Three-dimensional Shock Structure of Orion KL Outflow with IGRINS
  We report a study of the three-dimensional (3D) outflow structure of a
15$\arcsec$ $\times$ 13$\arcsec$ area around H$_{2}$ peak 1 in Orion KL with
slit-scan observations (13 slits) using the Immersion Grating Infrared
Spectrograph. The datacubes, with high velocity-resolution ($\sim$ 7.5 {\kms})
provide high contrast imaging within ultra-narrow bands, and enable the
detection of the main stream of the previously reported H$_{2}$ outflow
fingers. We identified 31 distinct fingers in H$_{2}$ 1$-$0 S(1) $\lambda$2.122
$\micron$ emission. The line profile at each finger shows multiple-velocity
peaks with a strong low-velocity component around the systemic velocity at
${\VLSR}$ = $+$8 {\kms} and high velocity emission ($|$${\VLSR}$$|$ = 45$-$135
{\kms}) indicating a typical bow-shock. The observed radial velocity gradients
of $\sim$ 4 {\kms} arcsec$^{-1}$ agree well with the velocities inferred from
large-scale proper motions, where the projected motion is proportional to
distance from a common origin. We construct a conceptual 3D map of the fingers
with the estimated inclination angles of 57$\degree$$-$74$\degree$. The
extinction difference ($\Delta$$A_{\rm v}$ $>$ 10 mag) between blueshifted and
redshifted fingers indicates high internal extinction. The extinction, the
overall angular spread and scale of the flow argue for an ambient medium with
very high density (10$^{5}$$-$10$^{6}$ cm$^{-3}$), consistent with molecular
line observations of the OMC core. The radial velocity gradients and the 3D
distributions of the fingers together support the hypothesis of simultaneous,
radial explosion of the Orion KL outflow.
