1. Non-Thermal Radiation from Intergalactic Shocks Uri Keshet 1, Eli Waxman 1, Abraham Loeb 2, Volker Springel 3, and Lars Hernquist 2 1) Weizmann Institute of Science; 2) Harvard University; 3) Max Planck Institute for Astrophysics 1.“Cosmic γ-ray background from structure formation in the intergalactic medium”, Loeb and Waxman 2000, Nature, 405, 156-158 2.“Fluctuations in the radio background from intergalactic synchrotron emission”, Waxman and Loeb 2000, The Astrophysical Journal, 545, L11-L14 3.“Gamma rays from intergalactic shocks”; Keshet, Waxman, Loeb, Springel and Hernquist 2003, The Astrophysical Journal, 585, 128-150 4.“The case for a low extragalactic gamma-ray background”; Keshet, Waxman and Loeb 2004, Journal of Cosmology and Astrophysics, 04 (006) 5.“Imprint of Intergalactic shocks on the radio sky”; Keshet, Waxman and Loeb 2004, submitted to ApJ [astro-ph/0402320] 6.“A statistical detection of γ-ray emission from galaxy clusters…”, Scharf & Mukherjee 2002, The Astrophysical Journal 580, 154-163 7.“EGRET observations of the extragalactic gamma-ray emission”, Sreekumar et al. 1998, The Astrophysical Journal 494, 523-534 Approximations: 1) Large scale structure (LSS) composed of halos 2) Halo mass distribution: isothermal sphere 3) Strong shocks only CONCEPT ANALYTICAL MODEL TREE-SPH COSMOLOGICAL SIMULATION BIBLIOGRAPHY Max Planck Institute for Astrophysics Converging flows during structure formation (SF) Electron acceleration Inverse-Compton (of CMB photons) and synchrotron emission Collisionless shocks Intergalactic shocks emit radiation in the following process: M,T r sh M e-e- e-e- γ γ γ γ Halo Dimensional Analysis: Halo Parameters: M- mass T- temperature r sh - shock radius - mass accretion rate f acc fTfT frfr fTfT frfr unknown dimensionless parameters Relativistic Electron Distribution Strong shocks energy cutoff γ max : cooling limited syn log 10 M/M ⊙ z IC z log 10 M/M ⊙ Emitted Radiation: electron energy ξ e ≈5% (2.5%-7.5%) magnetic energy ξ B ≈1% (0.05%-2%) Parameterization (no complete model): halo luminosity: Integration over halo abundance: (images: the integrands in the mass- redshift plane) % out of shock thermal energy Cosmological model ΩΛΩΛ vacuum energy0.7 Ω dm dark matter energy0.26 ΩbΩb baryon energy0.04 h Hubble coefficient0.67 nfluctuation power1 σ8σ8 fluctuation normalization0.9 Simulation parameters NbNb number of SPH particles224 3 N dm # of dark matter particles224 3 Lsimulation box size200 Mpc M SPH SPH particle mass 3.6 ⅹ 10 11 M ⊙ M res mass resolution~10 11 M ⊙ Z0Z0 initial redshift50 Cooling is inefficient in the relevant regions (panel 1) Adiabatic simulations suffice Entropy changes (panel 2) of SPH particles trace the shocks (panel 4) SHOCK IDENTIFICATION n [cm -3 ] Simulated sky Δθ=42’ Δθ=12’ INTEGRATED EMISSION South North Previous estimate (Sreekumar et al. 1998) South North 70% syn. tracer (22 GHz) 30% gas tracer (21 cm) EXTRAGALACTIC GAMMA-RAY BACKGROUND GAMMA-RAY SIGNAL n [cm -3 ] MODEL CALIBRATION CMB Bremsstrahlung from Lyα clouds IGM shocks Galactic synchrotron ∝ ℓ -1/2 discrete sources ∝ ℓ IGM fluctuation dominate on 1 ’ -0 0.5 scales ~ const for 400< ℓ <4000 21 cm tomography MHz RADIO SKY very dense, beyond shocks Panel 1: phase space with t cool /t H contours already cold Translates ΔS * to Mach number M Mpc Panel 3: density slice (100x100x10 Mpc) Panel 4: same density slice as shown in panel 3, but including the M>4 shocked particles only M 10 3 10 2 10 1 10 4 10 0 10 -1 10 -2 10 -3 10 -4 M=4 dN/dΔS * ∫ dN/dΔS * 10 0 10 5 Panel 2: histogram of entropy change ΔS * ≡ ΔS/C V accumulated by SPH particles in the epoch 0<z<2 Particles with ΔS * above the cutoff trace all shocks of Mach number M>4 Shock fronts may be identified >100 MeV >10 GeV log 10 T J/ Conclusions: >10 sources well resolved by GLAST (for ξe≈0.05) γ-ray clusters: targets for MAGIC, HESS, VERITAS γ-ray morphology: accretion rings with bright emission at filament intersections J/ Mpc deg Mpc Model halo parameters (column 1) are calibrated with various features of the simulation (column 2). Agreement between the radiation fields extracted from the simulation and from the calibrated model (column 3) provides an independent check of the calibration scheme. Param.Calibrated usingValue (range) fTfT Mass average temperature: M ≈ 4 X 10 6 e -0.9z K0.5 (0.45-0.55) f acc Mass fraction processed by strong shocks, e.g. f(z<2) ≈ 41%0.12 (0.08-0.17) frfr Typical size of bright emitting region (e.g. 2 Mpc for 10 15 M ⊙ )0.1 (0.05-0.2) ε 2 dJ/dε[keV s -1 cm -2 sr -1 ] 10 -3 10 -2 10 -1 10 0 keV GeV ε[eV] MeV J ∝ ξ e simulation J ∝ ξ e J ∝ ξ e f acc f T EGRET F[ph s -1 cm -2 ] N(>F) GLASTEGRET ξ e= 5% non-calibrated calibrated SpectrumSource Number Count non-calibrated Conclusions: IGM ≥ 10% of EGRB flux > a dozen GLAST sources for ξe>0.03 Cross-correlation with LSS (e.g. Scharf & Mukherjee 2002) calibrated model simulation CMB Galactic synchrotron IGM shocks total ERB estimates ν [MHz] IGM shocks: significant fraction of the ERB Radio sky brightness Intensity fluctuations δI ℓ on 0 0.5 scales modeled EGRB [ref 7]408 MHzPrevious EGRB estimates are: Non isotropic on large scale Correlated with Galactic tracers High (≈ total polar intensity) EGRET >100 MeV Fit EGRET latitude profile as a sum of 2 components; one linear in a Galactic gas tracer and the other linear in a synchrotron tracer: Results: Robust EGRB flux upper limit (~1/3 of previous estimates) CONCLUSIONS AND IMPLICATIONS Conclusions γ-ray sources detectable by GLAST and Ćerenkov detectors Signal fluctuations dominate the radio sky on ~1’-0.5 0 scales Indirect detection, e.g. cross correlations with LSS tracers Extragalactic backgrounds: EGRB low, ERB unknown Calibrated analytical model, fast shock identification in SPH Implications of signal detection First identification of intergalactic shocks Reconstruction of large-scale flows Tracer of warm-hot IGM (WHIM) Probe of intergalactic magnetic fields ξ e= 5% SNR observations B cluster ≈ 0.1μG isothermal sphere: velocity dispersion Hubble’s coefficient effective mass The emission from strong shocks dominates the radiation from the periphery of galaxy clusters and from galaxy filaments; traces LSS e.g. according to the Press- Schechter halo mass function