Galactic Archaeology withSuMIRe HSC/PFS
Masashi Chiba(Tohoku University)with W. Aoki, J. Cohen, M. Ishigaki+ N. Hwang, D. Kawata , and more

Galaxy formation in CDM models
By Moore

Assembly of CDM

Galactic dark halo

Bright parts arecentrally concentrated

Key science goals
1. Formation of Galactic structuresMerging history of the Milky Way (MW)?
Formation of old MW components (thick disk, halo)?
Star-formation history of dwarf satellites?
Formation of M31: is it different from the MW?

2. The nature of galactic dark matter How is dark matter distributed in the MW?
 Dark matter of dwarf satellites: is CDM correct?

All are recorded in old stellar populations

Fossil records of galaxy formation
Debris of building blocks
1. Space and velocity distributions ofancient stars
 Past collapse and merging events
 Tracer of dark matter profiles

2. Chemical abundance of ancient stars
 Star formation and chemical evolution
Phase space

A building block
Thick diskThin disk

What data do we need?
 Photometry :HSC, SDSS, PanStar

 mag., color ( → color-mag. diagram) Spectroscopy : metallicity , Vrad (kinematics)
 abundance pattern ( → SF & chemical evol.)PFS

 proper motion, distance (→ 6d phase space)Gaia Astrometry :Structure, dynamics, star formationand chemical evolution⇒ galaxy formation and evolution

Gaia(2012~)

Cf. Hipparcos
V<12, 1mas

Astrometry:
V=15, 12~25 μas
V=20, ~300 μas
Photometry:V < 20
RV measurement:
V < 17 (150M stars)
R~11,500,
λ=8450-8750A (CaT)ΔVrad~15 km/s
[Fe/H] measurement:
V<12 (2M stars)

Key science goals

Extracting recent merging events in the MW
Spatial substructures in the halo
⇒ kinematics and metallicities

SDSS(Belokurov+ 06)

Extracting past merging history of the MWclumpL⊥

Halo stars in phase space（w. Hipparcos sample）• measurement error ofa few 100 (kpc km/s)
smears out substructures
MC & Beers 00

Lz
Building block

Astrometry with Gaia
(precise distances andproper motions)+ Vrad & [Fe/H] distrib.
with PFS• resolves each of blocks
and its chemical evolution
Helmi & de Zeeuw 00

Accretion time of a satellite can be deduced
from phase-space distribution of stars(McMillan & Binney 2008, Gomez+ 2010)

Orbital freq.
Ωr-Ωφ

Ωr-Ωφ

ΩφP(kφ)Lzkφ
7.9 Gyr

8.9 Gyr

7.6 Gyr

How many stars are needed to trace
the merging history?
Stellar halo component
with mass Mtot
• Mtot ~ 109 Msun
• max. ~ 104 building blocks(if n(L)dL~L-1.5 dL
for L=103~107 Lsun, M/L~1)• Total sample:
max. ~ 1 M stars(if ~100 sample stars
for each building block)Formation of M31: Is it different from MW?
Halo substructures as merging remnants
Northern SpurGiant Stream (w. SCam)

G1 Clump
Giant Stream
Ferguson+02

Tanaka+10

HSC

M31 covered with180 CCDs

HSC survey of M31’s halo with NB515
to select M31’s RGB stars with g<22.5
giantsdwarfs

Metallicities and RVs of substructuresand satellites with PFS (+ star clusters)
130 pointings

ITRGB=20.5

Several stellar halos from CDM models(Johnston+08)[Fe/H]Vrad

Gilmore+07

Dark matter of dwarf satellites:
Is CDM correct?
dSphs:• DM dominated(M/L) = 102 ~ 103• σ ~ a few to 10 km/s
• Cuspy or core profile?
CDMCarLeo I

Proposed survey andPFS requirements

Proposed survey with PFS
1. The Milky Way survey••••

Sample: ~ 106 MW stars with b>20 deg,18<V<21.5(Halo ~55%, Thick disk ~30%, Thin disk ~5%),targets are taken from HSC, SDSS & PanStar
Total area: ~ 1000 sq. deg (~560 pointings)
Survey time: ~ 112 nights
Δ[Fe/H]~0.2, ΔVrad~a few km/s

2. The M31 halo survey•••

Sample: RGBs, V < 21.5, from HSC
Total area: ~ 230 sq. deg (~130 pointings)
Survey time: ~ 30 nights (can be PI-led programs)

3. Dwarf galaxy survey••

Sample: RGBs, V < 21.5, from SCam & HSC
Survey time: ~ 30 nights (can be PI-led programs)

Requested performance of PFS
 Synergy with Gaia for Galactic stars• V > 12 mag for RVs• V > 17 mag for [Fe/H]• Early data release in 2015
 Enable to determine metallicity and velocity
distributions of stars• Δ[Fe/H] ~ 0.2, ΔVrad ~ a few km/s
 Enable to observe M31 and satellite stars• ITRGB=20.5 mag, i.e., Vlim ~ 21.5 magCa II lines as [Fe/H] indicatorBlue:
Ca II K (3933A) & (B-V)
For both dwarfs and giants
with -4.0 < [Fe/H] < 0.5[Fe/H]=-4.0

Beerrs+99

Red:
Ca II triplet(8400-8700A)& (VHB-V)
For RGBs with-3 < [Fe/H] < -0.5
Starkenburg+10

PFS requirements
1. Spectral resolution, λ coverage, and SNR
CaII lines at blue and red regions for [Fe/H],
λ5150A (Mgb) for logg, SNR~30, V<21.5•••

R=3,000, λ=3,900-6,700A
targets: metal-poor stars in the MW(If R=5,000 in blue, then many lines incl. Ba, Mg, etc.
would be resolved. Wavelength coverage being fixed.)
R=3,000, λ=6,500-9,900A
targets: (bright) RGBs in the MW and M31
IR range: will be very useful for studying disk stars

2. Fibers
MW: ~1,400 stars/PFS field at V=17, b=|45|
M31: ~5,000 stars/sq.deg at V=22.5, R=30kpc•

2,000-3,000 fibers with size 1.2” are sufficientNecessity of HR spectroscopy
Chemical tagging of each building block⇒ detailed chemical evolution history
1. Spectral resolution, λ coverage, and SNR• R = 35,000, SNR ~ 100, V < 17 mag• Any of λ = 4112-4322A, 5015-5268A, 62806593A, 6456-6779A, 8380-8804A
2. Fibers• ~200 fibers are sufficient for follow-up
studiesOther major facilities and projects• AAO/RAVE
 1.2m UKST, R=8,500,150fibers, 9<I<12• AAT/HERMES 3.9m, R=28,000, 392fibers, λ4708-4893A, 5649-5873A,64816739A,7590-7890A, 10<V<14• LAMOST 4m, R=1,800, 4,000fibers, λ3700-5900A, 5700-9000A• VLT/FLAMES 8.2m,R~5,000, 20,000,130fibers, V<16 for [Fe/H], V<19 for RVs, 105stars• CFHT/GYES

 4m, R=20,000, 500fibers, λ3900-4500A, 5880-6700A, V<16 ~18• WHT/WEAVE
 4.2m, R=5,000 + 20,000, 800fibers, λ4000-9500A, 2sq.deg, V<20?
• VISTA 4m, R=3-5,000 & 20,000, 1500fibers, 2sq.deg, V?

Blue: South
Yellow: NorthPFS HR

HROS/TMTHERMES FLAMES HRGYESAPOGEE

104[Fe/H]

RVGaia

RAVE

R

WEAVE
FLAMES LR

PFS LRLAMOST1031015V (mag)2025Summary: GA with PFS
 PFS LR in synergy with Gaia• R=3,000, ~3,000 fibers,
λ=3900-9000A+IR mode, 18<V<21.5• Discover many substructures andidentify merger history Hope: PFS HR for follow-up studies• R=35,000, ~ 200 fibers, V<17,
Any of λ=4112-4322A, 5015-5268A,6280-6593A, 6456-6779A, 8380-8804A• Chemical history of each building blockEnd