Talks

The upcoming COLIBRE project promises to provide a generational leap in the capabilities of cosmological, hydrodynamical simulations of galaxy formation. The simulations model the evolution of cold gas down to temperatures of 10 K, alongside the formation and evolution of dust, in large cosmological volumes, and incorporate new prescriptions for cooling, chemical enrichment, and feedback associated with star formation and black hole growth. COLIBRE’s flagship simulations have been run in much larger cosmological volumes, at a given resolution, than its predecessor (EAGLE), producing commensurately larger galaxy populations to study. In my talk I will present a census of baryons in the circumgalactic medium (CGM) for the flagship COLIBRE simulations, as a function of halo mass and gas phase, and present some initial comparisons with available observational data. I will discuss how the properties of the CGM are influenced by COLIBRE’s new prescriptions for feedback from star formation and AGN, and compare the importance of these feedback channels for different halo mass ranges. In turn, I will demonstrate how the properties of the CGM relate to the cold atomic and molecular gas reservoirs of galaxies, and how the effects of feedback on the CGM play a crucial role in future star formation activity and quenching. I will end by exploring why diversity exists in the properties of galaxies and their CGM in haloes of the same mass, by showing that galaxy-CGM ecosystems with different properties exhibit markedly different histories in terms of mass assembly, mergers, and feedback.

The ultra-diffuse nature of the Intergalactic Medium (IGM) makes it inherently difficult to resolve at high spatial resolution in simulations. Typical cosmological simulations are resolution limited by large box sizes (L > 50 Mpc) used to capture accurate statistical properties of large-scale structure, while higher-resolution zoom-in simulations rarely focus on the IGM. Thus, few simulations to date resolve IGM gas at sub-kpc scales, leaving potentially important scales for gas physics unresolved. We present semi-idealized simulations of cosmic sheet collapse at higher resolutions than previously explored to study the substructure and characteristics of IGM gas. We introduce a small 1D density perturbation to the initial conditions, allowing us to use small box volumes (L = 4-8 cMpc) to resolve IGM gas at kpc scales. We confirm previous work suggesting the IGM is inherently multiphase due to cooling-based instabilities causing fragmentation. We explore how IGM multiphase fragmentation manifests with both changing resolution and sheet-virial mass/temperature. With increasing resolution, we observe enhanced neutral hydrogen column densities through the cosmic sheet. Similar to subgrid-feedback physics, the unknown effects of resolution-limited cooling instabilities represent a fundamental limitation in our understanding of diffuse baryons in the universe. We aim to quantify this phenomenon and its broader implications for Lyman limit system statistics and the Lyman-alpha forest.

I will present work on measuring thermal and kinetic Sunyaev-Zeldovich signals alongside x-ray fluxes from clusters and groups of galaxies identified either in the DESI Legacy Survey or selected from eROISTA x-ray observations. I will show joint inference of matter and gas density as well as temperature and x-ray emissivity to better understand the structure within these objects and the feedback processes which are relevant to the modelling of cosmological observables. Among other aspects, I will address claims of discrepancy between the feedback observed in x-ray cross-correlations with cosmic shear and inferred from kSZ observations.

As cosmic microwave background photons travel through the Universe a small fraction of them interact with the intervening cosmic gas and thereby imprint the properties of this gas on our CMB observations. In this talk I will describe how data from the Atacama Cosmology Telescope can be used to isolate the signals arising from hot gas throughout the Universe and how the data can be used to measure both the integrated electron pressure and temperature of galaxy clusters. I will discuss how upcoming CMB experiments, such as the Simons Observatory, will allow us to improve our characterisation of the properties and evolution of cosmic gas.

Galaxies and their surroundings imprint shadows on the cosmic microwave background. These shadows contain tantalizing information about galaxy formation: from the baryon density, temperature, pressure, velocities, to the dark matter potential and its time-evolution due to accretion. In this talk, I will review the unique opportunities and challenges in learning about galaxy formation and cosmology from CMB observables.

Information about the late-time Universe is imprinted on the small-scale CMB as photons travel to us from the surface of last scattering. Several processes are at play and small-scale fluctuations are very rich and non-Gaussian in nature. I will review some recent and exciting results that use the Sunyaev-Zel'dovich (SZ) effects and gravitational lensing to paint a full picture of the visible and dark matter in and around DESI galaxies. I will discuss how a combination of measurements can probe velocity fields at cosmological distances and inform us on galaxy energetics. I will also show recent measurements of weak lensing of the CMB and its cross-correlation with DESI, and how they can help us interpret intriguing discrepancies in cosmological parameters between the high and low redshift Universe.

I will present evidence from both simulations and observations that the inner CGM (≲0.3 Rvir) of ≲L* galaxies departs significantly from the conventional paradigm of cool clouds embedded in a volume-filling hot phase. Instead, these regions are characterized by a supersonically turbulent medium in which kinetic energy dominates over thermal energy, with gas temperatures 10^4 –10^5 K and wide lognormal density distributions. I will show that UV absorption features observed at redshifts z ≲ 1, as well as DLAs at z ≳ 2, support this turbulence-dominated CGM framework. I will also discuss the broader implications of the transition from kinetic to thermal energy dominance for models of galaxy accretion, feedback processes, and the evolution from thick to thin star-forming disks.

The hot circumgalactic medium (CGM), a reservoir of missing baryons, metals, and energy, plays a key role in our understanding of galaxy evolution. However, extraordinary observational challenges make the hot CGM one of the least understood components of galaxies. Studying the hot CGM was not the objective of current X-ray or mm facilities during the design phase. However, as an excellent byproduct, observing the hot CGM has emerged as a promising field over the last two decades, coming at the forefront of priority science goals for the current and upcoming decades. I will discuss three snippets of our recent efforts to detect and characterize the hot CGM: 1) X-raying the Milky Way: Investigating thermal, chemical, and kinematic anomalies; 2) Is CGM detectable? Conducting deep searches in individual external galaxies using X-ray; and 3) Test for self-similarity: stacking many galaxies in mm (Sunyaev-Zeldovich Effect). I will highlight how our findings provide insights into the impact of galactic feedback on the hot CGM, establish our confidence in leveraging current telescopes to inform theoretical simulations, and set a benchmark for designing experiments with next-generation X-ray and mm facilities.

Presenters: Bhuvan Manojh Calvin Osinga Cassandra Lochhaas Daria Kozlova Dorsa Sadat Hosseini Emily Costello Guandi Zhao Henry Liu Ian Roberts Isaac Cheng Joe Bhangal John Pharo Jonah Conley Junwu Huang Mukesh Singh Bisht Nihar Dalal Noah Sailor Pierre Burger Ray Wang Stephanie Ho Yongming Liang

Understanding the impact of baryonic feedback across different cosmic environments is crucial for accurate interpretation of large-scale structure in Stage-IV cosmological surveys. Hydrodynamical simulations offer a valuable tool for capturing how gas is redistributed by energetic processes, such as AGN feedback, and for predicting how this redistribution alters observable tracers of structure formation. Traditionally, feedback models have been constrained through X-ray and Sunyaev-Zel’dovich measurements of galaxy groups and clusters. However, new observational tracers are emerging that open up alternative windows into the baryonic content of the cosmic web. One such tracer is the patchy screening effect, a subtle CMB anisotropy arising from excess Thomson scattering along the line of sight to groups/clusters due to their higher electron optical depths. This effect is sensitive to the diffuse baryons in the outer regions of the gas profile of the halo, tracing the structure of the cosmic web. It is complementary to the kinetic Sunyaev-Zel’dovich effect, as it probes optical depth without dependence on velocity. In this talk, we present predictions of the patchy screening signal from the FLAMINGO suite of large-volume cosmological hydrodynamical simulations. By generating mock patchy screened CMB maps and cross-correlating them with simulated galaxy populations, we explore how feedback and cosmology shape the optical depth field. Our goal is to assess the sensitivity of this signal to the cosmology and baryonic physics, and to evaluate its potential as a new probe of the gas distribution within the anisotropic structure of the cosmic web.

Lyman-alpha forest probes matter distribution on scales inaccessible to other observables, presenting a unique and under-explored testing ground for new physics. I will discuss recent advances in using forest observations to constrain particle interactions in the neutrino and dark matter sectors, and highlight promising opportunities for discovery in the coming decade.