Ionization fronts and shocked flows - The structure of the Orion Nebula at 0.1 arcsec

Abstract

We present HST Wide-Field Camera images of a field in the Orion Nebula obtained in emission from [S II], Hp, and [0 II]. The morphology of the [S II] emission is markedly different from the other lines. While HP and [0 II] are distributed fairly smoothly, [S II] is dominated by filamentary features with widths between 0':1 and 1" which sharply highlight ionization fronts moving into dense neutral material. These photoionization fronts act as probes of the structure of the cavity walls of this blister H II region. Their morphology indicates that while the surfaces into which they are moving are textured, subarcsecond clumps with high density contrast are uncommon. An exception is a bow shock-shaped ionization front seen along the face of a solar system-sized (0':6 = 270 AU) clump which is itself seen in extinction.