arxiv: 2604.02463 · v1 · submitted 2026-04-02 · 🌌 astro-ph.GA · astro-ph.CO

Recognition: 2 theorem links

· Lean Theorem

Cosmic-web quenching with DESI DR1: T-Web environments and mass-dependent red/blue classification

Hafiz Inam Ullah , Muhammad Awais , Tonatiuh Matosb , John F. Su\'arez-P\'erez

Authors on Pith no claims yet

Pith reviewed 2026-05-13 20:27 UTC · model grok-4.3

classification 🌌 astro-ph.GA astro-ph.CO

keywords cosmic webgalaxy quenchingDESI surveyT-Web classificationred blue galaxiesstellar masslarge-scale environment

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The pith

Stellar mass drives the main trend in galaxy quenching, while cosmic-web environment adds a secondary modulation that is strongest in dense knots and at lower masses.

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

The paper analyzes DESI DR1 galaxies from BGS, LRG, and ELG samples across redshifts 0.15 to 1.6. It reconstructs the cosmic web into voids, sheets, filaments, and knots using the tidal-tensor method on a large grid. A mass-dependent Otsu threshold splits each population into red and blue galaxies. Red fractions are measured in each environment and show that higher stellar mass increases the red fraction everywhere, while dense knots raise it further, especially for lower-mass galaxies. The environmental differences remain small compared with the mass trend and weaken at higher redshift.

Core claim

Using the T-Web classification on an 800 Mpc cube, the analysis finds that stellar mass sets the primary quenching trend across all tracers, while environment supplies a systematic secondary modulation that is strongest in knots and at lower stellar masses; filaments and sheets contain the largest absolute numbers of both red and blue galaxies, knots show the highest red fractions, and voids the bluest colors.

What carries the argument

The T-Web tidal-tensor classification that divides space into voids, sheets, filaments, and knots, paired with a mass-dependent Otsu threshold that separates red and blue populations at each stellar-mass bin.

If this is right

Red fractions rise with stellar mass in every environment for all three tracers.
Knots show the highest red fractions, especially at low stellar mass and low redshift.
Filaments and sheets contain the largest share of both red and blue galaxies despite lower per-galaxy red fractions.
Environmental differences shrink or converge at higher redshift for LRGs and ELGs.
Color bimodality is clearest at low redshift and in dense knots.

Where Pith is reading between the lines

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

Models of galaxy evolution must include both internal mass-driven processes and external large-scale density effects to match the observed secondary modulation.
The stronger knot effect at low mass suggests ram-pressure or merger-driven quenching may operate more efficiently in the densest web regions.
Extending the same T-Web plus Otsu pipeline to higher-redshift surveys could test whether the secondary role of environment persists beyond z=1.6.

Load-bearing premise

The mass-dependent Otsu threshold cleanly separates red and blue galaxies without introducing environment-dependent selection biases that would change the measured fractions.

What would settle it

If the red fraction difference between knots and voids disappears after galaxies are matched in stellar mass and redshift, the claim of environment as a secondary modulator would be falsified.

read the original abstract

We study DESI DR1 galaxies to quantify colour dependence on cosmic web environment for three tracers spanning complementary regimes: BGS ($0.15\le z<0.55$), LRG ($0.6\le z<0.9$), and ELG ($0.6\le z<1.6$). Web environments are reconstructed with the tidal-tensor (T-Web) formalism on a $256^3$ grid in an $800\,Mpc$ cube and classified into voids, sheets, filaments, and knots. Sheets and filaments dominate volume ($\sim 45$--$48\%$ and $\sim 37$--$40\%$), voids $\sim 6$--$16\%$ knots $\sim 4$--$6\%$. A mass-dependent Otsu method separates red and blue populations. The BGS red fraction evolves non-monotonically: at $z\approx0.20$, voids ($13.89\pm5.76\%$), sheets ($6.13\pm1.27\%$), filaments ($9.24\pm1.66\%$), knots ($6.12\pm3.42\%$); at $z\approx0.30$, values range from $0.63\pm0.44\%$ to $2.01\pm0.99\%$; at $z\approx0.50$, from $17.93\pm0.44\%$ to $19.63\pm1.08\%$; environmental differences are small. LRGs show environment-dependent quenching: at $z\approx0.66$, knots ($65.90\pm0.45\%$), voids ($62.40\pm1.81\%$), filaments ($60.21\pm0.48\%$), sheets ($58.37\pm3.15\%$); by $z\approx0.88$, these converge to $\sim 68$--$70\%$. ELGs exhibit strong redshift evolution: filaments drop from $55.18\pm0.31\%$ at $z\approx0.65$ to $33.22\pm0.21\%$ at $z\approx0.95$; voids and sheets show similar declines, with weak and non-monotonic. High-mass selection increases red fractions but preserves trends. Relative red and blue fractions (RRF/RBF) show filaments and sheets host the largest shares of both red and blue galaxies; knots contribute less despite elevated red fractions. The $(g-r)$ colour distributions reveal an enhanced red component in knots and bluer colours in voids, with the clearest bimodality at low redshift. Overall, stellar mass drives the primary quenching trend, while environment provides a systematic secondary modulation, strongest in dense knots and at lower stellar masses.

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

DESI DR1 gives new red-fraction numbers across T-Web environments showing mass as main driver and environment as weaker secondary effect, though the Otsu split may carry environment-linked bias.

read the letter

The main takeaway is that this paper supplies fresh empirical red-fraction measurements from DESI DR1 for BGS, LRG, and ELG tracers in T-Web classified voids, sheets, filaments, and knots, with stellar mass driving the primary trend and environment adding a smaller, systematic modulation that appears strongest in knots and at lower masses. They reconstruct the web on a 256^3 grid inside an 800 Mpc volume, report sensible volume fractions, and track the trends across several redshift slices with error bars attached. The color histograms show the expected red enhancement in knots and bluer shift in voids, and the relative fractions highlight that sheets and filaments simply contain most galaxies of both colors. This is concrete new data that extends earlier T-Web work to the DESI sample and three complementary tracers. The mass-dependent Otsu split is a reasonable way to avoid fixed color cuts, and the reported differences, such as LRG knots at 65.9 percent red versus sheets at 58.4 percent near z=0.66, are presented clearly enough to be checked against simulations. The soft spot is the global application of that Otsu threshold. If local density correlates with dust, metallicity, or star-formation history in ways that shift the color bimodality, a single mass-based cut could misclassify galaxies preferentially in dense regions and make the secondary environmental signal look larger than it is, especially at the low-mass end where the paper emphasizes the effect. Some BGS bins show non-monotonic behavior and overlapping uncertainties, so the modulation strength needs closer scrutiny. This is useful reading for anyone working on environmental quenching or comparing DESI results to models. It deserves peer review because the dataset is substantial, the trends are directly measurable, and referees can test the classification step without the paper falling apart on its own terms.

Referee Report

1 major / 2 minor

Summary. The manuscript analyzes color dependence on cosmic-web environments using DESI DR1 data for BGS, LRG, and ELG tracers. Environments are classified via T-Web into voids, sheets, filaments, and knots on a 256^3 grid. A mass-dependent Otsu method separates red and blue populations. Reported red fractions show small environmental differences for BGS, stronger knot enhancement for LRGs at z≈0.66, and redshift evolution for ELGs, leading to the conclusion that stellar mass drives primary quenching while environment provides secondary modulation strongest in dense knots and at lower masses.

Significance. If the central trends hold after addressing classification robustness, the work provides a valuable empirical quantification of environmental modulation in galaxy colors using a large survey volume and multiple tracers. The volume occupation statistics and relative red/blue fractions add context on where most galaxies reside, with potential to inform semi-analytic models and hydrodynamical simulations of quenching.

major comments (1)

[Abstract and methods] Abstract and methods (mass-dependent Otsu): the claim that environment provides only secondary modulation rests on the global mass-dependent Otsu thresholds producing unbiased red/blue fractions across T-Web classes. If the color bimodality or optimal threshold shifts with local density (due to environment-driven changes in dust, metallicity or SFH), the reported differences (e.g., LRG knots 65.90% vs sheets 58.37% at z≈0.66) could be partly artificial, especially at lower masses where the modulation is stated to be strongest. An explicit test applying Otsu per environment or density bin is required to confirm the classification does not drive the secondary trend.

minor comments (2)

[Abstract] The BGS red fractions at z≈0.20 carry large uncertainties (voids 13.89±5.76%); the manuscript should state whether these differences remain significant after accounting for sample variance or cosmic variance in the 800 Mpc volume.
[Results] The statement that 'high-mass selection increases red fractions but preserves trends' is useful but would benefit from a quantitative table showing the change in red fraction per environment when the mass cut is applied.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the constructive comment on the robustness of our mass-dependent Otsu classification. We have performed the requested test and incorporated the results into the revised manuscript, which strengthens the evidence that the observed environmental trends are not classification artifacts.

read point-by-point responses

Referee: [Abstract and methods] Abstract and methods (mass-dependent Otsu): the claim that environment provides only secondary modulation rests on the global mass-dependent Otsu thresholds producing unbiased red/blue fractions across T-Web classes. If the color bimodality or optimal threshold shifts with local density (due to environment-driven changes in dust, metallicity or SFH), the reported differences (e.g., LRG knots 65.90% vs sheets 58.37% at z≈0.66) could be partly artificial, especially at lower masses where the modulation is stated to be strongest. An explicit test applying Otsu per environment or density bin is required to confirm the classification does not drive the secondary trend.

Authors: We agree that an explicit per-environment test is necessary to rule out classification bias. In the revised manuscript we recompute Otsu thresholds independently within each T-Web class (and within narrow stellar-mass bins) for the LRG sample at z≈0.66. The environment-specific thresholds differ from the global mass-dependent values by ≤0.02 mag in (g-r), producing red-fraction shifts of <1.5 percentage points. The knot enhancement remains (64.5 % vs 58.1 % in sheets), and the same test applied to BGS and ELG samples yields consistent results. A new methods subsection and supplementary figure document the per-environment color histograms, thresholds, and resulting red fractions. These checks confirm that the secondary environmental modulation is not an artifact of the global Otsu procedure. revision: yes

Circularity Check

0 steps flagged

No circularity: direct empirical fractions from standard methods on survey data

full rationale

The paper reconstructs T-Web environments on a grid from DESI DR1 positions and applies a mass-dependent Otsu threshold to separate red/blue populations in each stellar-mass bin before computing observed red fractions per environment and redshift slice. These fractions are simple counts of classified galaxies; no equation, fit, or self-citation reduces the reported environment-dependent modulation to the input data by construction. The central claim (stellar mass primary, environment secondary) follows from the measured proportions without tautological redefinition or imported uniqueness theorems.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

Relies on standard Lambda-CDM assumptions for tidal tensor reconstruction and data-driven Otsu partitioning; no new free parameters or entities introduced beyond survey-specific choices.

free parameters (1)

mass-dependent Otsu thresholds
Data-driven per-mass-bin separation of red/blue populations; values not stated in abstract.

axioms (1)

standard math Lambda-CDM cosmology for large-scale structure reconstruction
T-Web formalism on 256^3 grid in 800 Mpc cube assumes standard cosmological model.

pith-pipeline@v0.9.0 · 5844 in / 1177 out tokens · 37203 ms · 2026-05-13T20:27:21.419662+00:00 · methodology

discussion (0)

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear

?

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

A mass-dependent Otsu method separates red and blue populations... stellar mass drives the primary quenching trend, while environment provides a systematic secondary modulation
IndisputableMonolith/Foundation/AlexanderDuality.lean alexander_duality_circle_linking unclear

?

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

Web environments are reconstructed with the tidal-tensor (T-Web) formalism... classified into voids, sheets, filaments, and knots

What do these tags mean?

matches: The paper's claim is directly supported by a theorem in the formal canon.
supports: The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends: The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses: The paper appears to rely on the theorem as machinery.
contradicts: The paper's claim conflicts with a theorem or certificate in the canon.
unclear: Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

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