1 Galactic Science and MOS on the WHT Amina Helmi

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

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

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

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

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

Science questions 1 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

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

Narrow streams Thin long streams better probes (more reliable tracers of underlying potential; Eyre & Binney 2009) Internal velocity dispersions are few km/s GD-1 stream in SDSS: dissolved cluster Koposov et al 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

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

-Very small number of extremely metal-poor stars known to date: 3 with [Fe/H] < 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 Spectroscopic survey of 10 5 halo stars at intermediate res. to identify candidates for follow up -> Wide-field, deep & 100 multiplex Halo metallicity distribution function

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?) Nomoto et al Cayrel et al Chemistry of metal-poor components

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 Helmi et al. 2010

Belokurov et al Outer halo: Clear evidence of substructure Limited to high-surface brightness features (progenitors/time of events) Font et al Abundance substructure also expected Characterize the properties of the building blocks of the halo 500 streams -> 100*/stream -> 5x10 4 stars, wide-field (2-3 deg 2 ) 100 multiplex, V ~ 17 for a survey of 2000 deg 2 (V ~ 15 for deg 2 ); HR ~ 20,000

Global Requirements Wide-field: 2- 3 deg 2  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: 10 6 stars for 17< V < 20  HR mode for field populations: 10 5 stars  HR mode for stream characterization: 5 x 10 4 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

The landscape Recio-Blanco 2009 Lamost?

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 Rocha-Pinto et al (2000)

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

Disentangle histories and relations between thin, thick, bulge and halo -> abundances as f(R) and f(z) Samples: 10 5 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