Cosmic ray induced ionisation of a molecular cloud shocked by the W28 supernova remnant

Abstract

Cosmic rays are an essential ingredient in the evolution of the interstellar medium, as they dominate the ionisation of the dense molecular gas, where stars and planets form. However, since they are efficiently scattered by the galactic magnetic fields, many questions remain open, such as where exactly they are accelerated, what is their original energy spectrum, and how they propagate into molecular clouds. In this work we present new observations and discuss in detail a method that allows us to measure the cosmic ray ionisation rate towards the molecular clouds close to the W28 supernova remnant. To perform these measurements, we use CO, HCO${}^{+}$, and DCO${}^{+}$ millimetre line observations and compare them with the predictions of radiative transfer and chemical models away from thermodynamical equilibrium. The CO observations allow us to constrain the density, temperature, and column density towards each observed position, while the DCO${}^{+}$/HCO${}^{+}$ abundance ratios provide us with constraints on the electron fraction and, consequently, on the cosmic ray ionisation rate. Towards positions located close to the supernova remnant, we find cosmic ray ionisation rates much larger ($\gtrsim 100$) than those in standard galactic clouds. Conversely, towards one position situated at a larger distance, we derive a standard cosmic ray ionisation rate. Overall, these observations support the hypothesis that the $\gamma$ rays observed in the region have a hadronic origin. In addition, based on CR diffusion estimates, we find that the ionisation of the gas is likely due to $0.1-1$ GeV cosmic rays. Finally, these observations are also in agreement with the global picture of cosmic ray diffusion, in which the low-energy tail of the cosmic ray population diffuses at smaller distances than the high-energy counterpart.

arXiv commentAccepted to A\&A

References in corpus (36)

• The chemical composition of the Sun
• The CO-to-H2 Conversion Factor
• The Milky Way in Molecular Clouds: A New Complete CO Survey
• The Interstellar Environment of our Galaxy
• Detection of the Characteristic Pion-Decay Signature in Supernova Remnants
• Rotational quenching of CO due to H${}_2$ collisions
• Cosmic-ray ionization of molecular clouds
• Investigating the Cosmic-Ray Ionization Rate in the Galactic Diffuse Interstellar Medium through Observations of H3+
• Enhanced cosmic-ray flux toward zeta Persei inferred from laboratory study of H3+ - e- recombination rate
• Thanatology in Protoplanetary Discs: the combined influence of Ohmic, Hall, and ambipolar diffusion on dead zones
• Discovery of very high energy gamma-ray emission coincident with molecular clouds in the W28 (G6.4-0.1) field
• Observations of the young supernova remnant RX J1713.7-3946 with the Fermi Large Area Telescope
• Polarization Observations of 1720 MHz OH Masers toward the Three Supernova Remnants W28, W44, and IC443
• Discovery of 35 New Supernova Remnants in the Inner Galaxy
• Fermi LAT Observations of the Supernova Remnant W28 (G6.4-0.1)
• The effect of uncertainties on chemical models of dark clouds
• A Detailed Study of the Molecular and Atomic Gas Toward the γ-ray SNR RX J1713.7-3946: Spatial TeV γ-ray and ISM Gas Correspondence
• Gamma ray emission from SNR RX J1713.7-3946 and the origin of galactic cosmic rays
• Shock Excited Maser Emission from the Supernova Remnant W28
• Gamma rays from molecular clouds illuminated by accumulated diffusive protons from supernova remnant W28
• Investigation of the large-scale neutral hydrogen near the supernova remnant W28
• Formaldehyde and methanol deuteration in protostars: fossiles from a past fast high density pre-collapse phase
• Ortho-H2 and the Age of Interstellar Dark Clouds
• Nitrogen hydrides and the H2 ortho-to-para ratio in dark clouds
• Theoretical HDO emission from low-mass protostellar envelopes
• AGILE detection of GeV gamma-ray emission from the SNR W28
• Anisotropic CR diffusion and gamma-ray production close to supernova remnants, with an application to W28
• Supernova enhanced cosmic ray ionization and induced chemistry in a molecular cloud of W51C
• Investigating the Cosmic-Ray Ionization Rate Near the Supernova Remnant IC 443 Through H3+ Observations
• ROSAT/Asca Observations of the Mixed-Morphology Supernova Remnant W28
• Further Evidence for Chemical Fractionation from Ultraviolet Observations of Carbon Monoxide
• Bistability in Interstellar Gas-Phase Chemistry
• Chemical sensitivity to the ratio of the cosmic-ray ionization rates of He and H2 in dense clouds
• Cosmic-ray propagation in molecular clouds
• Radio continuum emission from the central stars of M20 and the detection of a new supernova remnant near M20
• Star Formation in the Trifid Nebula

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