Life at the Edge: Emission From the H II Region/Photodissociation Region Interface

Abstract

Preliminary results of an imaging survey of Galactic H II regions are presented and discussed with respect to the character of low-ionization potential lines and the structure of the H II region/photodissociation region (PDR) interface. A model of (S II) emission is developed according to the preliminary results and the interpretation of the structure and effects of the region. The highly concentrated emission is theorized to be an intrinsic result of spatially peaked product of S(+) density and the electron density. The emission from the photoevaporation region is theorized to vary with position in a galaxy, making abundance determinations difficult. The observations support the notion that the (S II) emission originates from the 'bar' being viewed face-on, and therefore the structural attributes of the feature require analysis. Other parameters which affect the edge of H II regions are listed and proposed for incorporation into a more complete model of the region.