arxiv: 2603.28208 · v1 · submitted 2026-03-30 · 🌌 astro-ph.GA

Recognition: no theorem link

The complex relationships between AGN, bars and bulges

Izzy L. Garland , Henry Best , Lucy F. Fortson , Tobias G\'eron , Chris J. Lintott , David O'Ryan , Brooke D. Simmons , Rebecca J. Smethurst

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Monika Viskotov\'a Mika Walmsley Norbert Werner Michal Zaja\v{c}ek

Authors on Pith no claims yet

Pith reviewed 2026-05-14 22:01 UTC · model grok-4.3

classification 🌌 astro-ph.GA

keywords AGNgalaxy barsbulgesgalaxy morphologysecular evolutionblack hole growthDESI survey

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The pith

AGN activity in galaxies rises with bar strength and bulge prominence independently after controlling for mass and color.

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

The paper tests whether the observed link between active galactic nuclei and bars is genuine or simply reflects both features correlating with bulges. Using a large low-redshift sample from the DESI Legacy Survey, the authors bin galaxies by bulge prominence and compare AGN fractions across bar strengths while holding mass and color fixed. They find AGN fractions increase with bar strength in each bulge bin. The same pattern holds when splitting by bar strength and examining bulge prominence. This points to bars and bulges each contributing separately to conditions that favor AGN through secular gas inflows.

Core claim

After controlling for stellar mass and color, the AGN fraction rises with increasing bar strength within fixed bins of bulge prominence, and rises with bulge prominence within subsamples of fixed bar strength. These trends show that AGN presence correlates with both bar strength and bulge prominence at the same time rather than one feature explaining the other.

What carries the argument

Comparison of AGN fractions across morphological bins of bar strength and bulge prominence from DESI Legacy Survey imaging, after mass and color controls.

If this is right

Bar-driven gas inflows can fuel AGN even in galaxies with weak bulges.
Bulge prominence increases AGN likelihood independently of bars.
The AGN-bar correlation cannot be fully attributed to shared links with bulges.
Morphological features add predictive information about AGN beyond mass and color alone.

Where Pith is reading between the lines

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

Secular internal processes may dominate black hole growth in the local universe.
Galaxy evolution models need to track bar and bulge effects on AGN activity as separate channels.
Higher-resolution imaging could check whether faint bars still produce measurable AGN enhancement.

Load-bearing premise

Visual classifications of bar strength and bulge prominence from the imaging are accurate and free of systematic bias when galaxies are grouped by mass and color.

What would settle it

Repeating the analysis with quantitative, automated measurements of bar strength and bulge prominence that erase the trend of rising AGN fraction with bar strength at fixed bulge prominence would falsify the central claim.

Figures

Figures reproduced from arXiv: 2603.28208 by Brooke D. Simmons, Chris J. Lintott, David O'Ryan, Henry Best, Izzy L. Garland, Lucy F. Fortson, Michal Zaja\v{c}ek, Mika Walmsley, Monika Viskotov\'a, Norbert Werner, Rebecca J. Smethurst, Tobias G\'eron.

**Figure 1.** Figure 1: The distributions of stellar mass (left column), (𝑔 − 𝑟)0 colour (middle column) and bulge prominence (right column) for AGN (top row), star-forming galaxies (middle row) and undetermined galaxies (bottom row). We show strongly barred galaxies in solid red lines, weakly barred in dashed navy blue, and unbarred in dotted teal. The AGN tend to have a higher bulge prominence, redder colour and higher stellar … view at source ↗

**Figure 3.** Figure 3: The effect of bulge prominence on AGN fraction ( 𝑓AGN) for each of strongly barred (red solid line), weakly barred (navy dashed line) and unbarred (teal dotted line) disk galaxies. Overall, 𝑓AGN increases in each bar strength category with bulge prominence. At lower bulge prominences, 𝑓AGN increases in each bulge bin with bar strength, however the difference between 𝑓AGN in strongly and weakly barred gala… view at source ↗

**Figure 4.** Figure 4 [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗

**Figure 5.** Figure 5: Variation of 𝑓AGN with the bulge surplus, as calculated in Equation 5. The relationship for strongly barred galaxies is shown in solid red, for weakly barred in dashed navy blue, and for unbarred in dotted teal. The horizontal lines show the mean 𝑓AGN for each bar category. Shaded regions show the 1𝜎 uncertainties. Galaxies at a given stellar mass are more likely to be hosting an AGN if they also have a gr… view at source ↗

**Figure 6.** Figure 6: The normalised distributions of bulge surplus for unbarred (left), weakly barred (centre) and strongly barred (right) galaxies, split between AGN (red) and non-AGN host galaxies (teal). We compare the AGN and non-AGN distributions in each bar category using KS tests, and the p-values are shown on the relevant plots. would help us to confirm or rule out the proposed duty cycle, however should be combined wi… view at source ↗

read the original abstract

Context. Via scaling relations, it is well-known that active galactic nuclei (AGN) and bulges are linked. This link was thought to be driven by mergers, but recent studies show that secular processes are the dominant mechanism of supermassive black hole growth. One such secular mechanism is gas inflow driven by large-scale bars. Since bulges can also grow via these bars, there is likely some common process between these three features. Aims. We investigate whether the observed correlation between AGN and bars is real or arises as a result of correlations between bars and bulges. Methods. Using a catalogue of AGN identifications and galaxy morphologies in the DESI Legacy Survey at $z\leq0.1$, we control for mass and colour and investigate the AGN fraction variation with bulge prominence and bar strength. Results. We first show that the variation in AGN fraction between strongly barred, weakly barred and unbarred galaxies does not qualitatively change if we additionally control for bulge prominence. Second, we find that in fixed bins of bulge prominence, the AGN fraction increases with increasing bar strength. In subsamples split by bar strength, the AGN fraction increases with bulge prominence, indicating that AGN presence correlates with both bar strength and bulge prominence simultaneously.

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

The paper shows AGN fraction rising with bar strength at fixed bulge prominence (and vice versa) after mass-color control in a large DESI sample, but leaves open whether morphology classifications carry AGN-related systematics.

read the letter

The central finding is that AGN activity tracks both bar strength and bulge prominence independently once mass and color are held fixed. In the binned data, strongly barred galaxies show higher AGN fractions than weakly barred or unbarred ones at the same bulge level, and the bulge trend persists across bar-strength subsamples. This is a direct, controlled check on whether the bar-AGN link is just a bulge byproduct, and the result survives the controls they apply. The work is straightforward and uses a uniform low-redshift catalog from DESI Legacy Survey imaging, which is a reasonable step beyond earlier studies that lacked the bulge control. The sample size gives decent statistics for the fractions. The soft spot is the absence of any reported tests on classification accuracy. Visual or automated bar and bulge labels from imaging can be affected by central AGN light, which might inflate bulge prominence or hide bars; without purity checks, inter-rater agreement numbers, or splits by AGN luminosity, the independence of the trends rests on an untested assumption. No error bars or completeness assessments appear in the summary either. This is the sort of incremental observational paper that belongs in a mid-tier journal. Readers tracking secular fueling mechanisms will want the numbers, but the claim needs the full methods vetted. I would send it to peer review rather than desk-reject; the core binning result is worth referee scrutiny even if revisions are needed on the systematics side.

Referee Report

3 major / 1 minor

Summary. The paper analyzes a catalog of AGN identifications and galaxy morphologies from the DESI Legacy Survey at z ≤ 0.1. After controlling for stellar mass and color, it reports that AGN fractions increase with bar strength in fixed bins of bulge prominence, and increase with bulge prominence in subsamples split by bar strength, indicating simultaneous correlations of AGN presence with both features.

Significance. If the morphological classifications prove robust against selection biases, the result provides empirical support for secular processes (such as bar-driven gas inflows) contributing to AGN activity alongside bulge growth, helping distinguish these from merger-driven scenarios in low-redshift supermassive black hole evolution.

major comments (3)

[Methods] Methods section: The control for mass and color is stated, but the manuscript provides no quantitative assessment of morphological classification accuracy, purity, or inter-observer agreement as a function of AGN luminosity or central concentration; this is load-bearing because the skeptic concern (DESI imaging biases from point-source contamination) directly affects the independence of the reported trends.
[Results] Results section: The binning analysis reports qualitative trends in AGN fractions but includes no error bars, bootstrap uncertainties, or statistical significance tests on the fraction differences across bar-strength and bulge-prominence bins, making it impossible to evaluate whether the increases are significant after the mass+color control.
[Results] Results section: No table or figure directly compares AGN fractions before versus after the additional bulge-prominence control, so the claim that 'the variation does not qualitatively change' cannot be verified quantitatively.

minor comments (1)

[Abstract] The abstract and methods should explicitly state the total sample size, the number of galaxies per bin, and the precise AGN selection criteria (e.g., emission-line or X-ray thresholds) to allow reproducibility.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for their constructive comments, which highlight important areas for improving the clarity and robustness of our analysis. We address each major comment below and will revise the manuscript accordingly to incorporate quantitative assessments and statistical details.

read point-by-point responses

Referee: [Methods] Methods section: The control for mass and color is stated, but the manuscript provides no quantitative assessment of morphological classification accuracy, purity, or inter-observer agreement as a function of AGN luminosity or central concentration; this is load-bearing because the skeptic concern (DESI imaging biases from point-source contamination) directly affects the independence of the reported trends.

Authors: We agree that a quantitative assessment of morphological classification reliability is needed to address potential biases from AGN point-source contamination in DESI imaging. The classifications are drawn from the DESI Legacy Survey morphology catalog, which has been validated in the literature for low-redshift galaxies. In the revised manuscript, we will add a new subsection in Methods that includes available metrics on classification accuracy and purity from prior studies, along with a targeted check comparing bar and bulge classifications for AGN hosts versus non-AGN galaxies to assess any central concentration effects. This will directly support the independence of the reported trends. revision: yes
Referee: [Results] Results section: The binning analysis reports qualitative trends in AGN fractions but includes no error bars, bootstrap uncertainties, or statistical significance tests on the fraction differences across bar-strength and bulge-prominence bins, making it impossible to evaluate whether the increases are significant after the mass+color control.

Authors: We acknowledge that the current presentation relies on qualitative trends without error estimates or significance tests. In the revised manuscript, we will add binomial or bootstrap-derived error bars to all AGN fraction plots and include statistical tests (such as chi-squared or Kolmogorov-Smirnov tests) to quantify the significance of differences across bar-strength and bulge-prominence bins after the mass and color control. revision: yes
Referee: [Results] Results section: No table or figure directly compares AGN fractions before versus after the additional bulge-prominence control, so the claim that 'the variation does not qualitatively change' cannot be verified quantitatively.

Authors: We will add a new supplementary figure (or table) in the revised manuscript that explicitly shows AGN fractions versus bar strength both before and after applying the bulge-prominence control. This will enable direct quantitative verification that the trends remain qualitatively unchanged. revision: yes

Circularity Check

0 steps flagged

No circularity: purely empirical binning of AGN fractions

full rationale

The paper performs an observational analysis by binning galaxies from the DESI Legacy Survey catalogue according to visual or automated morphological classifications of bar strength and bulge prominence, then computes AGN fractions after controlling for stellar mass and colour. No equations, derivations, fitted parameters, ansatzes, or uniqueness theorems appear in the abstract or described methods. The central results (AGN fraction increasing with bar strength at fixed bulge prominence, and vice versa) are direct counts from the data splits and do not reduce to any input quantity by construction. Self-citations, if present, are not load-bearing for any claimed derivation because none exists. This matches the default expectation of an honest non-finding for an empirical study.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The analysis rests on standard domain assumptions about the reliability of photometric morphology and AGN identification rather than new postulates or fitted parameters.

axioms (2)

domain assumption Bar strength and bulge prominence can be measured reliably and consistently from DESI Legacy Survey images
Required for the binning procedure and fraction comparisons described in the results.
domain assumption AGN identifications in the catalog are sufficiently complete and pure for statistical fraction measurements
Central to computing the AGN fractions that form the main results.

pith-pipeline@v0.9.0 · 5566 in / 1314 out tokens · 54375 ms · 2026-05-14T22:01:06.147609+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

64 extracted references · 64 canonical work pages

[1]

N., Adelman-McCarthy, J

Abazajian, K. N., Adelman-McCarthy, J. K., Agüeros, M. A., et al. 2009, ApJS, 182, 543 Alonso,S.,Coldwell,G.,Duplancic,F.,Mesa,V.,&Lambas,D.G.2018,A&A, 618, A149 Astropy Collaboration, Price-Whelan, A. M., Lim, P. L., et al. 2022, ApJ, 935, 167 AstropyCollaboration,Price-Whelan,A.M.,Sipőcz,B.M.,etal.2018,AJ,156, 123 Astropy Collaboration, Robitaille, T. P...

work page 2009
[2]

2005, MNRAS, 358, 1477

Athanassoula, E. 2005, MNRAS, 358, 1477

work page 2005
[3]

A., Phillips, M

Baldwin, J. A., Phillips, M. M., & Terlevich, R. 1981, PASP, 93, 5

work page 1981
[4]

M., & Zhu, Y

Beifiori, A., Courteau, S., Corsini, E. M., & Zhu, Y. 2012, MNRAS, 419, 2497

work page 2012
[5]

F., Monachesi, A., Harmsen, B., et al

Bell, E. F., Monachesi, A., Harmsen, B., et al. 2017, ApJ, 837, L8

work page 2017
[6]

R., Schlegel, D

Blanton, M. R., Schlegel, D. J., Strauss, M. A., et al. 2005, AJ, 129, 2562

work page 2005
[7]

R., Athanassoula, E., et al

Cheung, E., Trump, J. R., Athanassoula, E., et al. 2015, MNRAS, 447, 506

work page 2015
[8]

2011, ApJ, 741, L11

Cisternas, M., Jahnke, K., Bongiorno, A., et al. 2011, ApJ, 741, L11

work page 2011
[9]

& Gadotti, D

Coelho, P. & Gadotti, D. A. 2011, ApJ, 743, L13 Combes,F.2009,inAstronomicalSocietyofthePacificConferenceSeries,Vol. 419,GalaxyEvolution:EmergingInsightsandFutureChallenges,ed.S.Jogee, I. Marinova, L. Hao, & G. A. Blanc, 31

work page 2011
[10]

C., Debattista, V

Du, M., Ho, L. C., Debattista, V. P., et al. 2021, ApJ, 919, 135

work page 2021
[11]

2012, ARA&A, 50, 455

Fabian, A. 2012, ARA&A, 50, 455

work page 2012
[12]

J., Garland, I

Fahey, M. J., Garland, I. L., Simmons, B. D., et al. 2025, MNRAS, 537, 3511

work page 2025
[13]

& Merritt, D

Ferrarese, L. & Merritt, D. 2000, ApJ, 539, L9 Frosst,M.,Obreschkow,D.,Ludlow,A.,Bottrell,C.,&Genel,S.2025,MNRAS, 537, 3543

work page 2000
[14]

A., Willett, K

Galloway, M. A., Willett, K. W., Fortson, L. F., et al. 2015, MNRAS, 448, 3442

work page 2015
[15]

D., Cora, S

Gargiulo, I. D., Cora, S. A., Vega-Martínez, C. A., et al. 2017, MNRAS, 472, 4133

work page 2017
[16]

L., Fahey, M

Garland, I. L., Fahey, M. J., Simmons, B. D., et al. 2023, MNRAS, 522, 211

work page 2023
[17]

L., Walmsley, M., Silcock, M

Garland, I. L., Walmsley, M., Silcock, M. S., et al. 2024, MNRAS, 532, 2320 Géron, T., Smethurst, R. J., Lintott, C., et al. 2021, MNRAS, 507, 4389

work page 2024
[18]

2015, ApJ, 806, 218

Glikman, E., Simmons, B., Mailly, M., et al. 2015, ApJ, 806, 218

work page 2015
[19]

D., Matthaey, E., Greene, J

Goulding, A. D., Matthaey, E., Greene, J. E., et al. 2017, ApJ, 843, 135

work page 2017
[20]

C., Debattista, V

Guo, M., Du, M., Ho, L. C., Debattista, V. P., & Zhao, D. 2020, ApJ, 888, 65

work page 2020
[21]

& Kormendy, J

Hamabe, M. & Kormendy, J. 1987, in IAU Symposium, Vol. 127, Structure and Dynamics of Elliptical Galaxies, ed. P. T. de Zeeuw, 379 Häring, N. & Rix, H.-W. 2004, ApJ, 604, L89

work page 1987
[22]

R., Millman, K

Harris, C. R., Millman, K. J., van der Walt, S. J., et al. 2020, Nature, 585, 357

work page 2020
[23]

Heckman, T. M. & Best, P. N. 2014, ARA&A, 52, 589

work page 2014
[24]

2013, ApJS, 208, 19

Hinshaw, G., Larson, D., Komatsu, E., et al. 2013, ApJS, 208, 19

work page 2013
[25]

2025, A&A, 704, A94

Huertas-Company, M., Shuntov, M., Dong, Y., et al. 2025, A&A, 704, A94

work page 2025
[26]

Hunter, J. D. 2007, Computing in Science and Engineering, 9, 90

work page 2007
[27]

Kataria, S. K. & Vivek, M. 2024, MNRAS, 527, 3366

work page 2024
[28]

M., Tremonti, C., et al

Kauffmann, G., Heckman, T. M., Tremonti, C., et al. 2003, MNRAS, 346, 1055

work page 2003
[29]

H., Shlosman, I., & Peletier, R

Knapen, J. H., Shlosman, I., & Peletier, R. F. 2000, ApJ, 529, 93

work page 2000
[30]

1933, Inst

Kolmogorov, A. 1933, Inst. Ital. Attuari, Giorn., 4, 83

work page 1933
[31]

1977, ApJ, 218, 333

Kormendy, J. 1977, ApJ, 218, 333

work page 1977
[32]

Kormendy, J., Drory, N., Bender, R., & Cornell, M. E. 2010, ApJ, 723, 54

work page 2010
[33]

Kormendy, J. & Ho, L. C. 2013, ARA&A, 51, 511

work page 2013
[34]

& Kennicutt, R

Kormendy, J. & Kennicutt, R. C. 2004, ARA&A, 42, 603

work page 2004
[35]

2012, ApJ, 757, 60 La Marca, A., Nardone, M

Kraljic, K., Bournaud, F., & Martig, M. 2012, ApJ, 757, 60 La Marca, A., Nardone, M. T., Wang, L., et al. 2026, A&A, 707, A152

work page 2012
[36]

H., & Peletier, R

Laine, S., Shlosman, I., Knapen, J. H., & Peletier, R. F. 2002, ApJ, 567, 97

work page 2002
[37]

2004, ApJ, 607, 103

Laurikainen, E., Salo, H., & Buta, R. 2004, ApJ, 607, 103

work page 2004
[38]

Laurikainen, E., Salo, H., Buta, R., & Knapen, J. H. 2007, MNRAS, 381, 401

work page 2007
[39]

2025, A&A, 699, A204

Marels, V., Mesa, V., Jaque Arancibia, M., et al. 2025, A&A, 699, A204

work page 2025
[40]

R., Clancy, D., & Bianconi, M

Marleau, F. R., Clancy, D., & Bianconi, M. 2013, MNRAS, 435, 3085

work page 2013
[41]

J., Dekel, A., & Teyssier, R

Martig, M., Bournaud, F., Croton, D. J., Dekel, A., & Teyssier, R. 2012, ApJ, 756, 26

work page 2012
[42]

2018, MNRAS, 476, 2801

Martin, G., Kaviraj, S., Volonteri, M., et al. 2018, MNRAS, 476, 2801

work page 2018
[43]

L., Lintott, C

Masters, K. L., Lintott, C. J., Hart, R. E., et al. 2019, MNRAS, 487, 1808

work page 2019
[44]

L., Nichol, R

Masters, K. L., Nichol, R. C., Haynes, M. P., et al. 2012, MNRAS, 424, 2180

work page 2012
[45]

M., Rosario, D

McAlpine, S., Harrison, C. M., Rosario, D. J., et al. 2020, MNRAS, 494, 5713

work page 2020
[46]

1987, MNRAS, 228, 635

Noguchi, M. 1987, MNRAS, 228, 635

work page 1987
[47]

Oh, S., Oh, K., & Yi, S. K. 2012, ApJS, 198, 4

work page 2012
[48]

K., Dubois, Y., et al

Park, M.-J., Yi, S. K., Dubois, Y., et al. 2019, ApJ, 883, 25

work page 2019
[49]

H., Eke, V

Parry, O. H., Eke, V. R., & Frenk, C. S. 2009, MNRAS, 396, 1972

work page 2009
[50]

J., Mendel, J

Rosario, D. J., Mendel, J. T., Ellison, S. L., Lutz, D., & Trump, J. R. 2016, MNRAS, 457, 2703

work page 2016
[51]

M., Charlot, S., et al

Salim, S., Rich, R. M., Charlot, S., et al. 2007, ApJS, 173, 267 Schawinski,K.,Koss,M.,Berney,S.,&Sartori,L.F.2015,MNRAS,451,2517

work page 2007
[52]

Sellwood, J. A. 2014, Reviews of Modern Physics, 86, 1

work page 2014
[53]

Sellwood, J. A. & Wilkinson, A. 1993, Reports on Progress in Physics, 56, 173

work page 1993
[54]

Shlosman, I., Frank, J., & Begelman, M. C. 1989, Nature, 338, 45 Silva-Lima,L.A.,Martins,L.P.,Coelho,P.R.T.,&Gadotti,D.A.2022,A&A, 661, A105

work page 1989
[55]

D., Smethurst, R

Simmons, B. D., Smethurst, R. J., & Lintott, C. 2017, MNRAS, 470, 1559

work page 2017
[56]

A., Masters, K

Skibba, R. A., Masters, K. L., Nichol, R. C., et al. 2012, MNRAS, 423, 1485

work page 2012
[57]

J., Beckmann, R

Smethurst, R. J., Beckmann, R. S., Simmons, B. D., et al. 2024, MNRAS, 527, 10855 Taylor,M.B.2005,inAstronomicalSocietyofthePacificConferenceSeries,Vol. 347,AstronomicalDataAnalysisSoftwareandSystemsXIV,ed.P.Shopbell, M. Britton, & R. Ebert, 29

work page 2024
[58]

Urrutia, T., Lacy, M., & Becker, R. H. 2008, ApJ, 674, 80

work page 2008
[59]

& Osterbrock, D

Veilleux, S. & Osterbrock, D. E. 1987, ApJS, 63, 295

work page 1987
[60]

E., et al

Virtanen, P., Gommers, R., Oliphant, T. E., et al. 2020, Nature Methods, 17, 261

work page 2020
[61]

2022, MNRAS, 509, 3966

Walmsley, M., Lintott, C., Géron, T., et al. 2022, MNRAS, 509, 3966

work page 2022
[62]

Wang, L., Obreschkow, D., Lagos, C. d. P., et al. 2019, MNRAS, 482, 5477

work page 2019
[63]

W., Lintott, C

Willett, K. W., Lintott, C. J., Bamford, S. P., et al. 2013, MNRAS, 435, 2835

work page 2013
[64]

G., Paudel, S., Moon, J.-S., & Yoon, S.-J

Zee, W.-B. G., Paudel, S., Moon, J.-S., & Yoon, S.-J. 2023, ApJ, 949, 91 Article number, page 8 I. L. Garland et al.: The complex relationships between AGN, bars and bulges Appendix A: Supplementary stellar mass, colour and bulge distributions Fig. A.1 shows the stellar mass (𝑀∗),(𝑔−𝑟) 0 colour and bulge prominence (𝐵) distributions for the LINERs, compos...

work page 2023