Complex Structure in Class 0 Protostellar Envelopes II: Kinematic Structure from Single-Dish and Interferometric Molecular Line Mapping

TL;DR

This study investigates the kinematic structures of dense gas in Class 0/I protostellar envelopes using molecular line mapping, revealing complex velocity patterns and signs of infall and rotation at multiple scales.

Contribution

It provides detailed velocity maps from single-dish and interferometric observations, highlighting the complexity of protostellar envelope dynamics beyond simple rotation models.

Findings

Large-scale velocity gradients are often perpendicular to outflows.

Interferometric data show small-scale velocity structures indicating infall or spin-up.

Detection of high-velocity emission near protostars suggests active accretion processes.

Abstract

We present a study of dense molecular gas kinematics in seventeen nearby protostellar systems using single-dish and interferometric molecular line observations. The non-axisymmetric envelopes around a sample of Class 0/I protostars were mapped in the N2H+ (J=1-0) tracer with the IRAM 30m, CARMA and PdBI as well as NH3 (1,1) with the VLA. 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 degrees 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\pc. 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/pc. In two systems, we detect high-velocity HCO+ (J=1-0) emission inside the highest-velocity \nthp\ 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.