FilDReaMS

Abstract

Context.Both simulations and observations of the interstellar medium show that the study of the relative orientations between filamentary structures and the magnetic field can bring new insight into the role played by magnetic fields in the formation and evolution of filaments and in the process of star formation.Aims.We provide a first application ofFilDReaMS, the new method presented in the companion paper to detect and analyze filaments in a given image. The method relies on a template that has the shape of a rectangular bar with variable width. Our goal is to investigate the relative orientations between the detected filaments and the magnetic field.Methods.We applyFilDReaMSto a small sample of fourHerschelfields (G210, G300, G82, G202) characterized by different Galactic environments and different evolutionary stages. First, we look for the most prevalent bar widths, and we examine the networks formed by filaments of different bar widths as well as their hierarchical organization. Second, we compare the filament orientations to the magnetic field orientation inferred fromPlanckpolarization data and, for the first time, we study the statistics of the relative orientation angle as functions of both spatial scale and H2column density.Results.We find preferential relative orientations in the fourHerschelfields: small filaments with low column densities tend to be slightly more parallel than perpendicular to the magnetic field; in contrast, large filaments, which all have higher column densities, are oriented nearly perpendicular (or, in the case of G202, more nearly parallel) to the magnetic field. In the two nearby fields (G210 and G300), we observe a transition from mostly parallel to mostly perpendicular relative orientations at an H2column density ≃ 1.1 × 1021cm−2and 1.4 × 1021cm−2, respectively, consistent with the results of previous studies.Conclusions.Our results confirm the existence of a coupling between magnetic fields at cloud scales and filaments at smaller scale. They also illustrate the potential of combiningHerschelandPlanckobservations, and they call for further statistical analyses with our dedicated method.