The impact of attenuation on cosmic-ray chemistry: I. Abundances and chemical calibrators in molecular clouds

Abstract

The chemistry of shielded molecular gas is primarily driven by energetic, charged particles dubbed cosmic rays (CRs), in particular those with energies under 1 GeV. CRs ionize molecular hydrogen and helium, the latter of which contributes greatly to the destruction of molecules. CR ionization initiates a wide range of gas-phase chemistry, including pathways important for the so-called "carbon cycle", C${}^{+}$/C/CO. Therefore, the CR ionization rate, $\zeta$, is fundamental in theoretical and observational astrochemistry. Although observational methods show a wide range of ionization rates -- varying with the environment, especially decreasing into dense clouds -- astrochemical models often assume a constant rate. To address this limitation, we employ a post-processed gas-phase chemical model of a simulated dense molecular cloud that incorporates CR energy losses within the cloud. This approach allows us to investigate changes in abundance profiles of important chemical tracers and gas temperature. Furthermore, we analyze analytical calibrators for estimating $\zeta$ in dense molecular gas that are robust when tested against a full chemical network. Additionally, we provide improved estimations of the electron fraction in dense gas for better consistency with observational data and theoretical calibrations for UV-shielded regions.

arXiv commentAccepted to A&A

References in corpus (44)

• The UMIST database for astrochemistry 2012
• 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
• H3+ in Diffuse Interstellar Clouds: a Tracer for the Cosmic-Ray Ionization Rate
• Herschel Survey of Galactic OH+, H2O+, and H3O+: Probing the Molecular Hydrogen Fraction and Cosmic-Ray Ionization Rate
• Cosmic-ray ionisation in circumstellar discs
• Photodissociation and X-Ray Dominated Regions
• The cosmic ray ionization rate in the Galactic disk, as determined from observations of molecular ions
• Effective destruction of CO by cosmic rays: implications for tracing H${}_2$ gas in the Universe
• Interstellar dust charging in dense molecular clouds: cosmic ray effects
• 3D-PDR: A new three-dimensional astrochemistry code for treating Photodissociation Regions
• A Simple and Accurate Network for Hydrogen and Carbon Chemistry in the ISM
• SILCC VI -- Multi-phase ISM structure, stellar clustering, and outflows with supernovae, stellar winds, ionising radiation and cosmic rays
• Chemistry in Cosmic-Ray Dominated Regions (CRDRs)
• The Deuterium Fractionation Timescale in Dense Cloud Cores: A Parameter Space Exploration
• CO/H2, C/CO, OH/CO, and OH/O2 in Dense Interstellar Gas: From High Ionization to Low Metallicity
• Observing a column-dependent zeta in dense interstellar sources: the case of the Horsehead Nebula
• GMC Collisions as Triggers of Star Formation. II. 3D Turbulent, Magnetized Simulations
• Cosmic rays in molecular clouds probed by H${}_2$ rovibrational lines -- Perspectives for the James Webb Space Telescope
• Penetration of cosmic rays into dense molecular clouds: role of diffuse envelope
• The Deuterium Fraction in Massive Starless Cores and Dynamical Implications
• Cosmic ray penetration in diffuse clouds
• Photodissociation Region Diagnostics Across Galactic Environments
• The Astrochemical Impact of Cosmic Rays in Protoclusters I: Molecular Cloud Chemistry
• Chemical Analysis of a Diffuse Cloud along a Line of Sight Toward W51: Molecular Fraction and Cosmic-Ray Ionization Rate
• Gas and dust temperature in pre-stellar cores revisited: New limits on cosmic-ray ionization rate
• Diffusive Versus Free-Streaming Cosmic Ray Transport in Molecular Clouds
• The cosmic-ray ionisation rate in the pre-stellar core L1544
• Are Infrared Dark Clouds Really Quiescent?
• A new proxy to estimate the cosmic-ray ionisation rate in dense cores
• Probing the physics of star formation (ProPStar): I. First resolved maps of the electron fraction and cosmic-ray ionization rate in NGC 1333
• Observational signatures of cosmic ray interactions in molecular clouds
• The impact of cosmic-ray attenuation on the carbon cycle emission in molecular clouds
• Ionization toward the high-mass star-forming region NGC 6334 I
• Astrochemical modelling of infrared dark clouds
• Parsec-scale cosmic-ray ionisation rate in Orion
• The evolution of HCO${}^{+}$ in molecular clouds using a novel chemical post-processing algorithm
• The Effects of Cosmic Rays on the Chemistry of Dense Cores
• Cosmic-ray-induced H${}_2$ line emission: Astrochemical modeling and implications for JWST observations
• Deuterium Chemodynamics of Massive Pre-Stellar Cores
• A new analytic approach to infer the cosmic-ray ionization rate in hot molecular cores from HCO${}^{+}$, N${}_2$H${}^{+}$, and CO observations
• Impact of cosmic-ray propagation on the chemistry and ionisation fraction of dark clouds
• An analytic formalism to describe the $N_{\mathrm{eff}}(\mathrm{H})$-$n_{\mathrm{H}}$ relationship in molecular clouds