(Re)solving the formation of galaxies in the 2020s

Over the recent decades, observational and theoretical developments have
lead to a consensus picture of the formation of galaxies in a LCDM
framework. With new large surveys and space missions on the horizon, we
are now suited to explore new, bold and more detailed questions in the
2020s: When did the first stars form and what were their properties?
Which sources of light were the main drivers of cosmic reionisation?
What drives the variation in galaxy’ star formation histories and their
chemical evolution, and how is this connected to the dark matter
assembly? These questions are particularly challenging as they describe
complex, multi-scale and multi-dimensional phenomena. Observations
furthermore are fundamentally limited by resolution and sensitivity and
can not be used for longitudinal studies. In this framework, I will
first discuss results from cosmological hydrodynamical simulations. I
will present explorations of the multi-dimensional relations between the
assembly of dark matter halos, star formation histories and stellar
alpha-enhancement that can be tested with large upcoming galaxy surveys.
I will then move to the mostly uncharted territory of the observational
study of the most distant galaxies and present results from recent
attempts to witness the assembly of galaxies in the first few Gyr of
cosmic time. I will emphasise the role of the bright Lyman-alpha line in
observations of faint distant galaxies to study the process of
reionisation, and to help identifying galaxies with very young stellar
populations. I will briefly discuss what we can expect to learn from
future observations with JWST and the ELT.