Do Gamma Rays reveal our Galaxy s DM?

Transcription

1 Do Gamma Rays reveal our Galaxy s DM? We don t know it, because we don t see it! WdB, C. Sander, V. Zhukov, A. Gladyshev, D. Kazakov, EGRET excess of diffuse Galactic Gamma Rays as Tracer of DM, astro-ph/ , A&A, 444 (2005) 51 W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

2 EGRET on CGRO (Compton Gamma Ray Observ.) Data publicly available from NASA archive 9 yrs of data taken in space! ( ) W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

3 Do Gamma Rays reveal the DM of our Galaxy? What is known about Dark Matter? 23% of the Energy of the Universe IF THERMAL RELIC THEN IT MUST BE Weakly interacting Massive Particle (WIMP) and annihilate with <σv>= cm 3 /s Annihilation into Quarkpairs -> Excess in galactic Gamma rays (π 0 decays) Indeed observed by EGRET satellite WIMP Mass GeV from spectrum From CMB + SN1a + surveys Halo distribution of DM by observing in many sky directions Data consistent with Supersymmetry DM halo profile of galaxy cluster from weak lensing W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

4 Thermal history of WIMPs as thermal relic Thermal equilibrium abundance Actual abundance Comoving number density T=M/22 x=m/t Jungmann,Kamionkowski, Griest, PR 1995 T>>M: f+f->m+m; M+M->f+f T<M: M+M->f+f T=M/22: M decoupled, stable density (when annihilation rate expansionrate, i.e. Γ=<σv>nχ(x fr ) H(x fr )!) WMAP -> Ωh 2 =0.113± > <σv>= cm 3 /s DM increases in Galaxies: 1 WIMP/coffee cup 10 5 <ρ>. DMA ( ρ 2 ) restarts again.. Annihilation into lighter particles, like Quarks and Leptons -> π 0 s -> Gammas! Only assumption in this analysis: WIMP = THERMAL RELIC! W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

5 Problems solved by DM annihilation Astronomy Structure in rotation curve Doughnut of stars at 14 kpc Doughnut of dust and H 2 at 4 kpc Astro-particle Physics Cosmology Excess of Gamma rays 23%DM, Hubble-> DM Annih. x-sect. How does DM annihilate? How is DM distributed? Particle Physics Where are signals from DM annihilation? Consistent with Supersymmetry? W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

6 The EGRET excess of diffuse galactic gamma rays without and with DM annihilation π 0 IC Brems π 0 IC WIMPS Brems Fit only KNOWN shapes of BG + DMA, i.e. 1 or 2 parameter fit NO GALACTIC models needed. Propagation of gammas straightforward If normalization free, only relative point-to-point errors of 7% important, not absolute normalization error of 15%. Statistical errors negligible. W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

7 What about background shape? No SM No SM Quarks from WIMPS Protons Electrons Quarks in protons Background from nuclear interactions (mainly p+p-> π 0 + X -> γ + X inverse Compton scattering (e-+ γ -> e- + γ) Bremsstrahlung (e- + N -> e- + γ + N) Shape of background KNOWN if Cosmic Ray spectra of p and e- known W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

8 PYTHIA processes: Contribution from various hadronic processes 11 f+f' -> f+f' (QCD) f+fbar -> f'+fbar' 0 13 f+fbar -> g + g 0 28 f+g -> f + g g+g -> g + g g+g -> f + fbar Single diffractive (XB) Single diffractive (AX) Double diffractive Low-pT scattering 0 Prompt photon production: 14 f+fbar -> g+γ 0 18 f+fbar -> γ +γ 0 29 f+g -> f +γ g+g -> g + γ g+g -> γ + γ 0 2 GeV 4 8 diff W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

9 DM Annihilation in Supersymmetry χ χ ~ f f f χ χ A f f χ χ Z f f χ χ χ W χ ± χ 0 W χ Z Z 37 gammas Dominant χ + χ A b bbar quark pair Sum of diagrams should yield <σv>= cm 3 /s to get correct relic density Quark-Fragmentation known! Hence spectra of positrons, Gammas and antiprotons known! W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

10 Background + signal describe EGRET data! Background + DMA signal describe EGRET data! 50 GeV IC π 0 WIMPS Brems. π 0 IC WIMPS Brems. IC 70 Blue: background uncertainty Blue: WIMP mass uncertainty W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

11 Analysis of EGRET Data in 6 sky directions A: inner Galaxy B: outer disc C: outer Galaxy Total χ 2 for all regions :28/36 Prob.= 0.8 Excess above background > 10σ. D: low latitude E: intermediate lat. F: galactic poles A: inner Galaxy (l=±30 0, b <5 0 ) B: Galactic plane avoiding A C: Outer Galaxy D: low latitude ( ) E: intermediate lat. ( ) F: Galactic poles ( ) W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

12 Conventional Model without DMA in 6 sky regions χ 2 of conventional model:663/42 Prob. = 0 W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

13 xy xz Expected Profile Dark Matter distribution v 2 M/r=cons. and ρ (M/r)/r 2 ρ 1/r 2 for const. xzrotation curve Divergent for r=0? NFW 1/r Isotherm const. Halo profile Observed Profile xy Rotation Curve x y 2002,Newberg et al. Ibata et al, Crane et al. Yanny et al. disk W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2, z bulge Inner Ring totaldm 1/r 2 halo Outer Ring 1/r 2 profile and rings determined from independent directions Normalize to solar velocity of 220 km/s

14 Rotation curve of Milky Way Honma & Sofue (97) Schneider &Terzian (83) Brand & Blitz(93) W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

15 Do other galaxies have bumps in rotation curves? Sofue & Honma W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

16 Possible origin of ring like structure Infall of dwarf galaxy in gravitational potential of larger galaxy into elliptical orbit start precessions, if matter is not distributed homogeneous. Tidal forces gradient of field, i.e. 1/r 3. This means tidal disruption only effective at pericenter for large ellipticity! Apocenter Pericenter Could tidal disruption of dwarf galaxy lead to ringlike structure of solar masses? N-body simulations no clear answer. All depends on initial conditions. Also no clear explanation for ring of stars of 10 9 solar masses. W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

17 Tidal disruption of satellite in potential of larger galaxy Hayashi et al., astro-ph/ W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

18 Inner Ring coincides with ring of dust and H 2 -> gravitational potential well! H 2 Enhancement of inner (outer) ring over 1/r 2 profile 6 (8). Mass in rings 0.3 (3)% of total DM 4 kpc coincides with ring of neutral hydrogen molecules! Forms in presence of dust-> grav. potential well at 4-5 kpc. W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

19 Halo profile without rings DISC 10 0 <b< <b< <b<90 0 W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

20 Halo profile with rings DISC 10 0 <b< <b< <b<90 0 W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

21 10 (wrong) objections against DMA interpretation 1) Proton spectra only measured locally. Spectra near center of galaxy, where protons are accelerated, can be different and produce harder gamma spectrum, as observed by EGRET. Answer: proton energy loss times larger than age of universe, so proton energy spectra will become equal by diffusion This is PROVEN by the fact that we can fit with SAME background spectrum in inner and outer galaxy. 2) Is background known well enough to make such strong statements? A: Background SHAPE is known, since mainly from pp fixed target collisions. Analysis does not depend on absolute fluxes from propagation models. Propagation.of gammas is straightforward.signature is not only excess, BUT SPATIAL DISTRIBUTION OF EXCESS AS 1/r 2 profile+substr. 3) Can unresolved point sources be responsible for excess? Answer: NO, if they have similar spectra as the many resolved point sources, they would reduce the data points at low energy, thus increasing the DMA contribution if shapes are fitted. Also do not expect 1/r 2 profile for point sources. W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

22 10 (wrong) objections against DMA interpretation 4) Does antiproton rate exclude interpretation of EGRET data? (L.B.) EGRET EXCESS Answer:Antiproton production: p+p->pbar+x: Npbar <ρ CR ρ Gas > Antiproton annihilation:p+pbar-> X: <ρ Gas2 > <ρ Gas2 >/ <ρ Gas > 2 can be much larger than 1 by clustering 5) Rotation Positrons curves in outer galaxy measured Antiprotons with different method than inner rotation curve. Can you combine? Also it depends on R 0. Answer: first points of outer RC have same negative slope as inner RC so no Statistical problem with method. Change of slope seen for every R 0. Preliminary 6) Ringlike structures errors only have enhanced density Sofue &Honma of hydrogen, so you expect R excess of gamma radiation there. Why you need DMA? 0 =8.3 kpc Answer: since we fit only the shapes of signal and BG, a higher gas density is automatically taken into account and DMA is needed to fit the spectral shape v of the Inner data. R 0 =7.0 rotation Outer RC 7) Is EGRET data reliable enough to make curvesuch strong statements? Answer: EGRET spectrometer was calibrated in photon Black hole beam at centre: at R SLAC. Calibration carefully monitored in space. 0 =8.0±0.4 kpc Impossible to get calibration wrong in such a way that it fakes R/R 0 DMA. W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

23 Propagation in GALPROP compared with DarkSusy (Leaky Box) LARGE DIFFERENCES Antiprotons Positrons Spectrum after propagation of a 1-3 GeV source in galactic center with DarkSusy (leaky box Model) und GalProp (numerical solution of diffusion equation including all terms, like scattering, radiation, decay, fragmentation, reacceleration etc. ) W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

24 10 (wrong) objections against DMA interpretation 7) How can you be sure that this outer ring is from the tidal disruption of satellite galaxy, so one can expect DM there? Answer: one observes rings for all three ingredients of a galaxy: gas, stars and DM. The stars cannot be part of the disk, since the thickness of the ring is a factor 20 larger than the thickness of the disk. Furthermore, very small velocity dispersion of stars 8) Is it not peculiar that the rings are in the plane of the disk? Answer: the angular momenta of halo and disk tend to align after a certain time of precession, so rings end up in plane of the disk.. 9) The inner ring was not observed as a ring of stars. How can you be sure DM concentrates there? Answer: The density of stars and dust is to high to obtain substructure in the star population. However, the ring of dust and molecular hydrogen are proof of a graviational well, which indicates DM. 10) How can one reconstruct 3D halo profiles, if one observes gamma rays only along the line of sight without knowing the distance? Answer: if one observes in ALL directions, one can easily unfold, see rings of Saturn (same problem). W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

25 Astrophysics solution: Optimize e,p spectra to fit gammas Optimized Model from Strong et al. astro-ph/ Electrons Protons B/C Nucleon and electron spectra tuned to fit gamma ray data. Have to assume we live in local Bubble. Production of secondary nuclei not described with same parameters. BUT gamma rays not well described either! W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

26 Optimized Model from Strong et al. astro-ph/ Change spectral shape of electrons AND protons A: inner Galaxy B: outer disc C: outer Galaxy π 0 IC Brems D: low latitude E: intermediate lat. F: galactic poles χ 2 of optimized model:110/42 Prob. < 10-7 W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

27 Fits for optimized Model including DM A: inner Galaxy B: outer disc C: outer Galaxy D: low latitude E: intermediate lat. F: galactic poles 3 Components: galactic background + extragalactic background + DM annihilation (with same WIMP mass and same boostfactor). Fit probability of optimized model improves from > 0.8 with DMA. W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

28 From original paper on Optimized Model Strong et al. astro-ph/ MeV 150 MeV 300 MeV 500 MeV 1000 MeV 2000 MeV longitude Real problem with conventional models: if data is perfectly fitted with sum of power spectrum+monoenergetic peak for quarks, then you cannot get good fit with whatever power spectrum you invent. In addition, DM has different spatial distribution, so fitting over all directions gives prob.<10-7 in all cases. W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

29 What about Supersymmetry? W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

30 Allowed msugra region LHC: light gauginos easily observable A 0 =0 tb=50 What about WMAP? Not used sofar. Large tanβ 50->WMAP ok. W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

31 Gauge unification perfect with SUSY spectrum from EGRET SM SUSY Update from Amaldi, db, Fürstenau, PLB With SUSY spectrum from EGRET + WMAP data and start values of couplings from final LEP data perfect gauge coupling unification! Also b->sγ and g-2 in agreement with SUSY spectrum from EGRET W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

32 7 Physics Questions answered SIMULTANEOUSLY by this analysis Astrophysicists: What is the origin of GeV excess of diffuse Galactic Gamma Rays? A: DM annihilation Astronomers: Why a change of slope in the galactic rotation curve at R 0 11 kpc? A: DM substructure Why ring of stars at 14 kpc? Why ring of molecular hydrogen at 4 kpc? Cosmologists: How is DM annihilating?a: into quark pairs How is Cold Dark Matter distributed? Particle physicists: Is DM annihilating as expected in Supersymmetry? A: isothermal cored profile+substructure A: Cross sections perfectly consistent with msugra for light gauginos, heavy squarks/sleptons W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

33 Summary 10σ EGRET excess shows all key features from DM annihilation: Excess has same shape in all sky directions: everywhere it is perfectly (only?) explainable with superposition of background AND mono-energetic quarks of GeV Results consistent with minimal SUPERSYMMETRY Excess follows expectations from galaxy formation: cored 1/r 2 profile with substructure, visible matter/dm 0.02 Excess is TRACER OF DM, since it can explain peculiar shape of rotation curve Significance >10σ with >1400 indep. data points Results rather model independent, since only KNOWN spectral shapes of signal and background used, NO model dependent calculations of abs.fluxes. Conventional models CANNOT explain above points SIMULTANEOUSLY, especially spectrum of gamma rays in all directions, 1/r 2 profile, shape of rotation curve, ring of stars at 14 kpc and ring of H 2 at 4 kpc,. W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

34 Summary of summary WIMP is thermal relic showing expected annihilation into quark pairs DM becomes visible by gamma rays from fragmentation (30-40 gamma rays of few GeV pro annihilation from π 0 decays) Spatial distribution of annihilation signal is signature for DMA Different background shape yields same spatial distribution, which shows that gamma ray excess indeed traces DM W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,

35 Cross sections for Direct DM detection EGRET? W. de Boer, Univ. Karlsruhe AMS-Meeting, CERN, Feb. 2,