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arxiv: 2605.23269 · v1 · pith:ZNWAOIGLnew · submitted 2026-05-22 · 🌌 astro-ph.GA

Suppression of star formation at the centre of barred AGN galaxies

Takashi Yamamoto , Nario Kuno , Daisuke Iono , Takuya Hashimoto , Sophia K. Stuber , Daizhong Liu , Thomas G. Williams , Akio K. Inoue This is my paper

Pith reviewed 2026-05-25 04:22 UTC · model grok-4.3

classification 🌌 astro-ph.GA
keywords barred galaxiesAGN feedbackstar formation suppressionconcentration indexmolecular gasH-alphagalaxy quenchingPHANGS survey
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The pith

AGN feedback suppresses central star formation in four barred galaxies even at low gas fractions.

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

The paper measures the concentration of H-alpha emission relative to CO emission in 17 nearby galaxies. Four barred galaxies that host AGNs show much lower H-alpha concentration than expected from the gas distribution, while the other thirteen galaxies match closely. This pattern indicates that AGN activity is preventing star formation from occurring where the molecular gas has collected. The authors argue that bars drive gas inward to trigger a starburst, after which AGN feedback rapidly quenches further star formation and leaves residual gas to sustain the AGN. A reader would care because the result identifies a specific, rapid quenching route that operates in barred AGN systems and may shape how such galaxies evolve.

Core claim

Four barred AGN galaxies exhibit C(Hα)/C(CO) ratios of ~0.3-0.4 while the other 13 galaxies show ratios ~1, indicating that AGN feedback suppresses central star formation even at low molecular gas mass fractions (<0.1). The formation of bar structures causes molecular gas to collect in the central region, leading to starburst activity. However, after the starburst, the remaining gas becomes inefficient for star formation rapidly due to AGN feedback. It can mean the quenching process occurs more rapidly in AGN-barred galaxies. Furthermore, since gas remains in the central region, AGN activity is likely to continue.

What carries the argument

The ratio of concentration indices C(Hα)/C(CO), which diagnoses whether recent star formation is suppressed relative to the distribution of molecular gas.

If this is right

  • Negative AGN feedback remains effective even when the molecular gas mass fraction drops below 0.1.
  • Quenching proceeds more rapidly in barred galaxies that contain AGNs than in galaxies without this combination.
  • Central gas that survives the starburst phase can continue to feed AGN activity.
  • The combination of bar-driven inflow followed by AGN quenching is a pathway specific to barred spiral galaxies.

Where Pith is reading between the lines

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

  • The same suppression signature could appear in non-barred AGN hosts if feedback strength is high enough to overcome other dynamical effects.
  • High-resolution maps of additional barred AGN systems could test whether the degree of suppression scales with AGN luminosity or Eddington ratio.
  • If confirmed, this mechanism may help explain why strongly star-forming barred galaxies with luminous AGNs are rare in local samples.

Load-bearing premise

The observed difference in concentration ratios is produced by AGN feedback rather than by differences in bar strength, dynamical timescales, dust obscuration, or selection effects.

What would settle it

Observing similarly low C(Hα)/C(CO) ratios in barred galaxies that lack AGNs would falsify the claim that AGN feedback is the cause.

Figures

Figures reproduced from arXiv: 2605.23269 by Akio K. Inoue, Daisuke Iono, Daizhong Liu, Nario Kuno, Sophia K. Stuber, Takashi Yamamoto, Takuya Hashimoto, Thomas G. Williams.

Figure 1
Figure 1. Figure 1: Effect of dust attenuation across 19 galaxies. The left panel (a) shows the correlation between (H ) and (H ). The (H ) value for NGC 4535 is significantly low, the dust attenuation is particularly pronounced in galactic centre. The middle panel (b) shows the correlation between (H ) and (H ). index values are clearly lined up on the one-to-one line. The right panel (c) shows correlation between (H ) and (… view at source ↗
Figure 2
Figure 2. Figure 2: Scatter plot for (CO) and (H ) in four types of galaxies. A-type barred galaxies show as blue squares, B-type barred galaxies as red diamonds, N-type (short bar) barred galaxies as orange triangles, and non￾barred galaxies as yellow-green circles. The diagonal line shows one-to-one correspondence. NGC 1087, NGC 1365 and NGC 7496 are plotted at points that lie some distance above and below the one-to-one li… view at source ↗
Figure 3
Figure 3. Figure 3: Four panels (b-e) represent histograms of of H and CO and their ratio (Ro), for each type of galaxy. In particular, panel (e) shows a histogram of Ro for AGN-host and non-AGN galaxies. Alt text: Four panels represent histograms of of H and CO and their ratio (Ro), for each type of galaxy. across all AGN. Otherwise, Appleby et al. (2020) argued that from the SIMBA simulation, which uses various AGN feedback… view at source ↗
Figure 4
Figure 4. Figure 4: Illustrates the relationship between ΔMS and Ro in 11 barred spiral galaxies. These barred spiral galaxies are distributed in bimodal, A-type, and B-type along the vertical axis (Ro), and are further divided into three populations: starburst galaxies, star-forming main sequence galaxies, and green valley galaxies along the horizontal axis (ΔMS). We defined the classification criteria for three galaxy popul… view at source ↗
Figure 5
Figure 5. Figure 5: Schematic diagrams of an AGN host galaxy and a non-AGN galaxy. The right panel shows several harsh environments for star formation. We assume that the outflow does not completely blow away the molecular gas and that turbulence makes it difficult for molecular cloud-cloud collisions to occur. Due to the intense radiation from AGN, the ionised gas regions may become dominant over a wide area in the centre. N… view at source ↗
read the original abstract

We measured the Concentration (C) index of H\alpha and CO (J = 2-1) in 17 nearby star-forming galaxies from the PHANGS survey. We have found four barred spiral galaxies with a C(H\alpha)/C(CO) ratio of ~ 0.3-0.4, while the other 13 galaxies exhibit ratios of ~ 1 (range from 0.7 to 1.3). All four barred galaxies with low ratios host active galactic nuclei (AGNs), consistent with a scenario in which star formation is suppressed by mechanical and radiative feedback from the AGN. Therefore, negative feedback is effective in these four barred galaxies with a low molecular gas mass fraction (< 0.1), even when AGN activity is relatively weak. The formation of bar structures causes molecular gas to collect in the central region, leading to starburst activity. However, after the starburst, the remaining gas becomes inefficient for star formation rapidly due to AGN feedback. It can mean the quenching process occurs more rapidly in AGN-barred galaxies. Furthermore, since gas remains in the central region, AGN activity is likely to continue. These quenching processes are a unique mechanism found in barred spiral galaxies and are essential to understanding galaxy evolution.

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

2 major / 0 minor

Summary. The manuscript measures the concentration index C for Hα and CO(J=2-1) emission in 17 nearby star-forming galaxies from the PHANGS survey. It reports that four barred AGN-hosting galaxies exhibit C(Hα)/C(CO) ratios of ~0.3-0.4, while the remaining 13 galaxies show ratios ~1 (range 0.7-1.3). The authors attribute the difference to AGN mechanical and radiative feedback suppressing central star formation even at low molecular gas mass fractions (<0.1), and discuss implications for rapid quenching and continued AGN activity in barred spirals.

Significance. If the central observational difference and its attribution to AGN feedback hold after controlling for confounders, the result would identify a specific quenching channel in barred galaxies where bar-driven inflows lead to starbursts followed by rapid suppression, leaving residual gas to sustain AGN activity. This could inform models of galaxy evolution by highlighting environment-dependent feedback efficiency at low gas fractions.

major comments (2)
  1. [Abstract] Abstract: The causal attribution of the low C(Hα)/C(CO) ratios specifically to AGN feedback is load-bearing for the central claim but is not isolated from alternatives; the text provides no breakdown of how many of the 13 comparison galaxies are barred non-AGN systems, no bar strength metrics (e.g., bar torque or length), and no AGN luminosity or Eddington ratio values to test whether the effect scales with AGN power.
  2. [Abstract] Abstract and results section: No uncertainties, error bars, or robustness tests are reported for the C indices or the ~0.3-0.4 vs. ~1 separation; the exact operational definition of the concentration index C (e.g., aperture radii or normalization) is not stated, and no checks against dust obscuration, dynamical timescale differences, or PHANGS selection effects are described.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive and detailed comments, which help clarify the presentation and robustness of our results. We address each major comment below and indicate where revisions will be made.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The causal attribution of the low C(Hα)/C(CO) ratios specifically to AGN feedback is load-bearing for the central claim but is not isolated from alternatives; the text provides no breakdown of how many of the 13 comparison galaxies are barred non-AGN systems, no bar strength metrics (e.g., bar torque or length), and no AGN luminosity or Eddington ratio values to test whether the effect scales with AGN power.

    Authors: We agree that an explicit breakdown strengthens the isolation of AGN feedback from bar-driven effects alone. The manuscript states that the four galaxies with low ratios (~0.3-0.4) are barred AGN hosts and that the remaining 13 show ratios near 1; however, it does not tabulate bar status or AGN presence for the full sample. We will add a table or section in the revised manuscript listing bar classification and AGN activity for all 17 galaxies. Available AGN luminosity data for the four AGN hosts will also be included. Bar strength metrics (torque, length) and Eddington ratios are not uniformly available across the PHANGS sample, but we will report the range for the AGN subset and discuss implications for scaling with AGN power. revision: yes

  2. Referee: [Abstract] Abstract and results section: No uncertainties, error bars, or robustness tests are reported for the C indices or the ~0.3-0.4 vs. ~1 separation; the exact operational definition of the concentration index C (e.g., aperture radii or normalization) is not stated, and no checks against dust obscuration, dynamical timescale differences, or PHANGS selection effects are described.

    Authors: We acknowledge these omissions limit the ability to assess robustness. The concentration index follows the standard definition C = flux within central aperture / total flux, with apertures tied to the effective radius as used in prior PHANGS analyses; we will state the precise radii and normalization explicitly in the methods. Error bars on C will be added based on the PHANGS flux uncertainties, along with a robustness test (e.g., varying aperture size). We will add a dedicated paragraph addressing dust obscuration (noting Hα is more affected than CO but the ratio offset exceeds typical extinction variations), dynamical timescales, and potential PHANGS selection biases. These additions will be incorporated in the revised results and discussion sections. revision: yes

Circularity Check

0 steps flagged

No circularity: observational ratio comparison with no fitted derivations or self-referential steps

full rationale

The paper reports direct measurements of the Concentration (C) index for Hα and CO (J=2-1) emission in 17 PHANGS galaxies, identifying a subset of four barred AGN hosts with C(Hα)/C(CO) ~0.3-0.4 versus ~1 in the remaining 13. No equations, parameter fits, or predictive models are invoked; the central claim is a straightforward empirical ratio comparison and qualitative interpretation. No self-citations are used to justify uniqueness theorems, no ansatzes are smuggled, and no known results are renamed as new derivations. The result is self-contained against external benchmarks as a catalog of observed ratios.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the domain assumption that the concentration index ratio directly traces suppression of star formation by AGN feedback, plus the implicit assumption that the PHANGS sample selection does not introduce systematic bias between barred AGN and non-AGN systems.

axioms (1)
  • domain assumption The concentration index C reliably quantifies the central concentration of Hα and CO emission without significant bias from dust or resolution effects.
    Invoked when interpreting the ratio difference as physical suppression rather than observational artifact.

pith-pipeline@v0.9.0 · 5779 in / 1331 out tokens · 20860 ms · 2026-05-25T04:22:34.880152+00:00 · methodology

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Reference graph

Works this paper leans on

12 extracted references · 12 canonical work pages

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    (A2) The Δ MS is calculated using equation ( A2) as follows, Δ MS[ dex] = log10 SFR[ /u1D440 ⊙ yr− 1] − log10 SFRMS ( /u1D440 ∗) [ /u1D440 ⊙ yr− 1] , (A3) where log10 SFR is the value of the specific galaxy obtained from observations, and log 10 SFRMS ( /u1D440 ∗) is the value on the MS line corresponding to the stellar mass /u1D440 ∗[ /u1D440 ⊙ ] of that ...

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    5, selected from the /u1D467 ∼ 0 galaxies (z0MGS) of Leroy et al. (2019). Based on MaNGA data, Belfiore et al. (2018) suggest that the GV galaxies constitute a ‘quasi-static’ po pulation undergoing a slow-quenching process. As part of the ALMaQUE ST survey (ALMA-MaNGA Quenching and Star Formation Survey; Lin et al. 2020 ), Pan et al. (2024) categorized the...

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    The lat- ter two are sub-classes of quenching galaxies

    0). The lat- ter two are sub-classes of quenching galaxies. These popula tions are represented by Δ MS values of -0.2 to +0.4, -0.7 to -0.2, and -1.7 to -0.7, respectively. We discuss below with the perspective of quenching along the Δ MS axis. Present-day galaxies’ star formation is thought tohave pro- gressed from the SFMS phase, through the GV phase, t...

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    After the starb urst and consumption of the available gas, galaxies are thought to un dergo a quenching process (e.g., Baba et al

    is a starburst galaxy whose elevated star formation may be rela ted to central gas inflow through the bar structure. After the starb urst and consumption of the available gas, galaxies are thought to un dergo a quenching process (e.g., Baba et al. 2022 ), observed in the decrease of the Δ MS value. We adopt the sSFR classification of Pan et al. (2024). Howe...

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    In Pan et al

    13). In Pan et al. (2024), the scatter range of SFMS galaxies’ Δ MS is 0.3 dex, and our sample scatter range is the same. That range is consistent with the EAGLE simulation of Matthee & Schaye (2019) at /u1D467 = 0, /u1D440 ∗ ≳ 3 ×

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    Each of these three populations has a distinctive gas mass fraction ( /u1D453gas = /u1D440 H2 / /u1D440 ∗) range

    Thus, our sample is distinguished into three populations (‘Starbursts’, ‘Main sequence’, ‘G reen Valley’) along the Δ MS axis. Each of these three populations has a distinctive gas mass fraction ( /u1D453gas = /u1D440 H2 / /u1D440 ∗) range. (see Table 2). These /u1D453gas values were taken from Table 3 of Yamamoto et al. (2025). T wo GV galaxies in our sa...

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    These galaxies are still star-forming mainly in the central regio n, but may be quenching on a relatively short time-scale

    7 per cent), similar to those of S0 galaxies. These galaxies are still star-forming mainly in the central regio n, but may be quenching on a relatively short time-scale. We note an important point from Pan et al. (2024): as galaxies move away from SFMS to GV , the radial profile of the SFR surface density is suppressed within the central regions compared w...

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    In NGC 136 5, located at the top right of Figure 4, is a starburst galaxy with SFR ∼ 20 M ⊙ yr− 1 (e.g., Schinnerer et al

    host AGNs, implying that the presence of an AGN does not nec- essarily lead to suppressed star formation or reduced Ro /u1D436 values, and may also increase the star formation activity. In NGC 136 5, located at the top right of Figure 4, is a starburst galaxy with SFR ∼ 20 M ⊙ yr− 1 (e.g., Schinnerer et al. 2023 ; Liu et al. 2023 ). The surface density of...

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    In NGC 1433, star for mation in the central region may also be suppressed by negative feed back from the AGN

    and extremely low star formation throughout the disc. In NGC 1433, star for mation in the central region may also be suppressed by negative feed back from the AGN. Meanwhile, Combes et al. (2013) report that NGC 1433 exhibits AGN-driven outflows, and, as a result, AGN posi tive feedback may slightly increase star formation in the centra l region. Neverthel...

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