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REVIEW 4 major objections 6 minor 27 references

Edge-on galaxies relative to edge-on view of the Local Supercluster

T0 review · 4 major / 6 minor · reviewed 2026-08-15 · deepseek-v4-flash

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Pith's one-line read Using 1,689 edge-on galaxies, this paper finds no significant spin alignment with the Local Supercluster plane except a 2-sigma perpendicular tendency in galaxies with stellar mass below about 10^8.7 solar masses.

desk verdict Useful null result on a classic claim, plus a 2-sigma faint-galaxy subtrend that probably won't survive a proper multiple-comparison test. read the letter →

arxiv 2505.07737 v1 pith:X7CWQX5R submitted 2025-05-12 astro-ph.GA

P. Dolgosheeva , D. Makarov , N. Libeskind This is my paper · ORCID
classification astro-ph.GA
keywords galaxyspinsedge-ongalaxiesLocalSuperclusterSupergalacticcoordinatestidaltorquetheoryKolmogorov-Smirnovtestlow-massalignment
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 re-examines whether galaxy spins are aligned with the plane of the Local Supercluster, following a method proposed by Navarro et al. (2004) that reduces the problem to measuring the position angles of edge-on disk galaxies in Supergalactic coordinates. Using a sample of 1,689 edge-on galaxies drawn from modern catalogs, it finds that the distribution of these angles is statistically indistinguishable from random for essentially every subsample defined by redshift, distance from the Supergalactic plane, color, and stellar mass. The sole exception is a subsample of faint galaxies with stellar mass below about $10^{8.7} M_\odot$, whose spin axes show a tendency to point perpendicular to the Local Supercluster plane at roughly 2-$\sigma$ significance. If the effect is real, it would contradict both the original 30-galaxy detection and the expectation from filament studies that low-mass galaxy spins align along large-scale structure. The broader message is that spin alignment with the Local Supercluster plane is not a robust, easily reproduced signal.

What carries the argument

The load-bearing object is the Supergalactic position angle (PA) of an edge-on disk galaxy: for such galaxies the inclination is fixed near 90 degrees and the orientation of the spin projected on the sky is directly read from the major-axis PA, with no need for a near/far side determination. The analysis converts PAs into Supergalactic coordinates, folds angles into the range $[0^\circ, 90^\circ)$, and applies a one-sample Kolmogorov-Smirnov test under the null hypothesis that PAs are uniformly distributed. The sample is assembled from three catalogs (EGIPS, EGIS, and HyperLeda), filtered by velocity relative to the Local Group centroid, morphological type, and visual inspection, then split into redshift layers and $\pm2$/$\pm5$ Mpc slices around the Supergalactic plane.

What would settle it

Generate a mock population of edge-on galaxies with randomly oriented spins, run them through the same Pan-STARRS/SDSS detection and visual-inspection pipeline, and compare the recovered Supergalactic PA distribution; if the pipeline itself produces a non-uniform PA distribution similar to the faint-galaxy signal, the reported perpendicular alignment is a selection artifact rather than a cosmic signal.

Watch

Extended reading notes

Core claim

The central claim is that the spins of nearby edge-on galaxies are not preferentially aligned with the Local Supercluster plane, contrary to the result of Navarro et al. (2004). The only departure from randomness appears in galaxies with stellar mass $M_* < 10^{8.7} M_\odot$, where the disk major axes tend to lie in the Supergalactic plane, so the spin axes point perpendicular to it; this subsample fails the Kolmogorov-Smirnov uniformity test at the 2.4-6.2% level (about 1.9-2.3 $\sigma$) in three of four considered spatial/redshift windows. The paper argues this is a weak but fairly robust detection, while cautioning that the samples are not fully independent and that the effect disappears in one of the four windows. It also proposes that the general absence of alignment may reflect complex time-varying tidal fields at filament intersections and sheet-like structures, which can randomize spin orientations.

Load-bearing premise

The entire analysis rests on the assumption that the measured Supergalactic position angles of the catalogs' edge-on galaxies would be uniformly distributed under the null, meaning that none of the survey geometry, neural-network detection, or visual inspection steps imprints a preferred orientation.

Editorial extensions

If this is right

  • The Navarro et al. (2004) perpendicular-alignment signal is not reproduced with roughly an order of magnitude more galaxies, so the earlier detection was not robust to sample size and selection.
  • Low-mass galaxies in the Local Supercluster may have a spin orientation opposite to the filament-aligned trend reported for low-mass galaxies in other studies, suggesting the local sheet environment, not filament membership, governs their angular momentum.
  • Future spin-alignment studies targeting the Local Supercluster should treat stellar mass as a primary variable and should test the $\pm5$ Mpc / $cz_{\rm LG}<1200$ km/s window where the faint-galaxy signal vanishes before claiming a universal alignment.
  • If the faint-galaxy perpendicular tendency is genuine, it implies that the densest nearby structure imprints a measurable, mass-dependent anisotropic angular momentum field even when the overall population appears isotropic.

Reading between the lines

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

  • A decisive check would be to measure the same Supergalactic PA distribution using an independent edge-on catalog built from another wide-field survey; if the faint-galaxy perpendicular signal reproduces there, the catalog-selection explanation becomes much less likely.
  • The mass threshold near $M_* \sim 10^{8.7} M_\odot$ is close to the scale where galaxy formation efficiency and angular momentum acquisition change character, so the authors' result, if confirmed, would connect the spin-alignment signal to the transition between different accretion regimes.
  • The paper's null result for the full sample is consistent with the idea that supercluster-scale alignment is washed out by the complex tidal field at knots and sheet-filament junctions; this could be tested in simulations by comparing spin orientation relative to the local shear tensor rather than to the global Supergalactic plane.
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Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

4 major / 6 minor

Summary. The paper re-examines the claim of Navarro et al. (2004) that edge-on galaxies in the Local Supercluster have spins preferentially aligned with the Supergalactic plane (i.e., disk axes perpendicular to the plane), using a modern sample of 1689 edge-on galaxies drawn from EGIPS, EGIS, and HyperLeda within czLG < 3600 km/s. The authors convert position angles to Supergalactic coordinates, split the sample by redshift layer, distance from the Supergalactic plane, stellar mass, and color, and test uniformity of the PA distribution with one-sample Kolmogorov-Smirnov tests. They find no significant alignment for the full sample or most subsamples, contradicting Navarro et al. (2004), but report that galaxies with stellar mass M* < 10^8.7 M_sun show a weak tendency to be perpendicular to the Local Supercluster plane, with KS p-values 0.024-0.062 in three of four configurations. The paper is transparent about the weakness of the signal and explicitly notes that a statistical fluctuation cannot be ruled out.

Significance. If the low-mass perpendicular-alignment signal is real, it is a tentative mass-dependent spin orientation that points opposite to filament-alignment trends found in recent surveys, and the non-confirmation of the Navarro et al. (2004) result is itself of interest for tidal-torque and galaxy-formation studies. The paper's strengths are its use of substantially larger, modern catalogs, the simple and appropriate application of KS tests, and the explicit caveats about the fragility of the claimed effect. The main limitation is that the headline finding rests on p-values near the 2-sigma level drawn from a large set of overlapping post-hoc subsamples, so the central claim is not yet convincing as stated.

major comments (4)
  1. [Section 3 / Table 2] The central positive claim rests on four KS p-values for the faint subsample (0.062, 0.279, 0.024, 0.041) obtained after many overlapping tests (2 redshift ranges x 2 plane layers x 5 subsample definitions) and after choosing the mass and color split points to divide the sample into roughly equal halves. Under the global null of uniform PAs, several p<0.05 values among correlated subsamples are expected, and the paper does not quantify the effective number of independent trials. A permutation or bootstrap procedure that preserves all cuts and evaluates the distribution of the minimum p-value across the full table is needed to support the claim that the faint-galaxy signal is not a chance fluctuation.
  2. [Section 4 / Abstract] The conclusion is internally inconsistent: Section 4 states that 'we do not find any statistically significant alignment of spins to the Local Supercluster plane either among the nearest galaxies ... or in any other subsample' and immediately adds 'except for a subsample of faint galaxies.' It also states the effect is observed 'at a significance level of 2.4-6.2%,' which ignores the p=0.279 for the czLG<1200, ±5 Mpc faint subsample. The paper should report unambiguously that only three of the four faint configurations show p<0.07, that only two are below p<0.05, and that one configuration is consistent with the null.
  3. [Section 2 / Section 3] The KS null hypothesis is that the Supergalactic position angles are uniformly distributed, but the catalog selection functions could violate this assumption. The text acknowledges that EGIPS undercounts large and low-surface-brightness galaxies and that the HyperLeda subsample required subjective visual inspection, while EGIPS and EGIS have different sky footprints. If incompleteness depends on galaxy orientation or position angle relative to the survey footprints, the PA distribution could be biased. The authors should provide a test or argument that selection effects are isotropic in Supergalactic PA, for example by comparing the PA distribution of a control sample of all galaxies (not just edge-on) or by repeating the analysis with orientation-independent weights.
  4. [Section 3 / Section 4] The mass threshold M* = 10^8.7 M_sun and color threshold (g-i)_0 = 0.86 are introduced solely to split the sample into approximately equal parts. The paper does not justify these thresholds a priori, and the claimed effect is not tested for sensitivity to the exact threshold. A more robust approach would be to treat stellar mass as a continuous variable (e.g., sliding-window or regression on mass) and to check whether the PA anisotropy varies smoothly with mass, or to present results for several explicitly justified thresholds.
minor comments (6)
  1. [Abstract / Section 4] The phrase 'at the 2-sigma level' is imprecise because KS p-values are not directly equivalent to Gaussian significance levels; reporting the p-values themselves is preferable.
  2. [Section 4] The statement that the effect is observed 'within the ±2 and ±5 Mpc layers' is not supported by the p=0.279 value in Table 2 for the czLG<1200, ±5 Mpc faint subsample; this should be corrected.
  3. [Section 2] Table 1 reports unique additions from each catalog, but the matching procedure (e.g., angular separation and velocity tolerance for cross-identification) is not described; a sentence on the matching rules would clarify the sample construction.
  4. [Section 4 / References] The comparison with Welker et al. (2020) and Kraljic et al. (2021) concerns alignment with filaments, whereas the present analysis measures the angle with respect to the Supergalactic plane; the connection between these geometries should be discussed explicitly to avoid overinterpreting the contradiction.
  5. [Various] Typographical and minor errors: 'Vigro' should be 'Virgo', 'Aito ff' should be 'Aitoff', and 'de Vaucouleur's' should be 'de Vaucouleurs'.
  6. [Section 4 / References] The reference to Arakelyan et al. (2024) is cited as 'upcoming,' but it is an arXiv preprint; please clarify its status in the final version.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: the paper reports empirical KS tests of galaxy position angles against a uniform null, with no fitted parameter renamed as a prediction and no load-bearing self-citation chain.

full rationale

The paper's derivation chain is an empirical statistical analysis. Supergalactic position angles are converted from catalog data, and the Kolmogorov-Smirnov test is applied under the explicit null hypothesis that PAs are uniformly distributed. The resulting p-values in Table 2 are computed from the data, not derived from the inputs by construction. The stellar-mass split at M* = 10^8.7 M_sun is a sample-division choice based on dividing the sample into approximately equal parts; it is not fitted to the position-angle distribution, so the faint-galaxy result is not a fitted parameter renamed as a prediction. The paper itself flags the relevant caveats: the subsamples are not fully independent, the result is at the 2-sigma level, and 'it cannot be ruled out that this is a consequence of some statistical fluctuation.' These are statistical-robustness concerns, not circularity. Self-citations to Makarov et al. (2014, 2022) and Libeskind et al. (2020) are to data catalogs and simulations, used as observational/simulation inputs rather than as unverified theorems that force the conclusion. The method of Navarro et al. (2004) is adopted from the literature, but the paper explicitly reaches a different conclusion from that work, so the method citation is not serving to import a predetermined result. No step in the paper reduces to its own inputs by definition, and no fitted parameter is presented as an independent prediction.

Assumptions & free parameters 4 free parameters · 5 assumptions · 0 invented entities

The central claim depends on choices about which galaxies belong to the Local Supercluster, the faith that edge-on PA traces spin, and the thresholds used to split the sample. The mass and color split points are the most consequential data-dependent inputs.

free parameters (4)
  • M_split = 10^8.7 M_sun
    Threshold for the bright/faint split, chosen to divide the sample into two approximately equal parts; the main positive claim concerns only the faint subsample below this threshold.
  • color_split = (g-i)0 = 0.86 mag
    Threshold for the blue/red split, chosen to create roughly equal subsamples; used in the subsample analysis.
  • distance_layer_widths = 2 and 5 Mpc
    Widths of the layers around the Supergalactic plane used to select Local Supercluster members; chosen by hand.
  • virgo_exclusion_radius = 6 degrees around M87
    Radius used to exclude Virgo cluster galaxies; chosen to remove a region where orientations are randomized.
assumptions (5)
  • domain assumption Edge-on galaxy major-axis position angle traces the projected spin orientation
    The method of Navarro et al. (2004) relies on this; for edge-on disks the spin lies in the plane of the sky and perpendicular to the major axis.
  • domain assumption The Supergalactic plane is the plane of the Local Supercluster
    The SG coordinate system is defined by the LS plane; used throughout as the reference for alignment.
  • domain assumption Selected galaxies belong to the Local Supercluster
    The velocity and distance-layer cuts (czLG<3600 km/s and +/-2 or +/-5 Mpc) are assumed to isolate LS members; other structures like the Leo Spur and Fornax are present in the maps (Section 3).
  • domain assumption Uniform PA distribution is the correct null hypothesis
    Used for the KS test; survey selection effects could bias PA and are not modeled.
  • domain assumption Photometric stellar masses and colors are reliable at the split values
    The mass and color splits rely on photometry from the 50 Mpc catalog; errors could scatter galaxies across the thresholds.

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Cite this review

Pith. "Pith review of Edge-on galaxies relative to edge-on view of the Local Supercluster." pith.science (2026). https://pith.science/paper/X7CWQX5R

@misc{pith2026250507737,
  author       = {Pith},
  title        = {Pith review of: Edge-on galaxies relative to edge-on view of the Local Supercluster},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/X7CWQX5R}},
  note         = {Machine review of arXiv:2505.07737}
}
abstract

Cosmological theories suggest that the angular momentum of galaxies should be closely linked to the structure of the cosmic web. The Local Supercluster is the closest and most studied structure where the orientation of galaxy spins can be studied. As noted by Navarro et al. (2004), the use of edge-on galaxies greatly simplifies this task by reducing it to an analysis of the distribution of position angles in the Supergalactic coordinates. We reexamine this correlation using modern catalogs that allow us to perform a more robust statistical analysis. We test the dependence on redshift, spatial position, luminosity, and color. We find that the spins of galaxies with stellar mass $M_*<10^{8.7}$ $M_\odot$ show a weak tendency to be aligned perpendicular to the plane of the Local Supercluster at the 2-sigma level. Other subsamples do not show statistically significant correlations.

Figures

Figures reproduced from arXiv: 2505.07737 by the authors.

Figure 1
Figure 1. All-sky maps of galaxy distribution in Supergalactic coordinates (Aito [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Supergalactic PA distribution of edge-on galaxies from [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Cumulative PA distributions of edge-on galaxies with respect to the Supergalactic plane. The panels show the distributions [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗

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Reference graph

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