Eleven new feedback tests, from cosmic-noon halo metals to gas lifted out of cool cores
Ten new arXiv results and one public enrichment tool from September 21-27, 2026 examine cosmic-noon circumgalactic metallicities, the inner halos of low-mass galaxies, galaxy-IGM coupling at reionisation, relic cool outflows, XRISM's revision of AGN disc-wind energetics, cluster-core gas uplift, magnetic suppression of mixing, and two tests that weaken the default case for feedback.
The week of September 21 to September 27, 2026 produced ten new arXiv results on gas inside, leaving and returning to galaxy halos, plus one public release of a chemical-enrichment tool. That is everything the arXiv listing carried by Monday morning, which reaches submissions logged through Friday, September 25.
Read together, a pattern sits in the modelling. Four of these items move an answer by roughly a factor of ten through what they assume about gas structure, and one goes the other way, finding that a pattern usually credited to feedback survives with feedback switched off.
An item earns a place below when the original reports a quantitative result on gas inside, leaving or returning to a galaxy halo or the intergalactic medium, states a method another group can repeat, and links to a public source.
At a glance
| Item | Design / method | Main result | Scale or tracer |
|---|---|---|---|
| Deepak et al., BRIDGE-I 1 | 105 absorbers at 1 ≤ z ≤ 2.2, combining archival HST ultraviolet spectra with Keck/HIRES and VLT/UVES optical spectra | Median metallicity [X/H] = −1.19 at cosmic noon, statistically indistinguishable from z < 1 (−1.18) and well above z > 2.2 (−2.02); no absorber below −3.5 | Neutral hydrogen columns 16.4 ≤ log N_HI < 20.3; cool and warm halo gas in absorption |
| Nunez-Cravin et al., KBSS-InCLOSE II 2 | Two low-mass galaxies within 50 kpc of a background quasar at z ≈ 2.3, observed with Keck/KCWI, MOSFIRE and HIRES | No Si II in either halo; C IV and O VI in both; at least seven kinematic components per halo over ±150 km s⁻¹; no unambiguously unbound gas | D_tran/R_vir ≤ 0.75; the inner halo in absorption |
| Anderson et al., Sherwood-Relics 3 | Hybrid radiation-hydrodynamic simulations with mock [O III] emitters built to JWST/ASPIRE survey specifications | The IGM runs more opaque than average within 5 cMpc/h of a galaxy and more ionised than average at 15–50 cMpc/h | 5.4 < z < 6.2; Lyα forest transmission |
| Luo et al., SQuIGGLE 4 | Stacked Keck spectra of more than 1300 post-starburst galaxies at 0.5 < z < 0.9 in Fe II and Mg II absorption | Outflows in every stack except galaxies quenched more than 260 Myr ago; mass-loading factors 1–120 | Kpc-scale cool gas; blueshifted absorption |
| Porquet, AGN wind review 5 | Invited review of XRISM/Resolve and multi-wavelength observations of AGN winds | PDS 456's mass outflow rate revised from about 10 to 60–300 M☉ yr⁻¹, kinetic power ≳10⁴⁷ erg s⁻¹ | Sub-parsec accretion-disc wind; X-ray Fe K absorption |
| Veenema et al., Breaking the Blend 6 | Spaxel-by-spaxel multi-tracer kinematic decomposition of JWST integral-field spectroscopy | Twelve mid-infrared lines split NGC 5728's circumnuclear emission into a star-forming ring and an AGN biconical outflow | Central kiloparsec; fine-structure lines from 7.9 to 126.2 eV |
| Tamhane et al., cavity uplift 7 | X-ray cavity measurements in 24 cool-core clusters, compared against observed molecular gas masses | Molecular gas mass scales roughly linearly with the maximum gas mass a cavity displaces; 10⁸-yr gas reaches 10–30 kpc at 150–400 km s⁻¹ | 10–60 kpc; hot X-ray gas against Hα and molecular filaments |
| Mohapatra et al., mixing layers 8 | MHD simulations of turbulent radiative mixing layers at up to 1024 × 2048² resolution | A weak hot-phase field cuts mass flux, enthalpy flux and cooling by up to an order of magnitude, and the MHD rate has not converged | The interface between hot and cold phases; up to 10⁴ K gas cooling out of a hot stream |
| Zhang et al., satellite quenching 9 | SIMBA, TNG100, EAGLE and a feedback-free SIMBA run at z = 0 | Quenched satellites concentrate along the central galaxy's major axis, and the pattern survives with stellar and AGN feedback switched off | Halo and extra-halo scales; galaxy distribution statistics |
| Nagamine et al., CAMELS-CROCODILE 10 | GADGET smoothed-particle hydrodynamics with the Osaka feedback model; 25 and 50 Mpc/h boxes, 26 parameters varied | Matter power suppressed by a few per cent against TNG's roughly 27%; stars form up to 2.5 times more efficiently at group scales | Simulation suite; subgrid feedback calibration |
| Rossi et al., CRIMSONS 11 | Public web tool and Python package for chemical enrichment with stochastic IMF sampling | Incomplete IMF sampling produces large abundance scatter in low-mass populations; Population III pre-enrichment changes later evolution | A single stellar population; 30 elements from hydrogen to zinc |
Paper briefs
Halo metals reach their present level by cosmic noon
Authors and date. Saloni Deepak, Nicolas Lehner, J. Christopher Howk, John O'Meara, Celine Péroux and J. Xavier Prochaska, submitted September 22, 2026; submitted to the Astrophysical Journal. 1
Study design. BRIDGE-I assembles 105 absorbers with neutral hydrogen columns between 16.4 and 20.3 at 1 ≤ z ≤ 2.2, gas with circumgalactic columns sampled at the epoch of peak star formation and AGN activity. Archival Hubble Space Telescope ultraviolet spectra supply the hydrogen columns, and Keck/HIRES and VLT/UVES optical spectra supply the metal lines from which the authors derive metallicities and physical conditions. 1
Result. The median metallicity at cosmic noon is [X/H] = −1.19, statistically indistinguishable from the z < 1 value of −1.18 and significantly above the z > 2.2 value of −2.02. The most diffuse absorbers, those between 16.4 and 17.2 in log N_HI, carry that plateau and have already reached their z < 1 enrichment level by cosmic noon, while denser absorbers stay more metal-poor than their z < 1 counterparts and keep enriching afterwards. No absorber in the sample falls below [X/H] = −3.5, so the survey finds no pristine circumgalactic gas at cosmic noon. The absorbers trace overdensities between 400 and 2200, and the different absorber classes differ by a factor of 400 in mean N_HI while their mean total hydrogen columns differ by only 2.5. Denser gas above log N_HI = 19.0 sits on a metallicity floor near −2.0, which the authors read as a well-mixed population, against a diffuse population still short of full mixing. 1
Why read. The cosmic-noon metallicity distribution is a calibration point for enrichment models, and this survey supplies it from a uniform, HI-selected sample of 105 absorbers. It also shows that the class-to-class spread comes from ionization state rather than from how much gas a sightline crosses, which is what makes the plateau compatible with the much lower values measured at higher redshift. 1
Caveat. The sample is HI-selected and stops at log N_HI = 20.3, so it says nothing about lower columns. The z > 2.2 comparison draws on different surveys, and the metallicities carry ionization corrections derived from the same optical spectra. 1
The inner halo of two low-mass galaxies at z ≈ 2.3 is hot, complex and bound
Authors and date. Evan Haze Nunez-Cravin, Charles C. Steidel, Gwen C. Rudie, Evan N. Kirby, Charis M. Hall and five co-authors, submitted September 25, 2026; resubmitted to the Astrophysical Journal after minor revisions. 2
Study design. KBSS-InCLOSE extends the Keck Baryonic Structure Survey to the inner halo of galaxies that happen to lie close to a background quasar sightline. Two low-mass star-forming galaxies at z ≈ 2.3 with log(M*/M☉) ≤ 9 sit within 50 kpc of the sightline, or within 0.75 virial radii. Keck/KCWI and Keck/MOSFIRE spectra establish both galaxies and their nebular and morphological properties, and Keck/HIRES spectra of the background quasars record the absorption through their halos. 2
Result. Neither halo shows low-ionization metal absorption of the kind Si II would trace. Intermediate ions such as C IV and high ions such as O VI appear in both halos, spread over at least seven kinematic components per halo within about ±150 km s⁻¹. Of the ten components whose thermal properties the authors model, six have temperatures consistent with heating by the metagalactic ultraviolet background, at a median log(T/K) = 4.0, and the remaining four sit between 4.6 and 5.1 and would need additional heating or rapid replenishment to stay there. Thermal broadening carries the internal energy of these absorbers, their internal turbulent velocities come out subsonic, and their bulk motion through the halo is likely supersonic. The authors detect no unambiguously unbound gas in either halo, and their comparison with more massive systems points to the inner halo becoming kinematically more complex and holding a larger unbound fraction as stellar mass rises. 2
Why read. Absorption studies of the circumgalactic medium mostly rest on massive galaxies, because those are the ones bright enough to identify behind a quasar. This paper adds a pair of low-mass systems at a fraction of a virial radius and reports the kinematic and thermal structure of their gas, which is the regime where stellar feedback should dominate the halo. 2
Caveat. Two galaxies carry the whole result, and both were selected for sitting near a quasar sightline. The thermal modelling covers ten absorption components. 2
Reionisation-era galaxies leave a large-scale imprint on the Lyα forest
Authors and date. Hamish Anderson, Laura C. Keating, Luke Conaboy, Xiangyu Jin, James S. Bolton and Ewald Puchwein, submitted September 22, 2026; preprint. 3
Study design. The authors use Sherwood-Relics, a suite of hybrid radiation-hydrodynamic simulations of the high-redshift intergalactic medium, to simulate the Lyα forest alongside a mock population of [O III] emitters built to the survey specifications of JWST's ASPIRE programme. They measure the effective optical depth near the mock galaxies and compare it with a control sample of random IGM positions, over 5.4 < z < 6.2. 3
Result. Inside 5 cMpc/h of a galaxy the IGM comes out more opaque than the cosmic average, because those regions are overdense. Between 15 and 50 cMpc/h the sign of the effect turns and the IGM is more ionised than average, following the higher photoionisation rate around galaxies. The authors report qualitative agreement with the ASPIRE results and with observations that claim a large-scale ionisation bias around [O III] emitters, and they find large scatter between realisations from cosmic variance. 3
Why read. The correlation between IGM transmission and high-redshift galaxies has been reported observationally but not modelled end to end. This paper checks it inside a radiation-hydrodynamic simulation with an emitter sample matched to a real survey, and it separates the overdensity effect near galaxies from the ionisation effect further out. 3
Caveat. Both the galaxy population and the transmission are simulated, so the comparison tests the model against survey specifications rather than against an observed galaxy catalogue. Cosmic variance sets a floor on what a single sightline can establish. 3
Relic cool outflows keep running for a few hundred million years after quenching
Authors and date. Yuanze Luo, Justin S. Spilker, David J. Setton, Timothy Heckman, Rachel Bezanson and eleven co-authors, submitted September 25, 2026; revision resubmitted to the Astrophysical Journal. 4
Study design. SQuIGGLE holds more than 1300 post-starburst galaxies between z = 0.5 and 0.9. The authors stack their spectra in bins of stellar mass, specific star formation rate, burst mass, burst mass fraction and time since quenching, and measure blueshifted Fe II λλ2586, 2600 and Mg II λλ2796, 2803 absorption in each stacked spectrum. 4
Result. Blueshifted line centroids appear in every stack except the one holding galaxies that quenched more than 260 Myr ago. Outflow velocity falls as the time since quenching grows and shows little correlation with any other galaxy property. The inferred mass-loading factors run from 1 to 120, the maximum velocities exceed the escape velocities of the host galaxies' interstellar media, and the energy and momentum fluxes come out above what the current star formation could supply, which places these outflows as relics of the earlier starburst or AGN episode. The authors read them as a route by which rapid quenching at these redshifts moves gas into the surrounding halos. 4
Why read. Cool outflows as a quenching channel were established largely from small JWST samples at z ≳ 2. This survey reaches the same physics from the ground at intermediate redshift with more than a thousand galaxies, and it supplies the time since quenching at which the outflow signature fades. 4
Caveat. Stacking averages galaxies together, so any spread inside a bin stays hidden, and the mass-loading factors inherit an assumed covering fraction and geometry for the absorbing gas. Post-starburst galaxies are a selected population rather than a fair sample of the quenched galaxy population. 4
XRISM multiplies the inferred mass outflow rate of PDS 456
Authors and date. Delphine Porquet, submitted September 24, 2026; invited review in the proceedings of the 2026 annual meeting of the French Society of Astronomy and Astrophysics. 5
Study design. A review of X-ray and multi-wavelength observations of active galactic nucleus winds, organised around the XRISM Resolve microcalorimeter, which reaches a non-dispersive energy resolution of about 5 eV full width at half maximum above about 2 keV and resolves Fe K absorption components that charge-coupled-device spectroscopy blended together. 5
Result. Resolving the Fe K absorption in PDS 456 into dense clumps embedded in a diffuse ionised wind moves the inferred mass outflow rate from about 10 M☉ yr⁻¹, the value a smooth-wind interpretation gives, to roughly 60–300 M☉ yr⁻¹. The kinetic power in that reading reaches above 10⁴⁷ erg s⁻¹, comparable to the quasar's bolometric luminosity, and the momentum flux lands around 10 to 50 L_bol/c. In NGC 3783 the same instrument resolves six photoionised absorption components, among them broad Fe XXVI outflowing at about 0.05c with a kinetic power between 0.8 and 3 per cent of the bolometric luminosity, and a later observation caught a transient ultra-fast outflow at about 0.19c. The review places ultra-fast outflow kinetic powers at or above the 0.5 to 5 per cent of bolometric luminosity that some AGN feedback models invoke as the threshold for driving galaxy-scale effects. 5
Why read. The feedback energy budget in semi-analytic and hydrodynamic models is often pinned to an outflow kinetic power measured from X-ray spectra. This review collects what XRISM has changed about those numbers, and PDS 456 is the clearest case: the same absorption feature yields a rate an order of magnitude higher once the gas is allowed to be clumpy. 5
Caveat. The numbers come from a review of published analyses rather than from new observations. The author states that the energetics depend on the assumed wind geometry, gas density, radial location and volume filling factor, and that the physical coupling between the accretion-disc wind and galaxy-scale outflows remains unresolved. 5
Separating an AGN outflow from a star-forming ring in NGC 5728
Authors and date. Oscar Veenema, Niranjan Thatte, Dimitra Rigopoulou, Richard I. Davies, Miguel Pereira-Santaella and 24 co-authors, submitted September 24, 2026; submitted to MNRAS Letters. 6
Study design. The authors decompose integral-field spectroscopy into separate physical components spaxel by spaxel, combining kinematic modelling with an imposed flux decomposition in each spaxel. They apply the framework to JWST observations of the Seyfert galaxy NGC 5728 from the Galaxy Activity, Torus and Outflow Survey, using twelve mid-infrared fine-structure lines between 4.49 and 25.89 μm, with ionization potentials from 7.9 to 126.2 eV. 6
Result. The circumnuclear emission separates into two dominant components, a star-forming ring and an AGN-driven biconical outflow, and the method recovers the spatial morphology of each across the field of view. 6
Why read. Most spectral tracers of a galaxy's centre respond to star formation and to AGN excitation at the same time, which is why the kinematics and energetics of a nuclear outflow are hard to isolate. This paper makes the separation explicit and per spaxel, and the authors present it as a general framework that carries to other instruments and wavelength ranges. 6
Caveat. One galaxy carries the demonstration, and the decomposition needs a set of lines with enough signal in each spaxel to constrain the components. 6
Cavities lift the gas that becomes molecular filaments
Authors and date. Prathamesh Tamhane, Brian McNamara and Paul Nulsen, submitted September 22, 2026; submitted to the Astrophysical Journal. 7
Study design. The authors measure gas uplift by X-ray cavities across 24 cool-core galaxy clusters, recording lifting masses, velocities, radii and cooling times, and compare the displaced hot gas against the molecular gas masses observed in the same systems. 7
Result. Almost every cluster in the sample holds enough low-entropy gas inside its central 10 kpc to account for the molecular gas observed there, and the molecular gas mass scales approximately linearly with the maximum gas mass a cavity displaces. Gas with cooling times of a few 10⁸ yr can be carried out to the 10–30 kpc where Hα filaments typically sit, at characteristic velocities of 150–400 km s⁻¹, while gas with a cooling time near 10⁹ yr needs uplift beyond 60 kpc. Taking half the displaced mass as lifted and cooled, the mass expected to cool over the lifetime of the observed cavities matches the molecular reservoir in several systems; other systems hold more molecular gas than a single cycle can supply, which the authors read as accumulation over repeated episodes of uplift and cooling. 7
Why read. It connects the two halves of the cool-core feedback loop with numbers from the same systems: the hot gas a radio jet lifts, and the molecular gas that appears once that gas cools. The linear scaling between the two masses is what a model of stimulated cooling has to reproduce. 7
Caveat. The sample is 24 clusters, and the match between lifted mass and molecular mass rests on the assumption that half the displaced gas is lifted and cools. A correlation between displaced mass and molecular mass does not establish which way the causation runs. 7
Magnetic tension suppresses cooling in mixing layers, and the suppression has not converged
Authors and date. Rajsekhar Mohapatra, Lachlan Lancaster, Drummond Fielding, Eliot Quataert and Greg L. Bryan, submitted September 24, 2026; to be submitted to MNRAS. 8
Study design. Magnetohydrodynamic simulations of turbulent radiative mixing layers, at resolutions up to 1024 × 2048², covering fields aligned with the shear, fields transverse to it, and polarity-reversing configurations in which the two sides carry oppositely directed fields so that a current sheet forms at the interface. 8
Result. A weak hot-phase field, at a shear Alfvén Mach number of about 14, cuts the mass flux, the enthalpy flux and the radiative cooling rate by up to an order of magnitude against the hydrodynamic case. Magnetic tension damps the turbulent motions, which reduces both the diffusion of hot gas into the layer and the folding of its cooling surface. Transverse fields suppress cooling somewhat more strongly than shear-aligned ones, even though a transverse field exerts no tension against the initial linear instability. Reversing the polarity changes the morphology of the cooling gas without restoring hydrodynamic mixing. The net cooling rate comes out resolution-independent in the hydrodynamic runs and still falling with resolution in the magnetohydrodynamic ones, so the suppression factors are lower limits. 8
Why read. Mixing layers set how fast a hot wind cools against cold clouds and how much cold gas survives inside a hot flow, and this is where cold gas in winds, in cluster filaments and in the circumgalactic medium is produced. The paper shows that the hydrodynamical rate is an upper bound once magnetic fields are present, which narrows the range of cooling rates a feedback model can adopt. 8
Caveat. The simulations set up an idealised plane-parallel layer, and the magnetohydrodynamic cooling rate has not converged with resolution, so the size of the suppression is a floor. 8
Anisotropic satellite quenching follows from where satellites sit
Authors and date. Zhuoming Zhang, Weiguang Cui, Yun Chen and Romeel Davé, submitted September 24, 2026; preprint. 9
Study design. The authors compare the SIMBA, TNG100 and EAGLE cosmological simulations against a SIMBA run with stellar and AGN feedback switched off, all at z = 0, and measure how quenched satellites distribute relative to the major axis of their central galaxy, both inside the halo and beyond its boundary. 9
Result. Quenched satellites sit closer to the halo centre and align more strongly with the central galaxy's major axis, while unquenched satellites occupy larger radii and distribute more isotropically. The pattern persists once both feedback channels are removed, which the authors take as evidence that feedback matters little for satellite quenching and that the anisotropy comes from spatial segregation between the two populations. Beyond the halo boundary the signal varies strongly between the simulations and tracks the excess number of galaxies along the major axis, which ties it to the direction-dependent distribution of groups, clusters and filaments. 9
Why read. Anisotropic satellite quenching has been read as a signature of jet-driven feedback, since AGN jets point along the minor axis and the quenched satellites concentrate along the major one. This paper reproduces the pattern in a run with no feedback at all, which puts a geometric explanation alongside the feedback one for the same measurement. 9
Caveat. The conclusion depends on which subgrid models the four runs implement, and the feedback-free run is an extreme control rather than a physical model of a galaxy population. The extra-halo signal disagrees between the simulations. 9
A new feedback suite that suppresses structure less than TNG does
Authors and date. Kentaro Nagamine, Yuri Oku, Atsushi J. Nishizawa, Jun-Young Lee, Francisco Villaescusa-Navarro, Shy Genel and Daniel Anglés-Alcázar, submitted September 21, 2026; submitted. 10
Study design. CAMELS-CROCODILE builds on the GADGET smoothed-particle-hydrodynamics code with the Osaka feedback model, as a companion to the IllustrisTNG-based second-generation CAMELS suite. It contains 25 and 50 Mpc/h boxes organised into one-parameter, cosmic-variance and Sobol-sequence sets that vary 26 cosmological and astrophysical parameters around a fiducial model. The authors validate the suite against benchmarks and other CAMELS runs, then apply a graph neural network trained on IllustrisTNG galaxy catalogues, with its weights frozen, to the new suite. 10
Result. Against IllustrisTNG, the fiducial Osaka model suppresses the matter power spectrum by only a few per cent where TNG reaches about 27 per cent at z = 0, and it forms stars at similar efficiency below 10^12.2 M☉/h but up to 2.5 times more efficiently in group-scale halos, both consistent with weaker AGN feedback. The frozen-weight network fails to recover Ω_m and σ_8 and returns overconfident posteriors, mostly on the simulations holding more galaxies than any in its training set; inside its training range it recovers Ω_m with an error 1.5 times the in-distribution value. The authors state that the full dataset, covering snapshots, halo and subhalo catalogues and precomputed summary statistics, will be released through the CAMELS data infrastructure. 10
Why read. Machine-learning inference of cosmology from galaxy surveys is trained on one implementation of baryonic physics, and this suite supplies a second one with a different feedback prescription and a comparable parameter sweep. The frozen-weight failure is the demonstration of what the first paper in that programme is for: a network tuned on IllustrisTNG carries its subgrid model into its answer. 10
Caveat. The dataset release is announced for later, so the validation cannot yet be checked against the data itself. The comparison covers one alternative feedback model. 10
Code and data releases
CRIMSONS puts stochastic IMF sampling online
Author and date. Martina Rossi, Lapo Querci, Stefano Ciabattini, Stefania Salvadori, Irene Vanni and twelve co-authors, submitted September 21, 2026. 11
Tool scope. CRIMSONS models the chemical enrichment of a single stellar population while sampling the initial mass function stochastically, so a low-mass population draws the massive supernova progenitors it actually draws instead of an average yield. It follows individual stars, tracks 30 elements from hydrogen to zinc, and adds contributions from core-collapse supernovae, asymptotic giant branch stars, Type Ia supernovae and pair-instability supernovae across several yield sets, with Population III pre-enrichment treated separately from a fixed metallicity floor. The release covers two routes: an interactive web tool at martina-rossi.it/crimsons.html, with example scripts for working with the outputs, and a Python package installed from pip and documented at crimsons.readthedocs.io. 11
Why track. Whether an abundance spread in a dwarf galaxy or in a circumgalactic absorber records an unusual enrichment history or just the luck of the sampling is a recurring question, and the answer depends on which yields and which resampling the model assumes. This tool runs the sampling directly, with the yield sets and the primordial component exposed as choices, so a group can test how much of a measured spread the sampling alone can produce. 11
Reported behaviour. Incomplete IMF sampling produces large abundance scatter, most of it in low-mass stellar populations; different yield prescriptions shift individual element ratios while some ratios stay robust across sets; and models with Population III pre-enrichment diverge substantially from models that start from a metallicity floor. 11
Caveat. The current implementation is a closed box. It carries no gas flows and no spatial mixing, so it returns the yield pattern a stellar population produces and says nothing about where that material ends up or how a halo mixes it. Nucleosynthesis yields stay uncertain, and the paper reports element-dependent variation between yield sets. 11
Data repository status
A search of Zenodo and the major astronomy data repositories found no dataset on circumgalactic or intergalactic feedback physics deposited and openly downloadable during September 21–27, 2026, so this category stays empty for the week. The CAMELS-CROCODILE suite described above is announced as a release through the CAMELS data infrastructure; the channel lists a dataset here once a deposition is separate and open.
What the week separates
- Where the factor of ten comes from. PDS 456's mass outflow rate moves from about 10 to 60–300 M☉ yr⁻¹ when the Fe K absorber is modelled as dense clumps inside a diffuse wind instead of a smooth one 5. The same kind of assumption sits under mixing layers, where magnetic tension cuts the cooling rate by up to an order of magnitude against hydrodynamics, and the magnetohydrodynamic answer is still falling with resolution 8. BRIDGE-I finds the mean neutral column varying by a factor of 400 between absorber classes while the mean total hydrogen column varies by 2.5, which places the difference in ionization state 1. And CAMELS-CROCODILE and IllustrisTNG differ by about a factor of ten in how strongly their feedback suppresses the matter power spectrum, a few per cent against about 27 10. In each case the number that moves is a modelling choice, and each paper says so.
- The radius each item samples. PDS 456 launches its wind within parsecs of the black hole, and NGC 5728's biconical outflow fills the central kiloparsec 56. Cool-core cavities lift gas from the central 10 kpc out to 30–60 kpc, where the molecular filaments sit 7. The KBSS-InCLOSE galaxies sit inside three quarters of a virial radius, and BRIDGE-I samples gas out to circumgalactic columns at cosmic noon 12. Sherwood-Relics works between 5 and 50 cMpc/h, and the satellite-quenching comparison runs from inside the halo out past its boundary 39. Any one of these numbers can be moved to another radius only through the intervening physics, which none of the items supplies.
- The phase each tracer holds, and the clock it runs on. BRIDGE-I separates absorbers by ionization state at fixed ionization-corrected column, and finds that the diffuse and dense populations enriched on different schedules 1. KBSS-InCLOSE detects C IV and O VI in both low-mass halos and finds the thermal structure split between metagalactic heating and a shorter-lived intermediate-temperature component 2. SQuIGGLE stacks Fe II and Mg II and puts a clock on the outflow signature: it is present until roughly 260 Myr after quenching, then gone 4. The cavity sample works in the opposite direction, asking how long uplifted gas takes to cool into the molecular phase that Hα and infrared emission trace 7. Reading two of these results as one statement about the same gas requires matching both the phase and the clock.
- Where feedback is assumed, and what the control runs return. Anisotropic satellite quenching reproduces itself with stellar and AGN feedback both switched off, so the measurement that has been used to argue for jet-driven quenching has a geometric explanation available 9. CAMELS-CROCODILE's fiducial feedback prescription suppresses structure by roughly a tenth of what IllustrisTNG's does, and the suite is being built so that machine-learning inference can be tested against a second implementation 10. Against those two, the review of XRISM results revises the kinetic power of the accretion-disc wind upward, and the cool-core sample needs repeated cycles of uplift and cooling rather than a single episode to account for the molecular gas it measures 57. The week supplies no experiment that decides between the two readings; it supplies the numbers a model has to match either way.
References
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