Can we observe the ion-neutral drift velocity in prestellar cores?. Issue 4 (20th March 2023)

• Record Type: Journal Article
• Authors: Tritsis, Aris; Basu, Shantanu; Federrath, Christoph
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 521:Issue 4(2023)
• Page Start: 5087
• Page End: 5099
• Publication Date: 2023-03-20
• Subjects: ISM: magnetic fields -- ISM: clouds -- ISM: molecules -- stars: formation -- radiative transfer -- methods: numerical; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stad829
• Languages: English
• ISSNs: 0035-8711

Abstract

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 $\rm {HCN}$ and $\rm {HCNH^+}$, being chemically co-evolving, could be used in future observational studies aiming to measure the ion-neutral drift velocity.