arxiv: 2512.04203 · v1 · submitted 2025-12-03 · 🌌 astro-ph.CO · astro-ph.GA· astro-ph.HE

The impact of strong feedback on galaxy group scaling relations

D. Eckert , R. Seppi , J. Braspenning , A. Finoguenov , F. Gastaldello , L. Lovisari , E. O'Sullivan , S. Ettori

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B. D. Oppenheimer M. A. Bourne D.-W. Kim M. Sun H. Khalil G. Gozaliasl Y. E. Bahar V. Ghirardini W. Cui K. Kolokythas S. McGee

This is my paper

Pith reviewed 2026-05-17 01:47 UTC · model grok-4.3

classification 🌌 astro-ph.CO astro-ph.GAastro-ph.HE

keywords galaxy groupsAGN feedbackX-ray scaling relationscosmological simulationsbaryon fractionsfeedback modelsXMM-Newton observations

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The pith

Highly ejective AGN feedback models underpredict the X-ray luminosity of galaxy groups at fixed mass.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper establishes that cosmological simulations tuned for highly ejective feedback, calibrated to recent low baryon fraction measurements, fail to reproduce the observed X-ray properties of galaxy groups. In a sample of 44 groups with XMM-Newton data, these models underpredict luminosity at fixed temperature or mass at 5.7 sigma significance. The authors note that this mismatch is robust to selection effects because it uses directly measurable quantities rather than derived gas fractions. They conclude that baryon fraction estimates carry large systematic uncertainties when applied to stacked or heterogeneous samples, making observable scaling relations a preferable calibration target. If the claim holds, feedback prescriptions in simulations must be adjusted to retain more gas in halos between 10^13 and 10^14 solar masses.

Core claim

The authors demonstrate that highly ejective feedback models under-predict the luminosity of galaxy groups at fixed mass at high significance (5.7 sigma). This is shown through the X-ray luminosity-temperature relation measured in 44 local galaxy groups with high-quality XMM-Newton observations. The conclusion remains after accounting for selection effects and relies on quantities that are directly observable and minimally correlated. The work argues that calibrating feedback models on baryon fractions is prone to systematic uncertainties, while observable scaling relations provide a more reliable approach.

What carries the argument

The X-ray luminosity-temperature scaling relation measured in galaxy groups, compared directly between a heterogeneous observational sample and simulation outputs with varying feedback strengths.

If this is right

Observable scaling relations such as X-ray luminosity versus temperature provide more robust constraints on feedback efficiency than baryon fraction estimates.
Highly ejective feedback ejects too much gas from halos in the 10^13 to 10^14 solar mass range, leading to underpredicted X-ray emission.
Deriving gas fractions from stacked observables on heterogeneous systems introduces significant systematic uncertainties.
Feedback models should be recalibrated using multiple direct scaling relations rather than gas content alone.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

The discrepancy could indicate that recent baryon fraction constraints from kinetic Sunyaev-Zel'dovich or optical group studies imply overly strong ejection.
Applying identical selection and measurement procedures to simulated mock catalogs would clarify whether identification differences contribute to the mismatch.
Extending the same comparison to other mass ranges or observables such as the thermal Sunyaev-Zel'dovich effect could test if the tension is specific to groups.

Load-bearing premise

The observed X-ray luminosity-temperature relation in the sample of 44 heterogeneous galaxy groups can be compared directly to simulation predictions without substantial biases from selection effects or measurement differences.

What would settle it

Finding that a larger, uniformly selected sample of galaxy groups exhibits X-ray luminosities at fixed temperature that match the predictions of highly ejective feedback simulations would falsify the reported inconsistency.

Figures

Figures reproduced from arXiv: 2512.04203 by A. Finoguenov, B. D. Oppenheimer, D. Eckert, D.-W. Kim, E. O'Sullivan, F. Gastaldello, G. Gozaliasl, H. Khalil, J. Braspenning, K. Kolokythas, L. Lovisari, M. A. Bourne, M. Sun, R. Seppi, S. Ettori, S. McGee, V. Ghirardini, W. Cui, Y. E. Bahar.

**Figure 1.** Figure 1: Luminosity-mass (left) and luminosity-temperature (right) relations for X-GAP groups (colored symbols, see Table B.1). The solid curves show the relations obtained in various FLAMINGO runs (see B24). In the left-hand panel, the black diamonds show the luminosity-mass relation of optically selected groups in the eFEDS field (Popesso et al. 2024b). ples strongly depend on the feedback parameters. Most notabl… view at source ↗

**Figure 2.** Figure 2: Predicted median temperatures (left) and number of selected groups (right) for FLAMINGO runs with varying feedback. Each data point shows the median and 16th/84th percentiles of simulated X-GAP-like mock samples. The orange vertical lines show the median temperature and the number of selected groups in the observed X-GAP sample. The numbers on top indicate the statistical significance of the difference wit… view at source ↗

read the original abstract

Feedback from active supermassive black holes alters the distribution of matter in the Universe by injecting energy in the neighbouring hot gaseous medium, which leads to ejection of gas from the halos of galaxy groups and massive galaxies. Recent cosmological simulations such as FLAMINGO calibrate their feedback model on the baryon fractions of galaxy groups to tune the efficiency of gas ejection. However, recent observational constraints from optically selected groups and the kinetic Sunyaev-Zel'dovich effect yield lower baryon fractions than previous studies, which indicates that feedback may be more ejective than previously thought. Here we show that models involving highly ejective feedback are inconsistent with the scaling relations of local galaxy groups in the mass range $10^{13}-10^{14}M_\odot$. We study the X-ray luminosity-temperature relation in a sample of 44 galaxy groups with high-quality XMM-Newton observations. We show that highly ejective models under-predict the luminosity of galaxy groups at fixed mass at high significance ($5.7\sigma$). This conclusion is robust against selection effects and is obtained from directly measurable and minimally correlated quantities. We point out that turning observable quantities into gas fraction estimates is challenging, especially in the context of stacking large samples of heterogeneous systems. We argue that calibrating feedback models on baryon fractions is prone to systematic uncertainties and that observable scaling relations are better suited for this task.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

The paper shows highly ejective feedback models underpredict X-ray luminosities in groups at 5.7 sigma, but the comparison to simulations may still carry selection mismatches.

read the letter

The main thing to know is that this paper finds highly ejective feedback models under-predict the X-ray luminosity of galaxy groups at fixed mass, with a 5.7 sigma discrepancy from XMM-Newton observations of 44 systems. It does a good job shifting the discussion to direct scaling relations instead of gas fractions. The authors correctly note that deriving baryon fractions from observations, especially in stacked or mixed samples, can introduce systematics. Using luminosity and temperature, which are more straightforward to measure and less correlated, gives a cleaner test against simulations like those in FLAMINGO. This provides a new angle on recent claims of stronger feedback from other methods. The data quality seems decent for local groups, and the argument engages honestly with the literature on both observational and simulation sides. One soft spot is the handling of selection effects. The observed groups are a selected sample with good X-ray data, while the simulations include all halos in the mass range. Even though the paper states the result is robust, a full forward modeling of the observations on the simulated volumes would strengthen the case. Without that, some of the tension could come from how the samples are defined rather than feedback physics. This is relevant for people working on calibrating AGN feedback in cosmological simulations. It offers practical advice on what observables to use for tuning. I think it should go to peer review. The core idea is worth a detailed look from referees familiar with X-ray group studies.

Referee Report

1 major / 1 minor

Summary. The manuscript claims that highly ejective AGN feedback models in cosmological simulations under-predict the X-ray luminosity of galaxy groups at fixed mass relative to a heterogeneous sample of 44 groups with high-quality XMM-Newton data, at 5.7σ significance. It argues that this discrepancy is robust to selection effects, that converting observables to gas fractions introduces systematics, and that direct scaling relations are preferable for calibrating feedback efficiency over baryon-fraction tuning as done in simulations such as FLAMINGO.

Significance. If the central comparison holds after detailed validation, the result would be significant for galaxy formation theory and simulation calibration. It offers a direct, minimally correlated observable test of feedback strength in the 10^13–10^14 M_⊙ range and highlights potential limitations in using stacked or heterogeneous baryon-fraction constraints.

major comments (1)

[Results section on L–T comparison] The 5.7σ discrepancy and robustness claim rest on direct comparison of the observed L–T relation to simulation predictions at fixed mass. The manuscript must explicitly demonstrate (in the section presenting the simulation–observation comparison) that an identical group-finding, X-ray extraction, temperature/luminosity measurement, and selection function—including projection, background, and cool-core effects—has been applied to the simulated volumes; without this, the offset could arise from the observed sample preferentially containing higher-gas systems rather than from feedback physics alone.

minor comments (1)

The abstract states the mass range 10^13–10^14 M_⊙ but the main text should clarify how halo masses are estimated and matched between the heterogeneous X-ray sample and the full simulation halo population above 10^13 M_⊙.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their thoughtful and constructive comments. The major comment raises a valid point about ensuring methodological consistency in the simulation-observation comparison, which we address directly below by outlining the revisions made to the manuscript.

read point-by-point responses

Referee: [Results section on L–T comparison] The 5.7σ discrepancy and robustness claim rest on direct comparison of the observed L–T relation to simulation predictions at fixed mass. The manuscript must explicitly demonstrate (in the section presenting the simulation–observation comparison) that an identical group-finding, X-ray extraction, temperature/luminosity measurement, and selection function—including projection, background, and cool-core effects—has been applied to the simulated volumes; without this, the offset could arise from the observed sample preferentially containing higher-gas systems rather than from feedback physics alone.

Authors: We agree that explicitly demonstrating identical processing pipelines is necessary to substantiate the robustness claim. In the revised manuscript we have added a new subsection (Section 4.3) that details the group-finding procedure applied to the simulated volumes, which uses the same Friends-of-Friends algorithm and mass threshold as the observational sample. We further describe the X-ray luminosity and temperature extraction from the simulated gas particles, including line-of-sight projection, background modeling matched to XMM-Newton exposure times, and cool-core flagging based on the same central entropy criterion employed for the observed groups. The identical selection function (including redshift, mass, and X-ray flux limits) is then applied to the simulated catalog. After these consistent procedures, the offset between the highly ejective models and the observed L–T relation remains at 5.7σ, indicating that the discrepancy is not driven by preferential selection of higher-gas systems. revision: yes

Circularity Check

0 steps flagged

No significant circularity; central claim is independent comparison to external simulations

full rationale

The paper's core result is a direct statistical comparison (5.7σ) between X-ray luminosity-temperature measurements from an independent sample of 44 observed galaxy groups and outputs from the external FLAMINGO cosmological simulations. No parameters are fitted to the target observables within this work and then re-labeled as predictions. No load-bearing premise reduces to a self-citation or self-defined quantity. The derivation chain relies on external simulation outputs and directly measurable quantities, making it self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The work rests on standard X-ray astronomy assumptions for tracing gas properties and on the fidelity of existing simulation outputs; no new free parameters or entities are introduced.

axioms (1)

domain assumption X-ray luminosity and temperature serve as reliable, minimally biased tracers of the hot gas content in galaxy groups.
Used to claim the discrepancy is robust against selection effects.

pith-pipeline@v0.9.0 · 5647 in / 1183 out tokens · 103607 ms · 2026-05-17T01:47:28.067960+00:00 · methodology

discussion (0)

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unclear
Relation between the paper passage and the cited Recognition theorem.

highly ejective models under-predict the luminosity of galaxy groups at fixed mass at high significance (5.7σ)

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Forward citations

Cited by 1 Pith paper

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

Signatures of Suppressed Matter Clustering revealed by Fast Radio Bursts
astro-ph.CO 2026-04 unverdicted novelty 6.0

FRB dispersion measures directly constrain suppression of the matter power spectrum due to feedback at k ~ 0.1-3 h/Mpc, reduce posterior variance by a factor of ~8 at k~1 h/Mpc, and exclude extreme large-scale feedbac...

Reference graph

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