2014MNRAS.440.2860H

Infrared dark clouds (IRDCs) are unique laboratories to study the initial conditions of high-mass star and star cluster formation. We present high-sensitivity and high-angular-resolution Institut de Radioastronomie Millimétrique (IRAM) Plateau de Bure Interferometer observations of N2H+ (1-0) towards IRDC G035.39-00.33. It is found that G035.39-00.33 is a highly complex environment, consisting of several mildly supersonic filaments (σ_NT/c_s ∼ 1.5), separated in velocity by <1 km/s. Where multiple spectral components are evident, moment analysis overestimates the non-thermal contribution to the line-width by a factor of ∼ 2. Large-scale velocity gradients evident in previous single-dish maps may be explained by the presence of substructure now evident in the interferometric maps. Whilst global velocity gradients are small (<0.7 km/s/pc), there is evidence for dynamic processes on local scales ( ∼ 1.5-2.5 km/s/pc). Systematic trends in velocity gradient are observed towards several continuum peaks. This suggests that the kinematics are influenced by dense (and in some cases, starless) cores. These trends are interpreted as either infalling material, with accretion rates ∼ (7±4)x10^–5 M_☉/yr, or expanding shells with momentum ∼ 24±12 M_☉ km/s. These observations highlight the importance of high-sensitivity and high-spectral-resolution data in disentangling the complex kinematic and physical structure of massive star-forming regions.