ALMA–IRDC: dense gas mass distribution from cloud to core scales

ABSTRACT Infrared dark clouds (IRDCs) are potential hosts of the elusive early phases high mass star formation (HMSF). Here, we conduct an in-depth analysis fragmentation properties a sample 10 IRDCs, which have been highlighted as some best candidates to study HMSF within Milky Way. To do so, obtained set large mosaics covering these IRDCs with Atacama Large Millimeter/submillimeter Array (ALMA) at Band 3 (or mm). These observations angular resolution (?3 arcsec; ?0.05 pc), and continuum spectral line sensitivity (?0.15 mJy beam?1 ?0.2 K per 0.1 km s?1 channel N2H+ (1 ? 0) transition). From dust emission, identify 96 cores ranging from low (M = 3.4?50.9 M?) that gravitationally bound (?vir 0.3?1.3) would require magnetic field strengths B 0.3?1.0 mG be in virial equilibrium. We combine results homogenized catalogue literature recover hierarchical structure over four orders magnitude spatial scale (0.01–10 pc). Using supplementary even higher resolution, find smallest fragments (<0.02 pc) this hierarchy not currently and/or density required form high-mass stars. None less, new ALMA presented paper facilitated identification 19 (6 quiescent 13 star-forming) retain >16 M? without further fragmentation. contain trans-sonic non-thermal motions, kinematically sub-virial, moderate for support against collapse. The sites represents key step allowing us test predictions cluster theories.