The Arcminute Morphology of the WIM Toward the Local Perseus Arm of the Galaxy

We used the Virginia Tech Spectral-Line Imaging Camera (SLIC) to image the warm ionized interstellar medium (WIM) toward the Local Perseus Arm. We obtained a series of images, each of which is 10$^\circ$-wide, and has arcminute-resolution. The images show three basic types of structures --- compact clouds with diameters greater than several degrees, those that are 1$^\circ$ or less in diameter, and extended filaments which span several degrees in length but have thicknesses of only a few tens of arcminutes. The data show that [S {\sc ii}]/H$\alpha$ ratios are, on average, nearly six times higher in the filaments than in the clouds, which indicates that emission from collisionally excited, singly-ionized S$^+$ is the dominant emission source within the filaments. In clouds, the lower [S {\sc ii}]/H$\alpha$ values are evidence that the H$\alpha$ recombination line of photoionized hydrogen dominates.