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Low Frequency Background and Cosmology

Low Frequency Background and Cosmology. Xuelei Chen National Astronomical Observatories. Kashigar, September 10th 2005. Outline. The angular power spectrum of the galactic synchrotron radiation (based on Chen, astro-ph/0409733)

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Low Frequency Background and Cosmology

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  1. Low Frequency Background and Cosmology Xuelei Chen National Astronomical Observatories Kashigar, September 10th 2005

  2. Outline • The angular power spectrum of the galactic synchrotron radiation (based on Chen, astro-ph/0409733) • The evolution of 21cm signal during the dark age and the epoch of reionzation (based on Chen & Miralda-Escude, ApJ 602, 1 (2004)), • The 21cm signature of the first stars (based on Chen & Miralda-Escude, in preparation)

  3. Foreground for CMB and 21cm observation: galactic synchrotron 408 MHz skymap Tgal ~ 280 (/150MHz)-2.5 K @ NCP • (MHz) Tgal (K) z 200 140 6.1 • 280 8.5 • 770 13 70 1900 19 50 4400 27

  4. Foreground Removal Synchrotron foreground is removable as long as it is smooth. Still, can we understand it physically? Wang et al astro-ph/0501081

  5. A spherical cow model • Understand the synchrotron radiation at • high galactic latitude • small scale • random field • Fourier space

  6. galactic synchrotron power law distribution of cosmic ray electron synchrotron emissivity Total intensity along a line of sight

  7. Angular power spectrum Separable spatial and frequency variation power spectrum angular power spectrum (Limber approximation)

  8. cosmic ray electron B ~ microgauss, for 70-200 MHz, radiation from electron 0.1 GeV < E < 10 GeV CR electron spectrum Local measurement (Casadei & Bindi 2004):

  9. Model • B ~ 4 microG • scale height ~ 1 kpc • brightness temperature ~ 20 K at 408 MHz

  10. Magnetic Field Variation small scale, out-of-galactic plane magnetic field large scale magnetic field on the galactic plane (Beurmann, Kanbach, Bekhuijsen 1985)

  11. Magnetic Field in Turbulent ISM Komolgorov turbulence E(k)~k-5/3 Observation (Faraday Rotation): on small scale(0.01-100pc), E(k)~k-5/3 on larger scale E(k)~k-2/3 Han, Ferriere, Manchester (2004)

  12. Cosmic Ray Variation Injection-Diffusion model: cosmic ray electrons are injected at some points (SNR), propagate in random magnetic field, and diffuse out. (Kobayashi et al 2004) (Casadei & Binsi 2004) scale height:

  13. Solution of the Diffusion Equation Fourier transformed Steady State solution power spectrum

  14. Injection Rate If SNe is Poisson, V: effective volume where SNe occur, tSN: average interval for SNe within V

  15. WMAP Result Field strength ~ OK magnetic field induced cosmic ray induced WMAP:

  16. Discussion Theoretical simplification • Geometry • Gaussianity • Large scale field • Variation of spectral index • Correlation between magnetic field and cosmic ray

  17. Discussion Observation: • some observations with steeper angular spectrum • extragalactic (unresolved point source) contribution

  18. What to do next • realistic geometry • variation of spectral index • include large scale field • polarization • multiwavelength cross correlation • connection with dynamo and CR model

  19. The Epoch of Reionization (EOR)

  20. VLBI 21CMA 21cm probe of EOR LOFAR MWA

  21. spontanous transition • collision induced transition • CMB induced transition • Lyman series scattering • (Wouthousian-Field mechanism) Ly  CMB Related processes n=1 n=0 F=1 21cm F=0

  22. collision atomic motion Ly  Ly  photons CMB spin The spin temperature Thermal systems: Chen & Miralda-Escude 2004

  23. 21cm tomography Simulation by Furlanetto, Sokasian, Hernquist, astro-ph/0305065 Modulation: • density • ionization fraction • spin temperature

  24. star formation Adiabatic Evolution of Temperatures CMB spin gas

  25. 21cm brightness temperature spin temperature evolution Chen & Miralda-Escude 2004 Star Formation and X-ray Heating of gas Heating of IGM: • Shock • ionizing radiation (limited to HII) • Lyman alpha? (Madau, Meiksen, Rees 1997) • X-ray X possibility of absorption signal

  26. Formation of first stars Frenk 2005 • primodial density fluctuation grow to form dark matter halos, small halos form first • gas fall in for sufficiently large halos (Jeans mass) • gas cool by molecule or atomic H radiation to form first stars • first stars may be very massive ~ a few hundred solar masses

  27. Property of first stars • pop I: disk stars Z~Zo • pop II: halo stars Z~0.01 Zo • pop III: ? Z<0.001 Zo Tumlinson & Shull 2000 Bromm et al 2000

  28. Comoving density

  29. The Evolution of Lyman alpha background

  30. Evolution of gas temperature

  31. 21cm signature of high-z objects: a quasar Lyman alpha photons emitted by the quasar couples spin temperature to the kinetic temperature Tozzi et al 2000

  32. Ly alpha sphere around a first star

  33. Heating function

  34. Lyman alpha sphere

  35. The 21cm signature of the first star Typical size: a few arcsec Typical width: 10 kHz Typical dT: 20mK/2000K Challenge for the future generation of radio astronomers! The 21cm brightness temperature around a first star

  36. The End

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