Which Stars Are Ionizing the Orion Nebula?

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.