Astrophys. J., 566, 910-924 (2002/February-3)
[Fe II] 1.257 µm and He I 1.083 µm emission in the central region of the Orion nebula: H II region, HH flows, jets, and proplyds.
TAKAMI M., USUDA T., SUGAI H., SUTO H., PYO T.-S., TAKEYAMA N., AOKI T., MIZUTANI K. and TANAKA M.
Abstract (from CDS):
The [Fe II] 1.257 µm and He I 1.083 µm emission lines were observed in the central 6'x8' region of the Orion Nebula, and their excitation in the photoionized H II region, HH flows, jets, and proplyds is investigated. Observations were carried out using the imaging Fabry-Perot spectrometer MUSE at the National Astronomical Observatory of Japan 1.5 m infrared telescope, which provides a 4'x4' field of view and a spectral resolution λ/δλ of ∼2000 at the observed wavelengths. The [Fe II] images exhibit (1) filamentary structures and diffuse emission, which presumably arise from ionization fronts of the photoionized H II region, and (2) a number of knots, some of which are newly identified. Centroidal velocities in most of the knots are negative relative to those in the ionization fronts by up to -60 km.s–1, and observed line profiles in the bright knots exhibit blueshifted wings, agreeing with bow shock models. The He I 1.083 µm emission in the observed region is dominated by the photoionized H II region, and its distribution reflects the complicated nature of the excitation. The He I images also contain blueshifted emission from several HH flows and jets and redshifted emission associated with proplyds. Our results for the shocks suggest that the [Fe II] 1.257 µm and He I 1.083 µm emission reflects the ionization of the preshock gas: the [Fe II] 1.257 µm emission is prominent in shocks propagating in molecular/atomic gas, while the He I 1.083 µm is prominent in shocks in the photoionized H II region. Different line excitation in these shocks can be explained by the following physical properties and processes: (1) difference of the excitation energies from the ground state (1 and 20 eV for the [Fe II] and He I lines, respectively), (2) resonance scattering and collisional excitation from the metastable state, enhancing the He I 1.083 µm line in shocks in the photoionized H II region, (3) a large photoionization cross section of Fe+, causing the absence of the [Fe II] emission in the same shocks, and possibly (4) charge exchange reactions of Fe, which could enhance the [Fe II] emission in neutral gas.
ISM: H II Regions - Infrared: ISM - ISM: individual (Orion Nebula) - Stars: Formation
Table 4, Text: [OW94] SSs-SSs N=29 added.
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