Properties of barred galaxies in the MaNGA galaxy survey

A. Arag\'on-Salamanca; A. Fraser-McKelvie; K. Masters; M. Merrifield; the MaNGA Survey Team

REVIEW 3 major objections 6 minor 10 references

Properties of barred galaxies in the MaNGA galaxy survey

T0 review · 3 major / 6 minor · reviewed 2026-08-14 · deepseek-v4-flash

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Pith's one-line read Bar length, scaled to galaxy size, tracks how far a galaxy has fallen from the star-forming sequence.

desk verdict Large MaNGA barred-galaxy census with a likely artifact-driven headline: the L_bar/R_e vs. passivity correlation probably just reflects the compactness of quiescent galaxies at fixed mass. read the letter →

arxiv 1908.08350 v1 pith:IFOI3TYJ submitted 2019-08-22 astro-ph.GA

A. Fraser-McKelvie , M. Merrifield , A. Aragón-Salamanca , K. Masters , the MaNGA Survey Team This is my paper · ORCID

classification astro-ph.GA

keywords barredgalaxiesgalaxyevolutionstarformationmainsequencequenchingH-alphaemissionbarlengthintegralfieldspectroscopystellarmass

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

This paper presents a census of 684 barred galaxies drawn from a large survey that maps each galaxy's gas and stars across its full face. It finds that bar length, once divided by the galaxy's effective radius, is not tied to stellar mass but to how far the galaxy sits below the star formation main sequence: more passive galaxies host bars that stretch a larger fraction of the galaxy. It also finds that ionised hydrogen emission runs along the bars only in low-mass, star-forming galaxies, while higher-mass galaxies more often show this emission in rings or at the bar centre and ends. The authors argue that these patterns reflect different formation and evolution processes for bars in low- and high-mass galaxies, and that bar growth may quench star formation.

What carries the argument

The analysis relies on three measurements. Bar length is derived from Fourier-transform decomposition of collapsed optical images, then divided by the r-band Petrosian half-light radius to obtain the scaled length $L_{\rm bar}/R_e$. The star formation main sequence provides the reference frame: distance below the main sequence, computed from infrared-based star formation rates and catalog stellar masses, serves as the measure of a galaxy's passivity. Finally, the H$\alpha$ maps from the survey's data analysis pipeline are sorted into five visual morphology classes (along-bar, central, ring, ends, undetected), and these classes are plotted on the main sequence diagram. The key identity is that $L_{\rm bar}/R_e$ tracks main-sequence offset rather than mass, which turns bar size into an evolutionary indicator.

What would settle it

A targeted deep H$\alpha$ observation of a sample of high-mass barred galaxies that currently show no bar emission would settle it: if significant along-bar emission appears at greater sensitivity, the claimed mass dependence of gas morphology is at least partly a detection artifact, weakening the two-process interpretation.

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Extended reading notes

Core claim

The central claim is that the normalized bar length, $L_{\rm bar}/R_e$, correlates with the galaxy's distance from the star formation main sequence: galaxies that have fallen further below the main sequence, i.e. that are more passive, host bars that are larger relative to the galaxy size. Physical bar length in kiloparsecs instead correlates chiefly with stellar mass. In the ionised gas census, H$\alpha$ emission is detected along the bars only in low-mass galaxies, which are generally star-forming and host short bars; higher-mass galaxies show H$\alpha$ more often in a prominent ring or at the centre and ends of the bar. The paper interprets this as evidence that bar growth and star-formation quenching are linked, and that low- and high-mass barred galaxies evolve through different physical processes.

Load-bearing premise

The paper assumes that the lack of detected H$\alpha$ along the bars of high-mass galaxies reflects a real difference in gas behaviour, not merely that those galaxies' fainter, more passive gas emission falls below the survey's detection threshold.

Editorial extensions

If this is right

Bar length normalized by galaxy size can serve as an observational gauge of how far a galaxy has progressed toward quiescence.
Gas flow along bars is a short-lived or low-mass-only phase; the along-bar H$\alpha$ seen in low-mass galaxies is a snapshot of recent bar formation in gas-rich disks.
In high-mass galaxies, rings associated with bar resonances may halt inward gas flow, keeping star formation away from the bar itself.
Galaxy stellar mass is the primary variable governing bar dynamics, with low- and high-mass systems following distinct evolutionary tracks.
Simulations that vary disk gas fraction and mass are needed to test whether these observed differences arise from formation conditions or later bar growth.

Reading between the lines

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

If scaled bar length truly tracks main-sequence offset, then bar length could be used to order galaxies on a quenching timeline without needing spectra, provided reliable bar lengths can be measured at higher redshift.
The correlation may partly reflect that high-mass galaxies have older bars that have had time to grow, while low-mass galaxies' short bars are recent; a direct test would compare bar length with independent age indicators such as stellar population gradients.
The 'no H$\alpha$ detected' class is the obvious confound: a deeper survey could reclassify some high-mass galaxies, potentially eroding the claimed dichotomy between low- and high-mass bar gas morphology.
If rings are resonance features that throttle gas inflow, then the presence of a ring should correlate with suppressed central star formation; this can be checked with resolved star formation maps.

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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

Quick take on arXiv:1908.08350. It's a short conference proceedings from Fraser-McKelvie et al., using 684 barred galaxies from MaNGA. The two new results are: (1) bar length normalized by effective radius (L_bar/R_e) increases with distance below the star-forming main sequence, and (2) H-alpha emission along the bar is seen mainly in low-mass galaxies, while high-mass galaxies show rings or central/end emission. The sample is large and the visual classification is clearly described, so the census is useful as a preliminary catalog. The problem is that the central interpretation in Section 3.1 does not survive contact with the normalization. At fixed stellar mass, passive galaxies are more compact than star-forming ones, so R_e is smaller for the passive galaxies. The figure shows that physical bar length (in kpc) tracks stellar mass, not SFR. If that is true, then L_bar/R_e will be larger for passive galaxies at the same mass simply because the denominator is smaller, not because the bar is more extended relative to its disk. The paper never shows a mass-binned comparison or a partial correlation controlling for R_e. Without that, the claim that bar growth quenches star formation is unsupported. This is not a minor omission; it is the load-bearing claim of the paper. The H-alpha morphology result in Section 3.2 has a softer version of the same problem: high-mass galaxies in this sample are mostly passive, so their H-alpha is fainter and less likely to be detected. The 'No H-alpha detected' class sits right where you'd expect a sensitivity limit. That said, the ring and central/end morphologies do appear in high-mass galaxies that are actively star-forming, so the classification scheme may be capturing something real. But the paper itself labels the source of ionization as uninvestigated, so treat this as qualitative. On credit: the paper is transparent about its method, cites the relevant literature, and the use of Galaxy Zoo 2 and the Fourier bar analysis is standard. The sample size is a real asset. The issue is not sloppiness; it's an untested interpretive step. Who is this for? Someone working on bar evolution who wants a quick preview of MaNGA-based distributions. It is not yet a solid result. For a full journal, I'd send it back for a much more rigorous analysis: mass-matched samples, uncertainty estimates, and a test of physical versus scaled bar length. As a conference proceedings, it's fine to have this as an initial report, but it should be flagged as provisional. My recommendation: engage with it cautiously. The data are worth mining, but the headline correlation should be treated as an artifact until proven otherwise.

Referee Report

3 major / 6 minor

Summary. This paper presents a census of 684 barred galaxies from the MaNGA MPL-8 survey, selected via Galaxy Zoo 2 classifications. Using Fourier-based bar lengths and NSA effective radii, the authors report that physical bar length correlates primarily with stellar mass, while the size-normalized bar length L_bar/R_e correlates with distance from the star-forming main sequence: more passive galaxies host larger-scale bars. The paper also visually classifies H-alpha morphologies into five categories, finding that H-alpha emission along bars appears only in low-mass galaxies, whereas high-mass galaxies more often show rings or central/end H-alpha. These results are interpreted as evidence that bar growth quenches star formation and that high- and low-mass galaxies experience different bar-driven evolution.

Significance. If the principal correlation is robust, the paper would provide a useful observational constraint connecting bar length to star formation quenching in a large IFU sample. The sample size and the use of resolved H-alpha maps to characterize gas morphology are notable strengths. However, the central claim is currently supported only by a color-coded plot without quantitative statistics, error bars, or control for the known mass–size relation. The paper is therefore best read as a promising but preliminary conference proceedings contribution; its headline inference requires additional analysis to be considered established.

major comments (3)

[Section 3.1, Fig. 1] The correlation between scaled bar length L_bar/R_e and distance below the star-forming main sequence may be dominated by the denominator R_e rather than by the bar itself. At fixed stellar mass, quiescent galaxies are known to be more compact than star-forming galaxies; therefore a passive galaxy with the same physical bar length will have a larger L_bar/R_e simply because its R_e is smaller. The paper does not present a mass-binned comparison, a partial correlation, or any test of whether physical bar length (in kpc) varies with SFMS offset at fixed mass. Without this control, the claim that bars are intrinsically longer (not just relatively longer) in more passive galaxies is not established.
[Section 3.2, Fig. 3] The conclusion that H-alpha emission is present along bars only in low-mass galaxies is confounded by sensitivity and selection effects. The 'No H-alpha detected' class contains mostly high-mass galaxies, which in this sample are also more passive and have intrinsically fainter H-alpha. The paper does not report the H-alpha detection limit, the SFR distribution within each morphology class, or the fraction of galaxies with undetected H-alpha as a function of mass. As presented, the absence of H-alpha along high-mass bars could reflect simply that star formation is faint or absent everywhere in these galaxies, rather than a bar-specific difference in gas dynamics.
[Section 4, Discussion] The interpretation that bar growth quenches star formation relies on a temporal reading of a cross-sectional correlation: the paper states 'If we assume that bars grow in length with time... a picture in which bar growth quenches star formation.' Alternative explanations, such as mass-dependent bar formation efficiency, environmental quenching, or compactness selecting for older bars, are not discussed. Given the lack of controls in the preceding sections, the causal claim is stronger than the data currently justify.

minor comments (6)

[Section 3.1] The paper defines distance from the main sequence visually but does not specify how the offset is measured or how sensitive the result is to the chosen Davies et al. (2016) reference relation. A quantitative definition of the offset would improve reproducibility.
[Fig. 1 and Fig. 3] The color bars in these figures are not accompanied by error bars or significance tests. Stating the correlation coefficient or an equivalent statistic for the L_bar/R_e–SFMS-offset relation would allow the reader to assess the strength of the claim.
[Fig. 2] The axis labels in the example galaxies are garbled (e.g., '20 10 0 10 20' and '10 2 10 1 100' appear to be axis tick values with missing labels). Clear arcsecond and flux units are needed.
[Section 2] The Galaxy Zoo 2 selection threshold p_bar > 0.5 is stated without justification. A brief comment on the purity/completeness trade-off or the sensitivity of the results to this threshold would be helpful.
[Section 3.2] The five-category visual classification scheme is presented without any reproducibility test, such as inter-rater agreement. A statement on the reliability of the scheme, even if based on a small subset, would strengthen the analysis.
[Throughout] There are several minor typographical issues, including 'the while physical bar length' in the final summary paragraph and unusual spacing in author names; these should be corrected.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the paper reports direct observational correlations between independent external measurements, with no fitted parameter being renamed as a prediction.

full rationale

The paper is an observational census rather than a derivation from a fitted model. Bar lengths come from the Fourier analysis code of Kraljic et al. (2012), stellar masses from the NSA catalog, SFRs from WISE 12-micron emission using the Cluver et al. (2017) relation, and main-sequence offsets are measured relative to the Davies et al. (2016) relation. These are independent external inputs. The central claim—that scaled bar length L_bar/R_e correlates with distance from the star-forming main sequence—is a direct comparison of two separately measured quantities; no parameter is fit to one and then used to predict the other. The use of MaNGA DAP maps (Westfall et al. 2019) is a pipeline product with public code and not a load-bearing self-citation. The skeptic's concern about R_e normalization is a potential astrophysical confound (quiescent galaxies are more compact at fixed mass), but that is an alternative interpretation of the correlation, not a circular derivation: the paper does not define the main-sequence offset in terms of R_e, nor does it fit the bar length to the offset. Therefore no circular step is exhibited, and the appropriate score is 0.

Assumptions & free parameters 1 free parameters · 3 assumptions · 0 invented entities

The paper introduces no new free parameters or entities. It relies on externally derived masses, SFRs, and the main sequence relation, and on subjective visual classification.

free parameters (1)

Galaxy Zoo selection threshold = p_bar > 0.5
Threshold for bar classification is chosen by hand, not fitted; it determines the sample of 684 galaxies.

assumptions (3)

domain assumption Galaxy Zoo 2 bar classifications with p_bar > 0.5 and p_not_edgeon > 0.5 select a reliable barred, non-edge-on galaxy sample.
The sample is defined by these thresholds in Section 2; if biased, conclusions about bar properties are biased.
domain assumption H-alpha emission traces ongoing star formation and gas inflow in bars.
The paper interprets H-alpha along bars as gas inflow/star formation (Section 3.2).
domain assumption The Kraljic et al. (2012) Fourier method yields accurate bar lengths without inclination corrections.
Bar lengths are derived from this code in Section 3.1; no tests or corrections are presented.

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Cite this review

Pith. "Pith review of Properties of barred galaxies in the MaNGA galaxy survey." pith.science (2026). https://pith.science/paper/IFOI3TYJ

@misc{pith2026190808350,
  author       = {Pith},
  title        = {Pith review of: Properties of barred galaxies in the MaNGA galaxy survey},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/IFOI3TYJ}},
  note         = {Machine review of arXiv:1908.08350}
}

read the original abstract

We present the initial results of a census of 684 barred galaxies in the MaNGA galaxy survey. This large sample contains galaxies with a wide range of physical properties, and we attempt to link bar properties to key observables for the whole galaxy. We find the length of the bar, when normalised for galaxy size, is correlated with the distance of the galaxy from the star formation main sequence, with more passive galaxies hosting larger-scale bars. Ionised gas is observed along the bars of low-mass galaxies only, and these galaxies are generally star-forming and host short bars. Higher-mass galaxies do not contain H{\alpha} emission along their bars, however, but are more likely to host rings or H{\alpha} at the centre and ends of the bar. Our results suggest that different physical processes are at play in the formation and evolution of bars in low- and high-mass galaxies.

Figures

Figures reproduced from arXiv: 1908.08350 by the authors.

**Figure 2.** The five Hα morphology classifications devised for this work. On the left is a gri image of the galaxy, and on the right, a MaNGA Hα map. Verley, S. , Combes, F. , Verdes-Montenegro, L. et al. 2007 A&A, 474, 1, 43 Westfall, K. B., Cappellari, M., Bershady, M. A. et al. submitted to AJ Willett, K. W., Lintott, C. J., Bamford, S. P. et al. 2013 MNRAS, 435, 2835 10 8 10 9 10 10 10 11 Stellar Mass (M ) 10 2 10 1 10 0 10… view at source ↗

**Figure 3.** Star formation main sequence of MaNGA barred galaxies. points are coloured [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗

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Reference graph

Works this paper leans on

10 extracted references · 10 canonical work pages

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[9]

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Westfall , K. B., Cappellari , M., Bershady , M. A. et al. submitted to AJ
[10]

W., Lintott , C

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2013

Pith tools

Reviewed August 14, 2026 · model on record in the stance chip above.

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Athanassoula , E., Machado , R. E. G., Rodionov , S. A. et al. 2013, MNRAS, 429, 3, 1949

work page 2013

[2] [2]

Blanton , M. R. , Kazin , E. , Muna , D. et al. 2011 AJ, 142, 31

work page 2011

[3] [3]

, Bershady , M

Bundy , K. , Bershady , M. A., Law , D. R. et al. 2015 ApJ, 798, 7

work page 2015

[4] [4]

Catinella , B., Schiminovich , D., Kauffmann , G. et al. 2010, MNRAS, 403, 2, 683

work page 2010

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Cluver , M. E. , Jarrett , T. H. , Dale , D. A. 2017, ApJ, 850, 1, 68

work page 2017

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Davies , L. J. M., Driver , S. P., Robotham , A. S. G. et al. 2016 MNRAS, 461, 1, 458

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, Bournaud , F., Martig , M

Kraljic , K. , Bournaud , F., Martig , M. 2012, ApJ, 757, 1, 60

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[8] [8]

, Combes , F

Verley , S. , Combes , F. , Verdes-Montenegro , L. et al. 2007 A&A, 474, 1, 43

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