ATLASGAL -- A Galaxy-wide sample of dense filamentary structures (1604.00544v3)

Abstract: [Abridged] Aims. We study the properties of filamentary structures from the ATLASGAL survey. Methods. We use the DisPerSE algorithm to identify spatially coherent structures located across the inner-Galaxy (300 < l < 60 and |b| < 1.5). Results. We have determined distances, masses and physical sizes for 241 of the filamentary structures. We find a median distance of 3.8 kpc, a mean mass of a few 10^3 m_sun, a mean length of ~6pc and a mass-to-length ratio of (M/L) ~200-2000M_sun/ pc. We also find that these filamentary structures are tightly correlated with the spiral arms in longitude and velocity, and that their semi-major axis is preferentially aligned parallel to the Galactic mid-plane and therefore with the direction of large-scale Galactic magnetic field. We find many examples where the dense filaments identified in ATLASGAL are associated with larger scale filamentary structures (~100 pc), and argue that this is likely to be common, and as such these may indicate a connection between large-scale Galactic dynamics and star formation. Conclusions. We have produced a large and Galaxy-wide catalogue of dense filamentary structures that are representative of a particular size and mass range not previously well studied in the literature. Analyses of the properties and distribution of these filaments reveals that they are correlated with the spiral arms and make a significant contribution to star formation in the Galaxy. Massive star formation is ongoing within ~20% of the filaments and is strongly correlated with the filaments with the largest mass-to- length ratios. The luminosity of the embedded sources has a similar distribution to the Galactic-wide samples of young massive stars and can therefore be considered to be representative.

Insights into Galactic Filamentary Structures from the ATLASGAL Survey

The paper titled "ATLASGAL — A Galaxy-wide sample of dense filamentary structures" by Guang-Xing Li and colleagues offers a comprehensive examination of the dense filamentary structures in the inner part of the Galaxy. Utilizing the ATLASGAL survey, the paper identifies and analyzes filamentary structures across the Galactic plane, contributing significantly to our understanding of their role in star formation and their association with larger Galactic structures.

Methodology and Data Analysis

The DisPerSE algorithm was employed to extract coherent structures from the ATLASGAL survey maps, allowing the researchers to identify approximately 1,800 structures, including 517 filaments. By smoothing the emission maps, the paper improved sensitivity to low-density connecting regions, thus enabling the identification of larger and more complex structures. The cataloguing of these structures and their classifications was carried out meticulously, with a rigorous assessment by multiple authors to ensure reliability.

Key Findings

1. Filament Properties: Filaments were found to have lengths ranging from 2 to 20 pc and widths between 0.1 and 2.5 pc, with mass-to-length ratios indicating a potential for instability and collapse. This size range fills a gap in the literature between smaller structures typically observed by Herschel studies and much larger filaments previously identified.

2. Galactic Alignment and Distribution: A pronounced alignment with the Galactic mid-plane was observed among the filaments, suggesting an influence from Galactic dynamics. The paper found that filaments are preferentially aligned with the spiral arms, supporting the view that large-scale Galactic processes play a role in filament formation.

3. Association with Star Formation: Approximately 22% of filaments were associated with massive star-forming clumps. Notably, filaments with high mass-to-length ratios correlated strongly with sites of massive star formation, supporting theories of their radial collapse due to gravitational instability.

4. Correlation with Large-Scale Structures: The paper posits that filaments detected in ATLASGAL are dense fragments of much larger structures, offering a continuum of hierarchical structure from sub-parsec scales up to ∼100 pc.

Implications for Star Formation Theories

The paper significantly extends the known catalogue of Galactic filaments, providing insights into the distribution and physical properties that underscore their importance in star formation processes. Filaments associated with massive star formation were found to have higher mass-to-length ratios, suggesting they are key structures in understanding the dynamics leading to star formation. The link between filamentary structures and spiral arms indicates that these arms are crucial regions for dense gas accumulation, likely causing radial collapse and star formation.

Future Directions in Galactic Research

The authors suggest further studies to better understand the interplay between filamentary structures and Galactic dynamics. In particular, the alignment of filaments with the Galactic magnetic field warrants deeper investigation, as does their relationship with other large-scale structures such as spiral arms. These findings set the stage for more targeted investigations into the processes governing star formation across different scales within the Galaxy.

This paper offers a foundational resource for researchers exploring the complex dynamics of the interstellar medium and its role in star formation. As data from ongoing and future surveys become available, it will be critical to integrate these findings to achieve a holistic understanding of Galactic structure and evolution.