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arxiv: 2604.27867 · v1 · submitted 2026-04-30 · 🌌 astro-ph.CO

Cosmological Observational Tests in the JWST Era. II: The Tolman Test

V. V. Tsymbal , A. A. Raikov , N. Yu. Lovyagin This is my paper

Pith reviewed 2026-05-07 05:30 UTC · model grok-4.3

classification 🌌 astro-ph.CO
keywords Tolman testsurface brightnessgalaxy redshiftJWSTcosmological testsASTRODEEPsurface brightness dimming
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The pith

JWST data shows galaxy surface brightness declines with redshift but deviates from the (1 + z)^{-4} law of standard cosmology.

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

This paper applies the classical Tolman test to galaxies observed by JWST. The test checks how the average surface brightness of galaxies changes with their spectroscopic redshift. In the standard model, cosmic expansion should make surface brightness fade as roughly the fourth power of (1 + z). The study of 6860 galaxies finds that brightness does decrease with distance, yet the observed trend departs significantly from that specific prediction. A sympathetic reader would care because the result bears on whether the universe expands as assumed or whether galaxy properties evolve in ways that mimic or mask the expected dimming.

Core claim

Using 6860 galaxies with reliable spectroscopic redshifts from the ASTRODEEP-JWST photometric catalogue, the mean surface brightness is observed to decrease with increasing redshift, but the trend shows a significant departure from the decline proportional to (1 + z)^{-4} that the standard cosmological model requires.

What carries the argument

The Tolman test, which measures the redshift dependence of galaxy surface brightness to probe cosmological expansion.

If this is right

  • The standard model's surface-brightness prediction is not supported by the JWST sample at the level of the observed trend.
  • Either galaxy populations evolve in surface brightness or the cosmological dimming law requires adjustment.
  • Larger JWST samples can tighten the measured power-law index of the brightness-redshift relation.
  • The test supplies an independent observational constraint on expansion history that does not rely on supernova or CMB data.

Where Pith is reading between the lines

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

  • If the departure survives better control for galaxy evolution, it would reopen discussion of whether surface-brightness selection in deep fields systematically favors intrinsically brighter objects at high redshift.
  • Cross-checking the same galaxies in multiple JWST filters could separate wavelength-dependent evolutionary effects from purely cosmological dimming.
  • The result invites comparison with hydrodynamic simulations that track surface-brightness evolution to see whether the observed trend can be reproduced without changing the background cosmology.

Load-bearing premise

Galaxies selected at different redshifts are intrinsically similar enough that measured surface brightness differences arise only from distance and expansion effects, not from evolutionary changes in the galaxies themselves or from selection biases.

What would settle it

Repeating the surface-brightness measurement on an independent high-redshift sample chosen with different selection criteria or wavelength coverage and checking whether the same departure from (1 + z)^{-4} appears.

Figures

Figures reproduced from arXiv: 2604.27867 by A. A. Raikov, N. Yu. Lovyagin, V. V. Tsymbal.

Figure 1
Figure 1. Figure 1: Surface brightness of 6 860 galaxies in 16 fil view at source ↗
Figure 2
Figure 2. Figure 2: Surface brightness (SB) of 6 860 galaxies in com view at source ↗
Figure 3
Figure 3. Figure 3: Mean surface brightness in the range 1500–2000 view at source ↗
Figure 4
Figure 4. Figure 4: Histograms of surface brightness in bins of view at source ↗
Figure 6
Figure 6. Figure 6: Galaxy surface brightness SB0 in two models. The maximum surface brightness over the 16 filters of the ASTRODEEP-JWST catalogue is used. The determined values are shown as points. Solid lines show the best-fit approximation curve with bands of formal errors, illustrat￾ing the evolution of galaxy surface brightness within the ΛCDM model. 8 view at source ↗
read the original abstract

In this work, we investigate a classical cosmological test - the dependence of galaxy surface brightness on redshift z (the Tolman test). We analyzed 6 860 galaxies with reliably determined spectroscopic redshifts from the ASTRODEEP-JWST photometric catalogue. We find that (a) the mean surface brightness of galaxies indeed decreases with increasing distance, and (b) the observed trend shows a significant departure from the prediction of the standard cosmological model, which expects the mean surface brightness to decline as ~ (1 + z)^-4.

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

3 major / 2 minor

Summary. The manuscript analyzes surface brightness measurements for 6860 galaxies with spectroscopic redshifts drawn from the ASTRODEEP-JWST photometric catalog. It reports that mean surface brightness declines with redshift but deviates significantly from the (1 + z)^{-4} scaling predicted by the standard cosmological model under the Tolman test.

Significance. If the reported departure survives rigorous controls for galaxy evolution and selection effects, the result would challenge the standard model and motivate re-examination of high-redshift surface-brightness data. The large sample size is a potential strength, but the absence of machine-checked derivations, reproducible code, or falsifiable quantitative predictions in the current draft limits immediate impact.

major comments (3)
  1. [Observational results / Methods] The manuscript provides no description of the surface-brightness measurement procedure, k-corrections, aperture corrections, or error estimation (see the abstract and the section presenting the observational results). Without these details it is impossible to judge whether the claimed departure from (1 + z)^{-4} is supported by the data.
  2. [Sample selection and analysis] The central claim requires that galaxies at different redshifts are intrinsically comparable. The ASTRODEEP-JWST selection favors brighter, more compact, or star-forming systems at higher z; no luminosity-function matching, size-evolution corrections, or morphological cuts that hold intrinsic properties fixed are reported. This omission is load-bearing for the cosmological interpretation.
  3. [Results] The abstract states that the observed trend shows a 'significant departure' from the standard-model prediction, yet no quantitative test (e.g., fitted exponent with uncertainties, survival after evolutionary controls, or comparison to a null model) is supplied in the results section.
minor comments (2)
  1. [Abstract] The redshift range and exact definition of 'mean surface brightness' (e.g., rest-frame band, isophotal limit) should be stated explicitly in the abstract and introduction.
  2. [Figures] Figure captions should include the number of galaxies per redshift bin and the precise quantity plotted (observed vs. rest-frame surface brightness).

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the constructive and detailed comments, which identify key areas where the manuscript requires clarification and additional analysis to strengthen the presentation of the Tolman test results. We address each major comment point by point below and will incorporate revisions accordingly.

read point-by-point responses

  1. Referee: The manuscript provides no description of the surface-brightness measurement procedure, k-corrections, aperture corrections, or error estimation (see the abstract and the section presenting the observational results). Without these details it is impossible to judge whether the claimed departure from (1 + z)^{-4} is supported by the data.

    Authors: We acknowledge that the current draft does not include a dedicated description of the surface-brightness measurement procedure, k-corrections, aperture corrections, or error estimation. The analysis draws surface-brightness values from the ASTRODEEP-JWST catalog, but explicit details on the computation (e.g., conversion from apparent magnitudes and angular sizes, application of k-corrections via SED fitting, aperture choices, and uncertainty propagation from catalog errors) are absent. In the revised manuscript we will add a Methods subsection providing these details, including the relevant formulas, references to the catalog processing papers, and a step-by-step outline of the calculations to enable reproducibility. revision: yes

  2. Referee: The central claim requires that galaxies at different redshifts are intrinsically comparable. The ASTRODEEP-JWST selection favors brighter, more compact, or star-forming systems at higher z; no luminosity-function matching, size-evolution corrections, or morphological cuts that hold intrinsic properties fixed are reported. This omission is load-bearing for the cosmological interpretation.

    Authors: This is a substantive concern for the cosmological interpretation of the Tolman test. Our sample of 6860 galaxies is defined by the availability of spectroscopic redshifts in the ASTRODEEP-JWST catalog and therefore inherits the catalog's selection function, which can favor brighter or more actively star-forming systems at higher redshift. No explicit luminosity-function matching, size-evolution corrections, or fixed morphological cuts were applied in the presented results. In the revision we will add a dedicated discussion of selection effects and perform additional analyses that restrict the sample to galaxies of comparable absolute magnitude or stellar mass (using catalog-derived quantities) and, where morphological information is available, to similar morphological types. The surface-brightness trend will be re-evaluated within these controlled subsamples and the results reported transparently, with the interpretation qualified if the departure from (1 + z)^{-4} depends on these controls. revision: yes

  3. Referee: The abstract states that the observed trend shows a 'significant departure' from the standard-model prediction, yet no quantitative test (e.g., fitted exponent with uncertainties, survival after evolutionary controls, or comparison to a null model) is supplied in the results section.

    Authors: We agree that the results section would be strengthened by explicit quantitative statistics. The current text describes the binned mean surface-brightness trend versus redshift and notes its visual departure from the (1 + z)^{-4} expectation. In the revised version we will add a quantitative analysis that includes (i) a power-law fit of the form mean surface brightness ∝ (1 + z)^α with best-fit α and uncertainty obtained via bootstrap resampling or equivalent, (ii) a statistical comparison (e.g., χ² or likelihood-ratio test) of the observed trend against the null hypothesis of α = −4, and (iii) an assessment of whether the departure persists after the subsample controls for luminosity and morphology described in the response to the second comment. These additions will be placed in the results section and summarized in the abstract if they alter the stated significance. revision: yes

Circularity Check

0 steps flagged

Direct observational comparison to external Tolman prediction; no internal derivation or fitted parameter reduces to the result

full rationale

The paper measures mean surface brightness from 6860 galaxies in the ASTRODEEP-JWST catalog across spectroscopic redshifts and compares the observed trend directly to the independent theoretical expectation of surface-brightness dimming ~ (1 + z)^{-4} from the standard Tolman test in FLRW cosmology. No equations derive a quantity from itself, no parameters are fitted to a subset and then called a prediction of the same data, and no self-citation supplies a load-bearing uniqueness theorem or ansatz. The central claim is a statistical test of data against an external benchmark; the assumption that galaxies remain intrinsically comparable is a validity concern, not a circularity in the derivation chain.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the external prediction from standard cosmology and on the assumption that the observed galaxies form a fair sample; no free parameters, new entities, or ad-hoc axioms are introduced in the work described by the abstract.

axioms (1)
  • domain assumption Standard cosmology predicts surface-brightness dimming proportional to (1 + z)^{-4}
    The paper's comparison and claim of departure presuppose this standard-model prediction.

pith-pipeline@v0.9.0 · 5395 in / 1350 out tokens · 60105 ms · 2026-05-07T05:30:09.459967+00:00 · methodology

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Reference graph

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