Kruger Gate Hotel, August 18-21, 2025

Galaxy evolution is driven by the interplay between galaxies and their environments. The critical elements are galaxy mergers and the accretion of gas from the circumgalactic medium (CGM) providing fuel for new star-formation, and feedback from AGNs or stars that expels gas from the galaxy disk and contributes to quenching star-formation activity. Understanding the changing balance between gas accretion, gas consumption in star-formation, galaxy interactions, and feedback is crucial for understanding galaxy evolution. 

The 21cm line of neutral atomic hydrogen provides a critical probe of gas in and around galaxies, allowing measurements of the total HI content of galaxies, and also providing windows on the accretion and feedback processes. The recent advent of new and upgraded radio telescopes (e.g. the GMRT, MeerKAT, ASKAP, JVLA, WSRT-Apertif, FAST, the EVN, etc) has energised the field, allowing us to detect 21cm emission from galaxies in the era of cosmic noon, to detect and map 21cm absorption against extended radio AGNs out to high redshifts, to detect 21cm emission from the circumgalactic, intragroup, and intracluster mediums, and to measure the kinematics of galaxies in large numbers. It is now feasible to use such 21cm studies to study the evolution of the HI content of galaxies, the scaling relations of HI content with other galaxy properties, the connections between HI content and galaxy location in the cosmic web, the fuelling of AGNs and AGN feedback, the properties of HI in the CGM and in group and cluster environments, etc. This improved knowledge of the HI properties of galaxies and their CGMs also provides new constraints on numerical models of galaxy formation.

The goal of this meeting is to compare and contrast the results of these different HI 21cm observations, to compare them to numerical models, and to build a consistent picture of galaxy evolution including HI. The meeting will look at the evolution of HI in and around galaxies, by addressing the following questions:

1. How do the HI content, morphology, and kinematics of galaxies evolve with redshift? 

2. How do the HI properties of galaxies and their CGMs relate to their environment, stellar content, SFR, etc?

3. How do gas accretion and feedback depend on galaxy properties and redshift?

4. How do AGN feeding and feedback depend on the AGN properties and redshift?

5. Do today's numerical simulations reproduce the observed HI properties of galaxies and their CGMs and what does that tell us?

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The meeting will be an informal one, entirely in person, with roughly 40 participants and lots of time for discussion. We anticipate that each participant will give a 15-20m talk, if they would like to do so; we do not plan on having posters.

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The meeting will be held at the world famous Kruger Gate Hotel, overlooking the Sabie River just outside the main gate of South African's premier game park, Kruger Park.  All conference activities, including all meals and the sessions, will be on-site.  There will be a conference registration fee of ZAR 4000 which covers lunch, coffee breaks, and conferencing costs for the participants.  Full-board accommodations is ZAR 3980 per night for a single, and ZAR 4729 per night for two people sharing a room.  Families are welcome, and there are a limited number of family rooms available.  We recommend staying for 5 nights from 17-22 August, and a block of rooms has been reserved for that period.

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Pre-registration, including abstract submission, is open until 1 March 2025.  If the meeting is oversubscribed, the Organising Commitee will make a decision on the final participants list and inform them by 1 April 2025.  The Committee will aim to balance career stage, gender, and nationality among accepted participants. All participants must book their accommodations by 1 May 2025.  Note that there is a specific procedure for booking at the Kruger Gate Hotel for this conference which will be communicated to accepted participants, and includes paying the conference registration fee; please do not book your room independently.  All participants must stay at the Kruger Gate in order to attend this conference.  

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ORGANISING COMMITTEE

Erwin de Blok

Romeel Davé

Kelley Hess

Nissim Kanekar (chair)

Raffaella Morganti

Paolo Serra

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Image credits: THINGS Survey, Roland Timmerman​​

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