The Milky Way Atlas for Linear Filaments

TL;DR

This paper presents the first catalog of 42 linear filaments in the Milky Way, analyzing their properties, dynamics, and relation to galactic structures, providing insights into star formation and ISM organization.

Contribution

It introduces a new catalog of straight-line filaments, characterizes their properties, and compares their orientation and dynamics with galactic features, advancing understanding of filamentary structures.

Findings

Filaments are highly linear with aspect ratios 7-48 and velocity coherence over 10+ pc.

About one-third of filaments are associated with spiral arms, but none are in the Galactic center.

Periodic oscillations in velocity and density suggest gas flows feeding star-forming clumps.

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 it 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 use molecular line cubes to investigate the dynamics along the filaments; compare the filaments with Galactic spiral arms; and compare 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 1/3 of them are associated with spiral arms, but only one is located in arm center, a.k.a. ``bones'' 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 which harbor diverse star formation activities. 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.