A dynamically young, gravitationally stable network of filaments in
  Orion B
  Filaments are a key step on the path that leads from molecular clouds to star
formation. However, their characteristics are heavily debated, and the exact
processes that lead to their formation and fragmentation into dense cores still
remain to be fully understood. We aim at characterising the mass, kinematics,
and stability against gravitational collapse of a statistically significant
sample of filaments in the Orion B molecular cloud, which is renown for its
very low star formation efficiency. We characterise the gas column densities
and kinematics over a field of 1.9 deg$^2$, using C$^{18}$O(J=1-0) data from
the IRAM-30m large programme ORION-B. Using two different Hessian-based
filters, we extract and compare two filamentary networks, each containing over
100 filaments. Independent of the extraction method, the filaments have widths
of 0.12$\pm$0.04 pc, and show a wide range of linear (1 - 100
$M_{\odot}$pc$^{-1}$) and volume densities (2.10$^3$ - 2.10$^5$ cm$^{-3}$).
Compared to previous studies, the filament population is dominated by
low-density, thermally sub-critical structures, suggesting that most of the
identified filaments are not collapsing to form stars. In fact, only ~1% of the
Orion B cloud mass covered by our observations can be found in super-critical,
star-forming filaments, explaining the low star formation efficiency of the
region. The velocity profiles observed across the filaments show quiescence in
the centre, and coherency in the plane of the sky, despite being mostly
supersonic. The filaments in Orion B apparently belong to a continuum which
contains a few elements comparable to already studied star-forming filaments as
well as many lower-density, gravitationally unbound structures. This
comprehensive study of the Orion B filaments shows that the mass fraction in
super-critical filaments is a key factor in determining star formation
efficiency.
