銀河系古成分の動力学構造

千葉柾司（東北大）

銀河系古成分
globular cluster

halo star

10Gyr
thick disk

inner halo

thin disk
thick disk, haloouter halo

銀河系形成の化石情報

12MASS survey

SDSS survey

Thick disk revealed from F- and G- stars in SDSS DR3(Prieto et al. 2005)• Vrot ↓as |z|↑
• no metallicity gradient
Hints for formation scenario(e.g. heating by subhalos: Hayashi’s talk)2

Dark matter distribution (by Moore)

Subhalo impact on extended HI disks(Bekki & Chiba 2006, ApJL)

NGC2403stellar disk

HI disk⇒star formation

Halo and disk structures
revealed from SDSS data
(Juric et al. 2005)
K3

Model: thin, thick disks, halo
 R − Rsun z + z sun −L1H1 

ρ = ρ D (Rsun ) exp − R − Rsun z + z sun + ε D ρ D (Rsun ) exp −−
L2H 2 


M0α



Rsun

+ ε H ρ D (Rsun )
 R 2 + ( z / q )2 H
L1 = 2.40kpc
H1 = 0.28kpc

M2

L2 = 3.50kpc

H 2 = 1.20kpc + substructures

ε D = 0.04
ε H = 0.001
q H = 0.45α = 2 .3(20~40 more clumps
are expected)
M33

data

data/model - 1

Most nearby satellite revealed from 2MASSCanis Major (Martin et al. 2004)

4

Sgr dwarf
2MASS

Majewski et a. 2003

Stream is confined onto an orbital plane⇒ round dark halo5Substructure in M31’s halo
(Ferguson et al. 2002)
Northern Spur

M32

G1 Clump
Stream(V, Ic) bands

Subaru Wide Area Survey (Tanaka, M. et al. in prep.)observedunobserved
CFHT Megacam
Keck DEIMOS
Keck LRIS
Ultra Deep HST ACS

4910

HST ACS32

15612 11m414 13m6P157168171825% overlapped

6Tentative results (Tanaka, M. et al. in prep)streamfield halo

銀河系古成分の特徴• Extended– Halo: ρ∝rα, α~ - 3– Thick disk: ρ∝exp(-z/H), H~1kpc• Lots of substructures– Evidence for dwarf merging• Old age (>10Gyr)• [α/Fe] overabundant
CDM-based galaxy formation?

7

High-resolution numerical simulation
for a galactic collapse(green: M=108-1010Msun, T>104K)
Moore et al. 2005, astro-ph/0510370
z=12z=0

Spatial distribution of old stellar systemsVelocity distribution of 2.5σdensity
peaks

radiallyanisotropicρ

2.5σisotropic

β = 1 − σ t2 / σ r2r
Moore et al. 2005
astro-ph/0510370

Diemand, Madau, Moore 2005
astro-ph/0506615

8

Field Horizontal Branch (FHB) stars as halo tracers• Bright and many
• Accurate distance is available⇒ halo kinematics,
mass distribution of a dark halo
Yamada, M. (2006, Master thesis)
using 444 FHBs in Wilhelm et al. (1999)
1169 FHBs in Sirko et al. (2003)

ZYX

X

L-o-s velocities of1613 FHB starsVcorr corrected for
LSR + the solar motion

Vcorr vs. r

σcorr vs. r

9

Jeans eq. in spherical limit
V21 dnσ r2
βσ r2+2=− cn drrrβ ≡ 1 − σ t2 / σ r2σrn ∝ r-3.5, Vc = const.

tangentially anisotropic
β<0σtradially
anisotropicβ>0

Simulations suggestβ≥0 and increasing with r.
(radially anisotropic inthe outer halo)
Really?

Possible Vrot

Derived Vrot
from model β& observed σr⇒unlikely!
(many distanthalo objects
are unbound)

10radiallyanisotropic

tangentiallyanisotropic＋β

simulation

observation

ーRelation with ages ofglobular clusters?
Young GCs

Old GCs11

Issues• ハロー天体の速度構造の理解– 銀河形成数値実験、データ解析の改良– 球状星団の年齢分布の関連• ダークハローの大局的な質量分布– 総質量、分布、形、サブストラクチャー• 化学元素パターンと動力学構造との関連– 矮小銀河降着の効果

Wide-field, fiber-fed, multi-object spectrograph(WFMOS)• Dark energy survey (determination of w)• Galactic archaeology survey~4,500 targets in a FOV~1.5deg,
R~1,000 - 40,000
Operation 2012? ~12