Opening Remarks Room: PI/1-100 - Theatre

Opening Talk

• Mark Voit (Michigan State University)

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Review Talk

• Joop Schaye (Leiden University)

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Research Talk

• Alexandra Amon (Princeton University)

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Research Talk

• Hiranya Peiris (University of Cambridge)

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A multi-observation view of feedback: joint kinetic Sunyaev-Zeldovich, X-ray, and weak lensing measurements

• Jared Siegel (Princeton University)

Room: PI/1-100 - Theatre 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.

Baryonic feedback: how extreme is too extreme?

• Leah Bigwood

Room: PI/1-100 - Theatre Cosmological hydrodynamical simulations are able to reproduce many fundamental galaxy properties, but there is no consensus on the impact of 'baryonic feedback' on the matter power spectrum. This uncertainty severely limits the precision of (and potentially biases) small-scale cosmological constraints obtained from weak lensing. It is also possible that baryonic feedback may be more extreme than predicted by the latest simulations, as we found by analysing weak lensing and stacked kSZ measurements. However, the question remains whether such extreme feedback is physically possible. I will present an exploration of a range of empirical AGN feedback models within the FABLE simulation suite, including XFABLE, a novel model with jets thermalising at relatively large cluster-centric distances. I will demonstrate that XFABLE agrees well with the latest constraints of 'extreme feedback', whilst maintaining consistency with observations of galaxy groups/clusters. Finally, to establish stacked kSZ as a benchmark for galaxy formation models, I will describe a comprehensive study of the effect across a number of hydrodynamical simulations. By isolating the effects of different feedback implementations, halo properties, and redshift evolution on the kSZ signal, this work is crucial for interpreting new and future measurements and for building a galaxy formation model that is consistent across a wide range of observables.

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Constraining AGN Feedback with Multiwavelength Measurements

• Evan Scannapieco (Arizona State University)

Room: PI/1-100 - Theatre 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.

Preventative Feedback in Cosmological Simulations: Insights from High Specific Energy Winds with Arkenstone

• Jake Bennett (Center for Astrophysics | Harvard & Smithsonian)

Room: PI/1-100 - Theatre Feedback from galaxies plays a central role in regulating star formation and shaping the cosmic distribution of baryons. In particular, preventative feedback—which inhibits gas accretion onto the interstellar medium (ISM) rather than ejecting it after the fact—offers a compelling mechanism for reconciling observed galaxy growth with cosmological expectations. Using the Arkenstone galactic wind model in cosmological simulations, we explore the impact of high specific energy winds on the circumgalactic and intergalactic media (CGM and IGM). Our results show that wind energy, not mass loading, most strongly regulates stellar mass buildup. Notably, increased mass loading at fixed energy leads to slightly enhanced star formation, as winds become less able to prevent future inflows. These winds deposit energy and metals into the CGM and IGM, slowing gas infall and polluting gas out to large scales without requiring strong ejection from the ISM. The result is a heated, extended CGM that slows the inflow of gas towards the galaxy and reshapes the baryon content of halos. This preventative mode of feedback offers a promising path toward understanding how galaxies self-regulate, how the CGM mediates gas flows, and how baryons are partitioned across cosmic structures.

X-raying CAMELS: Constraining Feedback Physics in Hot Halo Gas with CAMELS and eRASS

• Erwin Lau (CfA)

Room: PI/1-100 - Theatre 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.

Compare the Hot Circumgalactic Medium of Star-Forming and Quiescent Galaxies

• Yi Zhang (MPE)

Room: PI/1-100 - Theatre Studying the distribution and properties of hot gas around galaxies (hot CGM) helps constrain the galaxy evolution models but its observation is challenging. The first four SRG/eROSITA all-sky surveys (eRASS:4) allow us to detect the hot CGM by stacking a large sample of galaxies. In this talk, I will present the results we obtained about the difference of the hot CGM around star-forming and quiescent galaxies. We find either selected in stellar mass or halo mass, the star-forming galaxies do not host brighter stacked X-ray emission from the hot CGM than their quiescent counterparts at the same mass range. The result provides useful constraints on the extent of feedback's impacts as a mechanism for quenching star formation.

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Research Talk

• Nick Frontiere (Argonne National Laboratory)

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Entangled: the co-evolution of cosmic filaments and galaxies as seen from the CGM

• Charlotte Welker (City University of New York)

Room: PI/1-100 - Theatre In the recent decade, the CGM has progressively emerged as the complex interface between large-scale structures, in particular cosmic filaments, and central galaxies and their satellites. In this presentation, I will first review the evidence that even halos at least as massive as the Milky Ways and up to cluster scale, show z=0 anisotropies inherited from the cosmic web present across the properties of their CGM gas and their distribution of satellites, with significant impact on satellite galaxies' gas reservoirs and star formation rates. I will then show that some of the most striking anisotropies detected to this date, the so-called "planes of satellites" around Milky-Way mass systems are actually a natural occurence in NewHorizon, a hydrodynamical simulation that combines optimally cosmological volume and resolution. I will show that their origin is strongly tied to the dynamics of the cosmic web across time and scales, with specific contributions from filament mergers on the one hand and small-scale streams formed in their midst through a cascade of shocks on the other hand. I will discuss implications for the future of investigations of the cosmic web, highlighting in particular the importance of detecting smaller scale filaments in observations with next-generations surveys like LSST or EUCLID.

Probing baryonic feedback and cosmology with patchy screening in the FLAMINGO Simulations.

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

Room: PI/1-100 - Theatre 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.

Multiphase analytic CGM models

• Yakov Faerman (University of Washington)

Room: PI/1-100 - Theatre 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.

Flash Talks - 1 min, 1 slide Room: PI/1-100 - Theatre

Review Talk

• Daisuke Nagai (Yale University)

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Research Talk

• Sanskriti Das (Stanford University)

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Research Talk

• Johnathan Stern (Tel Aviv University)

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Research Talk

• Simone Ferraro (Lawrence Berkeley National Laboratory)

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Research Talk

• Emmanuel Schaan (SLAC National Accelerator Laboratory)

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Research Talk

• William Coulton (University of Cambridge)

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Constraining cluster and group ecosystems with joint and consistent SZ and x-ray observations

• Gerrit Farren (Lawrence Berkeley National Laboratory)

Room: PI/1-100 - Theatre 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.

Resolving Multiphase Gas Production in the kpc-Scale Intergalactic Medium

• Charles Willard (University of Washington)

Room: PI/1-100 - Theatre 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.

The properties of the CGM and its relationship with galaxies in the COLIBRE simulations

• Jonathan Davies (Liverpool John Moores University)

Room: PI/1-100 - Theatre 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.

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

• Chloe Neufeld (Yale University)

Room: PI/1-100 - Theatre 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.

Probing the Magneto-Ionized Circumgalactic Medium of M31 with HI and Rotation Measures

• D.J. Pisano (University of Cape Town)

Room: PI/1-100 - Theatre 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.

Discussion Room: PI/1-100 - Theatre

Research Talk

• Boryana Hadzhiyska (University of California, Berkeley)

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The Kinematics of the Hot and X-ray Emitting Circumgalactic Medium: Predictions from Simulations

• John ZuHone (Center for Astrophysics | Harvard & Smithsonian)

Room: PI/1-100 - Theatre 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.

Unveiling the Multi-phase CGM and ISM in MACS1931-26 with JWST and ALMA

• Laya Ghodsi (University of British Columbia)

Room: PI/1-100 - Theatre 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.

Discussion Room: PI/1-100 - Theatre

Flash Talks - 1 min, 1 slide Room: PI/1-100 - Theatre

Review Talk

• Nir Mandelker (Racah Institute of Physic)

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Research Talk

• Chris Martin (California Institute of Technology)

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Growing in the Wind: Emission-Line Imaging of OVI in the Circumgalactic Medium

• David Rupke (Rhodes College)

Room: PI/1-100 - Theatre 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.

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Mapping the z ~ 2 Circumgalactic Medium with KBSS Galaxy Pairs

• Nikolaus Prusinski (Caltech)

Room: PI/1-100 - Theatre 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 $z\sim 2$.

The circumgalactic medium in emission and absorption, from dwarf galaxies to massive quasar hosts

• Sean Johnson

Room: PI/1-100 - Theatre 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.

Complex Dynamics of Stars and Nebular Gas in Active Galaxies Centred in Cooling X-ray Atmospheres

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

Room: PI/1-100 - Theatre 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.

The enriched circumgalactic and intergalactic medium of star-forming dwarf galaxies

• Nishant Mishra (University of Michigan)

Room: PI/1-100 - Theatre 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.

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Review Talk

• Irina Zhuravleva (University of Chicago)

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Research Talk

• Irina Butsky (Stanford University)

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The Simulated CGM at 200 pc

• Scott Lucchini (Center for Astrophysics | Harvard & Smithsonian)

Room: PI/1-100 - Theatre 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.

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Kinetic simulations of the cosmic ray pressure anisotropy instability: cosmic ray scattering rate in the saturated state

• XIAOCHEN SUN (Princeton University)

Room: PI/1-100 - Theatre Cosmic ray (CR) feedback plays a vital role in shaping the formation and evolution of galaxies through their interaction with magnetohydrodynamic waves. In the CR self-confinement scenario, the waves are generated by the CR gyro-resonant instabilities via CR streaming or CR pressure anisotropy and saturate by balancing wave damping. The resulting effective particle scattering rate by the waves, $\nu_{\text{eff}}$, critically sets the coupling between the CRs and background gas, but the efficiency of CR feedback is yet poorly constrained. We employ 1D kinetic simulations under the Magnetohydrodynamic-Particle-In-Cell (MHD-PIC) framework with the adaptive $\delta f$ method to quantify $\nu_{\text{eff}}$ for the saturated state of the CR pressure anisotropy instability (CRPAI) with ion-neutral friction. We drive CR pressure anisotropy by expanding/compressing box, mimicking the background evolution of magnetic field strength, and the CR pressure anisotropy eventually reaches a quasi-steady state by balancing quasi-linear diffusion. At the saturated state, we measure $\nu_{\text{eff}}$ and the CR pressure anisotropy level, establishing a calibrated scaling relation with environmental parameters. The scaling relation is consistent with quasi-linear theory and can be incorporated to CR fluid models, in either the single-fluid or $p$-by-$p$ treatments. Our results serve as a basis for accurately calibrating the subgrid physics in macroscopic studies of CR feedback and transport.

Tracing the Galactic Fountain in Spiral Galaxies with JWST

• Chris Howk (University of Notre Dame)

Room: PI/1-100 - Theatre The circulation of baryons and metals from the disk to the CGM and back again plays a fundamental role in the evolution of galaxies. This deep connection between disk and CGM plays out through an interface layer in the first several kpc above the disk. I will present new JWST/MIRE observations of PAH emission from this thickened interstellar disk of material in the edge-on galaxy NGC 891. We find PAH-emitting filaments and clouds to at least 8 kpc above the disk. We use computer vision-related techniques to identify and characterize filaments in the thick disk. Our analysis demonstrates that there is more filamentary power above heavily star forming regions, and that the star formation-connected filaments are vertically-oriented. This provides a path to quantifying the vertical scale over which large-scale fountain flows shape the thick disk and CGM as a function of star formation intensity.

Investigating Galaxy Ecosystems with Multi-wavelength Observations of Gas and Dust

• Varsha Kulkarni (University of South Carolina)

Room: PI/1-100 - Theatre 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.

From Disk to IGM: A Comprehensive Mapping of Andromeda's Circumgalactic Medium

• Nicolas Lehner (University of Notre Dame)

Room: PI/1-100 - Theatre 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.

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Research Talk

• Andrew Pontzen (Durham University)

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Panel Discussion Room: PI/1-100 - Theatre

Baryon Fraction in Halos: Observational Constraints from HI, X-ray, and Stellar Components

• Ajay Dev (ICRAR - UWA)

Room: PI/1-100 - Theatre 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.

Chemical enrichment patterns as a tool to identify feedback processes in the CGM

• Suyash Kumar (The University of Chicago)

Room: PI/1-100 - Theatre 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.

Cosmic Infrared Background Tomography and a Census of Cosmic Dust and Star Formation

• Yi-Kuan Chiang (ASIAA)

Room: PI/1-100 - Theatre 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][1] 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][2], 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][3]. 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][4] as a public resource for future studies of the CIB, both as a cosmological matter tracer and CMB foreground. [1]: https://arxiv.org/abs/2504.05384 [2]: https://arxiv.org/abs/2306.03926 [3]: https://arxiv.org/abs/2006.14650 [4]: https://zenodo.org/records/15149425

Flash Talks Room: PI/1-100 - Theatre

Review Talk

• Chuck Steidel (California Institute of Technology)

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Research Talk

• Andrew Newman (Carnegie Observatories)

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Mergers, Radio Jets, and Quenching Star Formation in Massive Galaxies: Quantifying Their Synchronized Cosmic Evolution and Assessing the Energetics

• Timothy Heckman (Johns Hopkins University)

Room: PI/1-100 - Theatre 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.

Discussion Room: PI/1-100 - Theatre

Research Talk

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

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Research Talk

• Stella Koch Ocker (California Institute of Technology)

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Probing Baryonic Feedback and Cosmological Tension with Fast Radio Bursts: Insights from CAMELS

• Isabel Medlock (Yale University)

Room: PI/1-100 - Theatre 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.

A hydrosimulations-based approach to relate the Fast Radio Burst dispersion measure -- redshift relation to the suppression of matter power spectrum

• Kritti Sharma (California Institute of Technology)

Room: PI/1-100 - Theatre 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.

Discussion Room: PI/1-100 - Theatre

Research Talk

• Vera Gluscevic (University of Southern California)

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Panel Discussion Room: PI/1-100 - Theatre

Closing Talk

• Peng Oh (University of California, Santa Barbara)

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