Origin of highly elongated magnetized interstellar filaments: Magnetized turbulence fuels and counterbalances thermal instability*

Cold neutral filaments are commonly found in interstellar media and are characterized by their large aspect ratios, often exceeding 100, and alignment with the background magnetic field. Traditionally, the formation of these filaments has been explained by single-fluid ideal MHD turbulence or the creation of small atomic structures through reconnection. However, previous research suggests that thermal instability may impede the development of high aspect-ratio magnetized filaments, necessitating the inclusion of additional physics to explain the existence of long filaments observed in the sky. In our study, we employ a newly developed chemistry network in Athena++ to investigate how the interplay between thermal conduction and turbulent transport can sustain the stability of extended, cold filaments in the presence of strong MHD turbulence. Broadly speaking, turbulence tends to elongate the filaments along the magnetic field, while the thermal instability in the interstellar medium tends to fragmentize any long features. Our simulations indicate that strong turbulence also promotes the extended lifetime of thermally unstable phases, allowing the filament to self-regulate during turbulent-driven thermal instability. Additionally, our findings suggest an inverse relationship between the adiabatic index in the unstable phase and the plasma β parameter. Furthermore, we predict the aspect ratio of the cold filament and verify our predictions through numerical simulations.