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avril 2018
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Eiichiro Komatsu (MPA) - Finding Cosmic Inflation

Vendredi 6 avril 11:00-12:00

The cosmic microwave background (CMB) research told us a remarkable story : the structure we see in our Universe such as galaxies, stars, planets, and eventually ourselves originated from tiny quantum fluctuations generated in the early Universe. With the WMAP we have confirmed many of the key predictions of inflation including flatness and statistical homogeneity of our Universe, Gaussianity and adiabaticity of primordial density fluctuations, and a small but non-zero deviation from the scale-invariant spectrum of density fluctuations. Yet, the extraordinary claim requires extraordinary evidence. The last prediction of inflation that is yet to be confirmed is the existence of primordial gravitational waves whose wavelength can be as big as billions of light years. To this end we have proposed to JAXA a new satellite mission called "LiteBIRD", whose primary scientific goal is to find signatures of gravitational waves in the polarisation of the CMB. In this presentation we describe the current state of affairs regarding our understanding of the early Universe, physics of polarisation of CMB, and the LiteBIRD proposal.

Gabriel Pratt (CEA Saclay) - The Advanced Telescope for High-Energy Astrophysics

Vendredi 13 avril 11:00-12:00

The Advanced Telescope for High-Energy Astrophysics (ATHENA) is ESA’s second Large mission, expected to launch in 2030. An observatory mission combining a telescope with large collecting area and state of the art imaging and high resolution spectroscopic capabilities, Athena is expected to give rise to a transformational leap in our understanding of hot cosmic plasmas. I will describe the current mission design and give an overview of some of the scientific goals, with an emphasis on large scale structure science.

Anne Verhamme (Obs. Genève) - Indirect probes of the escape of ionizing radiation from galaxies to unveil the nature of the sources of Cosmic Reionization

Vendredi 20 avril 11:00-12:00

Cosmic reionization corresponds to the period in the history of the Universe during which the predominantly neutral intergalactic medium was ionised by the emergence of the first luminous sources. Young stars in primeval galaxies may be the sources of reionization, if the ionising radiation, called Lyman continuum (LyC), that they produce can escape their interstellar medium : the escape fraction of LyC photons from galaxies is one of the main unknowns of reionization studies. The increasing opacity of the intergalactic medium with redshift renders direct LyC detections impossible during reionisation. Indirect methods are the only probes of LyC leakage in the distant Universe. I will discuss three indirect diagnostics of LyC leakage that were recently reported in the literature. The first diagnostic for LyC leakage relates the escape of the strongly resonant Lyman-alpha radiation from galaxies to the LyC escape (Verhamme et al. 2015), and was recently validated by observations (Verhamme et al. 2017). The second diagnostic proposes that the strength of Oxygen lines ratios can trace density-bounded interstellar regions. It was the selection criterion for the successful detection of 6 strong Lyman Continuum Emitters from our team (Izotov 2016a,b, 2018). The third diagnostic relates the metallic absorption line strengths to the porosity of the absorbing interstellar gas in front of the stars. These diagnostics will soon become observables at the redshifts of interest with JWST.

No seminar - spring holidays

Vendredi 27 avril 11:00-12:00

No seminar

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