Astrophysics

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

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

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

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

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

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.

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.

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.

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.

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