Far-ultraviolet studies in the orion-eridanus superbubble region

Abstract

In this paper, we presented two major results for the far-ultraviolet (FUV) studies in the Orion-Eridanus Superbubble (OES) region. First, the FUV continuum and spectral images of C IV and H2 emission lines for the OES region are hereby presented and compared with maps obtained in other wavelengths. While the region shows complex structures, consisting of hot gases and cold dust, a close examination reveals that the FUV emission in this region can be understood reasonably as the result of their interactions. We confirm the origin of most diffuse FUV continuum to be starlight scattered by dust, but we also find that ionized gas contributes 50-70% of the total FUV intensity in the regions of Hα arcs. We note the bright diffuse FUV continuum in the eastern part of the northern region, which has a lot of dust, and attribute it to a greater abundance of bright, early-type stars in this region than in the west, as the amount of dust itself does not seem to be much different across “arc A,” which separates the two regions. In addition, two P Cygni-type stars are identified in this eastern region and their peculiar spectral profiles around the C IV emission line are manifested in the scattered diffuse spectrum. Besides this, the C IV emission is generally enhanced at the boundaries of the hot X-ray cavities where thin dust regions are located, confirming the thermal interface nature of the origin of this cooling emission line. The morphology of the H2 emission shows a general correlation with dust extinction features, but its intensity peaks are located in thin dust areas, rather than the peak dust regions. Furthermore, H2 emission is weak in the arc A region even though the arc passes through the center of the dust-rich area. Hence, the H2 emission and dust features, together with those of X-ray and ion line emissions, show the stratified structure of arc A quite well, again confirming its thermal interface nature. Second, we present the results of dust scattering s...