Complex structure in class 0 protostellar envelopes. II. Kinematic structure from single-dish and interferometric molecular line mapping

We present a study of dense molecular gas kinematics in 17 nearby protostellar systems using single-dish and interferometric molecular line observations. The non-axisymmetric envelopes around a sample of Class0/I protostars were mapped in the N₂H⁺ (J = 1 → 0) tracer with the IRAM 30 m, CARMA, and Plateau de Bure Interferometer, as well as NH₃ (1,1) with the Very Large Array. The molecular line emission is used to construct line-center velocity and linewidth maps for all sources to examine the kinematic structure in the envelopes on spatial scales from 0.1 pc to 1000 AU. The direction of the large-scale velocity gradients from single-dish mapping is within 45° of normal to the outflow axis in more than half the sample. Furthermore, the velocity gradients are often quite substantial, the average being 2.3 km s^-1 pc^-1. The interferometric data often reveal small-scale velocity structure, departing from the more gradual large-scale velocity gradients. In some cases, this likely indicates accelerating infall and/or rotational spin-up in the inner envelope; the median velocity gradient from the interferometric data is 10.7 km s^-1 pc^-1. In two systems, we detect high-velocity HCO⁺ (J = 1 → 0) emission inside the highest-velocity N₂H⁺ emission. This enables us to study the infall and rotation close to the disk and estimate the central object masses. The velocity fields observed on large and small scales are more complex than would be expected from rotation alone, suggesting that complex envelope structure enables other dynamical processes (i.e., infall) to affect the velocity field.