Can we observe the ion-neutral drift velocity in prestellar cores?

Abstract

Given the low ionization fraction of molecular clouds, ambipolar diffusion is thought to be an integral process in star formation. However, chemical and radiative-transfer effects, observational challenges, and the fact that the ion-neutral drift velocity is inherently very small render a definite detection of ambipolar diffusion extremely non-trivial. Here, we study the ion-neutral drift velocity in a suite of chemodynamical, non-ideal magnetohydrodynamic (MHD), two-dimensional axisymmetric simulations of prestellar cores where we alter the temperature, cosmic-ray ionization rate, visual extinction, mass-to-flux ratio, and chemical evolution. Subsequently, we perform a number of non-local thermodynamic equilibrium (non-LTE) radiative-transfer calculations considering various idealized and non-idealized scenarios in order to assess which factor (chemistry, radiative transfer and/or observational difficulties) is the most challenging to overcome in our efforts to detect the ion-neutral drift velocity. We find that temperature has a significant effect in the amplitude of the drift velocity with the coldest modelled cores (T = 6 K) exhibiting drift velocities comparable to the sound speed. Against expectations, we find that in idealized scenarios (where two species are perfectly chemically co-evolving) the drift velocity ``survives" radiative-transfer effects and can in principle be observed. However, we find that observational challenges and chemical effects can significantly hinder our view of the ion-neutral drift velocity. Finally, we propose that $\mathrm{HCN}$ and $\mathrm{HCN}{\mathrm{H}}^{+}$, being chemically co-evolving, could be used in future observational studies aiming to measure the ion-neutral drift velocity.

arXiv comment14 pages, 11 figures. Accepted for publication in MNRAS

References in corpus (29)

• Array Programming with NumPy
• An atomic and molecular database for analysis of submillimetre line observations
• A Multi-Code Analysis Toolkit for Astrophysical Simulation Data
• Systematic Molecular Differentiation in Starless Cores
• Effects of Ohmic and ambipolar diffusion on the formation and evolution of the first cores, protostars and circumstellar discs
• Probing the Turbulence Dissipation Range and Magnetic Field Strengths in Molecular Clouds
• CARMA Large Area Star Formation Survey: Structure and Kinematics of Dense Gas in Serpens Main
• The nonisothermal stage of magnetic star formation. II. Results
• Magnetically Controlled Spasmodic Accretion During Star Formation. II. Results
• Magnetically-Regulated Fragmentation Induced by Nonlinear Flows and Ambipolar Diffusion
• The Nonisothermal Stage of Magnetic Star Formation. I. Formulation of the Problem and Method of Solution
• The Initial Conditions of Clustered Star Formation. II. N2H+ Observations of the Ophiuchus B Core
• Detection of the HC${}_3$NH${}^{+}$ and HCNH${}^{+}$ ions in the L1544 pre-stellar core
• CARMA Large Area Star Formation Survey: Project Overview with Analysis of Dense Gas Structure and Kinematics in Barnard 1
• Non-ideal magnetohydrodynamics vs turbulence I: Which is the dominant process in protostellar disc formation?
• Observational Determination of the Turbulent Ambipolar Diffusion Scale and Magnetic Field Strength in Molecular Clouds
• Protostar Formation in Magnetic Molecular Clouds beyond Ion Detachment: I. Formulation of the Problem and Method of Solution
• Tentative Detection of the Nitrosylium Ion in Space
• Neutral vs Ion Linewidths in Barnard 5: Evidence for Penetration by MHD Waves
• Non-Equilibrium Chemistry of Dynamically Evolving Prestellar Cores: II. Ionization and Magnetic Field
• CARMA Large Area Star Formation Survey: Dense Gas in the Young L1451 Region of Perseus
• Non-ideal MHD simulations of subcritical prestellar cores with non-equilibrium chemistry
• Constraint on ion-neutral drift velocity in the Class 0 protostar B335 from ALMA observations
• Probing the Turbulence Dissipation Range and Magnetic Field Strengths in Molecular Clouds. II. Directly Probing the Ion-neutral Decoupling Scale
• Investigating the role of magnetic fields in star formation using molecular line profiles
• First survey of HCNH${}^{+}$ in high-mass star-forming cloud cores
• Collisional polarization of molecular ions: a signpost of ambipolar diffusion
• Python Radiative Transfer Emission code (PyRaTE): non-LTE spectral lines simulations
• A search for co-evolving ion and neutral gas species in prestellar molecular cloud cores

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