MWG: Halo; Bulge; Thick & Thin disks; open clusters and associations • 240+60nights (30n/semester) over 5 (4+1) years; start 1/ 2012 (P88), end 9/2016 (P97)+; visitor mode • will yield: >105 Giraffe spectra (R~20,000); • > 104 UVES spectra (R~47,000) • [Mg,Ca,Ti, Si, Cr, Mn, Ni]

  22. Summary: we don’t know what “stellar population” means: dispersions in element ratios are always very small • Big picture: pure disk formation problem • Disks are old – thick disks very common – Angular momentum disks link? • Vertical chemistry DF seems separate – also element ratios – why? • dG problem – chemistry DF narrow in Fe and element ratios - limits gradients and secular effects?? • Chemical evolution – none seen over 8Gyr: winds etc move gas round? • continuity to thick disk and halo? – constant IMF, efficient mixing, minimal or no local self-enrichment. Short-lived star formation formed thick disk. • Q: how much scatter in elements in OCs at same age, radius? • Massive GC age/Na-O problems! MDF => not primordial building blocks • Secular models very uncertain – don’t know history of disk spiral/bar structure. Comparing SFR and cluster survival numbers might help. • Merger models ditto – tough to test. • Turbulent disk formation – leads to thick disks but bulges – not dominant • Clusters – OCs only in thin disk – just age? Red GCs? But then inner halo/bulge link – opposite to angular momentum relation? • .................. • Gaia will be here soon, to help – and challenge • Gaia-ESO spectroscopic survey an example of those to come.

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