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