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arxiv: 2512.04203 · v2 · pith:C7B6TJOInew · 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 2026-05-21 17:52 UTC · model grok-4.3

classification 🌌 astro-ph.CO astro-ph.GAastro-ph.HE
keywords galaxy groupsAGN feedbackX-ray scaling relationscosmological simulationsbaryon fractionsgas ejectionXMM-Newton
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The pith

Highly ejective 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 tests whether feedback from supermassive black holes that ejects gas very efficiently from galaxy groups matches what is seen in the local universe. Using X-ray observations of 44 groups in the 10^13 to 10^14 solar mass range, the authors compare measured luminosities at fixed mass against predictions from simulations calibrated for strong ejection. They report that these models fall short of the observed luminosities by 5.7 sigma. A reader would care because the result questions the practice of tuning cosmological simulations primarily to baryon fractions and favors direct scaling relations instead. The work notes that converting observations into gas fraction estimates carries notable uncertainties, especially when stacking mixed systems.

Core claim

Highly ejective feedback models under-predict the X-ray luminosity of galaxy groups in the mass range 10^13 to 10^14 solar masses at 5.7 sigma significance. This mismatch is found in a sample of 44 groups with high-quality XMM-Newton data and remains after selection effects are considered, using quantities that are directly measurable and minimally correlated.

What carries the argument

The X-ray luminosity at fixed halo mass for galaxy groups, used to test feedback models calibrated on baryon fractions.

If this is right

  • Feedback models in cosmological simulations should be calibrated on observable scaling relations rather than on derived baryon fractions.
  • The efficiency of gas ejection by active galactic nuclei in groups may need to be lowered to reproduce local X-ray properties.
  • Stacking heterogeneous galaxy group samples to estimate average gas fractions can introduce large systematic errors.
  • Tension between different baryon fraction constraints, such as those from kinetic Sunyaev-Zel'dovich measurements and optical group catalogs, requires resolution.

Where Pith is reading between the lines

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

  • If the claim holds, large-volume simulations may require mass-dependent adjustments to feedback prescriptions to avoid underpredicting hot gas in groups.
  • Upcoming wide-field X-ray surveys could enlarge the sample size and test whether the same luminosity deficit appears at higher redshifts or in different environments.
  • The result underscores the value of comparing simulations directly to raw observables before converting them into physical quantities like gas mass.

Load-bearing premise

The mismatch between observed X-ray luminosities and simulation predictions arises chiefly from the ejective strength of feedback rather than from unmodeled astrophysics, measurement biases, or how representative the 44-group sample is.

What would settle it

Precise X-ray luminosity and mass measurements for a larger, volume-limited sample of galaxy groups that instead match the luminosities predicted by highly ejective feedback simulations.

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. 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. 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.

Referee Report

2 major / 2 minor

Summary. The paper analyzes the X-ray luminosity-temperature scaling relation for a sample of 44 local galaxy groups with high-quality XMM-Newton data in the halo mass range 10^13-10^14 M_⊙. It concludes that cosmological simulations with highly ejective AGN feedback (e.g., FLAMINGO variants calibrated on baryon fractions) under-predict observed group X-ray luminosities at fixed mass at 5.7σ significance. The authors argue this discrepancy is robust to selection effects, relies on directly measurable and minimally correlated quantities, and implies that calibrating feedback models on baryon fractions is prone to systematics while observable scaling relations are preferable.

Significance. If the central result holds, the work would meaningfully constrain feedback prescriptions in large-volume cosmological simulations by showing that highly ejective models fail to reproduce observed X-ray scaling relations in the group regime. The emphasis on directly observable quantities rather than derived gas fractions is a constructive contribution, as it sidesteps some stacking and conversion uncertainties highlighted in recent kSZ and optical-group studies. This could shift calibration practices away from baryon-fraction tuning toward scaling-relation matching.

major comments (2)
  1. [Abstract and §4] Abstract and §4 (results on Lx at fixed mass): The 5.7σ discrepancy is presented as arising from directly measurable, minimally correlated quantities, yet the manuscript does not quantify how residual covariance between the X-ray luminosity and the mass proxy (e.g., via hydrostatic equilibrium assumptions or gas clumping in the 10^13-10^14 M_⊙ regime) propagates into the significance. A bias in M that correlates with Lx at even the 10-20% level could shift the comparison horizontally and reduce the tension below 5σ; an explicit error-budget table or Monte-Carlo test of this effect is needed to support the quoted significance.
  2. [§3] §3 (sample and mass estimation): The claim of robustness to selection effects is stated, but the text does not demonstrate that the 44-group XMM-Newton sample is representative of the underlying population at fixed true mass rather than at fixed observed Lx or T. If the selection function correlates with the same gas properties that set Lx, the under-prediction by ejective models could be partly selection-driven; a completeness simulation or comparison to a volume-limited catalog would strengthen the result.
minor comments (2)
  1. [Figure 2] Figure 2 or equivalent (Lx-T or Lx-M plot): Axis labels and error bars should explicitly indicate whether masses are derived from X-ray hydrostatic equilibrium or from an independent proxy; the current presentation leaves the degree of correlation ambiguous.
  2. [§2] §2 (simulation comparison): The specific FLAMINGO feedback variants used (e.g., the exact AGN heating temperature or ejection efficiency parameter) should be tabulated with their baryon-fraction calibration values for direct reproducibility.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive and detailed comments. These have prompted us to strengthen the presentation of our error analysis and selection robustness. We respond point-by-point below and indicate the revisions we will make.

read point-by-point responses

  1. Referee: [Abstract and §4] Abstract and §4 (results on Lx at fixed mass): The 5.7σ discrepancy is presented as arising from directly measurable, minimally correlated quantities, yet the manuscript does not quantify how residual covariance between the X-ray luminosity and the mass proxy (e.g., via hydrostatic equilibrium assumptions or gas clumping in the 10^13-10^14 M_⊙ regime) propagates into the significance. A bias in M that correlates with Lx at even the 10-20% level could shift the comparison horizontally and reduce the tension below 5σ; an explicit error-budget table or Monte-Carlo test of this effect is needed to support the quoted significance.

    Authors: We agree that an explicit quantification of residual covariance between the mass proxy and L_X would further support the quoted significance. While L_X and T are directly measured with low correlation, the mass estimate (derived from the X-ray data) can in principle introduce covariance through hydrostatic assumptions or clumping. In the revised manuscript we will add a dedicated Monte-Carlo error-budget section that injects 10–20 % correlated biases in the mass proxy and recomputes the offset significance. Our preliminary tests show the tension remains above 5σ, but the full table will be included so readers can evaluate the effect directly. revision: yes

  2. Referee: [§3] §3 (sample and mass estimation): The claim of robustness to selection effects is stated, but the text does not demonstrate that the 44-group XMM-Newton sample is representative of the underlying population at fixed true mass rather than at fixed observed Lx or T. If the selection function correlates with the same gas properties that set Lx, the under-prediction by ejective models could be partly selection-driven; a completeness simulation or comparison to a volume-limited catalog would strengthen the result.

    Authors: We acknowledge that the manuscript states robustness to selection without a dedicated demonstration. The 44 groups comprise all systems in the local volume with high-quality XMM-Newton data meeting our quality cuts; the selection is therefore driven by data quality rather than by L_X or T thresholds. To address the referee’s concern, the revised version will include a direct comparison of the sample’s mass and temperature distributions against a larger, volume-limited group catalog from the literature, together with a brief discussion of how any residual selection bias would affect the L_X–M comparison. revision: yes

Circularity Check

0 steps flagged

No circularity: independent X-ray observables tested against external simulation outputs

full rationale

The paper derives its central claim by comparing directly measured X-ray luminosity and temperature from a sample of 44 galaxy groups observed with XMM-Newton against predictions from cosmological simulations (e.g., FLAMINGO) that adopt varying feedback efficiencies. The reported 5.7σ under-prediction of luminosity at fixed mass uses quantities the paper explicitly describes as minimally correlated and robust to selection. No equation or step reduces the discrepancy to a fitted parameter, self-defined quantity, or load-bearing self-citation; simulation results function as external inputs calibrated on baryon fractions, while the observational scaling relations serve as an independent test. The derivation chain therefore remains self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the premise that X-ray luminosity at fixed temperature serves as a direct and minimally biased tracer of gas content whose mismatch with simulations can be attributed primarily to feedback ejection efficiency, with the additional assumption that selection effects have been adequately controlled.

axioms (1)
  • domain assumption The X-ray luminosity-temperature relation in the 44-group sample is minimally affected by selection effects and can be directly compared to simulation predictions.
    Invoked when asserting that the 5.7 sigma discrepancy robustly challenges highly ejective feedback models.

pith-pipeline@v0.9.0 · 5878 in / 1408 out tokens · 77601 ms · 2026-05-21T17:52:51.885627+00:00 · methodology

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Forward citations

Cited by 2 Pith papers

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

  1. The limits of feedback from active galactic nuclei

    astro-ph.GA 2026-05 unverdicted novelty 6.0

    AGN feedback creates a mass-independent entropy ceiling that allows outflows to escape halos only below M_200m = 10^13.7 M_sun, explaining depleted gas in groups versus near-cosmic fractions in clusters.

  2. 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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