Résumé / Abstract Seminaire_IAP
« Two milestones in the life of the Universe: Last Scattering Surface and Black Body Photosphere »

Rashid Sunyaev
Max-Planck-Institut für Astrophysik (Garching, Allemagne)

Hydrogen recombination at redshifts z ~ 1100 - 1300 leads to the rapid decrease of the optical depth of the Universe due to the Thomson scattering. As a result, we can directly observe the density and velocity perturbations leading to the formation of acoustic peaks in the observed CMB angular distribution. Spectral features in the CMB spectrum contain a wealth of information about physical processes in the early Universe at redshifts z < 2 10^6, i.e. when the Universe was more than 2 months old. The Cosmic Microwave Background Radiation (CMB) spectral distortions are complementary to all other probes of cosmology. In fact, most of the information contained in the CMB spectrum is inaccessible by any other means. This talk outlines the main physics behind the spectral features in the CMB throughout the history of the Universe, concentrating on the distortions which are inevitable and must be present at a level observable by the next generation of proposed CMB experiments. The spectral distortions considered here include spectral features from a) cosmological recombination of hydrogen and helium, b) resonant scattering of CMB by metals during reionization which allows us to measure their abundances at redshifts z ~ 3 - 20, c) y-type spectral distortions during and after reionization and d) µ - type distortions created at redshifts z > 10^5 due to any significant energy release (for example: due to decay or annihilation of dark matter particles or due to viscous decay of primordial sound waves). Special attention will be given to the existence of Blackbody Photosphere of our Universe at redshift z ~ 2 10^6, behind which Comptonization, double Compton and Bremsstrahlung are able to remove spectral distortions arising due to arbitrary strong energy release and create a perfect black body spectrum. CMB spectral distortions detected on the sky by Planck spacecraft, South Pole Telescope and Atacama Cosmology Telescope permitted us to discover more than thousand hitherto unknown clusters of galaxies (most massive gravitationally bound objects in the Universe, containing thousands of galaxies, hot (kTe > 1 KeV) intra-cluster gas, a huge amount of dark matter and gravitational lenses). These clusters of galaxies are serving as probes for modern cosmology today and are reflecting the continuous growth of the Large Scale Structure.
vendredi 27 mai 2016 - 11:00
Amphithéâtre Henri Mineur, Institut d'Astrophysique de Paris
Page web du séminaire / Seminar's webpage