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arxiv: 2512.07239 · v2 · submitted 2025-12-08 · 🌌 astro-ph.HE · astro-ph.EP· astro-ph.GA· astro-ph.SR

Interplay between Escaping Cosmic Rays and Interstellar Medium: Driving of Galactic Winds and Shaping the Local Proton Spectrum

Jiro Shimoda , Katsuaki Asano , Shu-ichiro Inutsuka This is my paper

Pith reviewed 2026-05-17 01:04 UTC · model grok-4.3

classification 🌌 astro-ph.HE astro-ph.EPastro-ph.GAastro-ph.SR
keywords cosmic raysgalactic windsinterstellar mediumsupernova remnantscosmic ray spectrumgalactic halodiffusion coefficient
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The pith

Escaping cosmic rays accelerate and heat the interstellar medium to drive galactic outflows with rates comparable to the star formation rate while offering an alternative account of the local proton spectrum.

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

This paper uses spherically symmetric simulations to examine how cosmic rays escaping from their sources interact with the surrounding interstellar medium. The simulations include the evolution of the cosmic ray energy spectrum along with radiative cooling and thermal conduction. Depending on the diffusion coefficient, cosmic rays can accelerate and heat the gas, potentially explaining unexpected emission lines in old supernova remnants. The resulting gas outflows have rates that can match the galactic star formation rate, supporting the idea of cosmic ray-driven winds that pollute the galactic halo with metals. Additionally, the work suggests that a locally reduced diffusion coefficient and a few nearby sources within the Local Bubble offer an alternative explanation for the cosmic ray proton spectrum observed near Earth.

Core claim

Escaping cosmic rays drive outflows in the interstellar medium with rates comparable to the star formation rate, which is consistent with the galactic wind needed to pollute the halo with metals, and a locally suppressed diffusion coefficient combined with nearby sources can account for the observed local proton spectrum.

What carries the argument

Spherically symmetric CR-hydrodynamical simulations that evolve the CR energy spectrum while including radiative cooling and thermal conduction, showing dependence on the CR diffusion coefficient.

Load-bearing premise

The model assumes a locally suppressed cosmic ray diffusion coefficient and the presence of a few nearby cosmic ray sources inside the Local Bubble to explain the observed local proton spectrum.

What would settle it

Direct measurements showing ISM outflow rates around cosmic ray sources much lower than the galactic star formation rate, or a local proton spectrum that cannot be reproduced even with nearby sources and suppressed diffusion.

Figures

Figures reproduced from arXiv: 2512.07239 by Jiro Shimoda, Katsuaki Asano, Shu-ichiro Inutsuka.

Figure 1
Figure 1. Figure 1: The CR pressure profiles for the cases of D0 = 1026 cm2 s −1 (red), 1027 cm2 s −1 (orange), and 1028 cm2 s −1 (blue). The dashed, solid, and dotted lines are the profiles at t = 0.5 kyr, 10 kyr, and 1 Myr, respec￾tively. 4.1. Acceleration of the fluid and deformation of the cosmic ray spectrum [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 3
Figure 3. Figure 3: Temporal evolutions of the differential CR en￾ergy density, ϵpNcr, for the case of D0 = 1026 cm2 s −1 . The energy transfer by the mechanical work by CRs, −tvg∂rPcr, is also shown by the black curves. The positive −tvg∂rPcr indicates the energy transfer from CRs to the fluid, while the negative value indicates the energy gain of CRs via the compression of the fluid. tion box at t = 1 Myr. This is consisten… view at source ↗
Figure 5
Figure 5. Figure 5: Temporal evolutions of the pressure Pg (the solid black curve) and temperature Tg (the dashed black curve) for D0 = 1027 cm2 s −1 . We also exhibit the CR heat￾ing term t|VA∂rεcr| (red) and the thermal conduction term −(t/r2 )∂r [PITH_FULL_IMAGE:figures/full_fig_p005_5.png] view at source ↗
Figure 4
Figure 4. Figure 4: The solid lines are the volume averaged CR en￾ergy spectrum in the whole simulation box (r ≤ 300 pc) at t = 1 Myr (upper) and 10 Myr (lower) for the cases of D0 = 1026 cm2 s −1 (red), 1027 cm2 s −1 (orange), and 1028 cm2 s −1 (blue). The dotted lines are spectra of the CRs escaped from the simulation box. The dashed thick lines are the sum of the escaped and remaining components. The thin dashed line (blac… view at source ↗
Figure 6
Figure 6. Figure 6: The comparison of the temperature profiles in the cases with (solid) and without (dots) the CR heating for D0 = 1027 cm2 s −1 [PITH_FULL_IMAGE:figures/full_fig_p006_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: The evolutions of the gas temperature (top) and number density (bottom) profiles from t = 10 kyr to 1 Myr for D0 = 1027 cm2 s −1 . CR heating effect. A large difference in the temperature inside the expanding region (cavity) is shown in the fig￾ure. Note that the heating due to the particle-particle collisions, (dϵ/dt)C, is not efficient inside the cavity. The effects of the CR heating with the supersonic … view at source ↗
Figure 10
Figure 10. Figure 10: The total mass expelled by CRs as a function of time. The horizontal dots indicate the expelled mass of 103 M⊙ as a guide. The dashed lines are the total CR energy in the calculation box. temporal evolution of the CR intensity at r = 1 pc for D0 = 1026 cm2 s −1 . Initially, the CR intensity decreases as the inner cavity evolves. At t ∼ 6 Myr, the local CR intensity temporarily increases due to the backflo… view at source ↗
Figure 11
Figure 11. Figure 11: The spectral intensity of the observed proton CRs around the Earth AMS-02 (M. Aguilar et al. 2015) and CALET (O. Adriani et al. 2022) and beyond the termination shock of the solar wind (Voyager I A. C. Cummings et al. 2016). The dashed lines are the intensities of CRs from the source with age of tage and distance of d from the Earth, as￾suming D0 = 1026 cm2 s −1 . The orange solid line represents the sum … view at source ↗
Figure 12
Figure 12. Figure 12: The same as [PITH_FULL_IMAGE:figures/full_fig_p009_12.png] view at source ↗
read the original abstract

We study the effects of escaping cosmic rays (CRs) on the interstellar medium (ISM) around their source with spherically symmetric CR-hydrodynamical simulations taking into account the evolution of the CR energy spectrum, radiative cooling, and thermal conduction. We show how the escaping CRs accelerate and heat the ISM depending on the CR diffusion coefficient. The CR heating effects are potentially responsible for the recent observations of the unexpected H$\alpha$ and [OIII]$\lambda5007$ lines in old supernova remnants. The implied gas outflow rate by CRs can be comparable to the Galactic star formation rate, compatible with the Galactic wind required for polluting the halo gas with metals. Assuming a locally suppressed CR diffusion and a few nearby CR sources in the Local Bubble, we also propose alternative interpretations for the Galactic CR proton spectrum around the Earth measured with CALET, AMS02, and Voyager 1.

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 presents spherically symmetric CR-hydrodynamical simulations that evolve the CR energy spectrum while including radiative cooling and thermal conduction. It examines how escaping CRs accelerate and heat the ISM around sources as a function of the diffusion coefficient, links this to observed Hα and [OIII] emission in old supernova remnants, claims that the resulting gas outflow rates can reach values comparable to the Galactic star-formation rate and thereby drive winds capable of polluting the halo with metals, and offers an alternative explanation for the local proton spectrum measured by CALET, AMS02, and Voyager 1 by invoking locally suppressed diffusion together with a small number of nearby sources inside the Local Bubble.

Significance. If the local CR-ISM coupling results are robust, the work would strengthen the case for CR-driven feedback in the ISM and provide a physically motivated route to interpreting both galactic-scale winds and the local CR spectrum. The explicit inclusion of spectral evolution, cooling, and conduction is a methodological strength that goes beyond simpler steady-state treatments. The global outflow-rate claim, however, rests on an extrapolation whose quantitative support is not yet demonstrated within the manuscript.

major comments (2)
  1. [Discussion of implied gas outflow rates] The assertion that CR-driven outflows can reach rates comparable to the Galactic SFR (∼1–3 M⊙ yr⁻¹) is made on the basis of spherically symmetric 1D simulations around individual sources. No integration over the Galactic supernova distribution, disk scale height, or collective streaming is performed, so the Galaxy-wide mass-loss rate remains an untested extrapolation. This step is load-bearing for the galactic-wind and halo-pollution conclusion.
  2. [Section proposing interpretation of CALET/AMS02/Voyager 1 spectrum] The alternative interpretation of the local proton spectrum invokes a locally suppressed diffusion coefficient and a few nearby sources inside the Local Bubble. The manuscript does not quantify how these assumptions affect the predicted spectrum relative to standard propagation models or demonstrate that they are required by the data rather than chosen to fit it.
minor comments (2)
  1. [Methods / Simulation setup] Numerical methods, grid resolution, convergence tests, and the precise functional form and normalization of the diffusion coefficient are not described in sufficient detail for independent reproduction of the reported outflow rates and spectral shapes.
  2. [Results on CR heating and emission lines] The manuscript would benefit from a direct comparison of the simulated Hα and [OIII] luminosities or line ratios with the specific observational data cited for old supernova remnants.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive and detailed report. Below we respond point by point to the major comments, indicating the revisions we will incorporate to address the concerns while preserving the scope of the present study.

read point-by-point responses

  1. Referee: [Discussion of implied gas outflow rates] The assertion that CR-driven outflows can reach rates comparable to the Galactic SFR (∼1–3 M⊙ yr⁻¹) is made on the basis of spherically symmetric 1D simulations around individual sources. No integration over the Galactic supernova distribution, disk scale height, or collective streaming is performed, so the Galaxy-wide mass-loss rate remains an untested extrapolation. This step is load-bearing for the galactic-wind and halo-pollution conclusion.

    Authors: We agree that a complete Galaxy-wide integration lies outside the present work. Our 1D simulations quantify the local mass flux driven by escaping CRs for a range of diffusion coefficients; the statement that this flux can reach levels comparable to the Galactic SFR follows from a simple scaling with the supernova rate per unit volume and the characteristic size of the affected region. In the revised manuscript we will expand the discussion to make this scaling explicit, include an order-of-magnitude estimate that incorporates the disk scale height, and clearly state the limitations arising from the neglect of collective streaming and source clustering. We believe this addition will clarify the extrapolation without requiring a full galactic simulation. revision: partial

  2. Referee: [Section proposing interpretation of CALET/AMS02/Voyager 1 spectrum] The alternative interpretation of the local proton spectrum invokes a locally suppressed diffusion coefficient and a few nearby sources inside the Local Bubble. The manuscript does not quantify how these assumptions affect the predicted spectrum relative to standard propagation models or demonstrate that they are required by the data rather than chosen to fit it.

    Authors: The proposed scenario is offered as a physically motivated alternative that reproduces the observed spectral shape when diffusion is reduced inside the Local Bubble, consistent with independent evidence for suppressed transport in that region. To address the referee’s concern we will add a quantitative comparison: we will show the propagated proton spectrum obtained with our locally suppressed diffusion coefficient and a small number of nearby sources, and contrast it directly with a standard propagation model that assumes uniform diffusion throughout the Galaxy. The revised text will also clarify that the parameters are chosen to be consistent with existing constraints rather than tuned exclusively to the data, while acknowledging that other explanations remain viable. revision: yes

Circularity Check

0 steps flagged

Forward CR-hydro simulations produce outflow rates and spectral shapes from explicit input assumptions without definitional reduction

full rationale

The paper runs spherically symmetric CR-hydrodynamical simulations that evolve the CR spectrum, cooling, and conduction as functions of an input diffusion coefficient and source placement. Outflow rates emerge as simulation outputs rather than being defined to match any target observation; the local proton spectrum is interpreted by adopting (not fitting) a suppressed diffusion coefficient and a small number of nearby sources inside the Local Bubble. No equation reduces an output quantity to a fitted parameter by construction, no self-citation supplies a uniqueness theorem that forces the result, and no ansatz is smuggled in. The global extrapolation to a Galaxy-wide wind rate comparable to the SFR is an interpretive step outside the local model, but it does not create circularity within the derivation itself.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The model rests on standard spherically symmetric hydrodynamics plus cosmic-ray transport with an adjustable diffusion coefficient; no new particles or forces are introduced.

free parameters (1)
  • CR diffusion coefficient
    Varied across simulations to demonstrate dependence of acceleration, heating, and outflow on its value; central to both wind and local-spectrum claims.
axioms (1)
  • standard math Spherically symmetric CR-hydrodynamical equations including radiative cooling and thermal conduction
    Invoked as the governing equations for the numerical setup around a source.

pith-pipeline@v0.9.0 · 5480 in / 1241 out tokens · 39770 ms · 2026-05-17T01:04:37.286414+00:00 · methodology

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Works this paper leans on

3 extracted references · 3 canonical work pages · 1 internal anchor

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    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1103/physrevlett.111.021103 2017