Some Astrophysical Implications from Dark Matter Neutralino Annihilation

戸谷　友則Tomo Totani

KIAS-APCTP-DMRC workshop on Dark Side of the UniverseMay 24-26, KIAS, Seoul

Outline

Neutralinos as the heating source: the solution to the “cooling flow problem” of galaxy clusters? Totani 2004, Phys. Rev. Lett. 92, 191301

earth-mass sized microhalos and their contribution to the galactic/extragalactic background Oda, Totani, & Nagashima 2005, astro-ph/050496

X-rays from galaxy clusters

thermal bremsstrahlung of hot gas: kT ~ 5-10 keV n ~ 10-3 cm-3 (virial) n~10-1 cm-3 (central) Mtot~1015 Msun

Mgas/Mtot ~ ΩB/ΩM~10%

Mstar/Mgas~10%

D=52 Mpc

(1Mpc x 1Mpc)

(50 kpc x 50 kpc)

the Cooling Flow Problem of Galaxy Clusters

“Cooling flow clusters” Central gas cooling time < the Hubble Time (~1010yr) Theory predicts cooling flow: ~100-1000 Msun / yr

Voigt & Fabian 03

the Cooling Flow Problem of Galaxy Clusters (2)

No evidence for strong cooling flows from latest X-ray observations A heating source required. Required heating rate: ~1045 erg/s during 1010yr for a rich cluster

AGNs? heat conduction? no satisfactory explanation yet….

Fabian ‘02 Peterson et al. ‘03

Green: STD CF modelGreen: STD CF model

Possible heat sources to solve the cooling flow problem of galaxy clusters

Heat conduction Effective if κ~0.3 Spitzer value Useful for stabilizing intracluster gas A fine tuning necessary, and central regions cannot be heated s

ufficiently by conduction (e.g. Bregman & David 98; Zakamska & Narayan ’03; Voigt & Fabian ‘04)

AGNs most cooling clusters have cD galaxies, X-ray cavities, and radio

bubbles Efficiency must be high (>~10% of BH rest mass to heat!) Stability?

AGNs generally episodic, intermittent tE~107 yr, LE >> 1045 erg/s

Actual heat process unclear (jet? buoyant bubbles?)

Heat conduction and AGN to heat the intracluster gas

Voigt et al. 2002Voigt & Fabian ’04

Clusters seen in optical and X-rays

Courtesy from K. Masai

SUSY Dark Matter (WIMPs, Neutralinos)

The most popular theoretical candidate for the dark matter SUperSYmmetry: well motivated from particle physics Lightest SUSY partners (LSPs) are stable by R-parity Neutralinos (l.c. of SUSY partners of photon, Z, and neutral Higg

s): the most likely LSP Predicted relic abundance depends on annihilation cross section

in the early universe (freeze out T~mχ/20), and is close to the critical density of the universe

Constraint on the neutralino mass 50 GeV ~< mχ <~ 10 TeV Lower bound from accelerator experiments Upper bound from cosmic overabundance

1-326

-13227

?

s cm 103

s cm )/(103

hχχ

Annihilation Signals

Line gamma-rays: χ χ ２ γ χ χ Zγ (σv)line ~ 10-29 cm3s-1 << (σv)cont ~ 10-26 cm3s-1

Continuum gamma-rays, e±, p, p-bar, ν’s

Search: Line/continuum gamma-rays from GC, nearby galaxies, galax

y clusters Positron/antiproton excess in cosmic-rays …

Annihilation yields by hadron jets Annihilation energy goes to gammas, e±,p, p-bars, neutrinos as: ~1/

4, 1/6, 1/15, 1/2 Particle energy peaks at: 0.05, 0.05, 0.1, 0.05 mχc2.

(From DarkSUSY package, Gondolo et al. 2001) Most energy is carried by ~1-10 GeV particles for mχ~100GeV

photon flux peak at ~70 MeV (~mπ/2)

An example for yieldSpectra from DarkSUSY

Line γ

Neutralino Annihilation as a Heat Source

Dark matter density profile for a rich cluster:

Annihilation （∝ ρ2) from the center is not important if γ<1.5 Contribution to heating is negligible if γ=1 (NFW).

C.f. 1044-45 erg/s required for cluster heating

ssimulation from 5.11

Mpc 0.5

cm g 10

)( )/(

0

3250

000

r

rrrr

GeV) 100/(

10 erg/s 102

/2

2

4515

1226

40

20

mm

Mm

mcML cl

Density spike by SMBH formation?

Density “spike” can be formed by the growth of supermassive black hole (SMBH) mass at the center. Young (1980); for stellar density cusps in elliptical galaxies Gondolo & Silk (1999); for DM cusps “Adiabatic” = growth time scale > orbital period at rs Annihilation rate divergent with r → 0 since γ>1.5

MrMss)( 4.233.2429

r

sr

r

sr

MrM s

s

)(

4.233.24

29

r

sr

r

Annihilation energy from the density spike at the cluster center

Density maximum determined by annihilation itself:

The annihilation luminosity from r<rc :

A factor of about 10 enhancement by r>rc and time average Steady energy production after turned on

pc 17.0

yr 10/

7/310

7/3

26

7/32

7/210,

1010

tmMr

ttm

c

clc

erg/s 102

3

42

7/510

7/2

26

7/22

7/610,

44

32

2

tmM

r

mcmL cc

ρ

rrsrc

Does density spike really form? The Galactic Center

If it is the case, a part of SUSY parameter space can be rejected (Gondolo & Silk 1999)

It is not necessarily likely (Ullio et al. 2001; Merritt et al.2002) The GC is baryon dominated.

• Is SMBH at the DM center?• Disturbed by baryonic processes, e.g., starbursts and supernovae• scatter by stars

Merger of SMBHs destroys the spike and cusps

The cooling-flow clusters of galaxies: A giant cD galaxiy always at the dynamical center DM dominates baryons to the center (e.g., Lewis et al. 2003) Adiabatic BH mass growth happens as a feed back to the cooling

flow in the past

yr 106~ kpc, 5.1~

yr10~10~

/yr10 ~ flow cooling

4/110,

72/110,

8

109

3-2

MtMr

ttMM

M

orbs

orbgrowth

sun

sun

The cluster density profiles from X-ray observations Abell 2029

Lewis et al. 2003

Moore

NFW

stars

gas

Heating Processes: AGN vs. Neutralinos clusters with short cooling times have giant cD galaxies a

t the center, X-ray cavities, radio bubbles --- indicating feedback from the cluster center. AGNs or Neutralinos?

heating process? relativistic particle production bubble formation mechanical/shock heating by bubble expansion and dissipatio

n energy loss of cosmic-ray particles

stability? neutralino annihilation is roughly constant once the density

spike forms, while AGNs generally sporadic

Blanton et al. ’03 Abell 2052 X-ray image + radio contour

Birzan+ ‘04

Efficiency of heating/CR production: AGN versus Neutralinos

AGN efficiency must be very high, Lheat ~ ε (m● c2/tage) ε~1 for some clusters with tage ~ 1010 yr

CR production from AGNs: LCR~(outflow efficiency) x (shock acceleration efficiency) x (m● c2 /tage) ε<~0.01 normally expected

neutralino annihilation: direct energy conversion into relativistic particles

Fujita&Reiprich ’04

gamma-ray detectability from clusters:test of this hypothesis

Continuum gamma-rays at ~1-10 GeV (for mχ~100GeV) ~40 gamma-rays per annihilation Very close to the EGRET upper limit for a cluster @ 100Mpc

Many positional coincidence between clusters and un-ID EGRET sources (e.g. Reimer et al. 2003)

GLAST will likely detect

Line gamma-rays A few photons for a cluster with <σv>line = 10-29 cm3s-1 for GLAST i

n ~5 yr operation. Negligible background rate (~10-3) within the energy and angular r

esolution Air Cerenkov telescopes may also detect superposition of many clusters will enhance the S/N

-1-2-21245

8 scm Mpc)100/(107~ dmLF

GC versus Clusters: quantitative comparison flux measure Mρav / (4πD2) in [GeV2 cm-5 ]

MW as a whole d=8kpc 3.9x1021

GC (within 0.1°or r<14pc), NFW: 1.9x1018

Moore: 1.5x1021

NFW+spike, r<rc: 5.4x1021

M+spike, r<rc: 2.6x1024

clusters (d=77Mpc, Lx=1045 erg/s: Perseus)NFW 1.5 x 1016

CF with Lχ=1045erg/s: 1.6 x 1021

Conclusions: Part I

neutralino annihilation can be a heat source to solve the cooling flow, if the density spike is formed by SMBH mass evolution in the cluster center

Better than heating by AGNs in: stability efficiency to produce relativistic particles/ bubbles

This hypothesis can be tested by GLAST / future ACTs

gamma-ray background from annihilation in the first cosmological objects

Gamma-rays from earth-mass subhalos!?

density power-spectrum of the universe:

SDSS 3D P(k), Tegmark et al. 04δ= （ ρ- ρav ） / ρ

1015Msun

~10-5 Msungreen+, 04

cut off by neutralino free streaming

Gamma-rays from earth-mass subhalos!?

earth mass (10-6 Msun), 0.01 pc size objects forming z~60 Hofmann+, 01, Berezinsky+, 03, Diemand+, 04

~50% of mass in the Galactic halo may be in the substructure n~500 pc-3 around Sun, encounter to the Earth for every 1,000 yr. controversial whether or not they are destroyed by tidal disruption at

stellar encounters

@ z=26, 3kpc width (comoving)

Diemand+, 04

the cosmic gamma-ray background

Strong et al. ‘04

Contribution to the cosmic gamma-ray background

Ullio et al ’02 substructures with M>~106 Msun model1:

M=171 GeV σv=4.5x10-26 cm3s-1

b2gamma=5.2x10-4

model2: M=76 GeV σv=6.1x10-28 cm3s-1

b2gamma=6.1x10-2

Assuming universal halo density profile, annihilation signal from GC exceeds if neutralinos have dominant contribution to EGRB (Ando 2005)

microhaloe contribution to EGRB

flux from nearby microhalo is very difficult to detect (see also Pieri et al. ’05)

When luminosity density is fixed, the flux from the nearest object scales as L1/3 if background flux is the same, small objects are difficult to resolve

microhalos form at very high z, with high internal density (1+z)∝ 3

Even if microhaloes are destructed in centers of galactic haloes, total flux hardly affected （ mass within 10kpc is ~6% of MW halo ） extragalactic background flux hardly affected.

Oda, Totani, & Nagashima, astro-ph/0504096

Microhalo formation in the Standard Structure Formation Theory

background on tocontributilargest thehave 3 with smicrohaloe

2expdensitynumber microhalo

,density internal microhalo

)1(18density l viria

)/(1)(1 1.69,~at collapse

60 ,1

1)(

1/ :nFluctuatioDensity Gaussian

2

3

30,

32

c

p

DMvir

nlvirc

nlnl

mh

z

zz

zz

zM

microhalo number density number density of all including those in sub(sub(sub…))structure number density around the Sun

Simulation by Diemand et al. ：　 n~500 pc-3 fsurv ~ 1 in their simulation. ~5% of total mass in the form of microhaloes

Berezinsky+ ’03 fsurv ~ 0.1-0.5% (based on analytical treatment) fsurv should be higher for those with high ν

the actual value of fsurv is highly uncertain

y)probabilit survival microhalo :(

pc 680

2exp

2

1)()(

3-

2

surv

surv

p

mh

sunsurvsun

f

f

M

RfRn

internal density profile of microhaloes

annihilation signal enhancement

simulation: concentration parameter c~

1.6 in the simulation （ α,β,γ)=(1, 3, 1.2)

fc = 6.1

crr

rrrr

virs

ss

/

])/(1[)/(

1/)(

)( density weighted-volume

weighted-mass

vir

cf

γ~1.7

internal density profile of microhaloes. 2

γ~1.7 in the resolution limit of the simulation similar to halo density profile soon after major merger: a

single power law with γ~1.5-2 (Diemand et al. ’05)

γ>1.5 divergent annihilation luminosity density core where annihilation time ~ 1010 yr

γ=1.5 fc = 31 γ=1.7 fc = 190 γ=2.0 fc = 1.4x104

fc=6.1 is a conservative choice.

Flux from isolated objects

the nearest microhaloes

M31 (the Andromeda galaxy) ~1.5x1011Msun within ~1° (13kpc)

8

122240

3/211

10~limit y sensitivit EGRET

scm 105.1~MeV) 100(

mYfF surv

99) ,(Blom101.6 :limitupper EGRET

scm 107.7~100MeV)(8

122240

9

mYfF surv

Galactic and extragalactic gamma-ray background from microhaloes

Oda et al. ‘05

Gamma-ray halo around the GC?Dixon et al. ‘98

excess from the standard CR interactionmodel of the Galactic gamma-ray background

excess from the standardmodel x 1.2

gamma-ray halo?Flux level ~ EGRB

Inverse Compton Model

Conclusions: Part II earth-mass sized microhaloes can be constrained by gal

actic/extragalactic background, much better than the flux from the nearest ones.

If fsurv ~ 1 (as suggested by simulations), microhaloes should have significant contribution to EGRB/GGRB, even with conservative choice of other parameters

flux expected from M31 is close to the EGRET upper limit if fsurv~1 a good chance to detect by GLAST