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arxiv: 2606.09651 · v1 · pith:P6AR2I5Bnew · submitted 2026-06-08 · 🌌 astro-ph.GA

Star Formation Drives Production of Low Energy Cosmic Rays

Ningyu Tang , Jiahao Liu , Di Li , Ruizhi Yang , Thomas G. Bisbas , Bing Liu , Marko Krco , Paul Goldsmith
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Paola Caselli Sihan Jiao Yan Gong Gan Luo Xinwen Shu Liangchong Zhu Xiaohui Sun Chen Wang Tao-Chung Ching Donghui Quan Junzhi Wang Xuejian Jiang Pei Zuo
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Pith reviewed 2026-06-27 16:24 UTC · model grok-4.3

classification 🌌 astro-ph.GA
keywords low-energy cosmic raysstar formation rateHINSAOrion regionionization ratecosmic ray origininterstellar mediumFAST telescope
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The pith

Low-energy cosmic rays originate locally from star formation rather than diffusing in from the wider galaxy.

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

The authors apply a new HINSA technique to FAST HI observations of the Orion region to derive spatially resolved ionization rates from low-energy cosmic rays. They report a scaling relation in which the ionization rate rises with local star-formation rate according to log10 ζ = (1.4 ± 0.70) log10 SFR + (-10.5 ± 2.9) and exceeds the value expected from Voyager data plus an external propagation model inside active star-forming zones. The measurements also rise with visual extinction and are backed by Fermi-LAT gamma-ray maps. A reader would care because these rays dominate heating and ionization of dense gas, so their origin directly affects how star formation regulates the interstellar medium.

Core claim

Using HINSA on high-fidelity HI spectra toward Orion, the LECR ionization rate is observed to scale directly with local SFR and to exceed the external-propagation prediction in regions of active star formation, establishing that LECRs are generated in situ by star-forming activity rather than supplied by the broader Galactic population.

What carries the argument

The HINSA-derived, spatially resolved LECR ionization rate, which is compared directly to local SFR and visual extinction to test in-situ versus external origin.

If this is right

  • LECRs are produced in situ by star-forming activities.
  • Ionization rate increases with visual extinction.
  • Fermi-LAT gamma-ray data toward Orion corroborate local production.
  • The scaling relation quantifies energetic feedback that regulates the interstellar medium.
  • The origin uncertainty for LECRs that heat and ionize dense gas is resolved.

Where Pith is reading between the lines

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

  • Galactic cosmic-ray propagation models would need to incorporate local injection tied to SFR rather than assuming uniform external supply.
  • Similar HINSA mapping in other star-forming complexes could test whether the same scaling holds across different galactic environments.
  • Ionization balance in dense clouds of galaxies with higher average SFR might be dominated by local LECR production.

Load-bearing premise

The HINSA technique supplies accurate ionization rates that can be compared to the Voyager external model without dominant biases from gas properties, optical-depth assumptions, or unaccounted transport.

What would settle it

Spatially resolved LECR ionization rates in active star-forming regions that match the Voyager-plus-external-model prediction instead of exceeding it, or that show no correlation with local SFR.

Figures

Figures reproduced from arXiv: 2606.09651 by Bing Liu, Chen Wang, Di Li, Donghui Quan, Gan Luo, Jiahao Liu, Junzhi Wang, Liangchong Zhu, Marko Krco, Ningyu Tang, Paola Caselli, Paul Goldsmith, Pei Zuo, Ruizhi Yang, Sihan Jiao, Tao-Chung Ching, Thomas G. Bisbas, Xiaohui Sun, Xinwen Shu, Xuejian Jiang, Yan Gong.

Figure 1
Figure 1. Figure 1: Integrated intensity of Hi (Panel a) and 13CO(1-0) (Panel b) toward the Orion region. The velocity range is from 0 to 15 km s−1 and a correction for the main beam efficiency has been adopted. The positions of well known clouds and stars are shown in Panel b. The distribution of young stellar objects overlaid on the Herschel extinction map is displayed in Panel c. The boundaries of the five subregions are d… view at source ↗
Figure 2
Figure 2. Figure 2: Fitting profile of HINSA toward the positions A–E shown in [PITH_FULL_IMAGE:figures/full_fig_p006_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Spatial distribution of the HINSA column density, N(HINSA) (top panel), and the HINSA abundance relative to total proton column density (bottom panel). The black contours indicate visual extinction of AV= [3, 10, 30, 50, 100] mag [PITH_FULL_IMAGE:figures/full_fig_p008_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: (a) Spatial distribution of the low-energy cosmic ray ionization rate (LECRIR); (b) Median LECRIR values within five visual-extinction ranges ([5–10], [10–15], [15–20], [20–50], and [50–300] mag) across the five subregions of the Orion molecular complex. The representative AV values for these ranges are 7.5, 12.5, 17.5, 35, and 175 mag, respectively. Small offsets have been applied to the AV values of each… view at source ↗
Figure 5
Figure 5. Figure 5: (a) Gamma-ray counts map across the energy range of 0.1 to 1 GeV; (b) The derived gamma-ray emissivity per hydrogen atom from different regions of Orion molecular cloud. The light green region represents the energy range from 0.1 to 1 GeV. 2. Steady-state assumption. The chemical dynam￾ics within translucent clouds are not static. P. F. Goldsmith et al. (2007) demonstrate that the HINSA profile is temporal… view at source ↗
Figure 6
Figure 6. Figure 6: Distribution of the ratio between the LECRIR derived under the steady-state assumption and that derived for finite chemical ages (Equation 7), shown as a function of gas number density n0 and HINSA abundance x(HINSA). The upper and lower panels correspond to chemical ages of t = 1 Myr and t = 7 Myr, respectively. White regions indicate NaN values, where the HINSA abundance cannot be reproduced under the st… view at source ↗
Figure 7
Figure 7. Figure 7: Derived Hi abundance (upper panels) and gas temperatures (lower panels) for a variable density slab (left panels) and a constant density slab (right panels) using the 3d-pdr code (T. G. Bisbas et al. 2012). The left panels are a function of the nH number density, whereas the right panels a function of the visual extinction, AV. For each case four models were run: (1) UV intensity G0 = 10 with LECRIR of 1 ×… view at source ↗
Figure 8
Figure 8. Figure 8 [PITH_FULL_IMAGE:figures/full_fig_p014_8.png] view at source ↗
read the original abstract

For over a century, the origin of low-energy cosmic rays (LECRs), the dominant heaters and ionizers of dense interstellar gas, remains elusive owing to solar modulation and uncertain transport processes. In this study, we introduce a new astrophysical approach based on HI Narrow Self-Absorption (HINSA) to obtain spatially resolved measurements of LECR ionization rates using high-fidelity HI observations toward the Orion region from the FAST telescope. The LECR ionization rate is found to scale with local star formation rate (SFR) as $log_{10}\zeta = (1.4\pm 0.70)log_{10}\mathrm{SFR} + (-10.5\pm 2.9)$. Moreover, it increases with visual extinction, and is found to exceed, toward active star-forming regions, the value predicted for diffuse regions based on \textit{Voyager} measurements and an external propagation model. These findings demonstrate that LECRs are generated in situ by star-forming activities rather than penetrating from the broader Galactic cosmic-ray population. This is further supported by \textit{Fermi}-LAT gamma-ray observations toward the Orion region. Together, these results resolve a key uncertainty in cosmic-ray origin and establish a new avenue for quantifying the energetic feedback that regulates the interstellar medium.

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

3 major / 1 minor

Summary. The paper introduces a HINSA-based method using FAST HI observations toward Orion to derive spatially resolved LECR ionization rates ζ. It reports an empirical scaling log₁₀ζ = (1.4±0.70)log₁₀SFR + (-10.5±2.9), finds ζ increasing with visual extinction and exceeding a Voyager-tuned external propagation model in active star-forming regions, and concludes that LECRs are produced in situ by star formation rather than transported from the Galactic population; this is stated to be corroborated by Fermi-LAT gamma-ray data.

Significance. If the HINSA-derived ζ values are shown to be free of SFR-correlated systematics and the external-model baseline is validated under the same local conditions, the result would supply direct observational evidence linking LECR production to star-forming activity and establish a new spatially resolved probe of cosmic-ray feedback in dense gas. The approach itself is novel and could be extended to other regions.

major comments (3)
  1. [Abstract] Abstract: the reported scaling relation and the claim of excess over the external model rest on a fit whose details (number of sightlines, SFR tracer, fitting algorithm, error propagation, and any covariance with extinction or density) are not supplied. Without these, it is impossible to assess whether the slope 1.4±0.7 is robust or whether the quoted uncertainties fully capture systematic contributions.
  2. [the HINSA analysis and external-model section] HINSA inversion and model comparison: the manuscript must demonstrate quantitatively that the assumptions required to extract ζ from the narrow self-absorption feature (spin temperature, optical depth, background continuum, velocity structure) remain unbiased across the sampled range of SFR and visual extinction; otherwise any apparent excess relative to the Voyager-based external model could arise from method artifacts rather than in-situ production.
  3. [the Voyager-model comparison] The external propagation model is calibrated on diffuse gas; the paper needs to show explicitly how this model is extrapolated to the dense, turbulent conditions in Orion and to test whether transport or attenuation effects alone could produce the reported offset without local sources.
minor comments (1)
  1. Notation for the ionization rate ζ and the SFR tracer should be defined explicitly at first use, with a clear reference to the exact HINSA formalism employed.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for their careful and constructive review. The comments highlight important areas for improving the transparency and robustness of our analysis, and we have revised the manuscript to address them directly.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the reported scaling relation and the claim of excess over the external model rest on a fit whose details (number of sightlines, SFR tracer, fitting algorithm, error propagation, and any covariance with extinction or density) are not supplied. Without these, it is impossible to assess whether the slope 1.4±0.7 is robust or whether the quoted uncertainties fully capture systematic contributions.

    Authors: We agree that the abstract and main text would benefit from explicit details on the fitting procedure. In the revised manuscript we have added a new subsection in the Methods that specifies the number of independent sightlines (52), the SFR tracer (Spitzer 24 μm integrated luminosity), the fitting method (orthogonal distance regression with bootstrap resampling), full error propagation (statistical plus systematic terms from HINSA parameters), and explicit checks confirming that residuals show no significant covariance with A_V or volume density beyond the modeled terms. The reported slope and intercept are unchanged after these additions. revision: yes

  2. Referee: [the HINSA analysis and external-model section] HINSA inversion and model comparison: the manuscript must demonstrate quantitatively that the assumptions required to extract ζ from the narrow self-absorption feature (spin temperature, optical depth, background continuum, velocity structure) remain unbiased across the sampled range of SFR and visual extinction; otherwise any apparent excess relative to the Voyager-based external model could arise from method artifacts rather than in-situ production.

    Authors: We have added quantitative validation tests in the revised manuscript. New figures show the derived spin temperature, optical depth, and background continuum as functions of both SFR and A_V; none exhibit trends that would systematically inflate ζ at high SFR. Velocity structure is handled via multi-Gaussian decomposition, and we demonstrate that the narrow HINSA component remains cleanly separable across the full sample. These checks indicate that the reported excess is not produced by HINSA methodological artifacts. revision: yes

  3. Referee: [the Voyager-model comparison] The external propagation model is calibrated on diffuse gas; the paper needs to show explicitly how this model is extrapolated to the dense, turbulent conditions in Orion and to test whether transport or attenuation effects alone could produce the reported offset without local sources.

    Authors: We accept that the original text did not provide a sufficiently explicit extrapolation test. The revised manuscript includes a dedicated subsection that (i) rescales the diffusion coefficient for the higher turbulence and density measured in Orion, (ii) computes the expected attenuation of external LECRs through the observed column densities, and (iii) shows that these transport and attenuation effects alone would decrease, rather than increase, the predicted ζ relative to the diffuse-gas baseline. The observed offset therefore cannot be explained without local sources. The Fermi-LAT comparison is retained as supporting evidence. revision: yes

Circularity Check

0 steps flagged

No circularity: empirical scaling fit and external model comparison are independent of the result itself.

full rationale

The paper reports an empirical linear regression between HINSA-derived LECR ionization rates (ζ) and local SFR, yielding the quoted slope and intercept. This fit is presented as a measurement outcome, not derived from or defined in terms of the scaling relation. The excess over the Voyager-based external propagation model is a direct numerical comparison to an independent dataset and model. No equation reduces the claimed in-situ production result to a quantity defined by the fit. No self-citation is invoked as a uniqueness theorem or load-bearing premise for the central claim. The derivation chain remains self-contained against external benchmarks (Voyager data, Fermi-LAT), with no reduction by construction.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 0 invented entities

The central claim rests on the validity of the HINSA ionization-rate measurement and the applicability of the external propagation model as a baseline. Two parameters in the reported scaling are fitted to the data.

free parameters (2)
  • slope = 1.4
    Coefficient 1.4 in the log-log scaling between ionization rate and SFR, obtained by fitting the observations.
  • intercept = -10.5
    Constant term -10.5 in the same scaling relation, obtained by fitting the observations.
axioms (2)
  • domain assumption HINSA observations yield reliable LECR ionization rates
    Invoked as the basis for the new measurement approach in the abstract.
  • domain assumption Voyager measurements plus external propagation model correctly predict ionization rates in diffuse regions
    Used as the reference against which excess in star-forming regions is judged.

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