IAU Symposium - Uncovering early galaxy evolution in the ALMA and JWST era, Viana do Castelo, Portugal, 3-7 June 2019

Thanks to deep observations in the last few decades with the Hubble Space Telescope, the Spitzer Space Telescope, and ground-based 8–10-metre class telescopes, we know more about the young Universe than ever before, having reached tantalisingly close to the dark ages and the formation of the first stars and galaxies. It is now well established that the rate of cosmic star formation rose rapidly from the epoch of reionization to a maximum at z~2. The first three billion years of cosmic time were therefore the prime epoch of galaxy formation. Characterising galaxies at this epoch, both observationally and theoretically, is thus crucial to achieve a major goal of modern astrophysics: to understand how galaxies such as our Milky Way emerged from the primordial density fluctuations in the early Universe and evolved through cosmic time. 

 

Many questions remain to be addressed with the next generation of observing facilities and theoretical models. For example, what physical processes drove the rise in star formation rate in the first three billion years? How is the formation and evolution of galaxies determined by their dark matter haloes and large-scale environment? How did black hole growth follow this rise, and how important is the galaxy-AGN connection at early cosmic times? Which star-forming galaxies are responsible for re-ionising the Universe, and how important is the contribution by early quasars? How do the gas, metals and dust in the interstellar medium of early galaxies evolve? What regulates star formation in galaxies, and what are the physical drivers behind the close correlation between stellar mass and star formation rate (the so-called ‘star-forming main sequence’)? Are there different star formation modes associated with secular and interaction-driven starbursts, and how important were those processes in shaping the general galaxy population? What dynamical processes established the morphologies of galaxies we observe today?  

 

Recent major international investments in facilities such as the Atacama Large Millimetre Array (ALMA) and the James Webb Space Telescope (JWST) promise to shed light on these questions. ALMA has been operating since 2011 and has already started changing our view of the distant Universe by detecting dust heated by young star formation and cold molecular gas i.e. the fuel for new star formation, with unprecedented sensitivity and spatial resolution, reaching all the way to the epoch of reionization (z>6). ALMA gives us an exquisite view into the physical state of the dense interstellar medium in the young Universe, which is determinant in understanding star formation and feedback processes. JWST, to be launched in 2020, will bring a necessary and complementary view of the stellar populations and ionised interstellar medium in galaxies at those epochs. It will directly observe young stars radiating in the rest-frame ultraviolet as well as more evolved stars emitting mostly in the optical and near-infrared (which comprise most of the total stellar mass), and it will access the nebular emission from gas ionised by the young stars, AGN, and shocks. Combining ALMA and JWST will be crucial to go beyond simply detecting large samples of galaxies in the young Universe, but also characterising in detail the physical processes governing their evolution. It is crucial for the extragalactic community to be prepared to maximise what we can learn from having those facilities simultaneously available during the lifetime of JWST. 

 

This symposium will bring together the community of theoretical and observational experts to discuss and strategise on how we can make the most of ALMA and JWST synergies in advancing our understanding of galaxy evolution in the young Universe during the next decade. The goal is to formulate the key questions that will be answered with ALMA+JWST, and discuss what observations, diagnostics, and theoretical models/simulations will need to be developed to address them. To achieve this goal, the symposium will include an overview of the state-of-the-art in observations and theoretical models of high-redshift galaxies, define strategic areas where the overlap between ALMA and JWST will be crucial, and foster exchanges and international collaboration between theorists and observers, as well as astronomers traditionally observing in different spectral regions. Organising this symposium shortly before the launch of JWST ensures that these discussions will happen at the most relevant time.