Unveiling the formation of the Galactic disks and Andromeda halo

with WFMOS

Masashi Chiba(Tohoku University, Sendai)

bulgethin disk

thick disk

stellar halo

Fossil records in Galaxy formationNear-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

Vφ

[Fe/H]

Halo

Thick disk

kinematics

metallicity

inner halo

outer halo

SDSS

Mean rotation velocity of the halo

Inner halo

Outer halo

Vφ

Zmax (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 Vlos, [Fe/H], [/Fe] group finder (Sharma &

Johnston 2009)

Halo: Mtot = 109 Msun

Munit=105-6Msun

N = 10×Mtot / Munit

~ 104-5 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

Lthick/Lthin vs. Vcirc

in external galaxies

Vcirc

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 Vlos distribution+ kinematic substructures

⇒ evidence of disk heating

Vlos distribution Model F

Model S

Model I

|Vlos|↓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 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

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 ismore 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 <

21.25 mag larger coverage &

much wider FOV than DEIMOS

~ 6900 sec exposure for ~ 200 deg2, 220 hours

Using S-Cam (Tanaka+ 2007)

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

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 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

Munit=105-6Msun

1. Dark energy survey (determination of w)2. Galactic archaeology survey~4500 targets in a FOV~1.5deg,R~2000, 40000 (3000, 1500 fibers)Operation 2012? ~ ~1400 stars

@V~17Original plan :• Low resolution mode R ~ 2000, 17<V<22 radial velocity & abundance 0.5 million stars, 500 deg2, 140 nights• High resolution mode R ~ 40000, V<17 abundance patterns 1.5 million stars, 3000 deg2, 490 nights

Original plan with WFMOS

RAVE1.2m UK-Schmidt, AAO

GAIAAstrometry satellite, ESA

WFMOSWide-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 magR=5000~100002 km/s

Sp: V<17 magR=115001~10 km/s, 10^8 stars

Sp: R=2000~30000Hi res. V<17 magLow res. 17<V<22 mag

Southern hemisphere All sky Northern hemisphere

2003~2010 2012? ~ 2019? 2012~?

V (mag)

R

12 17 22

10000

20000

30000

40000

RAVE

GAIA

WFMOS

WFMOS

(1 million stars)

(0.5 million stars)

Inner halo

Outer haloPhotometryto V=20