Dense cores with multiple protostars: The velocity fields of L1448 IRS 3, NGC 1333 IRAS 2, and NGC 1333 IRAS 4

The embedded cores L1448 IRS 3, NGC 1333 IRAS 2, and NGC 1333 IRAS 4 are mapped in emission from the C¹⁸O, H¹³CO⁺, and N₂H⁺ J = 1 → 0 transitions. The maps are created by combining BIMA and FCRAO observations and are tuned to resolutions of ∼50″, 10″, 5″, and 3″. The higher resolution maps reveal emission structures that are considerably smaller than the characteristic core radius (∼0.1 pc) identified in earlier single-dish studies. We focus our study on the kinematics of the envelope material traced by the emission lines. We find that although the FCRAO data show relatively smooth velocity gradients across the cores, the velocity fields seen with higher resolution are more random, with central velocities varying over a range of ∼1 km s ^-1. In general, the distribution of velocities, as well as the complexity of the fields, increases with resolution. To analyze variations in the widths of the emission lines, we employ a method of gridding the datacubes that was initially developed to quantify properties of turbulent cloud models. The cores exhibit a broad range of line widths even at the smallest measurable scales. Pure thermal broadening at the prevailing envelope temperatures (T ≈ 20 K) is insufficient to produce the measured line widths; the narrowest lines must have a turbulent component at least as great as the thermal component, and for nearly all lines, the turbulent component makes the dominant contribution. Our results suggest that turbulent motions persist down to subcore scales of at least 2400 AU.