Robust estimate of the dark matter haloof the Milky-way's dwarf spheroidal galaxies
Koji Ichikawa
In collaboration withKohei Hayashi , Masahiro Ibe, Miho N. Ishigaki,Shigeki Matsumoto and Hajime Sugai.
arXiv:1701.xxxxx
arXiv:1608.01749 (submitted in MNRAS)MNRAS, 461, 2914 (1603.08046 [astroph.GA])

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Kashiwa, Dec. 16, 2016

Contents
1. Importance of the halo estimation
Indirect detectiondSph

2. Halo estimation
Observables
Fit

3. Biasesfrom modelfrom fitfrom data

4. FutureDark Matter Search

Direct Detection

Indirect Detection
DMSMDMSM

Collider Production
3

Indirect Detection
dSphs
Milky-Way Galaxy

ExtraGalaxy/
Cluster～10 Mpc～100 kpc～8.5 kpc

ChargedCRs
4

Dwarf spheroidal galaxies
dSphs:
1. Satellite galaxies: d= 10~100kpc
2. Clean (no strong gamma-ray source)
3. DM richdSph TypeMNRAS, 406 (2010) 1220

dSph = Strong Probe
WWFermi (6yrs)
Classical + UF

Cluster: Fermi-LAT (2015)
GC: H.E.S.S. (2015)
isotropic: Fermi (2015)
antiproton: Hong-Bo Jin+(2015)
CMB: Plank (2014)6dSph = Strong ProbeWWFermi (6yrs)
Classical + UF

Cluster: Fermi-LAT (2015)
GC: H.E.S.S. (2015)
isotropic: Fermi (2015)
antiproton: Hong-Bo Jin+(2015)
CMB: Plank (2014)7

O(1) TeV Line Search = CTA !

Lefranc et al. JCAP 1609 (2016) no.09, 043

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O(1) TeV Line Search = CTA !

Line γ = DM’s smoking gun!
+
Thermal WIMP = O(1) – O(10) TeV↓

CTA + dSph = Novel Prize?
Lefranc et al. JCAP 1609 (2016) no.09, 043

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O(1) TeV Line Search = CTA !

Line γ = DM’s smoking gun!
+Thermal WIMP = O(1) – O(10) TeV↓

CTA + dSph = Novel Prize?
Lefranc et al. JCAP 1609 (2016) no.09, 04310

Signal Flux
Dwarf galaxy
γ-RaysObserved
γ-Ray Flux

DM Property

Halo Profile(J-factor)→ J-factor is determined bystellar kinematics of dSph

Observables
Distance from center: Rproj
Luminosity, Color⇒By photometry ( V ~ 26)
Recession velocity: vlos
Metalicity=> By spectroscopy (V ~ 20)
Data set {Rproj, vlos} is typicallyO(100-1000) for classical dSphs and< O(50) for UF-dSphs• vlos cannot be directly used for fit.
• binned vlos data w.r.t. Rporj gives adispersion curve σ(Rproj).

Spectroscopy
V ～ 20 →Photometry
V ~ 26 →Dispersion CurveDM Density profileCusp

ρ s (r / rs ) −1 (1 +r / rs ) −2

ρ s (1+ r / rs ) −1 (1 +r / rs ) −2 Cored
Stellar Density
Profile: ν(r)Jeans equation
for starsσ2 (Theory)
l.o.s

Fit

σ

2 (obs)l.o.sGeringer-Sameth et al., Astrophys.J. 801 (2015) 213

Current Status
Is the fit model accurate enough?
Enough data?
Is the data pure enough?

Current Status
Spherical
Is the fit model accurate enough?
Assumption
Enough data?
Is the data pure enough?

O(10) – O(100)95%Current Status
Spherical
Is the fit model accurate enough?
Assumption
Enough data?
Is the data pure enough?

O(10) – O(100)95%Non Sphericity
Most of the studies assume
spherical profile.
But…

1. Stellar distributions of dSphs are notspherical.
2. Simulation suggest axisymmetric profile.

G. Battaglia et al. Astron.Astrophys.
459

3. Non-Spherical fit include sphericalpossibility.

→ non-spherical fit

is more conservative

K. Hayashi and M. Chiba 2012, 2015b,
K. Hayashi, KI, S. Matsumoto, M. Ibe, M. N. Ishigaki, H. Sugai, arXiv:1603.08046 [astro-ph.GA]

C. Vera-Ciro, et al. MNRAS 439(2014).

Axisymmetric fit
Assumptions

1. Dynamical equilibrium.
2. DM dominate system.
3. Collisionless system.
4. Axisymmetry in both stellar and DM components.
5. Constant velocity anisotropy.

Parameters

Halo Sizeρ0
Halo Radius bhalo
Halo Shape αAxis-ratio
Q
Inclination iVelocity anisotropy βzAxisymmetric Jeans equations →18

Our Fit Results
Classical dwarfs※The fit is still affected by the range of the parameter region.
Empirical condition: r* < rs is required for UF dSph
with small J-factors.

Effect on constraints

Our estimation gives 3 times weaker constraints

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Current Status
Spherical
Is the fit model accurate enough?
Assumption

Axisymmetric fit

Enough data?
Is the data pure enough?

O(10) – O(100)95%Current Status
Spherical
Is the fit model accurate enough?
Assumption

Axisymmetric fit

Enough data?
Is the data pure enough?

O(10) – O(100)95%

Prime Focus SpectrographFoV 1.3 deg (diam)with 2394 Fiber

MMFS (M. G. Walker et al,. (2007))

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Prime Focus SpectrographFoV 1.3 deg (diam)with 2394 Fiber

MMFS (M. G. Walker et al,. (2007))

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Current Status
Spherical
Is the fit model accurate enough?
Assumption

Axisymmetric fit

Enough data?

O(10) – O(100)Increase #data
Is the data pure enough?

95%

Current Status
Spherical
Is the fit model accurate enough?
Assumption

Axisymmetric fit

Enough data?

O(10) – O(100)Increase #data
Is the data pure enough?

95%

Hidden Systematics…
Prior Bias?/Cut?

In the future…

N < 100: > O(1) uncertainty

Non Spherical?
0.2～0.4 uncertainty

Increasing#Obs Star can reducethese errors

Velocity anisotropy?
Etc. (Halo truncation, stability, binary stars…)

Foreground Contamination?
N < 100: O(1) uncertainty
N ～1000: < 0.4

Remains!

Q. How to treat this FG
contamination?

Purpose
Q. How many stars will be observed?
Q. How can we obtain purer dSph member
star data?
Q. How can we include the FG contaminationin the fit?

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Set up
1. Mock Observable:

dSph Stellar + ForegrounddSph Stellar Mock

FoV 1.3 deg (diam)
Member Star
with 2394 FiberMock⇒Assign stellar information(Age, metalicity, luminosity, color, etc)

Preliminary⇒Assign velocity and distance,(Boltzmann Equation under DM profile)

Foreground Mock

⇒Besancon Model (Robin+ (2003))

2. Detector:
Prime Focus Spectrograph

Foreground Mock

Preliminary

ObsCut Strategy
ROI Cut:
0.65 deg radius for 1 pointing
velocity Cut
vLower < v < vUpper
Surface Gravity Cut∝M/4πR2∝MT4/L ∝(Luminosity)^(-1)
Eliminate Darker Foreground Star

Thin Disk
Thick Disk
Halo StarColor –Magnitude Cut* Teff, Chemical Cut do not so efficient

Chem. -> degenerate

MemberFG#Obs Expectation

DracoUrsa Minor

Ursa Major 2

Current

i > 21i > 21.5

i > 22450

9001150

-300

1100

1400

-2050

115

195

37

33

135

43

41

180

220
31

Fit including FG model
Member Fraction

Prob. Dist. Of FG
Member Parameter= halo information

FG ParameterCan be considered to be
Gaussian after several cuts.
32Fit Results
ContaminatedPreliminary(consider FG as Member star)
5% Contamination biasesdLogJ = ~0.3-0.5⇒Overestimates sensitivity line
~ 2-3 times stronger

21.5 22i < 21Our FitReproduce Ref val.
SumObs StarsFGMemSummary• Indirect detection is essential for O(1) TeV DM search.
• Gamma-ray observation of dSphs can give robust constraints (～1TeV or More) if dLogJ is small enough.
• However, many hidden systematic errors still exist.
• We give more conservative results by the axisymmetric DM model.
• Prior bias gives too aggressive results.
• Investigation of stellar kinematics (PFS) will play a crucial role.
• Reduction of foreground stars can be achieved by our cut and newlikelihood.
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Thank You !
Koji Ichikawa
In collaboration withKohei Hayashi , Masahiro Ibe, Miho N. Ishigaki,
Shigeki Matsumoto and Hajime Sugai.

Kashiwa, Dec. 16, 201635