Unveiling the formation of the Galactic disks and Andromeda halo with WFMOS

1. Unveiling the formation of the Galactic disks and Andromeda halo with WFMOS Masashi Chiba (Tohoku University, Sendai)

2. Galactic Archaeology thick disk thin disk bulge stellar halo Fossil records in Galaxy formation Near-field Cosmology

3. Galaxy formation: tracing assembly history Fossil (DNA) records in ancient stars Building blocks • Spatial distributions • Global distribution • Localized structures • Kinematics • Rotational velocity • Integral of motions (phase space distribution) • Chemical abundance • [Fe/H], [α/Fe] etc.

4. Issues addressed here • Milky Way halo • Global and local structures deduced from kinematics and chemical abundance • Thick disk • How did it form? • Andromeda halo • Is it different from the Milky Way halo?

5. 1. Milky Way halo kinematics SDSS Vφ Thick disk inner halo Halo outer halo metallicity [Fe/H]

6. Mean rotation velocity of the halo Vφ Inner halo • Assembly process • is at work (monolithic • collapse is unlikely). • star formation history • of each halo comp. • is yet unknown. Outer halo Zmax (max. Z distance)

7. Formation of a stellar halo based on CDM models(Johnston+08) [/Fe]  Vlos [Fe/H]

8. Distribution in the sky (Bullock & Johnston 2005) Outer halo (SDSS) Halo realization 1

9. Galactic Halo Survey • Chemical tagging of the stellar halo with high-res survey • inner/outer halo (Ishigaki-san’s talk) • halo substructure • Mapping halo substructure patterns with low-res survey • Vlos, [Fe/H], [/Fe] • group finder (Sharma & Johnston 2009) Halo: Mtot = 109 Msun Munit=105-6Msun N = 10×Mtot / Munit ~ 104-5 halo stars

10. 2. Thick disk Vertical velocity dispersion • Milky Way thick disk • distinct kinematics, chemistry, and age: independent Galactic component • dynamically hot, large scale height, [Fe/H]~ -0.6, old age (~10Gyr) • Extra-galactic thick disks • common in disk galaxies • relatively old and metal rich (km/s) log Age (Gyr) Lthick/Lthin vs. Vcirc in external galaxies Vcirc

11. Formation scenario of a thick disk • Dissipative collapse • metallicity gradient, no gradient in kinematics • homogeneous age distribution • Direct accretion of thick-disk material (satellites) • no gradient in chemistry and kinematics • contamination of young, low-[/Fe] stars • Dynamical heating of a pre-existing thin disk by sub-galactic dark halos (subhalos) • no gradient in chemistry, gradient in kinematics ( V as |z| ) • asymmetry and substructures in kinematics but not in chemistry

12. Numerical simulation of disk heating by subhalos (Hayashi & Chiba 2006) Distribution of dark halos in a galactic scale (by Moore) young disk

13. Model F Vlos distribution Model S Asymmetric Vlos distribution + kinematic substructures ⇒ evidence of disk heating Model I

14. Model F Model S |Vlos|↓as |b|↑ i.e. |Vrot|↓as |z|↑ ⇒ evidence of disk heating Model I

15. Galactic Thick-Disk Survey • Kinematics distribution with low-res survey • mapping of Vlos • [Fe/H] for each substructure + age • Chemical tagging with high-res survey • , Fe-peak, s-process elements • Aoki-san’s talk Thick disk: Mtot = 3 ×109 Msun Munit=105-6Msun N = 10×Mtot / Munit ~ 104-5 disk stars

16. 3. Andromeda halo • How typical is the Milky Way? • metallicity, age, kinematics, global structure • External view of a stellar halo • substructure, metallicity gradient, age gradient

17. Keck/DEIMOS observation(Koch+08) DEIMOS target fields Spectroscopic metallicity is more reliable.

18. Metallicity distribution (Koch+08) metal-poor halo? • Too small FOV with DEIMOS • ~20 RGB / pointing • Susceptible to substructure contamination • distinguish local and global structures

19. Using S-Cam (Tanaka+ 2007) Andromeda Halo Survey • Metallicity and Kinematics of the Andromeda Halo with low-res survey • RGB with 20.5 < I < 21.25 mag • larger  coverage & much wider FOV than DEIMOS • ~ 6900 sec exposure for ~ 200 deg2, 220 hours

20. Current survey design • Key Science Program • High-res survey • R=30,000, 16<V<17 • =628-659.3nm • ~ 5×105 stars (disk and halo) • ~1000 deg2, ~280 nights • Low-res survey • R=1,800, 18<V<21.5, B-V<1 • =390-900nm • ~ 106 stars (halo and disk) • ~ 1000 deg2, ~250 nights • PI Science Programs • Galactic bulge, M31/M33 halo, dwarf galaxies b=20 l=0

21. Conclusions • WFMOS GA survey will provide legacy-value datasets, which no other observatories enable to do over decades. • Subaru/Gemini communities will be benefit from these datasets and resulting science achievements.

22. Thank you

23. high-z universe (snapshots of various galaxies) complementary stellar system in local universe (tracing evolution of a galaxy) Bekki & Chiba 2001

24. WFMOS survey of halo and disk stars Munit=105-6Msun Total halo or disk mass Mtot Mtot = 109-10 Msun N = 10×Mtot / Munit ~ 104-5 halo stars ~ 105-6 thick disk stars RVs, metallicities, ages (turn-off/subgiants), distances (giants) Mtot

25. Original plan with WFMOS • Dark energy survey (determination of w) • Galactic archaeology survey • ~4500 targets in a FOV~1.5deg, • R~2000, 40000 (3000, 1500 fibers) • Operation 2012? ~ ~1400 stars @V~17 • Original plan : • Low resolution modeR ~ 2000, 17<V<22 • radial velocity & abundance • 0.5 million stars, 500 deg2, 140 nights • High resolution modeR ~ 40000, V<17 • abundance patterns • 1.5 million stars, 3000 deg2, 490 nights

27. 40000 R 30000 WFMOS Inner halo (1 million stars) 20000 Photometry to V=20 Outer halo GAIA 10000 (0.5 million stars) RAVE WFMOS 12 17 22 V (mag)