2016ApJ...833..275O

We report a study of the three-dimensional (3D) outflow structure of a 15'' x 13'' area around the H₂ peak 1 in Orion KL with slit-scan observations (13 slits) using the Immersion Grating Infrared Spectrograph. The datacubes have a high-velocity resolution (∼7.5 km s^–1), provide high-contrast imaging within ultra-narrow bands, and enable the detection of the main stream of the previously reported H₂ outflow fingers. We identified 31 distinct fingers in the H₂ 1-0 S(1) λ2.122 µm emission. The line profile at each finger shows multiple-velocity peaks with a strong low-velocity component around the systemic velocity at V_LSR = +8 km s^–1 and high-velocity emission (|V_LSR| = 45-135 km s^–1), indicating a typical bow-shock. The observed radial velocity gradients of ∼4 km s^–1 arcsec^–1 agree well with the velocities inferred from large-scale proper motions, where the projected motion is proportional to the distance from a common origin. We construct a conceptual 3D map of the fingers with estimated inclination angles of 57deg-74deg. The extinction difference (ΔA_v > 10 mag) between blueshifted and redshifted fingers indicates high internal extinction. The extinction, the overall angular spread, and the scale of the flow argue for an ambient medium with a very high density (10⁵-10⁶ cm^–3), consistent with molecular line observations of the Orion Molecular Cloud core. The radial velocity gradients and the 3D distributions of the fingers together support the hypothesis of a simultaneous radial explosion of the Orion KL outflow.