Cosmic Ecosystems
I organized and chaired Cosmic Ecosystems at the Perimeter Institute for Theoretical Physics (2025), bringing together leading cosmologists and astrophysicists to explore how the formation and evolution of cosmic structures operate as a dynamic, interconnected ecosystem.
Motivation
A central insight in cosmology over the past three decades has been the realization that cosmic structures — supermassive black holes, galaxies, clusters, and the vast filamentary web connecting them — do not evolve in isolation. They operate within a dynamic ecosystem where matter and energy flow across scales, driving the growth and transformation of cosmic environments. Understanding this system, especially the circumgalactic medium (CGM) and its role in cycling and redistributing baryons, is essential both for astrophysics and for advancing precision cosmology.
I organized Cosmic Ecosystems to bring together communities that approach these questions from different directions: cosmologists studying large-scale, hot, virialized gas from the top down, and astrophysicists investigating cooler, small-scale phases from the bottom up. The conference focused on how combining data from DESI, Euclid, LSST, and Roman with CMB measurements from the Simons Observatory — alongside observations from JWST, X-ray and UV absorption measurements, 21-cm emission, and FRBs — can illuminate how matter and energy flow between different gas phases and scales. Invited speakers included leaders in observational and theoretical astrophysics from Princeton, Caltech, Cambridge, Yale, Stanford, Chicago, and other major centers.
Conference Themes
The program was built around five themes linking scales, phases, and epochs into a coherent picture of the cosmic ecosystem.
1. From subgrid feedback to cosmic large-scale structure. How do AGN jets, supernovae, and turbulence on the smallest scales propagate through simulations to shape the baryonic distribution and clustering on cosmological scales? Topics included matter power spectrum suppression, AGN/SNe-LSS scaling laws, and feedback imprints on the thermal and kinetic SZ effects.
2. Baryon cycling: linking hot gas to cold gas. How do feedback processes mediate phase transitions between the hot ionized gas in clusters and the CGM, and the cold neutral and molecular gas that fuels star formation? Topics included shock heating, cooling flows, condensation, and feedback-regulated star formation.
3. From the circumgalactic to the intergalactic medium. How do feedback-driven outflows extend beyond galaxies into the cosmic web, redistributing metals and energy into the IGM? Topics included metal enrichment, galactic winds, Lyman-alpha forest statistics, and the thermal history of the IGM.
4. Connecting the diffuse to the dense. How do energy transfer, turbulence, and cosmic ray interactions bridge the vastly different density and temperature regimes of diffuse and compact gas?
5. Bridging cosmic history to present-day observables. How do feedback processes evolve from the reionization era to the present, and what imprints do they leave in observables such as the SZ effect, Lyman-alpha forest, and FRBs?
Committees and Invited Speakers
The meeting surfaced new opportunities for cross-community collaboration, particularly around joint modeling of the multi-phase CGM and analysis frameworks that connect upcoming survey data across wavelengths and scales.