CTA-Japan workshop 2017

Dark Matter Search indwarf Spheroidal galaxies
work in progress (2017)
Nagisa Hiroshima (ICRR, KEK)
andMasaaki Hayashida (Chiba.U), Kaz Kohri (KEK, SOKENDAI)

Contents:
1. Introduction
motivations for searching dark matter in dwarf spheroidal galaxies

2. Method
How can we search DM in dSph with certain density profile?

3. Prediction
4. Conclusion
1

Introduction
Dark Matter search in dwarf spheroidal galaxies2

Evidence for the Dark Matter
1, Large Scale Structure
Ω"# ℎ% ~ 0.258

2, Rotation Curves of Galaxies

3, Bullet clusters
We need something with little electromagnetic interactions
3Strategies:
collider???
Dark MatterdirectsearchStandard Model Particles

Indirect Search4

Advantages of CTA:
DM + DM -> (particles in the Standard Model)
DM+DM -> 2 𝜸
DM+DM -> qq-> π0+...-> 𝜸 +...
DM+DM -> W+W-> µ+nµ+...-> 𝜸 +...
DM+DM -> l+ l±-> l + 𝛾(CMB) -> 𝜸 +...

with Δ𝜃~0.03 deg

5Why ‘TeV’?
DM as a thermal relic of our universe: Ω"# ℎ% ~ 0.258
𝑑𝑛"#%%+ 3𝐻𝑛"# = −< 𝜎𝑣 > (𝑛"#− 𝑛"#,@A)𝑑𝑡%@ thermal freeze out (zf)
3𝐻𝑛"# ~ < 𝜎𝑣 > 𝑛"#𝐻
conserved 𝑛"#~∝ (< 𝜎𝑣 > 𝑇)EK𝑠< 𝜎𝑣 > 𝑠mDM/Tzf~ 20 − 30

𝜌"#∝ 𝑚"# < 𝜎𝑣 > 𝑚"# EK ∝ < 𝜎𝑣 >EK𝑠
< 𝜎𝑣 >%
Ω"# ℎ = 0.1
3×10E%F 𝑐𝑚I 𝑠 EK

EK

0.1 E%, < 𝜎𝑣 > ~TeV 6

gamma-ray flux:γγ
distance (D)sourceγ

Solid angle (∆Ω)

observerJ-factor[GeV2/cm5]
denser is better7

target: dwarf spheroidal galaxies (dSph)

Ackermann et al., 2014,arXiv 1310.0828

1, galactic center : J=1022-1024 ◎ , contamination △2, dwarf spheroidal : J=1017-1020 ○ , contamination ○galaxies (dSphs)
8

Methods

9spatial extension of dSphs
𝜃𝑚𝑎𝑥: position of the outermost member star (O(1) degree )****dSphSolid angle (∆Ω)

distance (D)XYZ[𝐽=S\observer%
2𝜋 sin 𝜃 𝑑𝜃 S 𝜌"#𝑟 𝑑𝑠^_`

𝜌"# (𝑟) & extension 𝜃𝑚𝑎𝑥 is derived from stellar kinematics data
see Geringer-Sameth et al., 2015 (spherical)
Hayashi et al., 2016 (axisymmetric), etc.

We take the density profile of dSphs into account10

DM profile of dSph
𝜌"# 𝑟 =generalized NFW

𝜌\𝑟 e𝑟
1+𝑟d𝑟dgEef f∝ 𝑟 Ee2E(gEe)/f 𝜌\∝ 𝑟 Eg
𝑟dstellar kinematics data gives (𝛼, 𝛽, 𝛾, 𝜌d , 𝑟d )11source selection
dSph of Geringer-Sameth 2015 in the Northen sky

𝜃𝑚𝑎𝑥[deg]

Draco

UMa2
Coma
Leo2log10(J[GeV2/cm5])

Targets: compact , dense dSph
namera[deg]

dec
[deg]

dist
[kpc]

𝜃𝑚𝑎𝑥
[deg]

log10(J𝜃𝑚𝑎𝑥) log10(J<0.5˚)[GeV2/cm5] [GeV2/cm5]

Draco

260

57.9

76

1.3

19.05

18.84

Coma

186

23.9

44

0.31

19.02

19.02

Leo II

168

22.2

233

0.23

17.97

17.97

Ursa
Major II133

63.1

32

0.53

19.42

19.42

(Geringer-Sameth et al., 2015)13

Profiles:

Leo2

Draco
𝜃𝑚𝑎𝑥

3deg

Coma𝜃𝑚𝑎𝑥

3deg

𝜃𝑚𝑎𝑥

3deg14

UMa2
𝜃𝑚𝑎𝑥

3deg

Profiles:

Leo2

Draco

𝜃
It is important to takethese structures into𝜃 account.
3deg
3deg
Then, what kind of DM do we search in these dSphs?
𝑚𝑎𝑥

𝑚𝑎𝑥

Coma

UMa2
𝜃𝑚𝑎𝑥

3deg

𝜃𝑚𝑎𝑥

3deg15

Particle Physics Model
E2dN/dE[GeV]e.g. DM + DM -> W+ + WmDM=1TeV
mDM=10TeV

E [GeV] 16

motivated in Wino DM model

Conclusion

20

Conclusion• CTA is very suitable for dark matter (DM) search• dwarf spheroidal galaxies (dSphs) are good targets
because of their clear environments• We should be careful about the spatial structure ofdSphs when we search DM in those with CTA• CTA is expected to reach <𝜎𝑣> ~1022 − 1023cm3/s
with 50h observations for dSph DM search21