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Some Astrophysical Implications from Dark Matter Neutralino Annihilation

Some Astrophysical Implications from Dark Matter Neutralino Annihilation. 戸谷　友則 Tomo Totani KIAS-APCTP-DMRC workshop on Dark Side of the Universe May 24-26, KIAS, Seoul. Outline. Neutralinos as the heating source: the solution to the “cooling flow problem” of galaxy clusters?

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Some Astrophysical Implications from Dark Matter Neutralino Annihilation

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  1. Some Astrophysical Implications from Dark Matter Neutralino Annihilation 戸谷　友則 Tomo Totani KIAS-APCTP-DMRC workshop on Dark Side of the Universe May 24-26, KIAS, Seoul

  2. 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

  3. 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% (1Mpc x 1Mpc) D=52 Mpc (50 kpc x 50 kpc)

  4. 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

  5. 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…. Green: STD CF model Fabian ‘02 Peterson et al. ‘03

  6. 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 sufficiently 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?)

  7. Heat conduction and AGN to heat the intracluster gas Voigt & Fabian ’04 Voigt et al. 2002

  8. Clusters seen in optical and X-rays Courtesy from K. Masai

  9. 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 Higgs): 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

  10. Annihilation Signals • Line gamma-rays: • χ χ ２γ • 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, galaxy clusters • Positron/antiproton excess in cosmic-rays • …

  11. Line γ 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 yield Spectra from DarkSUSY

  12. 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

  13. 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

  14. ρ r rc rs 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

  15. 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

  16. The cluster density profiles from X-ray observations Abell 2029 Lewis et al. 2003 NFW Moore stars gas

  17. Birzan+ ‘04 Blanton et al. ’03 Abell 2052 X-ray image + radio contour Heating Processes: AGN vs. Neutralinos • clusters with short cooling times have giant cD galaxies at 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 dissipation • energy loss of cosmic-ray particles • stability? • neutralino annihilation is roughly constant once the density spike forms, while AGNs generally sporadic

  18. Fujita&Reiprich ’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

  19. 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 in ~5 yr operation. • Negligible background rate (~10-3) within the energy and angular resolution • Air Cerenkov telescopes may also detect • superposition of many clusters will enhance the S/N

  20. 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

  21. 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

  22. gamma-ray background from annihilation in the first cosmological objects

  23. cut off by neutralino free streaming green+, 04 ~10-5 Msun Gamma-rays from earth-mass subhalos!? 1015Msun • density power-spectrum of the universe: δ=（ρ- ρav）/ ρ SDSS 3D P(k), Tegmark et al. 04

  24. Gamma-rays from earth-mass subhalos!? Diemand+, 04 • 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)

  25. Strong et al. ‘04 the cosmic gamma-ray background

  26. 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)

  27. microhaloe contribution to EGRB Oda, Totani, & Nagashima, astro-ph/0504096 • 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.

  28. Microhalo formation in the Standard Structure Formation Theory

  29. 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

  30. 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 γ~1.7

  31. 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.

  32. Flux from isolated objects • the nearest microhaloes • M31 (the Andromeda galaxy) • ~1.5x1011Msun within ~1° (13kpc)

  33. Galactic and extragalactic gamma-ray background from microhaloes Oda et al. ‘05

  34. Inverse Compton Model Gamma-ray halo around the GC? Dixon et al. ‘98 excess from the standard model x 1.2 excess from the standard CR interaction model of the Galactic gamma-ray background gamma-ray halo? Flux level ~ EGRB

  35. Conclusions: Part II • earth-mass sized microhaloes can be constrained by galactic/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

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