The common assumption that θ1 Ori C is the dominant ionizing source for the Orion Nebula is critically examined. This assumption underlies much of the existing analysis of the nebula. In this paper we establish through comparison of the relative strengths of emission lines with expectations from Cloudy models and through the direction of the bright edges of proplyds that θ2 Ori A, which lies beyond the Bright Bar, also plays an important role. θ1 Ori C does dominate ionization in the inner part of the Orion Nebula, but outside of the Bright Bar as far as the southeast boundary of the Extended Orion Nebula, θ2 Ori A is the dominant source. In addition to identifying the ionizing star in sample regions, we were able to locate those portions of the nebula in 3D. This analysis illustrates the power of MUSE spectral imaging observations to identify sources of ionization in extended regions.

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Published in The Astrophysical Journal, v. 837, no. 2, 151, p. 1-7.

© 2017. The American Astronomical Society. All rights reserved.

The copyright holder has granted the permission for posting the article here.

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G.J.F. acknowledges support by NSF (1108928, 1109061, and 1412155), NASA (10-ATP10-0053, 10-ADAP10-0073, and ATP13-0153), and STScI (HST-AR- 13245, GO-12560, HST-GO-12309, GO-13310.002-A, HST-AR-13914, HST-AR-14286.001, and HST-AR-14556). W.K. was supported in part by DFG grants KO 857/32-2 and KO 857/33-1.