CGM/IGM Feedback Physics Weekly: July 14-20, 2026

This week's five qualifying arXiv papers split the feedback problem across two scales. Three probe how gas enters or is processed around galaxies, while two test how AGN and stellar feedback prescriptions redistribute baryons from halos to cluster outskirts. No standalone GitHub release or public astronomy dataset release tied to this topic was verified for July 14-20, so those categories remain empty.

Authors: Glenn G. Kacprzak et al.; submitted July 15, 2026. Read the arXiv paper.

What it does: The study combines cloud-by-cloud ionization modeling with galaxy rotation kinematics for 21 galaxies from the Multiphase Galaxy Halos Survey. It asks whether the usual geometric picture of disk-plane inflow and bipolar outflow is also visible in metallicity and gas microphysics. 1

Method: The analysis uses 63 photoionization-equilibrium clouds and 14 lower-ionization time-dependent clouds; 27 higher-ionization clouds provide only metallicity upper limits and are not used in the main analysis. Kaplan-Meier survival estimates handle censored values, and 5,000 bootstrap resamples set the uncertainties. 1

Finding: For rotation-consistent low-ionization clouds within 30 degrees of the projected major axis, the mean metallicity is lower by dex, a 2.6-sigma difference. These clouds also have higher neutral-hydrogen column density and density, and less non-thermal line broadening by km/s. The pattern is consistent with dynamically cold, metal-poor inflow along the disk plane. At larger azimuthal angles, the same kinematic class is more compatible with enriched, turbulent recycled accretion. 1

Why prioritize: This is a useful observational discriminator for baryon-cycle models. Geometry alone can suggest inflow or outflow; the combination of metallicity, rotation, density, and line broadening is harder for a model to match by accident.

Caveat: A censored two-sample survival test for the PIE metallicity distributions gives , and the authors caution that the test may be underpowered. The paper supports a physical interpretation of the sample, not a population-wide separation of inflow and recycling.

Authors: Zhiyuan Yao, Nir Mandelker, and S. Peng Oh; submitted July 15, 2026. Read the arXiv paper.

What it does: The paper studies cylindrical cold streams penetrating a hot CGM and tracks when they survive, fragment, merge back together, or disperse before reaching the galaxy. 2

Method: The authors run idealized three-dimensional RAMSES simulations with radiative cooling, heating, and photoionization. They vary stream radius, density contrast, Mach number, and initial pressure contrast. Representative runs span density contrasts of 50, 100, and 300; Mach numbers from 0.1 to 2; and final stream radii from 0.1 to 50 kpc. 2

Finding: The simulations produce three main regimes: coagulation, fragmentation, and disruption. After pressure equilibration, shear and radiative cooling control the evolution. At large pressure contrasts, an oblique shock becomes a bow shock and survival depends on post-shock cooling relative to the virial-crossing time. A cylindrical stream has a representative survival threshold near 0.3 kpc under the paper's fiducial scalings. The authors infer that cold streams are more likely to survive in dense high-redshift peaks at , while stronger bow shocks and longer cooling times suppress penetration at . 2

Why prioritize: It gives simulation users a concrete way to interpret whether a cold stream is being destroyed by mixing, broken into a multiphase structure, or growing through radiative entrainment. That distinction matters when comparing accretion histories across redshift.

Caveat: The calculation omits magnetic fields, thermal conduction, self-gravity, and a complete galaxy-feedback model. The quoted regime boundaries are therefore useful diagnostics for the idealized flow setup, not universal thresholds for cosmological simulations.

Authors: Isaac Rosenberg et al.; submitted July 14, 2026. Read the arXiv paper.

What it does: This study varies AGN jet velocity, direction, and hydrodynamic coupling in zoom-in simulations of three galaxy clusters. It connects subgrid jet choices to the thermal state of the WHIM, baryon redistribution, star formation, and possible tSZ signatures. 3

Method: The simulations use the Three Hundred cluster regions with the Simba-C galaxy-formation model. The jet-velocity cases include no jets, a 7,000 km/s cap, and a 35,000 km/s cap; the study also tests random directions and delayed coupling. The selected regions are high-overdensity, strongly superclustered environments rather than a representative cosmic sample. 3

Finding: Jet velocity is the dominant tested parameter for heating low-density gas at . The tSZ signal changes by roughly 10% in the central cluster and filaments but can rise by roughly 100% outside filaments. Faster jets also suppress star formation, expel baryons from the central regions, and reduce black-hole growth. In the paper's case study, the fast-jet model is the best match to BCG properties from eRASS1 and related X-ray surveys. 3

Why prioritize: The paper turns a familiar subgrid ambiguity into an observational question. Low-density gas outside filaments may carry a stronger jet-feedback imprint than the cluster core, where different models produce more similar tSZ signals.

Caveat: Only three specially selected cluster regions are simulated, and the paper is a preprint submitted for journal consideration. Its large-scale predictions need broader volumes, more halos, and careful treatment of projection and foreground systematics before they can be treated as a general constraint.

Authors: Francisco Maion et al.; submitted July 14, 2026. Read the arXiv paper.

What it does: The authors introduce a multi-zoom re-simulation campaign to test how star-formation and AGN feedback parameters affect the galaxy stellar-mass function and gas fractions in massive halos. 4

Method: Thirty-one physics combinations are run in high-resolution zooms selected from MillenniumTNG. Gaussian-process emulators predict the stellar-mass function to about 0.1 dex and halo gas fractions to about 10% precision, allowing both observables to be fitted without rerunning the full simulation grid. 4

Finding: A parameter combination that gives a qualitatively good joint fit to the observed stellar-mass function and group or cluster gas fractions uses significantly less energetic stellar feedback, paired with stronger and less frequent kinetic AGN feedback events. The result is consistent with a scenario in which AGN feedback removes substantial gas from groups and clusters, but the paper does not claim that this setting is uniquely determined. 4

Why prioritize: It is a compact demonstration of why matching stellar statistics alone is not enough. Halo gas fractions add a second constraint that pushes the feedback balance in a different direction.

Caveat: The new parameter setting has not been checked against all quantities for which MillenniumTNG already makes successful predictions. The fit is described as qualitatively good, so it should be read as a calibration result and a parameter-space map rather than a finished replacement model.

Authors: Runyu Zhu et al.; submitted July 14, 2026. Read the arXiv paper.

What it does: Using DESI DR1 spectra, the study compares Mg II absorption around massive brightest cluster galaxies with a redshift- and stellar-mass-matched field-galaxy sample. It traces cool gas from 40 kpc to 15 Mpc using more than one million background quasars. 5

Method: The final BCG sample contains 103,809 objects, with 72,913 in the matched analysis, and the field comparison contains 364,565 massive luminous red galaxies. The analysis uses projected separation rather than scaling every system by an estimated . 5

Finding: Within 200 kpc, the typical Mg II equivalent width is about 0.5 Å around BCGs versus about 0.8 Å around field galaxies, corresponding to roughly 37.5% less cool gas absorption. From 200 kpc to 10 Mpc, the BCG environment shows an excess of cool gas; beyond about 10 Mpc, the two samples converge near 0.014 Å. 5

Why prioritize: This is the week's largest observational baseline for environmental processing. It supplies a radial pattern that feedback and stripping models must reproduce together: depletion near the BCG and enhancement across the surrounding cluster environment.

Caveat: The first seven radial bins are forced measurements rather than independently detected absorption features, and the outer excess may partly reflect intrahalo clustering. The result constrains environmental gas regulation but does not isolate AGN feedback from stripping, assembly history, or other cluster processes.

Start with the AGN-jet paper if your priority is feedback energy transport into the WHIM and its observable tSZ imprint. Read the MillenniumTNG study next for model calibration, then the DESI BCG result for a large-scale observational target. The Kacprzak et al. paper is the best match for inflow versus recycled accretion, while the cold-stream study supplies the idealized fluid picture behind that accretion problem.