Thermal infrared imaging of the bipolar H II region S106

The extended infrared emission from Sharpless 106 shows complex structure in ground-based images obtained at wavelengths from 3 to 20 μm. The structure of the ionization fronts and photodissociation regions are resolved in Brα emission at 4.05 μm and emission from polycyclic aromatic hydrocarbons at 3.29 μm, with the H I emission residing interior to the hydrocarbon emission. The mid-infrared observations at 10 to 20 μm reveal the distribution of continuum emission from warm dust in the nebula. These images have a higher spatial resolution than previous mid-infrared maps, but they support earlier findings of a relatively constant dust color temperature of ∼ 135 K in the extended dust, excluding the dust near the self-luminous sources IRS 2 and 4. All infrared images presented here show a dark lane bisecting the nebula, which probably results from shadowing of light from the central engine rather than line-of-sight extinction. If this shadow is caused by a compact disk around IRS 4, its ionized inner edge would be within the radio photosphere of the stellar wind at wavelengths longer than about 1.5 cm. There appears to be a faint point source seen at near-infrared wavelengths that is coincident with the position of a bright far-infrared source. This source is adjacent to some bright near-infrared nebulosity but is not clearly detected in thermal infrared dust emission.