Galactic Science and MOS on the WHT

1. Galactic Science andMOS on the WHT Amina Helmi

2. ESA-ESO report on Galactic populations(Turon, Primas, Binney, Chiappini, Drew, AH, Robin, Ryan) GREAT WG3 on Chemical Tagging Brown, Feltzing, AH, Korn, Walton • GCDS: Gaia chemo-dynamical Survey • First meeting: Paris 26 April 2010 2

3. stellar halo thick disk The Galaxy thin disk bulge How did the Galaxy come to be like this ? What is the origin/formation epoch/mechanism and relation between the various components?

4. The Gaia era 4 ESA-ESO Galaxy WG ESA-ESO meeting, ESTEC, 10 October ESA-ESO 2008

6. Gaia The volume and quality of data that Gaia will provide will revolutionise the study of the Galaxy • Full 6D phase-space information only available for a subset • Not as accurate as proper motions • -> Incomplete dynamical map of the Galaxy • e.g. substructures (clusters, resonances) in disk limited to few kpc from Sun 6

7. Gaia: spectroscopy Only gross abundances measurable for a subset of brightest stars -> MDF only known within few kpc from the Sun, in sections of the bulge or in dwarf galaxies (100 x farther away) Detailed elemental abundances missing -> crucial for chemical history, star formation and assembly history 7

8. Science questions1 Dynamics of the Milky Way Velocity distributions along the disk; resonance maps; coupling of dark halo, bar and disk Halo shape, density and granularity Streams as tracers of mass distribution and evolution Structure and history of the disks Characterization of star formation and chemistry as f(R) Models of the formation of thick disk Inter-relation between various components Metal-poor components Streams in the halo to trace merger history Constrain the IMF, and star formation in the early Universe (1) not exhaustive

9. Milky Way Dynamics CDM strong predictions on density profile, shape and granularity Springel et al. 2008 A great amount of dark substructure

10. Narrow streams GD-1 stream in SDSS: dissolved cluster Thin long streams better probes (more reliable tracers of underlying potential; Eyre & Binney 2009) Internal velocity dispersions are few km/s • Halo granularity: need very accurate radial velocities • Distant streams preferred (d ~ 10 – 40 kpc) to isolate other effects • -> faint stars • Low surface brightness -> need to go as far down on RGB • Need to follow stream across large area on the sky • -> Wide-field, accurate RV, faint magnitudes, multiplex ~ 100 Koposov et al. 2009

11. Chemistry Elemental abundances track ISM at formation Different elements are produced on different timescales -> their ratio is a clock e.g.  -> SNII (short-lived massive stars); Fe: mainly SNI -> [/Fe] enhanced implies fast star formation r, s processes Matteucci 2001

12. Halo metallicity distribution function • -Very small number of extremely metal-poor stars known to date: • 3 with [Fe/H] < -4.5 • Direct counts provide constraints on the IMF at high-redshift • e.g. there may be a critical Z below which only very massive stars form • -Currently limited by small number statistics Salvadori et al. 2007 Spectroscopic survey of 105 halo stars at intermediate res. to identify candidates for follow up -> Wide-field, deep & 100 multiplex

13. Chemistry of metal-poor components Nomoto et al. 2006 Cayrel et al. 2004 • Knowledge of very metal-poor stars detailed abundance patterns • Constraints on the IMF • On the nature of the first stars and explosions (SN or HN) • On the early history of the Galaxy (e.g. why lack of scatter?)

14. Merger history and streams Latest cosmological simulations predict much substructure in the halo 75% of stars near Sun from 3-5 parents Memory in kinematics -> 100’s streams crossing Solar neighbourhood Should be visible with Gaia! Cooper et al. 2010 Helmi et al. 2010

15. Outer halo: • Clear evidence of substructure • Limited to high-surface brightness features (progenitors/time of events) Abundance substructure also expected Belokurov et al. 2007 Font et al. 2006 Characterize the properties of the building blocks of the halo 500 streams -> 100*/stream -> 5x104 stars, wide-field (2-3 deg2) 100 multiplex, V ~ 17 for a survey of 2000 deg2 (V ~ 15 for 10000 deg2); HR ~ 20,000

16. Global Requirements Wide-field: 2- 3 deg2 Galaxy is an all-sky object Stars in halo and thick disk are rare -> build up large samples in reasonable time Spectral resolution and multiplexing R ~ 5,000 for radial velocities (1 – 2 km/s); #fib < 1000s R ~ 20,000 for metal-weak thick disk, halo studies; #fib ~ 100s Survey sizes LR mode for disk: 106 stars for 17< V < 20 HR mode for field populations: 105 stars HR mode for stream characterization: 5 x 104 stars Large spectral coverage blue sensitive: well-known region of the spectrum; many useful lines; little atmospheric lines for metal-poor stars (halo-like): there are fewer lines -> gain e.g. Eu (r-process) two lines around 6500 A

17. The landscape Lamost? Recio-Blanco 2009

18. Structure and history of the disks Characterization of star formation and chemistry as f(R) Test models of the formation of thick disk Inter-relation between various components star formation history in galactic thin disk from Solar Neighbourhood: roughly uniform, with episodic star bursts for ages < 10 Gyr, but lower for ages > 10 Gyr Rocha-Pinto et al (2000)

19. Age-metallicity-velocity relations Only known for the solar neighbourhood (GCS, d < 100 pc) Holmberg et al. 2008

20. Disentangle histories and relations between thin, thick, bulge and halo -> abundances as f(R) and f(z) Samples: 105 stars with 0.1 dex precision -> RGB Local study with MS stars within 2 kpc, with 0.05 dex Only for Solar neighbourhood Bensby et al. 2003