Phillip Nelson (Virginia Tech)
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 degree-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 degree 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 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 II]/H-alpha values are evidence that the H-alpha recombination line of photoionized hydrogen dominates.