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arxiv: 2604.11905 · v1 · submitted 2026-04-13 · 🌌 astro-ph.GA

Introducing Delta V_(star-g): a new universal kinematic disturbance parameter

Jonah M. Powley , Rebecca J. Smethurst , Chris J. Lintott , Tobias G\'eron This is my paper

Pith reviewed 2026-05-10 16:18 UTC · model grok-4.3

classification 🌌 astro-ph.GA
keywords kinematic disturbanceactive galactic nucleiintegral field spectroscopyMaNGAstellar velocitygas velocitygalaxy kinematicsAGN triggering
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The pith

A new kinematic parameter finds no excess disturbances in galaxies hosting active black holes.

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

The paper introduces Delta V star-g as a measure of the difference between a galaxy's stellar and gas velocity maps from integral field spectroscopy data. The goal is to detect kinematic disturbances while avoiding biases tied to galaxy size, shape, or specific data characteristics. When applied to obscured active galactic nuclei in the MaNGA survey, the values match those from a control sample of inactive galaxies matched only by mass and redshift. This leads to the conclusion that AGN do not arise from any special set of kinematic processes beyond what happens in normal galaxies. A reader would care because it reframes the question of what turns on supermassive black holes away from rare dynamical events.

Core claim

Delta V star-g quantifies discrepancies between stellar and gas velocity maps. For AGN hosts there is no statistically significant difference in its distribution compared with a mass-redshift matched sample of inactive galaxies. This indicates that AGN triggering does not depend on distinct kinematic disturbance processes or combinations of processes beyond those already present in inactive galaxies.

What carries the argument

Delta V star-g, the quantified difference between stellar and gas velocity maps from integral field spectroscopy, used to capture kinematic disturbances while limiting bias from galaxy properties or data features.

If this is right

  • Kinematic disturbances occur at similar rates whether or not a galaxy hosts an active nucleus.
  • AGN activity must be driven by factors other than unique large-scale kinematic events.
  • Standard galaxy evolution processes already include whatever disturbances are needed for black hole growth.
  • The parameter offers a uniform way to compare dynamical states across active and inactive populations.

Where Pith is reading between the lines

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

  • Delta V star-g could be checked against known merging systems to confirm it registers expected disturbances.
  • The same comparison might be run on higher-redshift IFS data to track how kinematic states evolve with cosmic time.
  • Pairing Delta V star-g with other disturbance metrics could tighten constraints on black hole fueling models.

Load-bearing premise

That the mass and redshift matching between AGN and control samples is enough to remove all other influences on measured kinematic disturbance levels.

What would settle it

Finding a statistically significant difference in Delta V star-g distributions between AGN and inactive galaxies in a larger sample with tighter matching on additional properties would disprove the no-difference result.

Figures

Figures reproduced from arXiv: 2604.11905 by Chris J. Lintott, Jonah M. Powley, Rebecca J. Smethurst, Tobias G\'eron.

Figure 1
Figure 1. Figure 1: Illustration of Δ𝑉★−𝑔. Left column: Stellar velocity maps for four MaNGA galaxies (PLATEIFUs shown in the top-left corner for reference), showing the normalized and unnormalized stellar velocity values in the colour bar ticks of each velocity map, with the latter enclosed in brackets. Second column: Gas velocity maps for the same galaxies, also showing normalized and unnormalized velocity values indicated … view at source ↗
Figure 2
Figure 2. Figure 2: Scatter plot of Δ𝑉★−𝑔 values for the four galaxies shown in [PITH_FULL_IMAGE:figures/full_fig_p005_2.png] view at source ↗
Figure 4
Figure 4. Figure 4: Histogram plot of the Δ𝑉★−𝑔 distribution for all galaxies (AGN and control) in our sample. The black dashed line shows a possible threshold at Δ𝑉★−𝑔 = 0.25, below which we find galaxies with aligned, rotation-supported stellar and gas velocity maps, and above which significantly fewer galaxies exhibit this kinematic morphology. 4 DISCUSSION 4.1 Processes that Δ𝑉★−𝑔 could be tracing in kinematically disturb… view at source ↗
Figure 5
Figure 5. Figure 5: Histograms of log10 (𝑀∗/𝑀⊙ ) for galaxies classified as kinematically undisturbed (blue) and kinematically disturbed (red). Right: Corresponding histograms of bulge fraction (𝐵/𝑇)𝑟 for the same samples, using the same colour scheme. In each panel, dashed lines indicate the median value of each population, and the Anderson–Darling test p-value is shown in the top-right corner. different approach taken in th… view at source ↗
read the original abstract

We introduce a new kinematic disturbance parameter, $\Delta V_{\star-g}$ (pronounced `DVSG'), which takes advantage of integral field spectroscopy (IFS) to quantify differences between a galaxy's stellar and gas velocity maps. The motivation behind $\Delta V_{\star-g}$ is to capture disturbances in the kinematics of a galaxy that might be missed by alternative methods, while also attempting to minimize bias towards galaxy properties or features of the IFS data. We first detail the reasons for introducing this parameter, and explain how the $\Delta V_{\star-g}$ value of a galaxy can be calculated. We then present initial results using $\Delta V_{\star-g}$ to quantify the kinematic disturbance of obscured active galactic nuclei (AGN) found in the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. We find that there is no statistically significant difference between the $\Delta V_{\star-g}$ distributions of AGN and a control sample (matched in mass and redshift) of inactive galaxies. This suggests that AGN triggering may not be preferentially caused by any distinct kinematic disturbance process, or combination of processes, beyond those observed in inactive galaxies.

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 / 2 minor

Summary. The paper introduces ΔV⋆-g, a kinematic disturbance parameter derived directly from differences between stellar and gas velocity maps in IFS data. The parameter is motivated as capturing disturbances potentially missed by other methods while minimizing biases from galaxy properties or data features. Applied to obscured AGN in MaNGA, the central result is a null finding: no statistically significant difference in ΔV⋆-g distributions relative to a stellar-mass and redshift-matched control sample of inactive galaxies, implying AGN triggering does not involve distinct kinematic processes beyond those in normal galaxies.

Significance. If the null result holds after adequate controls, the work offers a new, observationally grounded tool for kinematic analysis that avoids fitted-model dependencies. The direct use of velocity maps and comparison to an external control sample are strengths. The finding bears on AGN fueling debates by suggesting kinematic disturbances are not a distinguishing trigger, consistent with secular processes being sufficient in many cases.

major comments (2)
  1. [Control sample section] Control sample construction (likely §3 or §4): Matching solely on stellar mass and redshift leaves open residual confounding by morphology, concentration, or local environment, each of which can drive stellar-gas velocity offsets independently of AGN activity. The central claim that the null result implies no preferential kinematic triggering process requires that the samples differ only in AGN presence; without additional matching or stratification on these variables, the distributions could be similar for reasons unrelated to the parameter's intended isolation of triggering mechanisms.
  2. [Results section] Statistical comparison and error handling (results section): The abstract and summary state 'no statistically significant difference,' yet the manuscript must specify the exact test (e.g., KS or Mann-Whitney), p-value threshold, sample sizes for AGN and control, and how uncertainties in velocity maps propagate into ΔV⋆-g. Without these, the null result cannot be verified as robust against the parameter's definition or data quality variations.
minor comments (2)
  1. [Methods] Notation consistency: Ensure ΔV⋆-g is defined with explicit formula (including any summation or averaging over spaxels) in the methods section to allow reproduction.
  2. [Figures] Figure clarity: Velocity map difference figures should include scale bars and explicit color-bar units to illustrate how the parameter is computed from raw maps.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive and detailed comments, which have helped us identify areas where the manuscript can be clarified and strengthened. Below we provide point-by-point responses to the major comments. We have revised the manuscript accordingly where appropriate.

read point-by-point responses

  1. Referee: [Control sample section] Control sample construction (likely §3 or §4): Matching solely on stellar mass and redshift leaves open residual confounding by morphology, concentration, or local environment, each of which can drive stellar-gas velocity offsets independently of AGN activity. The central claim that the null result implies no preferential kinematic triggering process requires that the samples differ only in AGN presence; without additional matching or stratification on these variables, the distributions could be similar for reasons unrelated to the parameter's intended isolation of triggering mechanisms.

    Authors: We agree that matching exclusively on stellar mass and redshift leaves potential for residual confounding by morphology, concentration, or local environment, which could independently influence stellar-gas velocity offsets. Although ΔV⋆-g is constructed to reduce sensitivity to galaxy properties through direct map comparison without model fitting, this does not fully eliminate the need for better sample control when interpreting the null result as evidence against distinct kinematic triggering. In the revised manuscript we will add stratification or supplementary matching on concentration (e.g., via Sérsic index or concentration index) and morphology where possible, and we will explicitly discuss the remaining limitations in the interpretation section. This will make the central claim more robust. revision: yes

  2. Referee: [Results section] Statistical comparison and error handling (results section): The abstract and summary state 'no statistically significant difference,' yet the manuscript must specify the exact test (e.g., KS or Mann-Whitney), p-value threshold, sample sizes for AGN and control, and how uncertainties in velocity maps propagate into ΔV⋆-g. Without these, the null result cannot be verified as robust against the parameter's definition or data quality variations.

    Authors: We acknowledge that the statistical details were insufficiently explicit. The revised manuscript will state that a two-sample Kolmogorov-Smirnov test was used, report the exact p-value and adopted significance threshold, give the sample sizes (AGN and control), and describe the propagation of velocity-map uncertainties into ΔV⋆-g via Monte Carlo resampling of the velocity fields within their reported errors. These additions will appear in the results section and will allow independent verification of the null finding. revision: yes

Circularity Check

0 steps flagged

No circularity: ΔV⋆-g defined directly from data and compared to external control

full rationale

The paper defines ΔV⋆-g from observed stellar and gas velocity maps in MaNGA IFS data, then performs a direct statistical comparison to a mass-redshift matched control sample of inactive galaxies. No parameter is fitted to the target result and then relabeled as a prediction, no self-citation chain supports the central null finding, and the definition does not reduce to the conclusion by construction. The null result is an empirical outcome of the comparison, not a tautology.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 1 invented entities

The central claim rests on the assumption that stellar and gas velocity maps can be differenced in a manner that isolates disturbance without bias, plus the adequacy of the control matching; no free parameters or invented physical entities are described.

axioms (1)
  • domain assumption Differences between stellar and gas velocity maps can be quantified to capture disturbances while minimizing bias to galaxy properties or IFS data features.
    Explicitly stated as the motivation for introducing the parameter.
invented entities (1)
  • ΔV⋆-g parameter no independent evidence
    purpose: Quantify kinematic disturbance between stellar and gas components.
    Newly defined derived quantity with no independent external validation or falsifiable prediction provided in the abstract.

pith-pipeline@v0.9.0 · 5514 in / 1399 out tokens · 68869 ms · 2026-05-10T16:18:10.175849+00:00 · methodology

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Reference graph

Works this paper leans on

1 extracted references · 1 canonical work pages

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    work page doi:10.14311/app.2014.01.0084 2007