2020A&A...639A.110A

In this study, we analyzed the [CII] 158 µm emission from the Orion-Eridanus region measured by the Cosmic Background Explorer. Morphologically, the [CII] emission traces prominent star-forming regions this area. The analysis takes into account five different components of the interstellar medium (ISM) that can contribute to the [CII] emission: compact HII regions, dense Photon-Dominated Region, surfaces of molecular clouds, the Warm Ionized Medium, and the Cold Neutral Medium. We estimate the contribution from each object of interest to the observed [CII] emission based upon the physical properties of the object and validate our results by making a comparison with existing "small" scale maps. Inside the ∼400 parsec aperture radius that we investigate, surfaces of molecular clouds exposed to radiation from nearby stellar clusters are the dominant contributor to the observed global [CII] flux. These molecular cloud surfaces are exposed to moderate radiation fields (G₀∼100 times the average interstellar radiation field) and are moderately dense (n_H∼10³cm^–3). In addition, extended low-density ionized gas, along with large-scale ionized gas structures (Barnard's Loop; λ Ori) also make a substantial contribution. The implications of this study for the analysis of extragalactic [CII] observations are assessed.