The cosmic-ray ionisation rate in the pre-stellar core L1544

Abstract

Context. Cosmic rays (CRs) play an important role in the chemistry and dynamics of the interstellar medium. In dense environments, they represent the main ionising agent, driving the rich chemistry of molecular ions and determining the ionisation fraction, which regulates the degree of coupling between the gas and magnetic fields. Estimates of the CR ionisation rate (${\zeta }_2$) span several orders of magnitude, depending on the targeted sources and on the used method. Aims. Recent theoretical models have characterised the CR attenuation with increasing density. We aim to test these models for the attenuation of CRs in the low-mass pre-stellar core L1544. Methods. We use a state-of-the-art gas-grain chemical model, which accepts the CR ionisation rate profile as input, to predict the abundance profiles of four ions: ${\mathrm{N}}_2{\mathrm{H}}^{+}$, ${\mathrm{N}}_2{\mathrm{D}}^{+}$, $\mathrm{H}{\mathrm{C}}^{18}{\mathrm{O}}^{+}$, and $\mathrm{DC}{\mathrm{O}}^{+}$. Non-LTE radiative transfer is performed to produce synthetic spectra based on the derived abundances. These are compared with observations obtained with the Institut de Radioastronomie Millimétrique (IRAM) 30m telescope. Results. Our results indicate that a model with ${\zeta }_2>10^{-16}{\mathrm{s}}^{-1}$ is excluded by the observations. Also the model with the standard ${\zeta }_2=1.3\times 10^{-17}{\mathrm{s}}^{-1}$ produces a worse agreement with respect to the attenuation model based on Voyager observations, which has an average ${\zeta }_2=3\times 10^{-17}{\mathrm{s}}^{-1}$ at the column densities typical of L1544. The single-dish data, however, are not sensitive to the attenuation of the CR profile, which changes only by a factor of two in the range of column densities spanned by the core model. Interferometric observations at higher spatial resolution, combined with observations of transitions with lower critical density are needed to observe a decrease of ${\zeta }_2$ with density.

Accepted in A&A on 15 Sept. 2021

References in corpus (12)

• The Critical Density and the Effective Excitation Density of Commonly Observed Molecular Dense Gas Tracers
• Observing the gas temperature drop in the high-density nucleus of L 1544
• H3+ in Diffuse Interstellar Clouds: a Tracer for the Cosmic-Ray Ionization Rate
• A Large Catalog of Accurate Distances to Molecular Clouds from PS1 Photometry
• The dynamics of collapsing cores and star formation
• Chemical differentiation in a prestellar core traces non-uniform illumination
• Benchmarking spin-state chemistry in starless core models
• The central 1000 AU of a pre-stellar core revealed with ALMA. I. 1.3 mm continuum observations
• The Ionization Fraction of Barnard 68: Implications for Star and Planet Formation
• Rapid Elimination of Small Dust Grains in Molecular Clouds
• Rigorous theory for secondary cosmic-ray ionization
• Search for grain growth towards the center of L1544

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