Cosmic Ecosystems

Jul 28, 2025, 8:00 AM → Aug 1, 2025, 5:00 PM America/Toronto

PI/1-100 - Theatre (Perimeter Institute for Theoretical Physics)

 

In the past three decades, one of the most transformative insights in cosmology has been the realisation that the formation and evolution processes of cosmic structures such as supermassive black-holes, galaxies and clusters are deeply interconnected with the vast cosmic web that underpins the Universe. These processes do not happen in isolation, but are part of a dynamic ecosystem where matter and energy flow across scales, driving the growth and transformation of cosmic environments. Understanding this complex system, in particular the circum-galactic medium (CGM), is not only key to deciphering how matter is cycled and redistributed through accretion via filaments and outflows from AGN and supernovae, but also crucial for unlocking the next generation of discoveries in areas such as dark matter, the behaviour of the cosmic web, the forces that shape cosmic evolution, and more.

 

This conference seeks to bring together cosmologists and astrophysicists to foster collaborative exploration of these interconnected cosmic ecosystems. By focusing on how structures interact with their environments across cosmic scales, this conference aims to catalyse groundbreaking discoveries in both astronomy and physics, providing fresh insights into the forces that govern the Universe. Special attention will be given to the joint analysis of large-scale structure and weak gravitational lensing data from surveys such as DESI, Euclid, LSST and Roman with CMB data from the Simons Observatory and CMB-S4, as well as how these can be integrated with observations of JWST, and existing and upcoming observations of X-ray emission, UV/X-ray absorption toward quasars, 21-cm emission, and FRBs.

 

The goal is to explore the complementarity of these data sets and how their alignment can provide new insights into the interconnected processes shaping cosmic environments, particularly through joint modelling and simulations of many phases of gas and feedback across different regimes. Attention will also be given to bridging the gap between how cosmologists and astronomers approach the CGM, either top-down large-scale and hot and virial phase, vs bottom-up, cooler phases, at smaller scales.

 

Topics will include:

· Cosmic mass budget, including a census of where the baryons are.

· Effect of baryons on dark matter structures on small and large scales.

· Cosmic evolution of large-scale structures.

· Bridging the gap between different probes.

Please see the Conference Themes for a more complete list of example topics.

 

The time has never been more right to unify these fields, as advances in observation, theory and simulations are poised to open new paths to revealing the cosmos’ most profound mysteries.

 

---

 

 

::  ::  ::

Organizing Committee (LOC) 
 

Selim Hotinli (Perimeter Institute) 

Neal Dalal (Perimeter Institute) 

Mike Hudson (University of Waterloo, Waterloo Centre for Astrophysics) 

Matt Johnson (Perimeter Institute) 

Katie Mack (Perimeter Institute) 

Brian McNamara (University of Waterloo, Waterloo Centre for Astrophysics) 

Arielle Phillips (University of Notre Dame / Simons Emmy Noether Fellow at Perimeter Institute) 

Kendrick Smith (Perimeter Institute) 

  

Scientific Organizing Committee (SOC) 
 

Nick Battaglia (Cornell) 

Hsiao-Wen Chen (University of Chicago) 

Megan Donahue (Michigan State University) 

Claude-André Faucher-Giguère (Northwestern) 

Cameron Hummels (Caltech) 

Selim Hotinli (Perimeter Institute) 

Ian McCarthy (Liverpool John Moores University) 

Daisuke Nagai (Yale) 

Gwen Rudie (Carnegie Institution for Science) 

Freeke van de Voort (Cardiff University) 

Jessica Werk (University of Washington) 

 

Confirmed Speakers 

 

Alexandra Amon (Princeton)  

Iryna Butsky (Stanford)  

William Coulton (Cambridge University)  

Sanskrti Das (Stanford)  

Simone Ferraro (Berkeley Lab)  

Nicholas J Frontiere (Argonne)  

Vera Gluscevic (USC)*  

Timothy Heckman (JHU)*  

Boryana Hadzhiyska (UC Berkeley & Berkeley Lab)*  

Stella Koch Ocker (California Institute of Technology)  

Khee-Gan Lee (IPMU)*  

Nir Mandelker (Hebrew University Jerusalem) 

Chris Martin (Caltech) 

Daisuke Nagai (Yale) 

Andrew Newman (Carnegie Institution for Science) 

Peng Oh (UC Santa Barbara) 

Hiranya Peiris (University of Cambridge) 

Andrew Pontzen (Durham University)  

Emanuel Schaan (SLAC)  

Joop Schaye (Leiden University)*  

Chuck Steidel (California Institute of Technology)  

Jonathan Stern (Tel Aviv University)  

Mark Voit (Michigan State University)  

Irina Zhuravleva (University of Chicago) 

 

 *Virtual presenters

Scavenger Hunt.docx.pdf

Mon, July 28

8:00 AM → 9:00 AM Registration

9:00 AM → 9:10 AM Opening Remarks

Speaker: Selim Hotinli (Perimeter Institute for Theoretical Physics)

9:15 AM → 9:45 AM Galaxies as Cosmic Ecosystems

Terrestrial ecosystems exhibit ecological stability: If an ecosystem is perturbed, biological feedback drives it back toward an equilibrium state, but an ecosystem does not remain stuck in its equilibrium state because it is continually perturbed. Are galaxies really similar to biological ecosystems in that regard? My talk will consider whether the atmospheres of galaxies have feedback-regulated equilibrium states and what the observational consequences of those states might be. While considering those questions I will lay out a framework for classifying how halo-scale feedback loops operate.

Speaker: Mark Voit (Michigan State University)

9:50 AM → 10:20 AM Review Talk: Simulations at the intersection of galaxy formation and cosmology

Observational surveys of the distribution of matter in the universe are becoming ever more precise and continue to be extended to smaller scales. This necessitates accounting for the fact that baryons do not precisely trace the dark matter. The redistribution of baryons by galactic winds, which is the major bottleneck in our understanding of galaxy evolution, therefore requires a convergence between models of large-scale structure and cosmology. I will discuss some of the insights gained from cosmological, hydrodynamical simulations, and challenges that need to be overcome to make further progress. I will present recent results from the FLAMINGO suite of large-volume cosmological, hydrodynamical simulations, which provide insight into the importance of baryonic effects for cosmology using large-scale structure and galaxy clusters. Finally, I will present the COLIBRE simulations of galaxy formation, a new suite of cosmological hydrodynamical simulations that removes important shortcomings of previous simulations.

Speaker: Joop Schaye (Leiden University)

10:30 AM → 11:00 AM Break

11:00 AM → 11:20 AM Baryon feedback: How extreme is too extreme?

Speaker: Alexandra Amon (Princeton University)

11:25 AM → 11:45 AM Cosmological feedback from a halo assembly perspective

The impact of feedback from galaxy formation on cosmological probes is typically quantified in terms of the suppression of the matter power spectrum in hydrodynamical compared to gravity-only simulations. In this paper, we instead study how baryonic feedback impacts halo assembly histories and thereby imprints on cosmological observables. We investigate the sensitivity of the thermal Sunyaev-Zel'dovich effect (tSZ) power spectrum, X-ray number counts, weak lensing and kinetic Sunyaev-Zel'dovich (kSZ) stacked profiles to halo populations as a function of mass and redshift. We then study the imprint of different feedback implementations in the FLAMINGO suite of cosmological simulations on the assembly histories of these halo populations, as a function of radial scale. We find that kSZ profiles target lower-mass halos (M200m∼10^13.1M⊙) compared to all other probes considered (M200m∼10^15M⊙). Feedback is inefficient in high-mass clusters with ∼10^15M⊙ at z=0, but was more efficient at earlier times in the same population, with a ∼5-10% effect on mass at 2<z<4 (depending on radial scale). Conversely, for lower-mass halos with ∼10^13M⊙ at z=0, feedback exhibits a ∼5-20% effect on mass at z=0 but had little impact at earlier times (z>2). These findings are tied together by noting that, regardless of redshift, feedback most efficiently redistributes baryons when halos reach a mass of M200m≃10^12.8M⊙ and ceases to have any significant effect by the time M200m≃10^15M⊙. We put forward strategies for minimizing sensitivity of lensing analyses to baryonic feedback, and for exploring baryonic resolutions to the unexpectedly low tSZ power in cosmic microwave background observations.

Speaker: Hiranya Peiris (University of Cambridge)

11:50 AM → 12:00 PM Establishing kSZ as a benchmark for simulations

TBD

Speaker: Leah Bigwood (Cambridge)

12:05 PM → 12:15 PM A multi-observation view of feedback: joint kinetic Sunyaev-Zeldovich, X-ray, and weak lensing measurements

There is no consensus on how baryonic feedback shapes the underlying matter distribution. This uncertainty is a limiting systematic for cosmic shear inference, particularly in the era of LSST, and a fundamental question in the study of galaxy evolution. Modern simulations are tuned to reproduce a variety of galaxy observations, however, previous studies demonstrated that the implied amplitude of baryon feedback is dependent on the chosen observable: e.g., X-ray gas fractions, which are sensitive to material within the virial radius of massive clusters, or kinematic Sunyaev Zeldovich (kSZ) profiles, which extend to a few virial radii [Bigwood+2024, McCarthy+2024]. In this talk, we address the uncertain observational landscape, by adopting a multi-observation view of feedback. We will present measurements for the gas and mass distribution as seen by eROSITA X-rays, DESI+ACT kSZ, and galaxy-galaxy lensing across a wide range of redshifts (0<z<0.8) and halo masses (13-15). Informed by the galaxy-galaxy lensing profiles, we perform a like-with-like comparison between the observations and the FLAMINGO simulations. By constraining the gas distribution across a range of scales (i.e., kSZ versus X-ray gas fractions), redshifts, and halo masses, we are working towards a complete picture of baryon feedback.

Speaker: Jared Siegel (Princeton University)

12:20 PM → 12:30 PM Discussion

12:30 PM → 1:45 PM Lunch

1:45 PM → 2:05 PM Exascale Class simulations -- A leap forward in Cosmological Hydrodynamics

Exascale computing is enabling a new generation of cosmological simulations, spanning both gravity-only and full hydrodynamics at unprecedented scale. The Frontier Exascale Simulation is the largest hydrodynamic run to date by over an order of magnitude, evolving more than 4 trillion particles in a 4.6 Gpc volume down to redshift zero. The simulation is well suited for predictive comparisons with multi-wavelength observations and for constructing full-sky mock surveys for upcoming observatories. In addition, a new suite of gravity-only simulations is now reaching beyond 10 trillion particles, producing survey-encompassing mocks ideal for large-scale structure analysis and tests of primordial non-Gaussianity. This talk will highlight these capabilities and their role in advancing predictive cosmology and survey science.

Speaker: Nick Frontiere (Argonne National Laboratory)

2:10 PM → 2:20 PM Self-consistent CMB secondaries in the FLAMINGO simulations

Secondary anisotropies in the cosmic microwave background (CMB) contain a wealth of cosmological and astrophysical information.  However, cleanly separating the individual contributions of the various kinds of anisotropies from each other can be a very challenging task, owing to uncertainties in their spatial, temporal, and spectral dependencies.  Realistic mock simulations of the CMB sky are invaluable for testing our methods of separating out the various signals and for making like-with-like comparisons between theory and observations.  Previous mocks have relied mostly on dark matter-only simulations with various prescriptions for "painting on" astrophysical signals.  Here we present a new set of mocks based on the FLAMINGO suite of cosmological hydrodynamical simulations, where the various anisotropies (tSZ, kSZ, screening, CIB, lensing, radio sources) are derived directly from the properties of the matter, gas and accreting black holes in the simulations.  We show that the simulations can reproduce various observational constraints with high accuracy.  We also show how these signals depend on cosmology and feedback modelling, and we predict interesting cross-correlations between some of the signals that differs significantly from that predicted by previous mocks.

Speaker: Ian McCarthy (Liverpool John Moores University)

2:25 PM → 2:35 PM X-raying CAMELS: Constraining Feedback Physics in Hot Halo Gas with CAMELS and eRASS

The circumgalactic medium (CGM) around massive galaxies plays a crucial role in regulating star formation and feedback. Using the CAMELS cosmological simulation suites, we develop emulators for the X-ray surface brightness profile and the X-ray luminosity–stellar mass scaling relation to investigate how stellar and AGN feedback shape the X-ray properties of the hot CGM. Our analysis shows that stellar feedback more significantly impacts the X-ray properties than AGN feedback within the parameters studied. Comparing the emulators to recent eROSITA All-Sky Survey observations, we found stronger feedback is needed than those currently implemented in the IllustrisTNG, SIMBA, and Astrid simulations, in order to match observed CGM properties. However, adopting these enhanced feedback parameters leads to deviations in the observed stellar-mass-halo-mass relations below the group mass scale. This tension suggests possible unaccounted systematics in X-ray CGM observations or inadequacies in the feedback models of cosmological simulations. Finally, I will also highlight upcoming X-ray constraints of feedback in the group and cluster scales with new CAMELS simulations and compare with those obtained at the CGM scale.

Speaker: Erwin Lau (CfA)

Erwin Lau.pdf

2:40 PM → 2:50 PM Constraining AGN Feedback with Multiwavelength Measurements

Feedback from active galactic nuclei (AGN) plays an essential role in current models of galaxy formation, yet the details of this process remain highly uncertain. I will describe our work combining numerical simulations with microwave, X-ray, and large-scale structure (LSS) survey data to better constrain this process. Our team has conducted a series of simulations spanning a broad range of feedback properties, enabling us to investigate their effects on the circumgalactic medium (CGM). At microwave wavelengths, we use these simulations to predict the thermal and kinetic Sunyaev-Zel’dovich (SZ) effects. We compare these predictions with stacked data from the Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT) to derive constraints on AGN feedback. Additionally, we outline plans to improve these constraints with the TolTEC camera on the Large Millimeter Telescope (LMT).
At X-ray wavelengths, we apply these simulations to predict soft X-ray emission, which we compare with stacked eROSITA observations. A persistent challenge in interpreting these comparisons is the influence of halo mass. I will discuss how weak gravitational lensing can help resolve this issue, offering new insights into the co-evolution of galaxies and their AGN.

Speaker: Evan Scannapieco (Arizona State University)

3:00 PM → 3:30 PM Break

3:30 PM → 3:50 PM New Physics from the Lyman-Alpha Forest

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.

Speaker: Vera Gluscevic (University of Southern California)

3:55 PM → 4:05 PM Probing baryonic feedback and cosmology with patchy screening in the FLAMINGO Simulations.

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.

Speaker: Jonah Conley (Astrophysics Research Institute - Liverpool John Moores Universtiy)

4:10 PM → 5:00 PM Flash Talks - 1 min, 1 slide

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

Tue, July 29

9:00 AM → 9:30 AM Review Talk

Speaker: Daisuke Nagai (Yale University)

9:35 AM → 9:55 AM Where the hot universe meets the energetic universe

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.

Speaker: Sanskriti Das (Stanford University)

10:00 AM → 10:20 AM Turbulence-Dominated versus Thermal Energy-Dominated CGM: Implications for Galaxy Evolution

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.

Speaker: Johnathan Stern (Tel Aviv University)

10:30 AM → 11:00 AM Break

11:00 AM → 11:20 AM A CMB view of DESI galaxies

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.

Speaker: Simone Ferraro (Lawrence Berkeley National Laboratory)

11:25 AM → 11:45 AM A skeptic's guide to CMB probes of galaxy formation

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.

Speaker: Emmanuel Schaan (SLAC National Accelerator Laboratory)

11:50 AM → 12:10 PM New views of cosmic gas from Atacama Cosmology Telescope observations of the millimeter sky

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.

Speaker: William Coulton (University of Cambridge)

12:15 PM → 12:25 PM Constraining cluster and group ecosystems with joint and consistent SZ and x-ray observations

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.

Speaker: Gerrit Farren (Lawrence Berkeley National Laboratory)

12:30 PM → 1:45 PM Lunch

1:45 PM → 1:55 PM Resolving Multiphase Gas Production in the kpc-Scale Intergalactic Medium

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.

Speaker: Charles Willard (University of Washington)

2:00 PM → 2:10 PM The properties of the CGM and its relationship with galaxies in the COLIBRE simulations

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.

Speaker: Jonathan Davies (Liverpool John Moores University)

2:15 PM → 2:25 PM Direct emission maps of cool gas in a star forming, low mass galaxy: connecting spatially resolved galactic processes to the CGM

Observing the cycling of baryons in and out of galaxies, which largely takes places in the circumgalactic medium (CGM), is key to understanding how galaxies grow and evolve. This is especially true for dwarf galaxies, whose shallow potential wells produce even more effective feedback than more massive haloes, and whose cold virial temperatures imply the possibility of a CGM rich in cold accretion, in which gas efficiently inflows and settles, perhaps explaining the degree to which nearly all isolated dwarf galaxies are actively star forming. Understanding how baryons cycle in and out of dwarf galaxies is thus essential for understanding how these galaxies connect to their large scale environment, and is now tractable with recent and upcoming state-of-the-art instrumentation. I will present sub-kiloparsec scale resolution integral field spectroscopy of emission lines mapping cool ionized gas inside and close to the optical extent of a star forming, low mass (M*~10^8 Msun) galaxy out to 10 kpc. This high spatial and spectral resolution data will be combined with the large scale gas distribution of diffuse, ionized gas on scales up to 1 degree (~200 kpc) with the one thousand lens, narrowband upgrade of the Dragonfly telephoto array concept. I will show results of the spatial distribution, kinematics, and ionization properties of gas in the galaxy itself and its inner and outer CGM and additionally provide insight into the degree of cospatiality of neutral to ionized extragalactic hydrogen in the outskirts of this low mass galaxy, connecting galactic processes such as star formation and feedback to those occurring in the CGM.

Speaker: Chloe Neufeld (Yale University)

2:30 PM → 2:40 PM Probing the Magneto-Ionized Circumgalactic Medium of M31 with HI and Rotation Measures

The circumgalactic medium (CGM) represents both a significant reservoir of baryons around galaxies as well as the region through which gas flows on to and out of galactic disks providing fuel for continued star formation. It is, however, challenging to study due to the low densities of gas in the CGM. Previous UV absorption studies have shown that the CGM is ubiquitous around star-forming galaxies. Project AMIGA has shown that the Andromeda Galaxy (M31), specifically, has an extensive CGM, which has further been confirmed by recent results from Fast Radio Bursts. Here, we present two complementary approaches to further characterize the CGM of M31. First, using archival rotation measure (RM) measurements of background radio point sources projected within the virial radius of M31, we present evidence of the existence of a magneto-ionized plasma extending out to $\gtrsim$100 kpc from M31. Second, using HI observations from the Green Bank Telescope (GBT) and MeerKAT, we show evidence of infalling gas being disrupted by the hot CGM at similar distances. Both observations confirm the presence of an extended, hot, ionized, and magnetized CGM around M31.

Speaker: D.J. Pisano (University of Cape Town)

2:45 PM → 3:00 PM Discussion

3:00 PM → 3:30 PM Break

3:30 PM → 3:50 PM New measurements of the gas fraction in galaxies and groups with the kinematic Sunyaev-Zel'dovich effect and CMB lensing

I will present new constraints on the halo masses and gas fractions of DESI galaxy groups via cross-correlations with the ACT DR6 CMB lensing map. This lensing-based calibration addresses a key uncertainty in interpreting kSZ measurements: the underlying halo mass distribution and allows us to estimate the amount by which baryons have been redistributed relative to the dark matter. Our results indicate that while baryons trace dark matter on large scales, the gas is significantly more extended, with cumulative gas fractions falling well below predictions from hydrodynamical simulations like TNG300. These discrepancies, seen at 4σ significance or higher, point to strong feedback processes in the real Universe. I will also highlight the excellent agreement between our lensing-based gas fraction measurements and recent results from X-rays, and discuss the implications for modeling feedback, galaxy formation, and baryon cycling in halos.

Speaker: Boryana Hadzhiyska (University of California, Berkeley)

3:55 PM → 4:05 PM The Kinematics of the Hot and X-ray Emitting Circumgalactic Medium: Predictions from Simulations

In massive galaxies a significant fraction by mass of the circumgalactic medium is expected to be in the hot, X-ray emitting phase. Little is known about this gas since it is faint and is outshone by the Milky Way's own hot circumgalactic medium, and X-ray observatories with CCDs are unable to distinguish the emission lines of the former from the latter. Future observatories with X-ray IFUs would be able to measure key emission lines of the hot CGM, and use them to map the velocity structure of this phase. In this talk, I will show predictions from galaxies from a range of cosmological simulations for the velocity field of the hot CGM, showing signatures of rotation, inflows, and outflows from AGN and SNe feedback. Crucially, the velocity structure depends on the feedback model used, so that future observations may be used to constrain models used in cosmological simulations.

Speaker: John ZuHone (Center for Astrophysics | Harvard & Smithsonian)

4:10 PM → 4:20 PM Unveiling the Multi-phase CGM and ISM in MACS1931-26 with JWST and ALMA

The circumgalactic medium (CGM) serves as the interface between galaxies and their cosmic environment, hosting the baryon cycle across a wide range of temperatures, densities, and energy scales. With its unprecedented sensitivity and spectral coverage, JWST is revolutionizing our view of this cycle by enabling direct detection of warm molecular hydrogen via mid-infrared rotational lines. We present a detailed analysis of the multi-phase molecular gas in the brightest cluster galaxy (BCG) of the cool-core cluster MACS1931-26 (z = 0.35), combining new JWST/MIRI and archival ALMA observations. This BCG hosts a powerful radio-loud AGN, elevated star formation, and one of the largest known H₂ reservoirs at this redshift. We trace cold molecular gas (10–100 K) using multiple CO and [CI] lines, finding highly excited gas in the ISM, similar to local LIRGs, while the CGM appears much less excited, pointing to distinct excitation sources. Our JWST data reveal warm H₂ (100–1000 K) spatially coincident with the CO-emitting gas and exhibiting comparable kinematics. Intriguingly, the CGM shows a higher H₂ excitation temperature than the ISM, suggesting the presence of more energetic heating mechanisms, including shocks and AGN-driven X-ray emission. This highlights the CGM as a key site of feedback-regulated gas transformation. Moreover, we will discuss our plans to use upcoming JWST Cycle 4 NIRCam + MIRI spectroscopy (2–28 μm) to perform comprehensive radiative transfer and shock modeling, aiming to constrain heating sources and baryon cycle in the CGM and ISM. This pilot study lays the groundwork for a broader framework to trace baryon cycling in cool-core BCGs, leveraging the synergy of JWST and cold gas tracers as a transformative tool for CGM studies.

Speaker: Laya Ghodsi (University of British Columbia)

4:25 PM → 5:00 PM Flash Talks - 1 min, 1 slide

Presenters:

Anjali Gupta
Aromal Pathayappura
Brad Koplitz
Dazhi Zhou
Denis Leahy
Doga Tolgay
Ghazal Geshnizjani
Imran Sultan
James Sunseri
John Pharo
Manami Roy
Matthew Charbonneau
Natanael de Isídio
Simon Foreman
Smita Mathur
Syeda Lammim Ahad
Y. Samuel Lu
Yakov Faerman
Zhiyuan Yao

6:00 PM → 8:00 PM Banquet

Wed, July 30

9:00 AM → 9:30 AM Review Talk: Galactic to intergalactic scales

Speaker: Nir Mandelker (Racah Institute of Physic)

9:35 AM → 9:55 AM Imaging the Cosmic Web

The intergalactic medium (IGM) represents the dominant reservoir of baryons at high red- shift, traces the architecture of the cosmic web dominated by dark matter, and fuels on-going galaxy evolution. Using a purpose-built instrument, with nod-and-shuffle and dual-field subtraction, we have detected, for the first time, an emission Lyman α forest (ELAF). The emission forest is highly extended, shows filamentary morphology with filaments connecting galaxies, exhibits statistics like the absorption Lyman α forest, displays spectra resembling the absorption forest, and is correlated with galaxy-traced overdensities consistent with bias like dark matter. We conclude that the ELAF may provide a new tool for tracing a significant fraction of the cosmic web of baryons and dark matter. Finally, I will present status of the STABLE Cosmic Web Imager (SCWI) program, a Brinson Exploration Hub balloon experiment, focused on emission from the Circum-QSO, the Circum-Galactic Medium, and the cosmic web. SCWI offers the opportunity to image the cosmic web in the local universe for the first time, and compare its properties to those at high redshift.

Speaker: Chris Martin (California Institute of Technology)

10:00 AM → 10:10 AM Growing in the Wind: Emission-Line Imaging of OVI in the Circumgalactic Medium

The baryon cycle of a galaxy involves a dynamic interplay between its star-forming disk and the environment of its virial halo, or circumgalatic medium. Simulations and observations agree that winds are a key seeding mechanism for the CGM, which serves as a reservoir for metals produced in disks. Cool clouds are predicted to form in the CGM from cooling halo gas, and are observed in absorbing sightlines to background quasars. This cloud growth may be accelerated by the action of winds. However, directly imaging the cold-hot interaction is extremely challenging, as most of the cooling channels lie in the UV and X-ray. I will present a deep image of OVI 1032, 1038 A and Lyman-alpha in the footprint of a prominent galactic wind. The OVI-emitting gas follows the morphology observed in lines at optical wavelengths. This represents only the second image of OVI in the halo or CGM of a galaxy, and is a signpost of cloud growth at large radii as the wind and CGM interact. This detection will help motivate further attempts to image the CGM-in-formation with existing or future facilities. It will also help inform models and simulations of the wind-CGM interaction.

Speaker: David Rupke (Rhodes College)

10:15 AM → 10:30 AM Discussion

10:30 AM → 11:00 AM Break

11:00 AM → 11:10 AM Mapping the z ~ 2 Circumgalactic Medium with KBSS Galaxy Pairs

Despite a growing body of observational and theoretical work, the connection between galactic-scale feedback processes, the underlying distribution of gas in the circumgalactic medium (CGM), and host galaxy properties remains uncertain. Focusing on the latter two points, we present new results on the spatial structure and kinematics of Ly$\alpha$ and several far-UV metallic ions in the CGM of Keck Baryonic Structure Survey (KBSS) galaxies using rest-frame far-UV spectra of foreground/background galaxy pairs with angular separations $\le 30$ arcsec. Medium resolution ($R\simeq 1500$) Keck/KCWI and Keck/LRIS spectra of 736 background galaxies with $\langle z_{\rm bg}\rangle=2.58 \pm 0.38$ probe sightlines through 1033 foreground galaxies ($\langle z_{\rm fg}\rangle=2.03 \pm 0.36$) at projected distances $8\leq D_{\rm tran}/\mathrm{kpc}\leq250$. For each ion, we measure rest-frame equivalent widths ($W_{\lambda}$) as a function of $D_{\rm tran}$; we observe higher ionization species (C IV) decrease less rapidly and extend to larger $D_{\rm tran}$ compared to low ions (O I, C II, Si II). Splitting the pair sample into subsets based on foreground galaxy properties, we find $W_\lambda(\text{C IV})$ exhibits a strong dependence on stellar mass ($M_*$) and a weaker dependence on star formation rate. Similarly, $W_\lambda(\text{Ly}\alpha)$ increases with $M_*$, albeit with more scatter. In 2D, we map the excess Ly$\alpha$ and C IV absorption as functions of line-of-sight velocity and $D_{\rm tran}$ and fit the observed Ly$\alpha$ map with a simple two-component model. Combining the 1D and 2D trends, we discuss the improved constraints these results place on CGM gas-phase kinematics in the context of previous studies at $z\sim 2$.

Speaker: Nikolaus Prusinski (Caltech)

11:15 AM → 11:25 AM The circumgalactic medium in emission and absorption, from dwarf galaxies to massive quasar hosts

The circum-galactic medium (CGM) is at the nexus of the gas inflows and outflows that regulate galaxy evolution. Consequently, the CGM provides an ideal laboratory for studying galaxy fueling, feedback, and interactions.
In the last decade, the simultaneous availability of UV spectra from the Cosmic Origins Spectrograph, deep integral field spectrographs, and wide galaxy redshift surveys have revolutionized our ability to characterize the CGM empirically. I will review recent progress enabled by the Cosmic Ultraviolet Baryon Survey (CUBS) and MUSE Quasar Blind Emitter Survey (MUSEQuBES), which combine these data for 31 intermediate redshift quasar fields. These surveys simultaneously provide for the first studies of physical conditions and abundances of the CGM and IGM around low-mass dwarf galaxies that constrain the physical conditions and abundances of the gas while also enabling the discovery of giant rest-frame optical emission nebulae around quasar hosts. I will highlight enlightening case studies, including filamentary accretion from 100 kpc scales into the ISM of a massive quasar host confirmed by down-the-barrel inflows observed in the UV and the first studies of relative abundances in the CGM/IGM around isolated dwarf galaxies that reveal surprisingly high metallicity and low [C/O] and [N/O] ratios, suggestive of core-collapse supernova outflows with modest mass loading.

Speaker: Sean Johnson

11:30 AM → 11:40 AM Complex Dynamics of Stars and Nebular Gas in Active Galaxies Centred in Cooling X-ray Atmospheres

Active Galactic Nuclei (AGN) feedback is known to play a key role in galaxy evolution and in regulating star formation. Studying the interplay between the central AGN and the different gas phases permeating galaxies is crucial to further our understanding of this powerful mechanism. We have observed the central regions of four brightest cluster galaxies at optical wavelengths using the Keck Cosmic Web Imager. With the high-resolution integral field unit data obtained from these observations, we map the fluxes and velocities of both emission lines and stellar absorption lines. This allows for a detailed tracing of gas cooling in galaxy centres. These galaxies have extensive X-ray and radio observations, allowing us to compare the dynamics of different gas phases and to study their interactions. Nebular emission extends up to tens of kiloparsecs from the central cluster galaxies of Abell 1835, PKS 0745-191, Abell 262, and RX J0820.9+0752. With the stellar continua, we map the kinematics and ages of the stars, learning about the systems’ star formation histories. Our findings highlight the complex stellar and gas dynamics which can be induced by radio-mechanical feedback. Surprisingly, three of the four systems have substantial (~ 150 km/s) velocity differences between their central galaxy and its associated nebular gas. This shows that the central galaxy is not at rest with respect to its surrounding nebula. In PKS 0745-191 and Abell 1835, nebular gas is churned up by buoyantly rising bubbles and jets. The churned gas is also surrounded by larger scale, lower velocity dispersion nebular emission. These complex motions will affect thermally unstable cooling, the interactions between the AGN and its atmosphere and how jet energy dissipates in its surroundings. These novel results highlight the deeply complex dynamics of AGN feedback and the multiphase gas in the centre of massive galaxies.

Speaker: Marie-Joëlle Gingras (Waterloo Centre for Astrophysics, University of Waterloo)

11:45 AM → 11:55 AM Cooling flows as a useful reference solution for the hot CGM of massive galaxies

TBD

Speaker: Claude-André Faucher-Giguère (Northwestern)

12:00 PM → 12:10 PM The enriched circumgalactic and intergalactic medium of star-forming dwarf galaxies

The circumgalactic/intergalactic medium (CGM/IGM) represents a significant baryon reservoir for sustaining star formation and provides insights into the inflows, outflows, and feedback history of galaxies.  Star-forming dwarf galaxies, with their shallow potential wells, are predicted to drive metal-enriched gas into the CGM/IGM. Therefore, a census of the CGM around dwarf galaxies can provide insights into the stellar feedback. We present highly sensitive absorption-line measurements in quasar sightlines adjacent to 91 isolated dwarf galaxies with a median stellar mass of M_star/M_sun≈8.4 from the Cosmic Ultraviolet Baryon Survey (CUBS). This survey uses HST absorption spectroscopy to access a range of ion transitions from 0.077<z<0.73 such as the Lyman-series transitions for HI, as well as a range of multiphase metal lines including low (e.g. CII, SiII), intermediate (e.g. CIII, SiIII) and high (e.g. CIV, OVI) ions. The CUBS Dwarfs sample represents a nine-fold increase in the number of star-forming field dwarf galaxies with CGM constraints on neutral hydrogen and metal absorption lines. We find that low and intermediate ionization metal absorption is rare and limited to the inner CGM of dwarf galaxies. In contrast, highly ionized OVI is commonly observed in sightlines that pass within the virial radius of a dwarf, and OVI detection rates are non-negligible at projected distances of 1-2x the virial radius. These measurements show that the OVI-bearing phase of the CGM/IGM accounts for the majority of the oxygen budget from star-formation, and the kinematic distribution of absorption systems suggests that a relatively modest fraction of this gas is formally unbound from the halo. Time permitting, I will show photoionization analysis of one system with evidence of absorption in the inner-CGM with ɑ-enhancement characteristic of core-collapse supernovae driven winds.

Speaker: Nishant Mishra (University of Michigan)

12:15 PM → 12:30 PM Discussion

12:30 PM → 12:40 PM Group Photo - Meet in the Atrium

12:40 PM → 2:00 PM Lunch

2:00 PM → 3:45 PM Poster Session

7:00 PM → 9:00 PM Public Lecture: The Universe in a Box - Andrew Pontzen (ticket required)

NOTE: This is a public event, advance ticket required. Conference participants are welcome to watch the livestream in the main floor Bistro or in the Time Room.

//

Abstract – Merging black holes, collapsing dark matter, giant supernova explosions: a tapestry of cosmic events stretching over the past 13.8 billion years have shaped our existence in a vast universe. Faced with this complexity, humanity has increasingly turned to computers to help extract a clear understanding of the cosmos and our place within it. This lecture will explore how the history of how these tools have developed, in parallel with more down-to-earth computational pursuits like weather forecasting. We will see how the resulting codes have unlocked our understanding of the universe, from galaxies and black holes to the essence of matter. And the lecture will conclude with a look at a contentious idea put forward by some philosophers and scientists – that we may already be living inside a simulation.

Bio – Andrew Pontzen is a professor of cosmology, and from January 2026 will direct Durham University’s Institute for Computational Cosmology. His research concerns how structure formed in our universe, from its opening moments to the present day. He has written for the New Scientist, BBC Sky at Night and BBC Science Focus; lectured at the Royal Institution; appeared on BBC, Amazon Prime and Discovery Channel documentaries; and contributed to BBC Radio 4 programmes including Inside Science and The Curious Cases of Rutherford & Fry. He is also the author of The Universe in a Box which dives into the role of simulations in cosmology and beyond, recently published to critical acclaim

Thu, July 31

9:00 AM → 9:30 AM Review Talk: Unveiling Hot Gas Motions in Galaxy Clusters with XRISM: First Results and New Puzzles

In its first year of operation, the recently launched XRISM X-ray satellite observed approximately ten galaxy clusters and galaxies, delivering high-resolution spectroscopic data. These observations enabled, for the first time in many systems, direct measurements of hot gas velocities. In this talk, I will present a selection of early XRISM results and discuss their implications for our understanding of AGN feedback and the dynamics of cluster mergers.

Speaker: Irina Zhuravleva (University of Chicago)

9:35 AM → 9:55 AM Cosmic Ray Coupling and Subgrid Modeling in the CGM

Despite its vast extent—spanning hundreds of kiloparsecs beyond the galactic disk—the circumgalactic medium (CGM) is shaped by microphysical processes operating on much smaller scales. One key example is the coupling between cosmic rays and gas. Under the right conditions, cosmic rays can dominate the pressure support in the CGM of low-redshift L* galaxies. However, this coupling depends sensitively on AU-scale magnetic field fluctuations—well below the resolution limit of modern galaxy-scale simulations. In this talk, I will highlight recent theoretical developments in cosmic-ray transport and their implications for CGM pressure profiles. I’ll also introduce CGSM, a new subgrid model designed to represent unresolved cold gas structures in hydrodynamic simulations, and discuss its potential to bridge the gap between microphysics and galaxy evolution.

Speaker: Irina Butsky (Stanford University)

10:00 AM → 10:10 AM The Simulated CGM at 200 pc

Simulations with fixed spatial resolution are an excellent tool to investigate the interplay between different phases of gas in and around galaxies because they mitigate the disparity in cell sizes due to density variations in traditional mass-based refinement schemes. Additionally, the moving-mesh technique implemented in Arepo has been shown to minimize numerical mixing and instability suppression. In this talk, I will introduce a new suite of cosmological zoom simulations with 200 pc resolution covering the inner CGM of a Milky Way-mass galaxy, utilizing the full IllustrisTNG galaxy formation model. At this high resolution, we find increased turbulent velocities, many small, cool cloudlets, and a smooth and homogeneous hot phase. I will outline these results and discuss the implications for high- and intermediate-velocity cloud studies and gas mixing in the CGM.

Speaker: Scott Lucchini (Center for Astrophysics | Harvard & Smithsonian)

10:15 AM → 10:30 AM Discussion

10:30 AM → 11:00 AM Break

11:00 AM → 11:10 AM Investigating Galaxy Ecosystems with Multi-wavelength Observations of Gas and Dust

We report results from observations of the CGM ionized, atomic, molecular, and condensed phases using a combination of integral field spectroscopy (MaNGA, VLT MUSE, JWST MRS), and imaging and spectroscopy from HST, VLT, Magellan. In a study of the warm and cool CGM of galaxies mapped with IFS, and a comparison of the kinematics, ionization, and metallicity of this gas with the ionized gas in star-forming regions in the galaxies, we find consistency with a co-rotation of the cool CGM with galaxy disks and hints of changes in gas ionization, potentially due to the stronger intergalactic radiation field at larger galactocentric distance. Our spatially resolved maps of gas metallicity and ionization around galaxies provide constraints on models of the metal distribution around galaxies. Our results are also consistent with higher metallicity and higher ionization parameter for gas at higher elevation angles, as expected for outflows. Our JWST studies of the composition, structure, and extinction properties of the dust grains in both the diffuse and dense ISM/CGM of galaxies at 0<z<1.5 indicate that dust grains in distant galaxies differ in physical and chemical properties from grains in local galaxies. Finally, our study of the ISM/CGM at 4<z<6 shows that high-redshift galaxies show a wide diversity of chemical enrichment histories, including some cases of highly accelerated chemical evolution.

We gratefully acknowledge support from NASA/STScI grants for HST GO-15939, GO-16242, GO-17121, JWST GO-2155, GO-5491, and from NASA grant 80NSSC20K0887.

Speaker: Varsha Kulkarni (University of South Carolina)

11:15 AM → 11:25 AM From Disk to IGM: A Comprehensive Mapping of Andromeda's Circumgalactic Medium

Project AMIGA (Absorption Maps In the Gas of Andromeda) provides an unprecedented view of the circumgalactic medium (CGM) of our nearest large galaxy neighbor. Using 55 sightlines obtained largely from two large HST COS programs, we map Andromeda's CGM across distances spanning from 10 to 570 kpc, nearly reaching twice its virial radius (Rvir=300 kpc). Using extensive diagnostics of different gas phases (OI/VI, SiII/III/IV, CII/CIV, FeII, AlII), this study uniquely bridges the smaller scales of the CGM with its largest scales extending into the intergalactic medium (IGM). In this talk, I will demonstrate how gas complexity and gas-phase structures significantly change with impact parameters but show little variation with azimuth relative to major/minor projected axes. Our program can differentiate components associated with the thick disk from those in the CGM, providing crucial insights for characterizing gas phases and accurately determining the total mass of Andromeda's CGM. I will place these findings in the broader context of other CGM observations, recent cosmological zoom simulations of Milky Way-mass galaxies at z~0, and how this pathfinder study may inform next-generation observations of the CGM/IGM with HWO.

Speaker: Nicolas Lehner (University of Notre Dame)

11:30 AM → 11:40 AM Magnetic fields and cosmic rays in cosmological simulations

Using zoom-in cosmological simulations, I will discuss some of the physical and observable properties of the circumgalactic medium (CGM). I will focus on non-thermal physical processes and how they impact the galactic ecosystem. The presence of magnetic fields and feedback from relativistic cosmic rays changes the flow of gas in the CGM, affecting the efficiency of outflows driven by stars or supermassive black holes as well as the turbulence-driven mixing in the CGM. This also affects our simulations’ predictions for neutral hydrogen and metal ions, observable through 21 cm emission and quasar absorption lines. I will show how these effects of magnetic fields and cosmic rays vary across a wide range in halo mass, from dwarf galaxies to galaxy groups.

Speaker: Freeke van de Voort (Cardiff University)

11:45 AM → 11:55 AM Chemical enrichment patterns as a tool to identify feedback processes in the CGM

The CGM is sensitive to various baryonic flows (e.g. stellar winds, supernovae, etc.) occurring on different timescales. Chemical abundance patterns in circumgalactic clouds provide a unique timing clock for constraining the dominant source of feedback regulating galaxy growth. In this talk, I will discuss how we leverage multiwavelength quasar spectra from surveys like the Cosmic Ultraviolet Baryon Survey (CUBS) to constrain the gas ionization state and elemental abundances of cool/warm-hot CGM absorbers. We find relatively cool (~1-5e4 K), diffuse (~0.001-0.01 cm^-3) photoionized gas clumps exhibiting a variety of chemical enrichment patterns. Several absorbers show an enhancement in non-alpha elements (e.g. carbon, nitrogen) reflecting metal production by secondary nucleosynthetic pathways. We also find chemically mature, metal-poor absorbers, showing evidence of mixing between pre-enriched gas and pristine inflows. These results demonstrate the value of using elemental abundances to understand which feedback processes are most critical in shaping the cosmic baryon cycle.

Speaker: Suyash Kumar (The University of Chicago)

12:00 PM → 12:10 PM Creating Mock Maps for Line Intensity Mapping Experiments

Line Intensity Mapping (LIM) experiments are innovative techniques for studying structures at high redshift. They allow us to uncover previously inaccessible astrophysical data by making 3D tomographic maps with 2D spatial line intensity fluctuations. As efforts like COMAP progress in detecting carbon monoxide (CO) and other spectral lines, generating precise mock maps becomes crucial for data analysis, prediction of future observations, and development of new statistical methods for LIM analysis. These mock maps are generated by interpolating line luminosities across the specified dark matter halo distribution, using response functions that are defined by the relationship between the line luminosities and both observable and derived properties of simulated galaxies.

In my presentation, I will elucidate the statistical relationship between the calculated line luminosity and inherent/derived observables for simulated FIRE (Feedback In Realistic Environment) galaxies, focusing on CO(1-0) to CO(8-7) lines at four different redshift regimes: z=0, 1, 2, and 3. I will examine the correlations between CO emission and galactic properties at different redshifts and explore the potential causal relationships they may suggest as well as how they can define essential response functions for creating mock maps.

Speaker: Doğa Tolgay (University of Toronto Physics / Canadian Institute for Theoretical Astrophysics (CITA))

12:15 PM → 12:30 PM Discussion

12:30 PM → 1:45 PM Lunch

1:45 PM → 2:05 PM Mergers in the cosmic ecosystem

I will present an overview of the work of the "GM Galaxies" project, which explores the relationship between history of a galaxy and its observable traits. I will give three examples of our work, looking at how dwarf galaxies change their properties based on their mass assembly, the Milky Way stellar halo responds to variations in its merging history, and the circumgalactic medium of massive galaxies mediates the transition from star-forming to quiescent.

Speaker: Andrew Pontzen (Durham University)

2:10 PM → 3:00 PM Panel Discussion

Speakers: Brian R. McNamara (Waterloo Centre for Astrophysics, University of Waterloo), Cassandra Lochhaas (Center for Astrophysics | Harvard & Smithsonian), Claude-Andre Faucher-Giguere (Northwestern University), Freeke van de Voort (Cardiff University)

3:00 PM → 3:30 PM Break

3:30 PM → 3:40 PM Measuring the cosmic ecosystem with weak gravitational lensing

Weak gravitational lensing is the only way to probe the total matter distribution on the scales of galaxies and the surrounding cosmic web. Understanding the dark matter distribution and its link to galaxies is critical not only galaxy formation and evolution, but also to correctly extract the cosmological parameters from weak lensing surveys. I will highlight recent results from the Ultraviolet Near Infrared Optical Northern Survey (UNIONS), a major weak lensing survey of 6000 square degrees of the northern sky, that probe the dark matter distribution around luminous red galaxies, allowing us to see the feedback-affected matter profiles, around galaxy mergers and in filaments of the cosmic web. If time permits, I will discuss prospect for future weak lensing surveys such as Euclid.

Speaker: Mike Hudson (Waterloo Centre for Astrophysics)

3:45 PM → 3:55 PM Baryon Fraction in Halos: Observational Constraints from HI, X-ray, and Stellar Components

Feedback processes, particularly from active galactic nuclei (AGN), play a crucial role in redistributing baryons within halos. These mechanisms can displace gas to halo outskirts or eject it entirely, leading to baryon fractions below the cosmic mean. While simulations such as TNG, SIMBA, and EAGLE predict these effects across a wide halo mass range, observational constraints remain largely limited to high-mass groups and clusters.
In this talk, I will present a systematic analysis of the observed baryon content of halos in the local universe across a mass range of $10^{10} - 10^{15} M_{\odot}$​, using a compilation of empirical measurements from the literature. We quantify the contributions of hot gas, stars, and cold gas to the total baryon budget, constructing baryonic mass-to-halo mass scaling relations. We also use the latest eROSITA and ASKAP data to provide the current constraints on the average hot gas and cold gas content in halos through stacking analysis. The baryonic scaling relations are constructed from group- and cluster-scale halos down to $10^{12} M_{\odot}$​ for all three components, while additional individual galaxy measurements allow us to extend HI and stellar mass scaling relations to $10^{10} M_{\odot}$​.
By combining these relations with the halo mass function, we then determine the baryon density distribution as a function of halo mass and calculate the cosmic mass densities of stars, HI, and hot gas within halos in the local universe. Our results provide key observational constraints on the distribution of baryons in the local universe, offering insights into potential mechanisms, such as feedback, that regulate baryon retention and redistribution.

Speaker: Ajay Dev (ICRAR - UWA)

4:00 PM → 4:10 PM Cosmic Infrared Background Tomography and a Census of Cosmic Dust and Star Formation

The cosmic far-infrared background (CIB) encodes dust emission from all galaxies and carries valuable information on structure formation, star formation, and chemical enrichment across cosmic time. However, its redshift-dependent spectrum remains poorly constrained due to line-of-sight projection effects. We address this in arXiv:2504.05384 by cross-correlating 11 far-infrared intensity maps spanning a 50-fold frequency range from Planck, Herschel, and IRAS, with spectroscopic galaxies and quasars from SDSS I-IV tomographically. We mitigate foregrounds using CSFD, a CIB-free Milky Way dust map, and also remove the tomographic SZ background from hot gas in the cosmic web detected in arXiv:2006.14650. These cross-correlation amplitudes on two-halo scales trace bias-weighted CIB redshift distributions and collectively yield a 60σ detection of the evolving CIB spectrum, sampled across hundreds of rest-frame frequencies over 0 < z < 4. We break the bias-intensity degeneracy by adding monopole information from FIRAS. The recovered CIB spectrum reveals a dust temperature distribution that is broad, spanning the full range of host environments, and moderately evolving. Using low-frequency CIB amplitudes, we constrain cosmic dust density, Ω_dust, which peaks at z = 1-1.5 and declines threefold to the present. Our wide spectral and sky coverages enable a determination of the total infrared luminosity density with negligible cosmic variance across 90% of cosmic time. This yields a more precise yet consistent constraint on the cosmic star formation history compared to the Madau & Dickinson (2014) compilation. Additionally, we find that star formation occurs in a mode that is, on average, 80% dust-obscured at z = 0 and 60% at z = 4. Our results, based on intensity mapping, are complete, requiring no extrapolation to faint galaxies or low-surface-brightness components. We release our tomographic CIB spectrum and redshift distributions in this link as a public resource for future studies of the CIB, both as a cosmological matter tracer and CMB foreground.

Speaker: Yi-Kuan Chiang (ASIAA)

4:15 PM → 4:25 PM Multiphase analytic CGM models

Recent observations of the CGM reveal that it is extended, multiphase, and ubiquitous, detected around star forming and quiescent galaxies. However, many questions remain open - how much gas is out there, what are its thermal properties, spatial distribution, and morphology? These are linked to the properties of gas accretion onto galaxies, star formation, and feedback processes, and are crucial to our holistic understanding of galactic ecosystems. I will present the multiphase CGM modeling framework I developed with collaborators and showcase examples of its application to a wide range of absorption measurements, constraining the CGM mass, thermodynamics, energetics, and cool gas cloud sizes. I will also demonstrate how predictions from these models can be used to test them with upcoming and future multi-wavelength observations.

Speaker: Yakov Faerman (University of Washington)

Fri, August 1

9:00 AM → 9:30 AM Review Talk: Reconciling the Past and Present IGM/CGM/Galaxy Ecosystems

Remarkable parallels exist between observations of diffuse baryons and their connections to galaxies in the high redshift universe compared to z~0 ... in spite of apparently vast differences between the properties of the galaxies themselves and the nature and intensity of the feedback processes operating within them. I will attempt to draw connections between "contemporaneous" observations of galaxy-scale feedback in the adolescent universe with observable signatures "today", and attempt to distinguish between evolutionary sequences and possible coincidences that need further investigation.

Speaker: Chuck Steidel (California Institute of Technology)

9:35 AM → 9:55 AM The Lyman-Alpha Tomography IMACS Survey (IMACS)

The cosmic web in the distant universe is generally mapped by observing the positions of galaxies. Recently a new perspective has been gained by mapping the diffuse gas in the intergalactic medium (IGM). The Lyman-Alpha Tomography IMACS Survey (LATIS) has now produced 3D maps of the IGM at redshift z~2.5, covering a volume of about 10^7 Mpc^3. I will present the LATIS maps and discuss how they inform our understanding of the interplay between early galaxies and their large-scale environments.

Speaker: Andrew Newman (Carnegie Observatories)

10:00 AM → 10:30 AM Discussion

10:30 AM → 11:00 AM Break

11:00 AM → 11:20 AM Probing the Effect of Feedback on the IGM with FRBs

The intergalactic medium gas is usually believed to simply trace the cosmic web structures traced by dark matter, but AGN feedback (especially jets) will probably modify this simple picture especially the IGM and CGM baryon budgets. I will talk primarily about the combining spectroscopic galaxy surveys with FRBs to probe the IGM and CGM balance, which is being implemented in the FLIMFLAM survey. I will highlight the role of Subaru PFS, the world's most powerful multiobject spectrograph, in efficiently mapping the cosmic web out to high redshift, and new applications of the field level inference technique towards this problem.

Speaker: Khee-Gan Lee (Kavli Institute for the Physics and Mathematics of the Universe)

11:25 AM → 11:45 AM Probing cosmic plasmas at sub-au scales with fast radio bursts

Fast radio bursts (FRBs) are dispersed and scattered by plasma density fluctuations along the line-of-sight, making them sensitive probes of diffuse ionized gas across interstellar, circumgalactic, and intergalactic media. In this talk I will discuss how FRB propagation effects are unveiling cosmic plasmas at extremely small (sub-au) spatial scales in both interstellar and circumgalactic media, and how they may be used in tandem with quasars to constrain the turbulent dynamics of ionized gas in these environments.

Speaker: Stella Koch Ocker (California Institute of Technology)

11:50 AM → 12:00 PM Probing Baryonic Feedback and Cosmological Tension with Fast Radio Bursts: Insights from CAMELS

Fast Radio Bursts (FRBs) are powerful probes of diffuse ionized baryons, offering unique insights into the cosmic ecosystems from the circumgalactic medium (CGM) to the intergalactic medium (IGM). Utilizing simulation suites from the CAMELS project—IllustrisTNG, SIMBA, and Astrid—we analyze FRB dispersion measures (DMs) across models with varying cosmological and astrophysical parameters. Our analysis shows that DM radial profiles around the CGM are highly sensitive to baryonic effects, with strong ejective feedback causing baryon spread in and around halos. On larger scales, we introduce "baryon spread" as a robust measure of baryonic impact on the matter power spectrum. Our study reveals a strong correlation between FRB statistics, particularly the F-parameter, and baryon spread in CAMELS simulations, independent of subgrid galaxy formation models. This correlation offers a novel pathway for using FRBs to correct for baryonic effects in ongoing and upcoming cosmological surveys, such as DESI, Euclid, Roman, and Rubin. With large FRB samples, our findings highlight the pivotal role of FRBs in bridging astrophysics and cosmology, offering new constraints on the CGM and enhancing the power of next-generation cosmological surveys.

Speaker: Isabel Medlock (Yale University)

12:05 PM → 12:15 PM A hydrosimulations-based approach to relate the Fast Radio Burst dispersion measure -- redshift relation to the suppression of matter power spectrum

The effects of baryonic feedback on matter power spectrum are uncertain. Upcoming large-scale structure surveys require percent-level constraints on the impact of baryonic feedback effects on the small-scale ($k \gtrsim 1\,h\,$Mpc$^{-1}$) matter power spectrum to fully exploit weak lensing data. The sightline-to-sightline variance in the fast radio bursts (FRBs) dispersion measure (DM) correlates with the strength of baryonic feedback and offers unique sensitivity at scales upto $k \sim 100\,h\,$Mpc$^{-1}$. We analytically compute the variance in FRB DMs using the electron power spectrum, which is modeled as a function of cosmological and feedback parameters in IllustrisTNG suite of simulations in CAMELS project. We demonstrate its efficacy in capturing baryonic feedback effects across several simulation suites, including SIMBA and Astrid. We show that with 10,000 FRBs, the suppression of the matter power spectrum can be constrained to percent-level precision at large scales (k < 1 h/Mpc) and ~10% precision at small scales (k > 10 h/Mpc). Insights into the impact of baryons on the small-scale matter power spectrum gained from FRBs can be leveraged to mitigate baryonic uncertainties in cosmic shear analyses.

Speaker: Kritti Sharma (California Institute of Technology)

12:20 PM → 12:30 PM Discussion

12:30 PM → 1:45 PM Lunch

1:45 PM → 2:05 PM Mergers, Radio Jets, and Quenching Star Formation in Massive Galaxies: Quantifying Their Synchronized Cosmic Evolution and Assessing the Energetics

The existence of a population of massive quiescent galaxies with little to no star formation poses a challenge to our understanding of galaxy evolution. The physical process that quenched the star formation in these galaxies is debated, but the most popular possibility is that feedback from supermassive black holes lifts or heats the gas that would otherwise be used to form stars. In this paper, we evaluate this idea in two ways. First, we compare the cumulative growth in the cosmic inventory of the total stellar mass in quiescent galaxies to the corresponding growth in the amount of kinetic energy carried by radio jets. We find that these two inventories are remarkably well-synchronized, with about 50% of the total amounts being created in the epoch from z ≈ 1 to 2. We also show that these agree extremely well with the corresponding growth in the cumulative number of major mergers that result in massive (>10^11 M_ ʘ) galaxies. We therefore argue that major mergers trigger the radio jets and also transform the galaxies from disks to spheroids. Second, we evaluate the total amount of kinetic energy delivered by jets and compare it to the baryonic binding energy of the galaxies. We find the jet kinetic energy is more than sufficient to quench star formation, and the quenching process should be more effective in more massive galaxies. We show that these results are quantitatively consistent with recent measurements of the Sunyaev–Zel'dovich effect seen in massive galaxies at z ≈ 1.

Speaker: Timothy Heckman (Johns Hopkins University)

2:10 PM → 3:00 PM Panel Discussion

Speakers: Gilbert Holder (University of Illinois Urbana-Champaign), Gwen Rudie (Carnegie Observatories)

3:00 PM → 3:30 PM Break

3:30 PM → 4:00 PM Closing Talk: What have we learnt?

Speaker: Peng Oh (University of California, Santa Barbara)