Large-scale gaseous filaments with length up to the order of 100 pc are on the upper end of the filamentary hierarchy of the Galactic interstellar medium .
Their association with respect to the Galactic structure and their role in Galactic star formation are of great interest from both observational and theoretical point of view .
Previous “ by-eye ” searches , combined together , have started to uncover the Galactic distribution of large filaments , yet inherent bias and small sample size limit conclusive statistical results to be drawn .
Here , we present ( 1 ) a new , automated method to identify large-scale velocity-coherent dense filaments , and ( 2 ) the first statistics and the Galactic distribution of these filaments .
We use a customized minimum spanning tree algorithm to identify filaments by connecting voxels in the position-position-velocity space , using the Bolocam Galactic Plane Survey spectroscopic catalog .
In the range of 7. ^ { \circ } 5 \leq l \leq 194 ^ { \circ } , we have identified 54 large-scale filaments and derived mass ( \sim 10 ^ { 3 } -10 ^ { 5 } M _ { \odot } ) , length ( 10–276 pc ) , linear mass density ( 54–8625 M _ { \odot } pc ^ { -1 } ) , aspect ratio , linearity , velocity gradient , temperature , fragmentation , Galactic location and orientation angle .
The filaments concentrate along major spiral arms .
They are widely distributed across the Galactic disk , with 50 % located within \pm 20 pc from the Galactic mid-plane and 27 % run in the center of spiral arms .
An order of 1 % of the molecular ISM is confined in large filaments .
Massive star formation is more favorable in large filaments compared to elsewhere .
This is the first comprehensive catalog of large filaments useful for a quantitative comparison with spiral structures and numerical simulations .