Formation of dust filaments in the diffuse envelopes of molecular clouds

The path to understanding star formation processes begins with the study of the formation of molecular clouds. The external layers of these clouds share properties with the diffuse warm neutral medium (WNM) from which they were formed. The low column densities allow the penetration of ultraviolet radiation, resulting in a non-negligible ionization fraction and the charging of the small dust grains that are mixed with the gas. Despite the general assumption that dust and gas are tightly correlated, several observational and theoretical studies have reported variations in the dust-to-gas ratio toward diffuse and cold clouds. The relative motion of dust and gas could interfere with the propagation of waves inside the clouds and thus would directly affect star formation. In this work, we present the implementation of a new charged particles module for analyzing the dust dynamics in the WNM. We study the evolution of a single population of small charged grains (0.05 $\mu$m) in the turbulent, magnetized WNM using this module. We show that variations in the dust-to-gas ratio arise due to the coupling of the grains with the magnetic field, forming elongated dust structures decoupled from the gas. This emphasizes the importance of considering the dynamics of charged dust when simulating the different phases of the interstellar medium, especially for star formation studies.