Scattered Nebular Light in the Extended Orion Nebula

Abstract

We have combined 327.5 MHz radio observations and optical spectroscopy to study conditions in the Extended Orion Nebula. We see a steady progression of characteristics with increasing distance from the dominant photoionizing star Theta1OriC. This progression includes a decrease in the F(Halpha)/F(Hbeta) ratio, an increase in the relative strength of scattered stellar continuum, decrease in electron density determined from the [S II] doublet, and increase in the ratio of Emission Measures derived from the Hbeta line and the 327.5 MHz radio continuum. We conclude that beyond about 5' south of Theta1OriC that scattered light from the much brighter central Huygens region of the nebula significantly contaminates local emission. This strengthens earlier arguments that wavelength and model dependent scattering of emission line radiation imposes a fundamental limit on our ability to determine the physical conditions and abundances in this and arguably other similar Galactic Nebulae. The implications for the study of extra-galactic HII regions are even more severe. We confirm the result of an earlier study that at least the eastern boundary of the Extended Orion Nebula is dominated by scattered light from the Huygens region.

References in corpus (6)

• Million-Degree Plasma Pervading the Extended Orion Nebula
• The three dimensional dynamic structure of the inner Orion Nebula
• Fine Scale Temperature Fluctuations in the the Orion Nebula and the t^2 Problem
• High Velocity Features in the Orion Nebula
• Physical Conditoins in Orion's Veil II: A Multi-Component Study of the Line of Sight Toward the Trapezium
• Large Scale Flows from Orion-South

Cited by in corpus (8)

• Expanding bubbles in Orion A: [CII] observations of M42, M43, and NGC 1977
• Spectrophotometry of the Huygens Region of the Orion Nebula, the Extended Orion Nebula, and M~43; Scattered Light Systematically Distorts Conditions Derived from Emission-Lines
• On the origins of the diffuse H-alpha emission: Ionized gas or dust-scattered H-alpha halos?
• Pumping up the [N I] nebular lines
• A global study of the HII region M43 and its ionizing star (I. Stellar parameters and nebular empirical analysis)
• Comparison of the Diffuse Halpha and FUV Continuum Backgrounds: On the Origins of the Diffuse Halpha Background
• The filling factor - radius relation for 58 HII regions across the disk of NGC6946
• Large Scale Wind Driven Structures in the Orion Nebula