The impact of galaxy bias on cross-correlation tomography

David Alonso; Ian McCarthy; Joop Schaye; Matteo Zennaro; Matthieu Schaller; Sara Maleubre

REVIEW 3 major objections 1 minor 1 cited by

The impact of galaxy bias on cross-correlation tomography

T0 review · 3 major / 1 minor · reviewed 2026-08-05 · deepseek-v4-flash

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Pith's one-line read The paper claims that tomographic cross-correlation measurements can reconstruct the cosmic mean, bias-weighted electron pressure and star-formation density to 1–3% accuracy without modelling the small-scale clustering of the galaxy samples

desk verdict The abstract describes a plausible bias-robust tomographic estimator with 1-3% accuracy in FLAMINGO, but the supplied full text is a different paper, so I can only assess the abstract and the main claim is a simulation self-consistency result. read the letter →

arxiv 2508.05319 v2 pith:EOJJVH3R submitted 2025-08-07 astro-ph.CO astro-ph.GA

Sara Maleubre , Matteo Zennaro , David Alonso , Ian McCarthy , Matthieu Schaller , Joop Schaye This is my paper · ORCID

classification astro-ph.COastro-ph.GA

keywords galaxybiascross-correlationtomographySunyaev-Zel'dovicheffectcosmicinfraredbackgroundFLAMINGOsimulationshalomodelelectronpressurestar-formationdensity

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

The paper sets out to show that cross-correlation tomography—pairing galaxies with maps of the Sunyaev-Zel'dovich effect or the cosmic infrared background—can recover the cosmic mean of two physical quantities without needing to model how the galaxies cluster on small scales. The target quantities are the halo-bias-weighted electron pressure $\langle bP_e\rangle$ and star-formation density $\langle b\rho_{\rm SFR}\rangle$. Using FLAMINGO hydrodynamic simulations, the paper reports that a robust estimator recovers these quantities to 1–3% accuracy over a wide redshift range and across different galaxy samples. If correct, this separates the astrophysical interpretation of these cross-correlations from galaxy-clustering uncertainties. The paper also argues that the recovered values can be interpreted with the halo model, provided the halo mass function, large-scale bias, and halo-mass dependence of the target quantities are modelled reliably.

What carries the argument

The central objects are two bias-weighted cosmic averages, $\langle bP_e\rangle$ and $\langle b\rho_{\rm SFR}\rangle$, reconstructed from tomographic cross-correlations. The estimator is designed so that the small-scale galaxy bias drops out of the measurement, leaving the signal controlled by well-understood large-scale bias; the halo model then provides the mapping from these averages to halo properties. The work this does is to decouple galaxy-clustering uncertainties from the astrophysical quantities of interest.

What would settle it

Run the same estimator on two FLAMINGO variants with deliberately different feedback efficiencies and check whether the recovered $\langle bP_e\rangle$ or $\langle b\rho_{\rm SFR}\rangle$ shifts by more than a few percent when the galaxy sample changes. Alternatively, apply the estimator to real SZ and CIB maps over overlapping sky and test whether reconstructions from widely different galaxy samples agree within the claimed 1–3% accuracy.

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Extended reading notes

Core claim

The central claim is that a robust tomographic estimator can be constructed whose result is independent of the small-scale galaxy bias. The estimator targets the bias-weighted electron pressure $\langle bP_e\rangle$, accessible through the thermal Sunyaev-Zel'dovich effect, and the bias-weighted star-formation density $\langle b\rho_{\rm SFR}\rangle$, accessible through the cosmic infrared background. On FLAMINGO simulations, the paper claims these can be reconstructed with an accuracy of 1–3% over a broad range of redshifts using different galaxy samples. It further claims that the reconstructed signals can be interpreted using the halo model, assuming a reliable model for the halo mass fun

Load-bearing premise

The 1–3% accuracy is measured against FLAMINGO simulations, so the result stands or falls on whether FLAMINGO's subgrid models for gas cooling, feedback, and star formation produce a faithful electron-pressure and star-formation ground truth; the paper's stated second condition is a reliable halo-model description of the mass function, large-scale bias, and halo-mass dependence of the target quantities.

Editorial extensions

If this is right

Tomographic reconstructions of $\langle bP_e\rangle$ and $\langle b\rho_{\rm SFR}\rangle$ can be compared across different galaxy samples without modelling each sample's small-scale clustering.
The error budget for these measurements shifts from galaxy bias to the halo-model ingredients: mass function, large-scale bias, and halo-mass dependence of the target quantities.
The same estimator should apply to other large-scale-structure tracers whose small-scale bias is uncertain, not only SZ and CIB maps.
Combined tSZ and CIB tomography could map the pressure and star-forming content of the universe as a function of redshift in a way that is robust to sample selection.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

The full text attached to this submission is a different manuscript, beginning with the title “F2F4-Additive Complementary Dual Codes”; the validation details behind the 1–3% accuracy claims are therefore not contained in this document, and the pith above rests on the abstract's assertions.
If the FLAMINGO subgrid treatment of cooling, feedback, and star formation is not faithful to real gas behaviour, the claimed accuracy could reflect internal consistency of the simulations rather than a property of the real universe; a test would be to repeat the reconstruction on simulations with deliberately different feedback implementations.
The bias-robustness idea should transfer to other tomographic cross-correlations, such as galaxy–weak-lensing or galaxy–21 cm studies, wherever small-scale galaxy bias is the dominant nuisance.
If the halo-model interpretation holds, these measurements could provide constraints on the baryon content of halos as a function of mass and redshift, since the reconstructed averages weigh the target signal by the halo bias.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

Short version: I can't review this paper, because the full text attached to the arXiv ID is not this paper—it's a coding theory manuscript about F2F4-additive codes. So what follows is an assessment of the abstract only.

The abstract announces a useful methodological result. For tomographic cross-correlations, it claims an estimator for the halo-bias-weighted electron pressure and star-formation density that does not require detailed knowledge of small-scale galaxy bias, validated in FLAMINGO at 1-3% over a wide redshift range. That is worth having if it holds: prior work in this area generally has to model or marginalize over galaxy clustering, so an estimator that is insensitive to those choices would make SZ/CIB tomography cleaner. The abstract also flags that the halo-model interpretation depends on having reliable models for the halo mass function, large-scale bias, and the mass dependence of the reconstructed quantities. That is the right caveat.

The soft spot is the interpretation of the accuracy number. The 1-3% is a recovery test against FLAMINGO's own maps, so it inherits any systematic in FLAMINGO's subgrid feedback, cooling, and star-formation physics. Using different galaxy samples inside FLAMINGO tests selection effects, but all samples share the same hydrodynamical model. So the headline accuracy is currently a simulation self-consistency result, not a validated prediction for real SZ/CIB observations. That is not a fatal flaw in a methods paper—simulation validation is the normal first step—but it should be stated as such. The abstract is honest about the halo-model condition, but it does not address subgrid fidelity.

Several authors are FLAMINGO members. That is context, not evidence of a flaw. The real problem is that I cannot check the estimator, the derivations, the error budget, or the sample selection because the body is the wrong paper.

Summary: the abstract is plausible and the result would be useful if the methods hold up. I would not cite it on the strength of the abstract. If the correct manuscript is uploaded, this deserves a serious referee; in its current form it cannot be reviewed.

Referee Report

3 major / 1 minor

Summary. The submitted manuscript under arXiv:2508.05319 consists of an abstract describing a cosmology paper on galaxy bias and tomographic reconstruction using FLAMINGO simulations, but the accompanying full text is an unrelated coding-theory paper titled 'F2F4-Additive Complementary Dual Codes' (arXiv:2508.05317v1). The abstract claims that a robust estimator independent of small-scale galaxy bias can reconstruct the bias-weighted electron pressure and star-formation density with 1-3% accuracy, and that the results can be interpreted with a halo model. None of these claims are supported by the supplied body text, which contains no cosmology content, no estimator derivation, no simulation analysis, and no discussion of galaxy bias, Sunyaev-Zel'dovich maps, cosmic infrared background, or halo modeling.

Significance. If the abstract's claims were substantiated, they would be significant for tomographic cross-correlation cosmology, as they would relax the need for detailed small-scale galaxy bias modeling. The claimed 1-3% accuracy against FLAMINGO simulations would provide a quantitative benchmark. However, the supplied manuscript does not contain the methods, equations, simulation results, or error analysis that would support these claims. The actual full text is a self-contained paper on additive complementary dual codes over F2F4, which is unrelated to the abstract. Consequently, the scientific contribution described in the abstract is entirely unevaluable from the submitted materials.

major comments (3)

[Full text] The full text is a different paper: 'F2F4-Additive Complementary Dual Codes' (arXiv:2508.05317v1, cs.IT), not the astro-ph.CO paper described in the abstract. No section, equation, or table addresses galaxy bias, tomography, electron pressure, star formation density, FLAMINGO simulations, or halo model interpretation. The central claim of the abstract is therefore completely unsupported. This is not a minor issue of formatting but a fundamental mismatch between the claimed contribution and the submitted content.
[Abstract] The abstract's key assertion — that a robust estimator independent of small-scale galaxy bias can reconstruct <bP_e> and <b rho_SFR> to 1-3% accuracy using different galaxy samples — has no accompanying derivation, simulation details, or error budget anywhere in the manuscript. The reader cannot verify the estimator's construction, the treatment of shot noise, the bias cancellation mechanism, or the definition of 'accuracy' against FLAMINGO. This is a load-bearing unsupported claim.
[Entire manuscript] Because the body text is a coding theory paper, the cosmology abstract functions as an unsubstantiated assertion. The halo-model interpretation mentioned in the abstract ('assuming a sufficiently reliable model...') is also not developed. There is no basis to assess whether the 1-3% accuracy generalizes from simulations to real data, nor whether the claimed bias-independence holds beyond the specific simulated galaxy samples.

minor comments (1)

[Full text] The coding theory paper contains numerous typesetting/OCR artifacts (e.g., garbled symbols in Definitions 2.1, 3.1, and many equations), which further impede evaluation. However, these are secondary to the fundamental content mismatch.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity in the supplied text: the full manuscript is an unrelated coding-theory paper, so the abstract's cosmology claims have no derivation to check; the coding-theory proofs are self-contained.

full rationale

The supplied full text (arXiv:2508.05317v1, cs.IT, on F2F4-additive complementary dual codes) does not contain the FLAMINGO tomography analysis announced in the abstract (arXiv:2508.05319); no estimator, simulation pipeline, or 1-3% recovery test appears. Consequently, there is no derivation chain in this manuscript to compare against the abstract's predictions, and no fitted-versus-predicted reduction can be exhibited. In the mathematics that is present, the central results (Lemma 3.4, Corollary 3.1, Theorems 4.1-4.3, 5.1-5.2, 6.1-6.3) are proved directly from the stated definitions of the inner product, the W map, and the ACD property, with standard external facts (e.g., the generator-matrix form of F4-additive codes, [8]) as the only invoked background. Citations to the authors' prior work ([1], [4]) are definitional or contextual, not load-bearing for any claimed derivation. Therefore, no circular step is identifiable; the abstract's cosmology claims are unsupported by the supplied body, but that is a manuscript-integrity/completeness issue, not a circularity.

Assumptions & free parameters 0 free parameters · 2 assumptions · 0 invented entities

Abstract-only review. The only identifiable assumptions are the fidelity of the FLAMINGO simulations as ground truth and the availability of accurate halo-model ingredients; no free parameters or invented entities are visible at the abstract level.

assumptions (2)

domain assumption FLAMINGO hydrodynamic simulations faithfully represent the real universe's electron pressure and star-formation distributions
The 1-3% reconstruction accuracy is quoted relative to simulated truth; transfer to real data requires the simulation's baryonic and subgrid physics to be sufficiently accurate. Invoked implicitly throughout the abstract.
domain assumption A sufficiently reliable halo model exists for the halo mass function, large-scale halo bias, and the mass dependence of the reconstructed quantities
Explicitly stated in the abstract: 'assuming a sufficiently reliable model can be constructed for the halo mass function, large-scale halo bias, and for the dependence of the physical quantities being reconstructed on halo mass.'

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Cite this review

Pith. "Pith review of The impact of galaxy bias on cross-correlation tomography." pith.science (2026). https://pith.science/paper/EOJJVH3R

@misc{pith2026250805319,
  author       = {Pith},
  title        = {Pith review of: The impact of galaxy bias on cross-correlation tomography},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/EOJJVH3R}},
  note         = {Machine review of arXiv:2508.05319}
}

abstract

The cross-correlation of galaxies at different redshifts with other tracers of the large-scale structure can be used to reconstruct the cosmic mean of key physical quantities, and their evolution over billions of years, at high precision. However, a correct interpretation of these measurements must ensure that they are independent of the clustering properties of the galaxy sample used. In this paper we explore different prescriptions to extract tomographic reconstruction measurements and use the FLAMINGO hydrodynamic simulations to show that a robust estimator, independent of the small-scale galaxy bias, can be constructed. We focus on the tomographic reconstruction of the halo bias-weighted electron pressure $\langle bP_e\rangle$ and star-formation density $\langle b\rho_{\rm SFR}\rangle$, which can be reconstructed from tomographic analysis of Sunyaev-Zel'dovich and cosmic infrared background maps, respectively. We show that these quantities can be reconstructed with an accuracy of 1-3\% over a wide range of redshifts, using different galaxy samples. We also show that these measurements can be accurately interpreted using the halo model, assuming a sufficiently reliable model can be constructed for the halo mass function, large-scale halo bias, and for the dependence of the physical quantities being reconstructed on halo mass.

Discussion (0). Continue with ORCID to comment.

Forward citations

Cited by 1 Pith paper

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

Low-redshift constraints on structure growth from CMB lensing tomography
astro-ph.CO 2025-10 conditional novelty 5.0 of 10

Low-redshift galaxy clustering and CMB lensing tomography with hybrid effective field theory gives S8=0.79±0.06, consistent with Planck, while data alone prefer Ωm=0.245±0.024.

Reference graph

Works this paper leans on

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Pith tools

Reviewed August 5, 2026 · model on record in the stance chip above.

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