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arxiv: 2606.27026 · v1 · pith:DDDCZLAOnew · submitted 2026-06-25 · 🌌 astro-ph.GA

Unveiling the roles of thermal and nonthermal processes in the ISM & IGM structure formation and evolution of galaxies with SKAO

Pith reviewed 2026-06-26 03:40 UTC · model grok-4.3

classification 🌌 astro-ph.GA
keywords SKAOISM processesnonthermal feedbackcosmic noonradio continuumHI emissiongalaxy evolutionhigh-redshift galaxies
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The pith

SKAO AA4 surveys will trace thermal and nonthermal ISM processes in galaxies beyond cosmic noon.

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

The paper establishes that thermal and nonthermal processes in the ISM and IGM drive galaxy evolution over cosmic time. Precursor observations show nonthermal processes involving magnetic fields and cosmic rays slow star formation and launch outflows in nearby galaxies, with stronger effects at higher redshifts due to elevated star formation. Simulations that scale radio continuum and HI emission from local galaxies like M51 and NGC6946 to earlier epochs demonstrate that SKAO AA4 surveys can detect continuum signals beyond z=2-3 and HI beyond z=1. This would reveal the role of nonthermal feedback during the peak epoch of cosmic star formation.

Core claim

Our simulations show that the AA4 surveys will make it possible to trace the thermal and nonthermal processes of the ISM in galaxies that are analogs to M51 and NGC6946, traced in continuum beyond cosmic noon (z=2-3) and the gas content traced by HI beyond z=1. Both simulations and precursor observations indicate the importance of nonthermal feedback at cosmic noon.

What carries the argument

Simulations scaling the radio continuum and HI emission of local galaxies to high redshifts.

If this is right

  • Nonthermal processes will be traceable in continuum emission beyond z=2-3.
  • HI gas content will be traceable beyond z=1.
  • Nonthermal feedback will prove important at cosmic noon.
  • Effects of nonthermal processes strengthen at higher redshifts due to higher star formation activity.

Where Pith is reading between the lines

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

  • Galaxy formation simulations may need to increase the weight given to magnetic and cosmic-ray feedback at peak star-formation epochs.
  • Repeated application of the same scaling method to other local templates could map how magnetic-field strength evolves with redshift.
  • Resolved SKAO maps at these redshifts could separate thermal free-free emission from synchrotron to quantify each process's contribution to outflows.

Load-bearing premise

The radio emission properties and ISM structure of local galaxies such as M51 and NGC6946 can be scaled directly to represent high-redshift analogs without major modifications from different cosmic conditions.

What would settle it

Detection or nondetection of the simulated levels of radio continuum emission from z=2-3 galaxy analogs in the AA4 surveys would test whether the local scaling holds.

Figures

Figures reproduced from arXiv: 2606.27026 by Cathy Horellou, Elizabeth A. K. Adams, Eric J. Murphy, Eva Schinnerer, Fatemeh S. Tabatabaei, Ilsang Yoon, Isabella Prandoni, Javier Moldon, Mahdiyar Mousavi-Sadr, Mark T. Sargent, Maryam Khademi, Masoumeh Ghasemi-Nodehi, Volker Heesen.

Figure 1
Figure 1. Figure 1: Artist’s illustration of the nonthermal feedback (due to cosmic rays in turbulent magnetic field, Tabatabaei et al., 2022) in star-forming regions (blue and green) superimposed on a VLT visible-light image (red and white). Credit: Institute for Research in Fundamental Sciences- IPM & European Southern Observatory (ESO). shows that the bulk of the CREs population is younger and more energetic as a result of… view at source ↗
Figure 2
Figure 2. Figure 2: Role of nonthermal processes on star-formation rate per free-fall (SFRff ≡ Σ SFR/Σ H2 × 𝜏ff with Σ SFR and Σ H2 the surface densities of the SFR and molecular gas, respectively, and 𝜏ff = 4.7 ( 𝑀𝐻2 106 𝑀⊙ ) 0.25 is the the free-fall timescale of molecular gas) in giant molecular cloud associations in the circumnuclear ring of NGC1097. Left- SFRff vs equipartition magnetic field strength. Right- SFRff vs tu… view at source ↗
Figure 3
Figure 3. Figure 3: Simulated surface brightness maps of thermal and nonthermal emission from analogs of M51, NGC6946, and M33 galaxies at different redshifts z=0.15, 0.3,0.5, 1, and 2 simulated for the SKA AA4 at 0.6" resolution at the observed frequency of 1.4 GHz (Ghasemi-Nodehi et al., 2022). an angular resolution of 𝜃 =0.6" (Ghasemi-Nodehi et al., 2022). Here, we revisit those simulations taking into account the SKA-AA4 … view at source ↗
Figure 4
Figure 4. Figure 4: Top: Redshift evolution of the nonthermal (left) and thermal (right) mean surface brightness at the observed frequency of 𝜈2 = 1.4 GHz (equivalent to a rest-frame frequency of 1.6–5.6 GHz at 0.15 ≤ 𝑧 ≤ 3) and the thermal fraction (bottom-left). Shaded regions show the 3𝜎 uncertainties of the fits of the form 𝑎(1 + 𝑧)𝑏 (see Ghasemi-Nodehi et al., 2022, for more details). Also shown is the evolution of 𝛼nt w… view at source ↗
Figure 5
Figure 5. Figure 5: Mean S/N based on the SKA AA4 band 2 UDT with the rms noise level of 𝜎 = 0.05 𝜇Jy (solid), DT with 𝜎 = 0.2 𝜇Jy (dashed-dotted), and WT with 𝜎 = 1 𝜇Jy (dotted) surveys at the observed frequency of 1.4 GHz (equivalent to a rest-frame frequency of 1.6–5.6 GHz at 0.15 ≤ 𝑧 ≤ 3). 5 Synergies with ALMA, VLT/JWST, Euclid Studying the ISM/IGM structure formation and energy balance requires a complete view of differ… view at source ↗
Figure 6
Figure 6. Figure 6: Top- Mean radio continuum surface brightness of star-forming galaxies at 𝑧 = 0.15 (5 𝜎 detection) vs the SKA Band2 integration time observed with AA★ at 𝜃 = 1.25” and AA4 at 𝜃 = 0.6” and 0.9” angular resolutions. Bottom- Same as in the top for galaxies at 𝑧 = 1 excluding the case for a low surface brightness galaxy such as M33 (M33 Analog). Solid lines just indicate the observational setups. 12 [PITH_FULL… view at source ↗
Figure 7
Figure 7. Figure 7: Faster rotating and/or more massive isolated galaxies have stronger large-scale magnetic fields (𝐵¯) traced by synchrotron polarization (Tabatabaei et al., 2016). The scatter at the higher mass end (rotation velocities 𝑣rot > 210 km s−1 ) is linked to an excess SF activity (enhancing 𝐵¯) and ejection from super-massive black holes (reducing 𝐵¯) in TNG50 simulations (Hosseinirad et al., 2023). This corelati… view at source ↗
Figure 8
Figure 8. Figure 8: The mean S/N of simulated HI moment 0 maps of M51 analogs vs redshift. Acknowledgement M. G.-N. acknowledges the support from the CAS Talent program and the Xinjiang Tianchi Talent program. JM acknowledges financial support from the Spanish grant PID2023-147883NB-C21, funded by MCIU/AEI/ 10.13039/501100011033, as well as support through ERDF/EU, and from the Severo Ochoa grant CEX2021-001131-S funded by MC… view at source ↗
read the original abstract

Investigating the thermal and nonthermal processes in the interstellar medium (ISM) and intergalactic medium (IGM) is vital to understanding the evolution of galaxies over cosmic time. Resolved observations with SKA pathfinders show that the nonthermal processes, in which magnetic fields and cosmic rays are involved, can decelerate the formation of massive stars in strongly magnetized regions in nearby galaxies. They can also contribute to the onset of winds and outflows in galaxies. The effects of these processes are stronger at higher redshifts as a result of star formation activities. The SKA Observatory will allow a major breakthrough by mapping the thermal and nonthermal processes in distant universe galaxies, shedding light on the role of the ISM and IGM in the evolution of galaxies. We demonstrate this by simulating the radio continuum and HI emission from local galaxies back to high redshifts. Our simulations show that the AA4 surveys will make it possible to trace the thermal and nonthermal processes of the ISM in galaxies that are analogs to M51 and NGC6946, traced in continuum beyond cosmic noon (z=2-3) and the gas content traced by HI beyond z=1. Both simulations and precursor observations indicate the importance of nonthermal feedback at cosmic noon.

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 / 1 minor

Summary. The manuscript claims that simulations projecting radio continuum and HI emission from local galaxies (M51, NGC6946) to high redshifts demonstrate that SKA AA4 surveys can trace thermal and nonthermal ISM processes in high-z analogs beyond z=2-3 (continuum) and z>1 (HI), with both simulations and precursor data indicating the importance of nonthermal feedback at cosmic noon.

Significance. If the simulations prove robust upon detailed description, this would provide useful forward-looking guidance on SKA's capabilities for studying ISM/IGM evolution and nonthermal processes in galaxies, building on resolved local observations.

major comments (2)
  1. [Abstract] Abstract / simulation description: The detectability claims at z=2-3 rest on unspecified simulations that scale local radio continuum and HI maps to high redshift. No details are provided on methods, input assumptions (including any adjustments for elevated star-formation rates, magnetic field evolution, or cosmic-ray densities), validation against real data, or error estimates, rendering the support for the redshift reach and nonthermal feedback claims difficult to evaluate.
  2. [Abstract] Abstract: The scaling of local M51/NGC6946 radio properties and ISM structure to represent high-z analogs assumes that thermal/nonthermal emission mechanisms and spatial distributions remain sufficiently similar after only cosmological dimming and frequency shifting, without major modifications from different cosmic conditions. This assumption is load-bearing for the central claims but receives no justification or sensitivity testing.
minor comments (1)
  1. The abstract would be clearer if it briefly indicated the simulation technique or key parameters employed when projecting local templates.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments, which identify key areas where the presentation of our methods and assumptions requires strengthening. We address each point below and will make the corresponding revisions.

read point-by-point responses
  1. Referee: [Abstract] Abstract / simulation description: The detectability claims at z=2-3 rest on unspecified simulations that scale local radio continuum and HI maps to high redshift. No details are provided on methods, input assumptions (including any adjustments for elevated star-formation rates, magnetic field evolution, or cosmic-ray densities), validation against real data, or error estimates, rendering the support for the redshift reach and nonthermal feedback claims difficult to evaluate.

    Authors: We agree that the current manuscript does not supply sufficient methodological detail to allow full evaluation of the simulation results. In the revised version we will add an expanded methods section that describes the scaling procedure, the specific input assumptions adopted for star-formation rates, magnetic-field evolution and cosmic-ray densities, the validation steps performed against existing data, and quantitative error estimates. revision: yes

  2. Referee: [Abstract] Abstract: The scaling of local M51/NGC6946 radio properties and ISM structure to represent high-z analogs assumes that thermal/nonthermal emission mechanisms and spatial distributions remain sufficiently similar after only cosmological dimming and frequency shifting, without major modifications from different cosmic conditions. This assumption is load-bearing for the central claims but receives no justification or sensitivity testing.

    Authors: The scaling is presented as a first-order extrapolation that accounts primarily for cosmological surface-brightness dimming and frequency shifting. We acknowledge that explicit justification and sensitivity testing of this assumption are currently absent. The revised manuscript will include a dedicated discussion of the rationale for treating local galaxies as analogs, supported by relevant high-redshift ISM literature, together with sensitivity tests that vary key parameters to quantify the robustness of the reported redshift reach. revision: yes

Circularity Check

0 steps flagged

No circularity: forward simulation of local templates to high-z detectability

full rationale

The paper describes cosmological projection of resolved local radio continuum and HI maps from galaxies like M51 and NGC6946 to demonstrate SKA AA4 survey reach at z>1-3. No equations, fitted parameters, or derivations are presented that reduce the claimed detection thresholds or nonthermal feedback inferences to quantities fitted from the target high-z data itself. The central method is template scaling under stated assumptions about ISM similarity; this is an external modeling choice, not a self-referential loop. No self-citation chain is invoked to justify uniqueness or forbid alternatives. The work is therefore self-contained as a predictive simulation exercise.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Based solely on the abstract, the central claim rests on the domain assumption that local galaxy templates remain representative at high redshift; no free parameters or invented entities are explicitly introduced in the provided text.

axioms (1)
  • domain assumption Local galaxies such as M51 and NGC6946 serve as valid structural and emission analogs for high-redshift galaxies
    The simulations extrapolate observed local properties to z=1-3 without stated adjustments for evolving ISM conditions.

pith-pipeline@v0.9.1-grok · 5833 in / 1328 out tokens · 48623 ms · 2026-06-26T03:40:52.480734+00:00 · methodology

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Reference graph

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