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No evidence for fast, galaxy-wide ionised outflows in a nearby quasar -- the importance of accounting for beam smearing

T0 review · 3 major / 4 minor · reviewed 2026-08-12 · deepseek-v4-flash

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Pith's one-line read Deep integral-field observations of the quasar F13451+1232 show that the apparent galaxy-wide high-velocity outflow is beam-smeared light from a compact 100-parsec nuclear outflow; once removed, the extended gas moves at modest velocities…

desk verdict A careful single-object beam-smearing analysis that makes a strong, if not airtight, case against galaxy-wide warm-ionised outflows in F13451+1232, with the PSF-subtraction completeness as the main residual uncertainty. read the letter →

arxiv 2411.17500 v2 pith:RAQIGFUA submitted 2024-11-26 astro-ph.GA astro-ph.HEastro-ph.IM

Luke R. Holden , Clive N. Tadhunter This is my paper · ORCID
classification astro-ph.GAastro-ph.HEastro-ph.IM
keywords AGNfeedbackionisedoutflowsbeamsmearingatmosphericseeingintegralfieldspectroscopygalaxymergersultraluminousinfraredgalaxiestype-2quasars
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 claims that the fast, warm-ionised outflows once thought to extend across the galaxy F13451+1232 are an illusion caused by atmospheric seeing. Using deep integral-field spectroscopy, the authors model the bright compact nuclear outflow (radius about 69 pc) and show that its point-spread function, blurred by the atmosphere, can account for all the high-velocity (W80 > 500 km/s) emission out to radii beyond 3.5 arcseconds (about 7.4 kpc). After subtracting this beam-smeared component, the remaining extended gas shows modest kinematics (W80 mostly below 500 km/s) consistent with gravitational motions in a galaxy merger. They further show that ignoring beam smearing would inflate mass outflow rates by up to an order of magnitude and kinetic powers by one to two orders of magnitude. The result matters because previous ground-based claims of galaxy-wide AGN outflows may largely be seeing artifacts, and warm-ionised outflows may actually be confined to the central kiloparsecs.

What carries the argument

The load-bearing object is the “nuclear model”: the two broad Gaussian components fitted to the [O III] line in a 0.4-arcsecond nuclear aperture, representing the compact outflow, whose spatial flux distribution is modelled by a two-dimensional Moffat profile. Because the peak flux of this component across the field is well described by a Moffat profile with FWHM consistent with the seeing disk measured from a star, the paper treats the entire extended broad-wing flux as PSF-smeared nuclear emission. It normalises the nuclear model, multiplies it by the Moffat profile in each spaxel, and subtracts this from the datacube before refitting the residual emission; the same procedure is applied to H$\alpha$+[N II]. The Moffat PSF is the mechanism that converts an unresolved nuclear outflow into a quantitative, spaxel-by-spaxel correction across the whole field.

What would settle it

High-spatial-resolution spectroscopy that resolves the broad-wing [O III] emission at radii beyond about 1 kpc, for example space-based integral-field observations with a PSF narrower than 0.1 arcsecond, would directly show whether the extended high-velocity flux exists independently of the nuclear PSF; if it does, the null result is an artifact of oversubtraction. A more targeted check would allow the subtracted nuclear component a small intrinsic size of a few hundred parsecs and test whether the claimed residual extended emission disappears only for exactly zero intrinsic size.

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Extended reading notes

Core claim

Working on the type-2 quasar/ultraluminous infrared galaxy F13451+1232, the paper establishes that a compact (radius less than 100 pc), luminous nuclear outflow produces a high-velocity wing in [O III] whose flux distribution across the field matches the seeing point-spread function (FWHM 0.74 arcseconds at 5000 Å, consistent with the stellar PSF of 0.79 arcseconds). Fitting a fixed “nuclear model” plus additional Gaussian components to every spatial pixel removes the circular patch of W80 ~ 1500–2500 km/s emission previously attributed to a galaxy-wide outflow; only a region to the northwest remains, with W80 below 500 km/s. The corrected velocity maps show blue- and redshifted gas extending to about 12 kpc with flux-weighted velocity shifts below 250 km/s and W80 mostly below 500 km/s, which the paper interprets as merger-driven gravitational motions rather than AGN outflows. The paper also quantifies the correction: for apertures out to about 9 kpc, beam-smearing-corrected mass outflow rates are $\dot{M}_{\rm out} = 0.14$\,$M_\odot$\,yr$^{-1}$ to $1.50$\,$M_\odot$\,yr$^{-1}$ and kinetic-power coupling efficiencies are below $0.002$ per cent of $L_{\rm bol}$, while the uncorrected values reach $7.4$\,$M_\odot$\,yr$^{-1}$ and $0.06$ per cent. This is presented as direct evidence that failing to account for atmospheric seeing can turn a compact nuclear outflow into an apparent galaxy-wide one.

Load-bearing premise

The argument assumes that the nuclear outflow’s light profile in the ground-based data is exactly point-like—identical to the stellar seeing PSF and describable by a single Moffat profile at all radii—so any residual broad-wing flux in a spaxel is attributed to the blurred compact outflow rather than to a genuinely extended outflow component.

Editorial extensions

If this is right

  • Outflow radii derived from ground-based integral-field data cannot be trusted unless beam smearing is modelled; for F13451+1232 the apparent high-velocity outflow radius drops from about 5.5 kpc to about 69 pc.
  • Failing to correct for seeing can overestimate mass outflow rates of extended gas by up to an order of magnitude and kinetic powers by one to two orders of magnitude, so some reported outflow coupling efficiencies may be too high.
  • The paper finds no galaxy-wide warm-ionised outflow in a system that galaxy-formation models use as a test case, supporting the view that warm-ionised AGN outflows are typically confined to the central kiloparsecs.
  • Circular patches of high velocity width in previously published velocity maps are likely seeing artifacts; in this object the beam-smeared component remains significant out to 3.5 arcseconds (7.4 kpc), more than eight times the HWHM of the seeing disk.
  • Because the kiloparsec-per-arcsecond scale increases with redshift, the beam-smearing bias becomes more severe for higher-redshift quasars observed from the ground.

Reading between the lines

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

  • The same PSF-subtraction recipe could be applied to archival ground-based integral-field cubes of other quasars to test whether claimed galaxy-wide outflows survive; objects with a compact nuclear outflow and a well-measured PSF star are the easiest targets.
  • If this result generalises, AGN feedback models that require kiloparsec-scale warm-ionised outflows to quench star formation may need to rely on other gas phases, such as hot X-ray gas, or on the cumulative effect of multiple AGN episodes.
  • The paper’s upper-limit argument implies that a genuinely extended warm-ionised outflow carrying model-level kinetic power would need electron densities below roughly $10^{-4}$ cm$^{-3}$, a testable prediction for future low-surface-brightness spectroscopy.
  • At higher redshift the same physical outflow would appear even more beam-smeared, so redshift-dependent claims of outflow sizes from ground-based surveys could be systematically biased; matched-resolution space-based integral-field observations would calibrate the effect.
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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

3 major / 4 minor

Summary. This paper analyses archival VLT/MUSE-DEEP observations of the type-2 quasar/ULIRG F13451+1232 to test whether the fast warm-ionised AGN-driven outflow seen near the nucleus is also present on galaxy-wide scales. The authors construct a two-Gaussian 'nuclear model' from the central 0.4-arcsec aperture, then fit this fixed-shape model plus additional free Gaussians to each spaxel, and also fit a Moffat profile to the spatial distribution of the nuclear-model flux. The Moffat FWHM matches the seeing measured from a field star for both [O III] and H-alpha, and subtracting this PSF-scaled nuclear model removes the circular high-velocity region that appears in free fits. The resulting residual maps show only modest kinematics, which the authors interpret as gravitational motions in a merger. They further quantify that ignoring beam smearing would overestimate mass outflow rates by up to an order of magnitude and kinetic powers by one to two orders of magnitude.

Significance. The paper addresses a key controversy in AGN feedback observations: whether ground-based IFU measurements of high-velocity extended emission represent genuine galaxy-wide outflows or seeing artifacts. The main result, if it holds, is a strong, direct demonstration that beam smearing of a compact nuclear outflow can mimic a kpc-scale high-velocity outflow in a representative quasar/ULIRG, and that correcting for it removes the evidence for galaxy-wide outflows in this object. The analysis is careful: the PSF is cross-checked against an independent field star at two wavelengths, the free-fitting versus corrected cases are explicitly compared, and the derived upper limits on extended outflow energetics are presented transparently. These strengths make the paper a valuable methodological case study for the field.

major comments (3)
  1. [Section 3.2.3, Fig. 3] The completeness of the PSF subtraction is the load-bearing step for the null result. The Moffat profile is fitted to the same nuclear-model flux distribution that is subsequently subtracted from each spaxel, and the residual map (right panel of Fig. 3) is displayed only over a ±0.04 range of the normalised peak, so any large-scale or asymmetric residuals that are absorbed by the fit would not be visible. I ask the authors to quantify the quality of the Moffat fit as a function of radius (e.g., radial profile with residuals in absolute flux units and a reduced chi-square) and to test explicitly whether an additional spatially extended component (e.g., a second Gaussian or Moffat) is statistically required by the nuclear-model flux distribution. Without this, the claim that all fast (W80 > 500 km/s) emission outside ~100 pc is beam-smeared nuclear emission is not fully established.
  2. [Sections 3.2.1–3.2.2, Table 1] The nuclear model fixes the relative amplitudes of the two broad Gaussian components to the values fitted in the 0.4-arcsec nuclear aperture. This implies that any genuine extended emission whose line profile resembles the nuclear outflow — for example, a more spatially extended component with a different ratio of broad-to-very-broad flux — would be absorbed by the scaled nuclear model and would not appear in the residual kinematics. I recommend a robustness test in which the two nuclear components are allowed independent spatial scalings (separate Moffat FWHMs) in the spaxel fits; if the two components were found to require different FWHMs, that would indicate that the subtraction is removing an extended component rather than pure seeing. This test would directly address the circularity concern.
  3. [Section 4.1 / Section 3.2.3] The paper cites the HST/ACS [O III] imaging of Tadhunter et al. (2018) as evidence that the nuclear outflow is compact, but it does not use that image as a quantitative check of the PSF subtraction. A direct comparison of the PSF-subtracted MUSE [O III] image with the HST image at matched spatial scales would provide an independent, non-seeing-limited test of whether genuine extended [O III] emission is being removed. If the MUSE residuals match the HST structures, the null result would be much more robust; if not, the residual map would reveal the presence of extended flux that the current subtraction removes.
minor comments (4)
  1. [Section 4.4] The text says 'T > 10^6 cm^{-3}' for the hot phase; the unit should be kelvin, not cm^{-3}, for temperature, so this is likely a typo.
  2. [Figure 3] The residual panel would be more informative if shown over a wider dynamic range (e.g., a symmetric logarithmic scale) or with contours at a few sigma, so that the reader can assess the level of residuals at large radii.
  3. [Equation (2)] Please clarify whether the sum is over the individual Gaussian components of the [O III] doublet and state how the flux-weighted shift is computed when both 4959 and 5007 lines are fitted simultaneously.
  4. [Table 2] The notation for upper and lower limits (e.g., '< 2.53' and '> 4.10' in the density column) should be explained in the table caption, as it is currently only described in the text.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the beam-smearing decomposition is a model-based subtraction with independent PSF cross-checks, and the null result is not forced by construction.

full rationale

The paper's derivation chain is not circular. The nuclear model (the two broad [O III] components) is measured once from the 0.4 arcsec nuclear aperture (Table 1) and then held fixed in shape, with only the overall peak flux free, when fitting every spaxel. The spatial PSF used for subtraction is not tuned to produce the null result: a 2D Moffat profile is fitted to the nuclear-model flux map (FWHM 0.74+/-0.02 arcsec) and independently cross-checked against a field star at the same wavelengths (0.79+/-0.10 arcsec for [O III]; 0.43+/-0.019 vs 0.44+/-0.02 arcsec for H alpha). The residual emission is then fitted with free additional Gaussians, so any genuinely extended broad component would in principle survive as a residual; the paper instead finds only modest W80 < 500 km/s emission, with a few 500-650 km/s patches interpreted as merger dynamics. The compactness prior that makes the subtraction meaningful (r[O III] ~ 69 pc) comes from HST/ACS imaging (Tadhunter et al. 2018), an external dataset independent of the MUSE fits; although the author group overlaps, this is real independent evidence under the stated rules, not a self-citation chain. The main vulnerability is model-dependence: assuming a single circular Moffat PSF identical to the stellar PSF and fixed relative nuclear-component amplitudes could in principle absorb a slightly extended or kinematically similar outflow. That is a systematic uncertainty about the astrophysical interpretation, not a circular reduction of the prediction to the fit.

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

No new physical entities are introduced. The central claim rests on a measured nuclear outflow template, a single-Moffat seeing PSF cross-checked against a field star, and standard warm-gas atomic physics. The main modeling burden is the assumption that all broad extended flux is PSF-smeared nuclear emission; the consistency of the fitted PSF with the stellar PSF is the key external check.

free parameters (4)
  • [OIII] nuclear model: broad component velocity shifts = -382 ± 44 and -1248 ± 36 km/s
    Fitted to the nuclear aperture spectrum (Table 1, Section 3.2.1), then fixed in all spaxel fits. The PSF-subtraction result depends on these values representing the outflow template.
  • [OIII] nuclear model: broad component FWHMs = 1006 ± 43 and 2847 ± 68 km/s
    Same origin and role as the velocity shifts; the broad wings subtracted across the field are defined by these widths.
  • Moffat PSF FWHM for [OIII] nuclear-model subtraction = 0.74 ± 0.02 arcsec
    Fitted to the spatial peak-flux distribution of the nuclear model (Section 3.2.3), consistent with the stellar seeing FWHM 0.79 ± 0.10 arcsec. The extent of the subtracted beam-smeared component is set by this value.
  • Moffat PSF FWHM for H-alpha nuclear-model subtraction = 0.43 ± 0.02 arcsec
    Fitted to the H-alpha nuclear model flux distribution (Section 3.2.4), consistent with the stellar H-alpha FWHM 0.44 ± 0.02 arcsec.
assumptions (4)
  • domain assumption The two broad [OIII] Gaussian components fitted in the nuclear aperture correspond to a compact nuclear outflow, and the narrow component to the kpc-scale disk.
    Section 3.2.1; identification based on prior spectroscopy (Rose et al. 2018) and HST imaging (Tadhunter et al. 2018). This is the template whose PSF smearing is subtracted.
  • domain assumption The atmospheric seeing PSF is a single Moffat profile, identical for the nuclear outflow emission and for field stars, and constant across the field of view.
    Sections 2.3, 3.2.3, 3.2.4; the Moffat FWHMs fitted to the nuclear model agree with the stellar FWHMs, supporting but not proving the assumption.
  • domain assumption Electron temperature T_e = 10,000 K and Case B recombination with j_Halpha/j_Hbeta = 2.863 apply to the extended warm-ionised gas.
    Section 3.4.3; standard assumptions for the warm ionised phase. They set the mass and energetics upper limits, not the kinematic conclusion.
  • domain assumption Residual gas with W80 < 500-650 km/s and |v_w| < 250 km/s in a major merger is gravitational (disordered merger dynamics) unless clearly outflowing.
    Section 3.3; the paper's interpretive framework. The authors explicitly state they cannot rule out lower-velocity outflows, so this assumption is acknowledged.

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Pith. "Pith review of No evidence for fast, galaxy-wide ionised outflows in a nearby quasar -- the importance of accounting for beam smearing." pith.science (2026). https://pith.science/paper/RAQIGFUA

@misc{pith2026241117500,
  author       = {Pith},
  title        = {Pith review of: No evidence for fast, galaxy-wide ionised outflows in a nearby quasar -- the importance of accounting for beam smearing},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/RAQIGFUA}},
  note         = {Machine review of arXiv:2411.17500}
}
abstract

To test the scenario that outflows accelerated by active galactic nuclei (AGN) have a major impact on galaxy-wide scales, we have analysed deep VLT/MUSE data for the type-2 quasar/ultraluminous infrared galaxy F13451+1232 - an object that represents the major mergers considered in models of galaxy evolution. After carefully accounting for the effects of atmospheric seeing that had smeared the emission from known compact nuclear outflows across the MUSE field of view, we find that the large-scale kinematics in F13451+1232 are consistent with gravitational motions that are expected in a galaxy merger. Therefore, the fast ($\mathrm{W_{80}}>500$ km s$^{-1}$) warm-ionised AGN-driven outflows in this object are limited to the central $\sim$100 pc of the galaxy, although we cannot rule out larger-scale, lower-velocity outflows. Moreover, we directly demonstrate that failure to account for the beam-smearing effects of atmospheric seeing would have led to the mass outflow rates and kinetic powers of spatially-extended emission being overestimated by orders of magnitude. We also show that beam-smeared compact-outflow emission can be significant beyond radial distances of 3.5 arcseconds (more than eight times the radius of the seeing disk), and support the argument that some previous claims of large-scale outflows in active galaxies were likely the result of this effect rather than genuine galaxy-wide ($r>5$ kpc) outflows. Our study therefore provides further evidence that warm-ionised AGN-driven outflows are limited to the central kiloparsecs of galaxies and highlights the critical importance of accounting for atmospheric seeing in ground-based observational studies of active galaxies.

Figures

Figures reproduced from arXiv: 2411.17500 by the authors.

Figure 1
Figure 1. 6400–6850 Å rest-wavelength image (covering H𝛼 + [NII]𝜆𝜆6548,6584, [SII]𝜆𝜆6717,6731, and continuum) of F13451+1232, produced from the archival MUSE-DEEP data. The primary (western: "W") and secondary (eastern: "E") nuclei are marked with black crosses. iteration is used to determine if another iteration (one more Gaus￾sian component) statistically improves the fit to the line profile, thus preventing over-fitting. L… view at source ↗
Figure 2
Figure 2. [OIII]𝜆𝜆4959,5007 line profile for the extracted circular 𝑟 = 0.4 arcsec aperture centred on the primary nucleus of F13451+1232 (black solid line). The overall fit to the line profile is shown as a solid red line; the broad Gaussian components of this fit (the ‘nuclear model’) are shown as dashed blue lines, the narrow Gaussian component is shown as a dash-dotted green line, and the first-order polynomial (accountin… view at source ↗
Figure 3
Figure 3. [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗
Figures from the paper (6 more)
Figure 4
Figure 4. Figure 4: [OIII]𝜆5007 line profile extracted from rectangular 2 × 1 arcsecond apertures (centred on the primary nucleus in the east-west direction) at increasing radial distances (labelled) to the north of the nucleus, for the original datacube (solid black line) and the datacub…
Figure 5
Figure 5. Figure 5: Non-parametric velocity width (W80 = 𝑣90 − 𝑣10; top panels) and flux-weighted velocity-shift (𝑣𝑤; bottom panels) maps of the central 6 × 6 arcsecond (13 × 13 kpc) region around the primary nucleus of F13451+1232 (black cross), as measured from free-fitting Gaussian com…
Figure 6
Figure 6. Figure 6: Non-parametric velocity width (W80: top panels) and flux-weighted velocity shift (𝑣𝑤: bottom panels) maps, centred on the primary nucleus (black cross), for the residual [OIII]𝜆5007 (left panels) and H𝛼 (right panels) emission in the MUSE-DEEP cube after the PSF of the…
Figure 7
Figure 7. Figure 7: Continuum-subtracted H𝛼 + [NII]𝜆𝜆6548,6584 + [SII]𝜆𝜆6717,6731 image (left: linear scale; right: logarithmic scale) of F13451+1232 with the locations and sizes of the selected apertures shown with solid blue lines; the dash-dotted red rectangle shows the region north of…
Figure 8
Figure 8. Figure 8: H𝛼+[NII] line profile extracted from a region (shown as a dash￾dotted red rectangle in [PITH_FULL_IMAGE:figures/full_fig_p011_8.png]
Figure 9
Figure 9. Figure 9: Fits to the [OIII]𝜆𝜆4959, 5007 doublet (top rows), H𝛼 + [NII]𝜆𝜆6548,6584 blend (middle rows), and [SII]𝜆𝜆6717,6731 doublet (bottom rows) in Aperture 3 using the nuclear model + 𝑁g Gaussian components (left column) and free-fitting (right column) approaches. The spectru…

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Pith tools

Reviewed August 12, 2026 · model on record in the stance chip above.