Dark matter on small scales
千葉柾司(東北大学)
観測的宇宙論ワークショップ 2017.10.23

ΛCDMの小スケール問題
小スケールの定義
M < 1011Msun, k>3 Mpc-1, r<1 Mpc⇒Rvir < 150 kpc, Vvir < 50 km/s
つまり、銀河・矮小銀河スケール

Bullock &Boylan-Kolchin 2017

• Missing satellites problem– Overabundance of dark subhalos• Core/cusp problem– Cuspy central density vs. cores in observed galaxies• Too big to fail problem– Most massive subhalos differ from observed satellites+ その他の問題 (非等方空間分布, 扁平度)

Milky Way sized dark haloWDM
2 keVCDMToo manysubhalos
Rotation curves
in most massive
12 subhalos

subhalos are
Internally too
concentrated

Anderhalden+12

Bright dSphs@half-light radii

Core/cusp problem

Satellites plane

NFW

small-scale crisis in ΛCDM?

Linking dark halos to galaxies- abundance matching

Bright dwarfs: M★=107-8 Msun
Classical dwarfs: M★=105-7 Msun
Ultra-faint dwarfs: M★=102-5 Msun

Solutions to small-scale problems?
・ バリオン効果（フィードバック）しかしClassical dwarfsやUFDsでは効かない・ ホスト銀河の潮汐力
Dwarfs の内部密度の減少
・ 観測情報の不足
UFDsの多くが未発見
・ 暗黒物質がCDMでないWDM, SIDM

Modifying DM particles
CDM

Density profile

SIDM

WDM

Number distribution

SIDM

Host haloWDM

矮小銀河• 銀河系のような明るい銀河の祖先– 銀河の形成史にヒントを与える• 暗黒物質が最も卓越した恒星系– バリオン成分の割合が最も小さい

局所銀河群（Local Group）にある矮小銀河
分離された恒星の振る舞いを通して銀河の形成史と暗黒物質の性質を研究する上ではベストサイト

矮小楕円体銀河
dwarf spheroidal galaxies (dSphs)• 銀河系・Ｍ３１で最も多い衛星銀河– 星間ガスがない、恒星系が暗く淡い
Sculptor

CarinaFornaxLeo II

Leo I

暗黒物質に大きく支配されたdSphs~暗黒物質研究のベストサイト~
Velocity dispersion of stars (km/s)(Walker+ 2009)

Velocity dispersion profile,σ(r), of member stars

This σ(r) is much larger thanthat provided by the stellarsystem itself.

Massive dark halo required⇒ mass profile from fitting恒星系のハーフライト半径内に含まれる暗黒物質(~ 4 x 107M¤)
Gilmore+ 2007

(M/L) = 101 ~ 103
dSphs are largely
DM dominated!

Total(M/L)

dSphs are ideal sites forstudying the nature of DM(old data)
11V-band absolute magnitude

矮小楕円体銀河のダークハローの構造と進化に関する新しい制限
Hayashi & MC 2015, ApJ, 810, 22
Hayashi & MC 2015, ApJ, 803, L11
Okayasu & MC 2016, ApJ, 827, 105
Hayashi, Ishiyama, Ogiya, MC et al. 2017, ApJ, 843, 97

Universal relation for the DM in dSphs
Hayashi & Chiba (2015a, b)

rmax: Vcirc is max (Vmax)
Mean density inside rmaxdSphs

Σvmax = const. for all halos !
・Independent of DM profiles(if NFW, Σvmax ∝ ρ0 rS)(Σvmax ～20 Msunpc-2, log Σvmax ～1.3)

Evolution of NFW halos with logΣVmax = 1.3
Okayasu & Chiba 2016
Evolution of NFW halosΣvmax
z=8 z=5z=2Mass growthis stopped

Host halolog Σvmax ~ 1.3 で一定になるには、DMの成長が止まらなければならない
Baryon fractionat zTT in units ofuniversal one

MTT:
Mass of tidally
truncated halos(when they arebound to a hosthalo at zTT, i.e.
when massaccretion isstopped)

MTTStar formation history under log Σvmax = 1.3
F=1log Mstar

And VIIFor
And I
And III

Leo I
Leo II

F=0.02And II

SclSexCar

Okayasu & Chiba 2016

F=0.1

F=0.002

DraobsAnd V

semi-ana

F = Mstar/Mbaryon
Star formation
efficiency

・Vmax<22km/s
High F・Vmax>22 km/s
Low Flog Mstar

1And VII

Leo IIComparison
with simulation
Dots: Illustrissimulation

And IFor

FmodelFmodel

Leo I
0.1

0.01

And III And II
Scl
Sex

DraCar

0.001
0.001

0.01

0.1

Fsimulation

Fsimulation

Vmax

Fmodel~ Fsimulation1高解像度N体
シミュレーションとの比較（Hayashi, Ishiyama,Ogiya, Chiba et al.2017）
MW-sized halosの中のsubhalos
Classical dSphs

Vmax > 20 km/s
では矮小銀河のDMのΣvmax は
ΛCDMとコンシステント

Higher resolution results
Vmax < 20 km/s
(at scales of UFDs)
Σvmax ∞ Vmax

Why Σvmax ∞ Vmax ?
Subhalos follows
rmax ∝ Vmax
ThenρVmax∝(Vmax/rmax)2~const.
Σvmax∝ρVmaxrmax∝Vmax

矮小楕円体銀河とダークマター問題に関する今後の展望
HSC:Homma, MC, et al. 2016, ApJ, 832, 21
Homma, MC, et al. 2017, PASJ, in press
PFS, JWST, TMT

HSC Subaru Strategic Program (SSP)• Wide, Deep, Ultra-deep layers– dSphs search from 1st 2 year data of Wide layer(~ 300 deg2 / 1,400 deg2)

新しいUFDs（Vir I, Cetus III）の発見
Cetus ＩＩＩ

Isochrone filter(old stellar population)の設定

Isochrone (上図の緑色)上にある星の空間分布

⾚緯︵度︶10.７σ10.8σの密度超過
⾚経（度）MW GCs

MW dSphs

Virgo I and Cetus IIIhave larger sizes thanglobular clusters.

MW GCs

MW dSphs

HSC-SSP is powerful
to identify very faintdwarf satellites.

Expected number of dSphs in HSC-SSP
based on ΛCDM
Error fromAbundance matching

Expected number
N = 9 +15-5
MV<0.0

HSC-wide survey over ~1,400 deg2
• ~ 9 new UFDs @ Mv<0.0• 2 new UFDs over ~ 300 deg2

So far
ΛCDM looks okayPrime focusPFS(Prime Focus Spectrograph)

FOV: 1.3 deg in diameter2400 fiber positioners
λ: 380~1,300 nm(3 channels: Blue, Red, IR)
R: ~3,000 (LR) 5,000 (MR)First light: 2019
Led by IPMU (U. of Tokyo) + NAOJ/Subaru community+ Caltech/JPL, Princeton, JHU, LAM, UK, Brazil, Taiwan,& Chinese consortiumGlobal density profile and total
mass of a dark halo
• True MF & DM profiles of Galactic dSphs?
DM is more extended but outer parts are unexplored（km/s）

PFS pointings

σ(R)R (pc)
Outer parts
are largely
unexplored
Previousmeasurements[α/Fe]

Previousmeasurementsof radial velocities

Global density profile and total
mass of a dark halo
Simulation for an isolated dark halo・Direct identification of rtid
・Correct DM profile
・Total DM mass

PFS pointings for 6 MW satellites
HSC imaging data are available for all samples ~Ursa Minor

Sextans

Draco

松野君

tidal radius ofstellar comp.
Sculptor

FornaxNGC6822

Ursa Minor by Komiyama-san
NB-selected RGBs
Nominal tidal
radiusDraco by Hana
Nominal tidal
radiusAll stars

Field tiling and fiber allocation for UMi# of stars
within 3 hr
exposure4158
UMi stars
5144
MW halostars

Probing evidence for CDM subhalos
from their gravitational effects on a stellar stream(Carlberg 2011)
dynamical effects
on stellar stream(Mstar=106Msun

CDM halo in a galaxy

No subhalos

Showing gaps

star cluster
Moore

1000 subhalos, M-1.9

HSC deep image for
Red Clump stars

150kpc

55kpc

NW stream

PAndAS image of M31’s RGBs
with i < 23.5 mag

2D Stream Structure

Komiyama+ 2017
submitted

RC stars across the stream

11

2
3
4

2 Kinematical substructures
PFS:of clean halo members along theRCstreamstars along the stream(blue histogram)
4⇒abundance of CDM subhalos
33

24skewed
Very clumpy density structure⇒perturbations by subhalos

1And more with TMT, JWST
• Proper motions of dSphs’ stars with TMT～ 0.03 mas/yr for stars of 10km/s at D=70kpc
Measureable with TMT/IRIS⇒ velocity anisotropy of stars⇒ ultimately very precise DM profile• Gravitational lens with JWST
– Anomalous flux ratios andtheir frequency⇒ abundance of subhalos

Conclusions• Local Group にある矮小銀河は、暗黒物質と銀河形成過程に対して重要な情報を提供する。
• Subaru/HSC, Subaru/PFS, TMT, JWSTにより、矮小銀河スケールの暗黒物質の存在形態が明らかになると期待される。
– Missing satellites problem, Too big to fail problemSupplementary files

銀河系の衛星銀河の分布

HST/WFPC2 results for SF history(Weisz et al. 2014)
Mv > -8 mag

Mv < -8 mag

非常に古い星形成が直ぐに中止

様々な星形成史

36

Star formation history under log Σvmax = 1.3
F=1log Mstar

And VII

F=0.1

For
And I

F=0.02And II

Scl
And III

Leo I
Leo IISex

F=0.002

DraCarAnd Vobs

semi-ana

F = Mstar/Mbaryon
Star formation
efficiency・Vmax<22km/s
High F・Vmax>22 km/s
Low F

Vmax
1000

inflow rate (Fornax)
outflow rate

900

Good match!

800
700

Fornax dSph
Predictedgas infall history

600
500
400300Fornax20SFR [103 Msun/Myr]

Flow rate [103 Msun/Myr]25

Fornax dSph
Observed
star formation history

15

10200
1000-100
14000

12000

10000

8000
6000
Lookback Time [Myr]Log Σvmax = 1.3
consistent with SFH

4000

Look back time

2000

0

50
14000

12000

10000

8000
6000
Lookback Time [Myr]4000

Look back time

2000

0

What we need to do? (II)On the “too big to fail” problem (Brook+2014)
Vcirc at half-light radius of stars
DC14 profile:
NFW + baryon effectyielding a larger Mhalo estimate

Vcirc

MstarNFW

DC14yields
no TBTF
problem

DC14

Outer massis crucial for
Mhalo estimate

theory

Mhalo

Mhalo

HSC imaging campaign of MW dSphs
with Subaru + Keck/Subaru time (Cohen+)
Name

Short exposure (RGBs)

Long exposure (~MSTO)

Notegi

NB515 gi

NB515

Draco (2 fields)

F1, F2

F1, F2

F1, F2

F1, F2 F1, F2

F1, F2

Sculptor (4 fields)

F1, F2,F3, F4

F1, F2,F3, F4

F1, F2, F1, F2, F1, F2, F1, F2,F3, F4 F3, F4 F3, F4 F3, F4

S15B, S16B, S17A

Fornax (4 fields)

F1, F2,F3, F4

F1, F2,F3, F4

F1, F2, F1, F2, F1, F2,F3, F4 F3, F4 F3, F4

F1, F2,F3, F4

S15B, S16B, S17A

Ursa Minor (4 fields)

F1, F2,F3, F4

F1, F2,F3, F4

F1, F2, F1, F2, F1, F2,F3, F4 F3, F4 F3, F4

F1, F2,F3, F4

S15A

F1 –
F19

F1 –
F1 –
F19
F19(4-6,1214, 18)

S16A

Field number
Red: done(Bold red:done in S17A)
Black: not yet

Leo ISextans (19 fields)

DracoSculptor

F1 ― F19

S14B, S16APFS targets
FornaxUrsa Minor

Sextans

PFS target selection (by Kohei Hayashi)

Blue: NB515 selected stars+ HB stars= Member stars in UMi
Red: MW halo dwarf stars
We can assign fibers to MW halo stars⇒ cut down the original survey planfor the halo stars.

NB515 filter for HSC
NB515 (CW: 515 nm, FWHM: 8nm) (from S15A)
Separation of RGB stars in M31 + MW satellites
from the foreground MW dwarfs
g – NB515ii

Tanaka+ in prepRGBsdwafs

g-i

g-i

g-i
(32% remained as RGBs)

Too big to fail problem

Bright dSphs@half-light radii