Jelic PhD thesis

ডিপথট থেকে

Chapter 1

  • At Planck time universe is isotopic, homogeneous, and in a hot, dense and quantum state.
  • inflation. Size of the universe increases by a factor of 10^26
  • baryogenesis. Survival of matters after matter antimatter annihilation. Ends when universe is 10^{-3} s old.
  • The first three minutes. Primordial nucleosynthesis.
  • the first months, photons scatter off electrons and light nuclei, universe opaque. Creation of thermal emission, CMB.
  • after one month, expansion of universe becomes faster than scattering process, CMB is fixed forever.
  • after 300 thousand years, recombination.
  • 400 million years after, structure formation begins.
  • after 400 to 1000 million years, epoch of reionization.
  • two probes of EoR, CMB and 21cm line.

CMB

  • CMB temperature is 2.7 K now.
  • this temperature is uniform in every direction to better than one part in a thousand.
  • temperature anisotropies have rms of only 20 microK.
  • two types of anisotropies, primary and secondary.
  • primary anisotropies arise from the last scattering surface, at z~1100. 3 mechanisms give rise to these,
    1. Sachs-Wolfe effect: Photons from high density regions are gravitationally redshifted while climbing out of potential wells. At largest scales.
    2. Intrinsic a diabetic effect: Matter-radiation coupling in high density regions compress radiation and raise temperature. Small scale.
    3. Doppler effect: Plasma with non-zero velocity Doppler shifts the CMB photons. Small scale.
  • Photon diffusion damping suppresses primary anisotropies. Diffusion of photons equalize temperatures of hot and cold regions, at smallest scales.
  • Secondary anisotropies are caused by interactions of these photons with matters along the line of sight towards us after the recombination epoch.
  • There are two types of interactions: gravitational and scattering. Gravitational interactions are:
    1. Integrated Sachs-Wolfe effect (ISW): like the primary SW but at a later period. They are of two types: early type ISW occurs when universe is radiation dominated. Late type ISW occurs when dark energy is dominating. Here we assume linear time-varying gravitational potential. Large scale effect.
    2. Rees-Sciama effect: A late type ISW effect that assuming non-linear gravitational potential, associated with gravitational collapse. Scales are of clusters and superclusters (5-10 arcm).
    3. Gravitational lensing: of CMB by matter, Significant on scales less than a few arcm.
  • The scattering interactions of CMB photons and matter are:
    1. Thermal Sunyaev-Zeldovich effect (tSZ): interaction of photons and hot plasma through inverse Compton scattering. Low energy photons boosted to higher energies. Thus less photon in the Rayleigh-jeans tail than in the Wein tail. Scales are of clusters and superclusters. But during EoR can affect at smaller scales.
    2. Kinetic Sunyaev-Zeldovich effect (kSZ): Doe to Doppler effect due to bulk motion of electrons that scatter photons. No distortion of CMB spectrum, instead the whole spectrum is red or blue shifted.
    3. Ostriker-Vishniac effect (OV): Same as kSZ but in linear regime.

Epoch of Reionization

  • Primary CMB radiation is linearly polarized due to Thomson scattering of photons with the free electrons before recombination epoch.
  • During EoR new electrons scatter the photons again which generates a new anisotropy in CMB polarization at large scales.
  • Size of polarization anisotropy depends on the horizon size at that z. So scattering at different redshifts will create anisotropies in the polarization intensity at different scales.
  • EoR electrons produces a bump in CMB angular power spectrum-
    • Position of the bump depends on the redshift of reionization.
    • height of the bump depends on the integrated optical depth of free electrons of EoR. Thus the height or amplitude of the bump is proportional to the duration of EoR.
  • Dunkley et al. (2009) found: <math>\tau_{eor}=0.087\pm 0.017</math> and <math>z_{eor}=11.0\pm 1.4</math>
  • Reionization signature is no more than 10% of primary signal.

Redshifted 21-cm line