Scientific Rationale

The hydrogen Lyman-alpha line is of utmost importance to many fields of astrophysics. This UV line being conveniently redshifted with distance to the visible and even near infrared wavelength ranges, it is observable from the ground, and provides the main observational window on the formation and evolution of high redshift galaxies. Absorbing systems that would otherwise go unnoticed are revealed through the Lyman-alpha forest, Lyman-limit, and damped Lyman-alpha systems, tracing the distribution of baryonic matter on large scales, and its chemical enrichment.

We are living an exiting epoch with the advent of new instruments and facilities, on board of satellites and on the ground. Wide field and very sensitive integral field spectrographs are becoming available: MUSE at the ESO VLT has already produced a wealth of dramatic results and promises many others, especially when the adaptive optics option will be activated. HETDEX at the Hobby-Eberly Telescope will measure a million Lyman-alpha emitting galaxies with the primary goal of constraining the equation of state of the universe through BAO; no doubt, however, that this wealth of data will shed light on many other astrophysical and cosmological topics. The Subaru Hyper Suprime Cam (HSC) and Prime Focus Spectrograph (PFS) will survey the formation and evolution of galaxies over the first billion years of the Universe, and the epoch of reionisation. The giant E-ELT and TMT will foster a quantum leap in sensitivity and both spatial and spectroscopic resolution, to the point of being able, perhaps, to measure directly the acceleration of the Hubble flow. In space, the JWST open new possibilities to the study the Lyman-alpha emission of primordial galaxies in the near infrared. As long as the Hubble Space Telescope will remain available, the UV-restframe properties of nearby galaxies are accessible to our knowledge. Therefore, this Saas-Fee course appears very timely and should meet the interest of many young researchers.

This resonant line undergoes complex radiation transfer effects, which need careful modelling in order to extract, from the alteration of the line shape, all informations on the kinematics and geometry of the gas in which light is scattered on its way towards the observer. This is the price to pay for the strength of this spectral line, which goes along its wide visibility, but modelling efforts also open a treasure of information.

The goal of this SAAS-FEE course is to give an overview of the major uses of the Hydrogen Lyman-alpha line to study astrophysical processes and cosmology, from spatially resolved radiation transfer effects tracing the kinematics and the distribution of gas flows around galaxies, to the formation and evolution of galaxies and the study of the largest structures of the Universe.