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

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

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

Issues addressed here 1.Milky Way halo Global and local structures deduced from kinematics and chemical abundance 2.Thick disk How did it form? 3.Andromeda halo Is it different from the Milky Way halo?

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

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

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

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

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  V los, [Fe/H], [  /Fe]  group finder (Sharma & Johnston 2009) Halo: M tot = 10 9 M sun M unit = M sun N = 10×M tot / M unit ~ halo stars

2. Thick disk  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 Vertical velocity dispersion L thick /L thin vs. V circ in external galaxies V circ log Age (Gyr) (km/s)

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

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

Asymmetric V los distribution + kinematic substructures ⇒ evidence of disk heating V los distribution Model F Model S Model I

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

Galactic Thick-Disk Survey  Kinematics distribution with low-res survey  mapping of V los  [Fe/H] for each substructure + age  Chemical tagging with high-res survey  , Fe-peak, s-process elements  Aoki-san’s talk Thick disk: M tot = 3 ×10 9 M sun M unit = M sun N = 10×M tot / M unit ~ disk stars

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

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

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

Andromeda Halo Survey  Metallicity and Kinematics of the Andromeda Halo with low-res survey  RGB with 20.5 < I < mag  larger coverage & much wider FOV than DEIMOS  ~ 6900 sec exposure for ~ 200 deg 2, 220 hours Using S-Cam (Tanaka+ 2007)

Current survey design  Key Science Program  High-res survey R=30,000, 16<V<17 = nm ~ 5×10 5 stars (disk and halo) ~1000 deg 2, ~280 nights  Low-res survey R=1,800, 18<V<21.5, B-V<1 = nm ~ 10 6 stars (halo and disk) ~ 1000 deg 2, ~250 nights  PI Science Programs  Galactic bulge, M31/M33 halo, dwarf galaxies b=20 l=0

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.

Thank you

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

WFMOS survey of halo and disk stars Total halo or disk mass M tot M tot = M sun N = 10×M tot / M unit ~ halo stars ~ thick disk stars RVs, metallicities, ages (turn-off/subgiants), distances (giants) M tot M unit = M sun

1. Dark energy survey (determination of w) 2. Galactic archaeology survey ~4500 targets in a FOV~1.5deg, R~2000, (3000, 1500 fibers) Operation 2012? ~ ~1400 Original plan : Low resolution mode R ~ 2000, 17<V<22 radial velocity & abundance 0.5 million stars, 500 deg 2, 140 nights High resolution mode R ~ 40000, V<17 abundance patterns 1.5 million stars, 3000 deg 2, 490 nights Original plan with WFMOS

RAVE 1.2m UK-Schmidt, AAO GAIA Astrometry satellite, ESA WFMOS Wide-field fiber-fed mos Optical, 8400 ~ 8750A Ca triplet Optical, 5 to 11 band photometry + Ca triplet Optical, ~4500 targets in a field Sp: V<12 mag R=5000~ km/s Sp: V<17 mag R= ~10 km/s, 10^8 stars Sp: R=2000~30000 Hi res. V<17 mag Low res. 17<V<22 mag Southern hemisphereAll skyNorthern hemisphere 2003~ ? ~ 2019?2012~?

V (mag) R RAVE GAIA WFMOS (1 million stars) (0.5 million stars) Inner halo Outer halo Photometry to V=20