A census of 163 large-scale (>=10 pc), velocity-coherent filaments in
  inner Galactic plane: physical properties, dense gas fraction, and
  association with spiral arms
  The interstellar medium has a highly filamentary and hierarchical structure,
which may play a significant role in star formation. A systematical study on
the large-scale filaments towards their physical parameters, distribution,
structures and kinematics will inform us of what kind of filaments have
potential to form stars, how the material feed protostars through filaments,
and the connection between star formation and Galactic spiral arms. Unlike the
traditional "by eyes" 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 catalogue. In the inner Galactic
plane ($|l| < 60^\circ$), we identify 163 large-scale filaments with physical
properties derived, including dense gas mass fraction, and compare them with an
updated spiral arm model in position-position-velocity space. Dense gas mass
fraction is found not to differ significantly in various Galactic position,
neither does it in different spiral arms. We also find that most filaments are
inter-arm filaments after adding a distance constraint, and filaments in arm
differ a little with those not in. One surprising result is that clumps on and
off filaments have no significant distinction in their mass at the same size.
