A new method for probing magnetic field strengths from striations in the interstellar medium

Recent studies of the diffuse parts of molecular clouds have revealed the presence of parallel, ordered low-density filaments termed striations. Flows along magnetic field lines, KelvinHelmholtz instabilities and hydromagnetic waves are amongst the various formation mechanisms proposed. Through a synergy of observational, numerical, and theoretical analysis, previous studies singled out the hydromagnetic waves model as the only one that can account for the observed properties of striations. Based on the predictions of that model, we develop here a method for measuring the temporal evolution of striations through a combination of molecular and dust continuum observations. Our method allows us to not only probe temporal variations in molecular clouds but also estimate the strength of both the ordered and fluctuating components of the magnetic field projected on the plane of the sky. We benchmark our new method against chemical and radiative transfer effects through 2D magnetohydrodynamic simulations coupled with non-equilibrium chemical modelling and non-local thermodynamic equilibrium line radiative transfer. We find good agreement between theoretical predictions, simulations, and observations of striations in the Taurus molecular cloud. We find a value of 27±7 μG for the plane-of-sky magnetic field, in agreement with previous estimates via the DavisChandrasekharFermi method, and a ratio of fluctuating to ordered component of the magnetic field of ∼10percent.