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The Ionization Structure of Sharpless 2-264: Multiwavelength Observations of the λ Ori H II Region

We present velocity-resolved maps taken with the Wisconsin H-Alpha Mapper (WHAM) in Hα, [S II] λ6716, and [N II] λ6583 around the well-known O8 III star λ Ori A (HD 36861) (l = 185° to 205°, b = -24° to -1°). The integrated intensity (v(LSR) = -80 to +80 km/s), I(Hα), within WHAM's one-degree beams varies from ~ 190 R near the center to ~ 10 R on the periphery of the nebula where it becomes comparable to foreground and/or background emission in this complex region. Intensity ratios for [N II]/Hα and [S II]/Hα average 0.28 and 0.35, respectively. In both ratios, higher values are found preferentially at larger radii from λ Ori, although the behavior of [N II]/Hα is complicated near the edges of the nebula. The [S II]/[N II] intensity ratio ranges from ~ 0.5 to ~ 1.0, with the value increasing toward larger radii (and lower Hα intensities). Variations of [S II]/Hα, [N II]/Hα, and [S II]/[N II] line ratios in this diffuse region show some similar trends to those seen in the warm ionized medium (WIM) but with generally lower metal-line ratios. As with the WIM, the trends are driven by changes in the underlying physical parameters, most notably the ionization states and gas temperature. We use these extremely high signal-to-noise observations to construct a map of temperature and non-thermal velocity throughout the nebula. Using the line widths of Hα and [S II], we separate thermal and non-thermal components and find spatial trends of these parameters within the nebula.