Probing Dark Matter With Radio Observations

1. Probing Dark Matter With Radio Observations Chorng-Yuan Hwang 黃崇源

2. Why do we need Dark Matter (DM)? • Rotation curve of Milky Way and galaxies • Mass of galaxy clusters • Large scale structures of the Universe • Cosmological model • Modified Newtonian Dynamics (MOND) might explain rotation curves but not large scale structures and CMB

3. Dark matter in galaxy • About 90% of the mass of galaxies is in the form of dark matter, which can not be observed. • The flat rotation curve of the Milky Way suggests that the dark halo of the Milky might distribute: • Total M  r • (r)  r-2

4. Rotational Curve of Milky Way

5. Rotation Curves of Four Spirals

6. Clusters in Optical

7. Dark Matter In Galaxy Clusters

8. Dark Matter in Large-Scale Structures

9. Dark Matter in the Universe (Hinshaw et al 2009) (WMAP)

10. Fluctuations of CMB (Hinshaw et al 2009)(WMAP)

11. Other Models/Theories • Modified Newtonian Dynamics (MOND) • This might explain the rotation curves of galaxies but is difficult to explain the large scale structures and CMB • It is not excluded that both dark matter and MOND are necessary.

12. Dark Matter Distribution • N-body simulation of dark matter halo structure: • NFW profile: • Cusp profile (Diemand 2007):

13. What is the Dark Matter (DM)? • DM must be non-baryonic • DM must be cold • A viable candidate for the DM is the Weakly Interacting Massive Particles (WIMPs). • The most favorable WIMPs are the neutralino  predicated in the supersymmetric (SUSY) extension of the standard model and Kaluza-Klein particles.

14. Neutralino  • A linear combination of two neutral higgsinos and two gauginos.  = B + W + H1 + H2 • The most likely mass of  is between ~ 50 GeV to 1 TeV • Self-annihilation of  will decay into fermion pairs or gauge boson pairs and will finally become gamma ray, electrons and positrons.

15. Kaluza-Klein particles • Particles from compact extra dimension. • the mass of the lightest Kaluza–Klein particle is expected to be greater than 300 GeV • The annihilation of Kaluza–Klein particles can proceed through direct production of electron-positron pairs resulting in a source spectrum that is dominated by a delta function at the particle mass.

16. Prediction and Observations of DM: Difficult to detect directly

17. (CDMSII Collaboration 2010)

18. Relativistic electrons positrons decayed from DM • If  is the relic particle from the hot big bang and constitute the DM, then the self-annihilating cross section is related to the abundance of dark matter • mh2 =h2 = 310-27 cm2 s-1/<v> • From WMAP, mh2 =0.127, so the self-annihilation cross section of  is about <v> = 2.36 10-26 cm2 s-1 • We might observe the resulting electrons and -rays that can be compared with models!

19. Where to Observe the DM • Simulations suggest that DM is clumped into sub-halos down to the Earth mass with a size of the solar system. • DM mass in clumps ~ 50% of total mass in halos • dN/dM ~ M-2 • The source function is proportional to n2 • Even small DM sub-halos can produce significant relativistic electrons and -rays!

20. Missing Subhalos? Diemand et al 2007

21. Dark halo mass distribution (Diemand et al 2005)

22. Illuminating Dark Halos?

23. Electron/positron spectra Source function: Evolution of electrons: Stationary spectra:

24. Equilibrium positron spectra in Milky Way from the annihilation of 100GeV  using clumpy model of Diemand et al 2005

25. Equilibrium positron spectra in Milky Way from the annihilation of 1TeV  using clumpy model of Diemand et al 2005

26. Spectrum of cosmic-ray electrons

27. ATIC results (2008): Kaluza-Klein particles?

28. Kaluza-Klein particles with mass of 620 GeV? (Chang et al 2008; ATIC)

29. FERMI Results (Abdo et al 2009)

30. Radio emission of electrons and positrons from decayed DM • Most of the astronomical objects have magnetic fields. • Relativistic electrons in magnetic fields can produce radio emission. • We can estimate the resulting radio emission and compare with radio observations of galaxies and galaxy clusters.

31. Radio Halos • Some clusters show radio halos from synchrotron radiation of relativistic electrons of unknown origins. • large scale and steep spectrum. • 1/3 of clusters with mass > 1015 solar mass show radio halos • Magnetic fields in all clusters are ~ 5-10G

32. A2163 Feretti (2003)

33. Models for Emission of DM Halo from Nearby galaxy Clusters and galaxies • Select several nearby rich clusters with measured X-ray profile and mass • Assume B=5 G and steady state • NFW profile • <v> = 2.36 10-26 cm2 s-1 • n = mass density/m • m =100GeV – several TeV • subhalo mass: ~ 1012-10-4 M

34. Source functionsof Coma main halo for 2TeV , solid line for fermion channels and dashed line for boson channels

35. Source functionsof Coma halo for 100GeV , solid line for fermion channels and dashed line for boson channels

36. Self-Annihilation flux from CDM of Coma cluster

37. Self-Annihilation flux from CDM of A754 cluster

38. Self-Annihilation flux from CDM of A85 cluster

39. Self-Annihilation flux from a 1011 M DM halos at z=0.02

40. Conclusion and Summary • The predicted radio halo emission from the self-annihilation of DM neutralinos could be detectable. • The non-detection of radio halos for some massive clusters with high magnetic fields might be used to constrain the properties of the DM neutralinos or/and to constrain the structure formation models of the universe.

41. The End