some astrophysical implications from dark matter neutralino annihilation 戸谷 友則 tomo totani...
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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