Letters of Intent received in 2022

LoI 2024-2183
Neutral hydrogen in and around galaxies in the SKA era

Date: 12 August 2024 to 16 August 2024
Category: GA Symposium
Location: Cape Town, South Africa
Contact: Elizabeth (Betsey) Adams (adams@astron.nl)
Coordinating division: Division J Galaxies and Cosmology
Other divisions: Division B Facilities, Technologies and Data Science
Division H Interstellar Matter and Local Universe
Co-Chairs of SOC: Betsey Adams (ASTRON)
Sarah Blyth (University of Cape Town)
Natasha Maddox (University of Bristol)
D.J. Pisano (University of Cape Town)
Anastasia Ponomareva (University of Oxford)
Chair of LOC: None (None)



HI in the life-cycle of galaxies
Connecting simulations of HI to observations
An unbiased and resolved view of HI in the local Universe
Evolution of (HI) galaxy scaling relations across cosmic time
Constraining our cosmological model with neutral hydrogen observations
Environmental processes as traced by HI
The smallest galaxies as revealed by their neutral gas content



Recent years have seen the opening of new observational frontiers in the study of neutral hydrogen (HI) with next-generation radio telescope facilities coming into operation. As the raw fuel for star formation, knowledge of the HI properties of galaxies is essential to construct a full understanding of the build-up of the stellar mass and evolution of galaxies. With the Square Kilometre Array (SKA) precursor and pathfinder telescopes, we can, for the first time, follow the HI emission from galaxies across cosmic time, key information that has until now been missing from the multi-wavelength census of galaxy evolution. These new observations, coupled with state-of-the-art cosmological simulations of galaxy formation and evolution, are providing a more complete understanding of the life cycle of galaxies.

With the unprecedented combination of sensitivity and resolution, the new facilities provide resolved detections of large samples of galaxies in HI emission beyond the local Universe, giving a clearer view of the gas cycle both in our own Galaxy and other galaxies. A major breakthrough is the ability to explore low column density gas with improved resolution to connect to the circumgalactic medium and investigate gas acquisition and loss, storage and consumption. These new observations, unbiased by the stellar content, enable detailed studies of the physical and environmental processes driving galaxy evolution.

The established scaling relations defined at z=0, which describe the link between HI and other properties of galaxies, are now being extended over billions of years of lookback time. Not only can we look for changes in these relations with time, but we can also investigate the influence of galaxy environment, known to strongly affect the evolution of galaxies. At the same time, the detailed HI kinematics beyond z=0 provide us with direct observational constraints on the properties of the dark matter haloes and their interplay with baryons. These results yield new inputs, as well as benchmarks to be reproduced, for the cosmological hydrodynamic simulations of galaxy formation and evolution. Increasingly sophisticated simulations following the ionised, neutral, and molecular gas phases can in turn provide predictions for upcoming observational campaigns, which can be directly tested with the new data.

The increased sensitivity of SKA-era telescopes allows us to trace the evolution of the cosmic HI density of the Universe through constraining the HI mass and velocity functions at z>0. At the same time, the HI properties of large samples of the lowest mass galaxies can be studied, illuminating discrepancies between observations and cosmological model predictions. Finally, the new statistically significant observational constraints on global HI and dark matter properties will be invaluable to further improve existing models of galaxy formation and evolution. As we enter the SKA era, the impact of these new observations on many aspects of galaxy evolution is clear, and a goal of this symposium is to highlight the value of HI in joining the extragalactic census in a way that has not been possible until now.

We plan to bring together the observational and theoretical communities to discuss the latest results, and identify topics that span multiple disciplines. We will do this by combining review talks from leaders in their fields with contributed talks. With MeerKAT based in South Africa, expanding into the SKA across southern Africa, there is an active and growing radio astronomy community across the African continent whose work we will highlight to achieve a truly global view on the current and future of HI science. Poster sessions and dedicated time for discussion will maximise opportunity for participation by all attendees. The timing of the 2024 IAU GA is perfect to highlight exciting results already flowing from the SKA precursor and pathfinder telescopes, and to prepare for the upcoming SKA era.