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The double signature of local cosmic-ray acceleration in star-forming regions
High Energy Astrophysical Phenomena · Submitted 15 Mar 2021
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim Beyond the modelling of the OMC-2 FIR 3/FIR 4 system, we show how the combination of continuum observations at cm wavelengths and molecular transitions is a powerful new tool for the analysis of star-forming regions: these two types of observations can be simultaneously interpreted by invoking only the presence of locally accelerated CRs, without having to resort to shock-generated UV photons.
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Recently, there has been an increased interest in the study of the generation of low-energy cosmic rays (CRs; < 1 TeV) in shocks situated on the surface of a protostar or along protostellar jets. These locally accelerated CRs offer an attractive explanation for the high levels of non-thermal emission and ionisation rate, $\zeta$, observed close to these sources. The high $\zeta$ observed in some protostellar sources is generally attributed to shock-generated UV photons. The aim of this article is to show that when synchrotron emission and a high $\zeta$ are measured in the same spatial region, a locally shock-accelerated CR flux is sufficient to explain both phenomena. We assume that relativistic particles are accelerated according to the first-order Fermi acceleration mechanism and compute $\zeta$ and the non-thermal emission at cm wavelengths. We then apply our model to the star-forming region OMC-2 FIR 3/FIR 4. Using a Bayesian analysis, we constrain the parameters of the model and estimate the spectral indices of the non-thermal radio emission. We demonstrate that the local CR acceleration model makes it possible to simultaneously explain the synchrotron emission along the HOPS 370 jet within the FIR 3 region and $\zeta$ observed near the FIR 4 protocluster. Our model constrains the magnetic field strength (~250-450$~\mu$G), its turbulent component (~20-40$~\mu$G), and the jet velocity in the shock reference frame for the three non-thermal sources of the HOPS 370 jet (~350-1000 km s$^{-1}$). Beyond the modelling of the OMC-2 FIR 3/FIR 4 system, we show how the combination of continuum observations at cm wavelengths and molecular transitions is a powerful new tool for the analysis of star-forming regions: these two types of observations can be simultaneously interpreted by invoking only the presence of locally accelerated CRs, without having to resort to shock-generated UV photons.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Recently, there has been an increased interest in the study of the generation of low-energy cosmic rays (CRs; < 1 TeV) in shocks situated on the surface of a protostar or along protostellar jets. | background 1.00 | 0.04 | 0.02 | asserted 0.95 |
| s1 | These locally accelerated CRs offer an attractive explanation for the high levels of non-thermal emission and ionisation rate, $\zeta$, observed close to these sources. | background 0.93 | 0.07 | 0.05 | hedged possibility 0.60 |
| s2 | The high $\zeta$ observed in some protostellar sources is generally attributed to shock-generated UV photons. | background 0.99 | 0.05 | 0.02 | asserted 0.86 |
| s3 | The aim of this article is to show that when synchrotron emission and a high $\zeta$ are measured in the same spatial region, a locally shock-accelerated CR flux is sufficient to explain both phenomena. | contribution 0.97 | 0.27 | 0.39 | asserted 0.92 |
| s4 | We assume that relativistic particles are accelerated according to the first-order Fermi acceleration mechanism and compute $\zeta$ and the non-thermal emission at cm wavelengths. | method 1.00 | 0.92 | 0.03 | asserted 0.96 |
| s5 | We then apply our model to the star-forming region OMC-2 FIR 3/FIR 4. | method 0.52 | 0.85 | 0.03 | asserted 0.66 |
| s6 | Using a Bayesian analysis, we constrain the parameters of the model and estimate the spectral indices of the non-thermal radio emission. | method 0.99 | 0.96 | 0.04 | asserted 0.94 |
| s7 | We demonstrate that the local CR acceleration model makes it possible to simultaneously explain the synchrotron emission along the HOPS 370 jet within the FIR 3 region and $\zeta$ observed near the FIR 4 protocluster. | result 0.96 | 0.93 | 0.59 | asserted 0.99 |
| s8 | Our model constrains the magnetic field strength (~250-450$~\mu$G), its turbulent component (~20-40$~\mu$G), and the jet velocity in the shock reference frame for the three non-thermal sources of the HOPS 370 jet (~350-1000 km s$^{-1}$). | result 1.00 | 0.95 | 0.08 | asserted 1.00 |
| s9 | Beyond the modelling of the OMC-2 FIR 3/FIR 4 system, we show how the combination of continuum observations at cm wavelengths and molecular transitions is a powerful new tool for the analysis of star-forming regions: these two types of observations can be simultaneously interpreted by invoking only the presence of locally accelerated CRs, without having to resort to shock-generated UV photons. | interpretation 0.84 | 0.88 | 0.59 | asserted 1.00 |
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Original abstract
Recently, there has been an increased interest in the study of the generation of low-energy cosmic rays (CRs; < 1 TeV) in shocks situated on the surface of a protostar or along protostellar jets. These locally accelerated CRs offer an attractive explanation for the high levels of non-thermal emission and ionisation rate, $\zeta$, observed close to these sources. The high $\zeta$ observed in some protostellar sources is generally attributed to shock-generated UV photons. The aim of this article is to show that when synchrotron emission and a high $\zeta$ are measured in the same spatial region, a locally shock-accelerated CR flux is sufficient to explain both phenomena. We assume that relativistic particles are accelerated according to the first-order Fermi acceleration mechanism and compute $\zeta$ and the non-thermal emission at cm wavelengths. We then apply our model to the star-forming region OMC-2 FIR 3/FIR 4. Using a Bayesian analysis, we constrain the parameters of the model and estimate the spectral indices of the non-thermal radio emission. We demonstrate that the local CR acceleration model makes it possible to simultaneously explain the synchrotron emission along the HOPS 370 jet within the FIR 3 region and $\zeta$ observed near the FIR 4 protocluster. Our model constrains the magnetic field strength (~250-450$~\mu$G), its turbulent component (~20-40$~\mu$G), and the jet velocity in the shock reference frame for the three non-thermal sources of the HOPS 370 jet (~350-1000 km s$^{-1}$). Beyond the modelling of the OMC-2 FIR 3/FIR 4 system, we show how the combination of continuum observations at cm wavelengths and molecular transitions is a powerful new tool for the analysis of star-forming regions: these two types of observations can be simultaneously interpreted by invoking only the presence of locally accelerated CRs, without having to resort to shock-generated UV photons.
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This method has been applied to observations carried out with the Atacama Pathfinder EXperiment (APEX) and IRAM-30m telescopes for a large sample of massive star-forming regions, obtaining $7×10^-18≲ζ/$s$^-1≲6×10^-17$ [ref] .
Survey of ortho-H$_2$D$^+$ in high-mass star-forming regions · Introduction · 0.86
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