The Milky Way atlas for linear filaments

Abstract

Filamentary structure is important for the ISM and star formation. Galactic distribution of filaments may regulate the star formation rate in the Milky Way. However, interstellar filaments are intrinsically complex, making them difficult to study quantitatively. Here we focus on linear filaments, the simplest morphology that can be treated as building blocks of any filamentary structure. We present the first catalog of 42 straight-line filaments across the full Galactic plane, identified by clustering of far-IR Herschel HiGAL clumps in position-position-velocity space. We investigated the dynamics along the filaments using molecular line cubes, compared the filaments with Galactic spiral arms, and compared ambient magnetic fields with the filaments' orientation. The selected filaments show extreme linearity ($>$10), aspect ratio (7-48), and velocity coherence over a length of 3-40 pc (mostly $>$10 pc). About one-third of them are associated with spiral arms, but only one is located in the arm center (known as the ``skeleton'' of the Milky Way). A few of them extend perpendicular to the Galactic plane, and none is located in the Central Molecular Zone (CMZ) near the Galactic center. Along the filaments, prevalent periodic oscillation (both in velocity and density) is consistent with gas flows channeled by the filaments and feeding the clumps that harbor diverse star formation activity. No correlation is found between the filament orientations with Planck measured global magnetic field lines. This work highlights some of the fundamental properties of molecular filaments and provides a golden sample for follow-up studies on star formation, ISM structure, and Milky Way structure.