The Cosmic Microwave Background and the WMAP satellite

The Cosmic Microwave Background and the WMAP satellite results Elena Pierpaoli (Caltech)

Outline: • What is the Cosmic Microwave Background (CMB) radiation and why it is important • Properties: frequency spectrum, temperature, (an)isotropy • The satellite missions: COBE, WMAP and Planck • The sky map and the power spectrum • Where we stand now: the WMAP results • Perspectives: Planck predictions

Recombination Reionization

Penzias and Wilson discovered the ~3 K CMB radiation in 1965 (and received the Nobel Prize for it in 1978)

The space experiments:

Properties: the frequency spectrum The CMB radiation is a black body with temperature T=2. 726

Properties: isotropy and anisotropies • The CMB radiation is isotropic • We are moving with respect to the CMB rest frame • There are tiny anisotropies, imprints of matter-radiation fluctuations.

The CMB anisotropies map

The power spectrum DT(q, f) = S a Y (q, f) c = S |a |2 l, m l, m The power spectrum is the most compact way to describe (all) the cosmological information in a sky map. It allows efficient comparison between theory and observation.

Measuring the power spectrum Pierpaoli, Scott, White (Science, 2000) The 1 yr WMAP power spectrum

The cosmological parameters • Hubble constant H 0 (v= H d) • Curvature Wk [ Cl ] • densities: 0 – matter density W = r /r – baryon density W [ Cl ] – dark matter density W = r /r [ Cl ] m m crit b dm dm crit • reionization/optical depth t [ Cl ] • nature of dark matter (Cold, warm or hot? ) and dark energy • nature of primordial density perturbations (e. g. primordial spectral index ns)

The cosmological parameters from WMAP 1) The Universe is flat 2) Precise history of the Universe t = 13. 7 Gyr (+ 0. 2) trecomb=380 Kyr (+ 10) treionization= 200 Myr Universe 3) Fluctuations are Gaussian (confirmation for inflation)

Perspectives: the Planck satellite • • Higher beam Lower noise Polarization Better frequency coverage Wm within 0. 5 per cent H within 0. 4 per cent W within 0. 5 per cent 0 b

Summary • The Cosmic Microwave Background is the relic radiation of the Big Bang • By studying the anisotropies of the CMB it is possible to determine the main cosmological parameter with the precision of a few percent • Future satellite missions (Planck) will improve these constraints by one order of magnitude

The Suniaev-Zeldovich clusters Frequencies of observation cluster g e- g vc - Thermal and kinetic signal expected - Signal is independent of redshift - Signal scales as ne - Need complementary information on redshift from other data. - Future surveys: SPT, ACT (high resolution), Planck (all sky)