Can we observe the ion-neutral drift velocity in prestellar cores?
| Autor: | Aris Tritsis, Shantanu Basu, Christoph Federrath |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2023 |
| Předmět: |
dense gas
star-formation field strengths FOS: Physical sciences Astronomy and Astrophysics formation - radiative transfer - methods formulation nonisothermal stage Astrophysics - Astrophysics of Galaxies clouds - ism numerical magnetic molecular clouds Astrophysics - Solar and Stellar Astrophysics Space and Planetary Science molecules - stars ambipolar diffusion turbulence dissipation range Astrophysics of Galaxies (astro-ph.GA) ionization magnetic fields - ism simulations Solar and Stellar Astrophysics (astro-ph.SR) ism |
| Popis: | 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. 14 pages, 11 figures. Accepted for publication in MNRAS |
| Databáze: | OpenAIRE |
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