Séminaires, soutenances

Galaxies at the Frontiers of the Universe

by Nicolas Laporte

amphi recherche ()

amphi recherche

The most intriguing question of modern extra-galactic astronomy is to locate and study the first galaxies in order to determine when they emerged from the dark ages, what are their physical properties and what role do they play in governing the transition of intergalactic hydrogen from a neutral state to one that is ionised. Measures of the optical depth of electron scattering by the Planck satellite indicates this `cosmic reionisation’ was a fast process occurring relative late over the redshift interval 12 < z < 6. Moreover recently high redshift galaxies discovered at fascinating distances  z= 8, 11 and more,  were interpreted  in terms of ages and intense star formation histories. These galaxies are revealed mature by spectral synthesis identifying the Balmer discontinuity, the dust-attenuated far-UV distribution  as well as very faint emission lines with ages of 500 million years, starting just after the Big-Bang, indicating a formation redshift of ~15 or more, earlier than expected by the current paradigm. Such early systems with significant stellar masses and star formation rates which decline with time are not easily reproduced by contemporary numerical simulations. After discussing the scientific context of this topic, I will describe the method used to identify distant galaxies, to measure the age of their stellar population, and to determine their physical properties. At the end of this talk, I will also discuss what we can expect from the future LSST on the search for and study of the first galaxies.