ner_tags: O O O O O O O O O O O O O B-CelestialObject I-CelestialObject I-CelestialObject O B-Citation I-Citation I-Citation I-Citation O O O O O B-Telescope O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model I-Model I-Model O B-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O B-Model O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O B-CelestialObject I-CelestialObject O B-Citation I-Citation I-Citation O B-CelestialObject O B-Citation I-Citation I-Citation I-Citation O B-Citation O B-CelestialObject I-CelestialObject O B-Citation I-Citation I-Citation I-Citation I-Citation O O B-CelestialObject O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O B-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialRegion I-CelestialRegion O O O O O O B-Telescope O O B-Wavelength I-Wavelength O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O B-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O
tokens: may have been found in the form of braided velocity-coherent substructure in the Taurus B211–3 filament ( Hacar et al. 2013 ). Another major result from Herschel in nearby clouds is that most (75%) low-mass prestellar cores and protostars are found in dense, supercritical filaments for which the mass per unit length exceeds the critical line mass of nearly isothermal long cylinders (e.g. Inutsuka Miyama 1997 ), /pc, where km s is the isothermal sound speed for molecular gas at K (e.g. Könyves et al. 2015 ). These Herschel findings support a scenario for low-mass star formation in two main steps (cf. André et al. 2014 ): First, large-scale compression of interstellar material in supersonic MHD flows generates a cobweb of filaments 0.1 pc in width in the ISM; second, the densest filaments fragment into prestellar cores (and subsequently protostars) by gravitational instability above , while simultaneously growing in mass through accretion of background cloud material. In addition to the relatively modest filaments found in non-star-forming and low-mass star-forming clouds, where rarely exceeds ten times the thermal value of , significantly denser and more massive filamentary structures have also been observed in the most active giant molecular clouds (GMCs) of the Galaxy and may be the progenitors of young massive star clusters. The DR21 main filament or ridge is probably the most emblematic case of such a massive elongated structure with about inside a 4.5 pc long structure (i.e., /pc; Motte et al. 2007 ; Schneider et al. 2010 ; Hennemann et al. 2012 ). Other well-known ridges include Orion A ( Hartmann Burkert 2007 ), Vela-C ( Hill et al. 2011 , 2012 ), IRDC G035.39–00.33 ( Nguyen Luong et al. 2011 ), and W43-MM1 ( Nguyen-Luong et al. 2013 ; Louvet et al. 2014 ). These ridges, which exceed the critical line mass of an isothermal filament by up to two orders of magnitude, are believed to be in a state of global collapse, to be fed by very high accretion rates on large scales ( Schneider et al. 2010 ; Peretto et al. 2007 , 2013 ), and to continuously form stars and clusters. The formation of these ridges is not yet well understood but may result from the large-scale collapse of a significant portion of a GMC ( Hartmann Burkert 2007 ; Schneider et al. 2010 ). Whether the low-mass star formation scenario summarized above – or an extension of it – also applies to regions dominated by hyper-massive clumps and ridge-like structures ( Motte et al. 2016 ) is not yet known. In particular, further work is needed to confirm that the inner width of interstellar filaments remains close to 0.1 pc in regions of massive star formation beyond the Gould Belt, where the moderate angular resolution of Herschel (–36 at –500 m) is insufficient to resolve this characteristic scale. At a distance of 1.7 kpc, NGC 6334 is a very active complex of massive star formation ( Persi Tapia 2008 ; Russeil et al. 2013 ) with about 150 associated luminous stars of O- to