A Census of 163 Large-scale (≥10 pc), Velocity-coherent Filaments in the Inner Galactic Plane: Physical Properties, Dense-gas Fraction, and Association with Spiral Arms

The interstellar medium has a highly filamentary and hierarchical structure that may play a significant role in star formation. A systematical study of the large-scale filaments toward their physical parameters, distribution, structures, and kinematics will inform us about which types of filaments have the potential to form stars, how the material feeds protostars through filaments, and the connection between star formation and Galactic spiral arms. Unlike the traditional by-eye searches, we use a customized minimum spanning tree algorithm to identify filaments by linking Galactic clumps from the APEX Telescope Large Area Survey of the Galaxy catalog. In the inner Galactic plane (∣ l ∣ < 60°), we identify 163 large-scale filaments with physical properties derived, including the dense-gas mass fraction, and we compare them with an updated spiral arm model in position–position–velocity space. The dense-gas mass fraction is found not to differ significantly in various Galactic positions or in different spiral arms. We also find that most filaments are interarm filaments after adding a distance constraint, and filaments in arms differ a little with those not in arms. One surprising result is that clumps on and off filaments have no significant distinction in their mass at the same size.