Fredagskollokvium: The brightest gravitationally lensed galaxies: What can they tell us about galaxy evolution and  reionization

A key phase in the evolution of the universe is the epoch of ionization of hydrogen in the intergalactic medium
which occurred during the first billion years after the Big Bang. “Which sources caused reionization?” is one of the key 
questions to be addressed with the James Webb Space Telescope. Currently missing parts in this puzzle include direct measurements of the spectral energy distribution of ionizing photons that are produced inside galaxies and the amount and mode of escape of ionizing radiation from galaxies. 

Another important epoch occurred when the global star formation rate reached its peak, when the universe was 2-6 billion years old.  Most of the stellar mass in present-day galaxies was formed during this period.  We want to investigate how the physical conditions of this star formation differed from star formation we observe today. 

Observational studies to probe the physical conditions in galaxies at these epochs are fundamentally limited by the spatial resolution of current telescopes. Hence, while it is possible to measure some global properties of galaxies  
at the epochs mentioned above, the magnification effect of gravitational lensing is crucial to probe the detailed internal structure and the fundamental astrophysical processes that act on sub-galaxy scales to shape the population of galaxies we see around us today. 

In this talk I will discuss results from ongoing efforts using the Hubble Space Telescope and ground-based telescopes plus planned future efforts, including an Early Release Science programme with JWST, to study gravitationally lensed galaxies that can help illuminate the questions raised above.