The Ionization Structure of Sharpless 2-264: Multiwavelength Observations of the {\lambda} Ori H II Region

TL;DR

This study uses multiwavelength, velocity-resolved observations of the Sharpless 2-264 nebula to analyze its ionization structure, temperature, and velocity components, revealing detailed physical conditions and their spatial variations.

Contribution

It provides high-resolution maps of ionization ratios, temperature, and non-thermal velocities in the {\lambda} Ori H II region, offering new insights into its physical state and structure.

Findings

Ionization ratios increase with radius from {\lambda} Ori.

Temperature and non-thermal velocities vary spatially within the nebula.

Line ratios are lower than those typically observed in the warm ionized medium.

Abstract

We present velocity-resolved maps taken with the Wisconsin H-Alpha Mapper (WHAM) in H{\alpha}, [S II] {\lambda}6716, and [N II] {\lambda}6583 around the well-known O8 III star {\lambda} Ori A (HD 36861) (l = 185{\deg} to 205{\deg}, b = -24{\deg} to -1{\deg}). The integrated intensity (v(LSR) = -80 to +80 km/s), I(H{\alpha}), 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]/H{\alpha} and [S II]/H{\alpha} average 0.28 and 0.35, respectively. In both ratios, higher values are found preferentially at larger radii from {\lambda} Ori, although the behavior of [N II]/H{\alpha} 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 H{\alpha} intensities). Variations of [S II]/H{\alpha}, [N II]/H{\alpha}, 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 H{\alpha} and [S II], we separate thermal and non-thermal components and find spatial trends of these parameters within the nebula.